![STRANGE
BUTTRUE
APPETITE FOR SELF-
DESTRUCTION
What is apoptosis? Answer:
Essentially a cell committing suicide, apoptosis is a
controlled biological system that kills off unneeded
or excess cells. One example is the removal of
webbing in between your fingers and toes before
you are born.
A Another type of cell division B Programmed
cell death C A new type of soft drink
113
A common theory is that every living cell is descended from a single ancestral cell from 3-4bn years ago
©Dreamstime;BBC;Thinkstock;Dr.CecilFox;Corbis
DID YOU KNOW?
What is the cell cycle?
The cell is the basic unit of life for all living things.
One of its many properties is the ability to reproduce.
The cell cycle is a series of processes that occur
between the birth of the cell and its division into two.
What is mitosis?
Mitosis describes what happens near the end of the
cycle. The replicated chromosomes are separated
from each other into opposite ends of the cell just
before the cell divides.
What are the different parts of the cycle?
The other major part occurs before mitosis and is the
process in which the DNA that makes up the
chromosomes replicates itself. This is called the
S-phase or DNA synthetic phase [which is part of
interphase]. The S-phase replicates and mitosis
separates and divides.
What is the difference between mitosis and
meiosis and does cell division occur in both?
Meiosis is usually considered to be the mitotic full
cycle and also leads towards cell reproduction.
However, in meiosis there are two M-phases or
divisions so the number of DNA and chromosomes
are halved. Meiosis uses gametes for fertilisation in
diploid cells in animal and plants.
Does it occur in eukaryotic or prokaryotic cells?
Only in eukaryotic cells. In prokaryotic cells there is a
cell cycle but it is not mitosis. This [process] is
simply the copying of DNA and then a much less
obvious separation of the copied DNA into the two
divided cells.
Why did you use yeast in your experiments?
Yeast is a very simple eukaryote, which reproduces
in much the same way as more complex cells in us. It
only has 5,000 genes compared to our 25,000. It
simplifies cell division so is extremely convenient to
study. It’s got fantastic genetics and genomics,
which allow you to investigate complicated
processes like the cell cycle.
Why do skin cells divide so quickly and nerve
cells so slowly?
Cells change at varying rates and some nerve cells
barely divide at all. This is one reason why it is
difficult to regenerate the nervous system when it
becomes damaged. Because the body has to deal
with cuts and abrasions, it is much easier to get skin
cells to divide.
What is tissue culture and why is it important?
It is simply a way of growing cells from animals and
plants in test tubes. They will divide under these
circumstances so you can study the cell cycle away
from the complexities of an animal or plant.
What are the differences between plant and
animal cell cycles?
Fundamentally, not very much. They both undergo
the same processes but are subject to different
overall controls.
What is proteolysis and how does that
mechanism help the cell cycle?
It is a biochemical mechanism that breaks down
protein. It takes away certain proteins as part of a
regulatory system for a variety of biological process
such as the cell cycle. It is used at the end of the
cycle to destroy excess protein and prepare for the
next cycle.
You discovered CDK (Cyclin-dependent kinase).
How do they contribute to the cell cycle?
CDK is a type of enzyme and my research group was
involved in discovering that they were the major
regulators in the cycle. CDK brings about the S-phase
and mitosis and controls them.
How can the cycle help understand potential
cures for cancer?
To understand cancer, you have to be able to
understand the cell cycle. Crudely blocking the cell
cycle is a problem as a therapy as our body is full of
other cells that have to divide.
An expert’s view
Paul Nurse, Nobel Prize winner and director of the Francis Crick Institute, chats
about cell cycle
Paul Nurse is also the
former director of Cancer
Research UK and president
of the Royal Society
Cytokinesis
The cytoplasm divides
and two or more
daughter cells are
produced. Mitosis and
the cell cycle have now
reached their end.
Telophase
The two new sets of
chromosomes form
groups at each pole and
a new envelope forms
around each as the
spindle disappears.
Every step of the cell
division cycle is vital for
life as we know it
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How it works._book_of_the_human_body_3rd_revised_edition_2015
- 1. NEW THE BODY AT WORK CURIOUS QUESTIONSHUMAN ANATOMY Anatomyof thetongue PACKED WITH AMAZING FACTS AND STUNNING ILLUSTRATIONS BOOK OF Respiration and oxygenation Uncover thescience ofDNA Understanding hormones Everything you need to know about the human body HUMAN BODY THE Explorethe sensory system Insidea humanheart Howmany bonesarein afoot? Theevolution ofthehand Alook inside theeye Foodand thebrain Howdoour muscleswork? Guidesto theessential organs Fracture healing process INCREDIBLEIMAGES 300 OVER Operating onthe brain Kidney function explained
- 3. The human body is truly an amazing thing. Capable of awe-inspiring feats of speed, agility and strength, while being mind-blowing in complexity, your body is unmatched by that of any other species on Earth. In this updated edition of How It Works Book of the Human Body, we celebrate the human body’s capabilities and beauty, as well as analyse how it can be impaired or hampered. From how you hear, to how your digestion works, through how your bones repair fractures and on to how we express emotions and experience touch, we explore the human body like never before. Packed full of high-quality anatomical illustrations, detailed photography and easy-to- understand authoritative explanations, this book is filled with incredible facts that will make you see yourself in a whole new light. Welcome to BOOK OF HUMAN BODY THE WorldMags.netWorldMags.net WorldMags.net
- 5. Imagine Publishing Ltd Richmond House 33 Richmond Hill Bournemouth Dorset BH2 6EZ +44 (0) 1202 586200 Website: www.imagine-publishing.co.uk Publishing Director Aaron Asadi Head of Design Ross Andrews Production Editor Hannah Westlake Senior Art Editor Greg Whitaker Designer Harriet Knight Photographer James Sheppard Printed by William Gibbons, 26 Planetary Road, Willenhall, West Midlands, WV13 3XT Distributed in the UK, Eire & the Rest of the World by Marketforce, Blue Fin Building, 110 Southwark Street, London, SE1 0SU Tel 0203 148 3300 www.marketforce.co.uk Distributed in Australia by: Network Services (a division of Bauer Media Group), Level 21 Civic Tower, 66-68 Goulburn Street, Sydney, New South Wales 2000, Australia Tel +61 2 8667 5288 Disclaimer The publisher cannot accept responsibility for any unsolicited material lost or damaged in the post. All text and layout is the copyright of Imagine Publishing Ltd. Nothing in this bookazine may be reproduced in whole or part without the written permission of the publisher. All copyrights are recognised and used specifically for the purpose of criticism and review. Although the bookazine has endeavoured to ensure all information is correct at time of print, prices and availability may change. This bookazine is fully independent and not affiliated in any way with the companies mentioned herein. How It Works Book of the Human Body Third Revised Edition © 2015 Imagine Publishing Ltd bookazine series Part of the BOOK OF HUMAN BODY THE WorldMags.netWorldMags.net WorldMags.net
- 6. 010 50 amazing body facts 018 Human cells 020 Illuminating cells 021 Inside a nucleus 022 Stem cells 024 How do we smell? 025 Taste / Taste buds 026 The tonsils 027 Vocal cords 030 Brain power 032 Vision and eyesight 034 How ears work 036 All about teeth 038 Anatomy of the neck 040 The human skeleton 042 How muscles work 044 Skin colour / Skin grafts 045 Under the skin 046 Rheumatoid arthritis 047 Bone marrow 048 The human spine 050 Heart attacks 051 Heart bypasses 052 Blood transfusions 053 Strokes / Blood clotting 054 Human kidneys 056 Kidney transplants 058 Vestigial organs 059 How the spleen works 060 Human digestion 062 How the liver works 064 The small intestine 006 Human anatomy CONTENTS 066 The human ribcage 068 How the pancreas works 070 How your bladder works 072 Human pregnancy 074 Embryo development 076 Inside the human stomach 078 How does angioplasty work? 080 The human hand 082 Nails / Knee-jerk reactions 083 Inside the knee 084 How your feet work 086 Achilles’ tendon / Smelly feet 087 Blisters / Cramp 028 022 The power of your brain What are stem cells? ©PatrickJLynch Your body explained 010 WorldMags.netWorldMags.net WorldMags.net
- 7. 007 142 The signs of ageing Curious questions 142 Ageing 146 Left or right brained? 148 Brain freeze 149 Runny nose / Comas 150 Ears / Freckles / Sore throat 151 Memory / Toothpaste / Epidurals 152 Blush / Caffeine / Fainting 153 Eyebrows / Earwax / Self 154 72-hour deodorant / Modern fillings 155 What powers cells? 156 Can we see thoughts? 158 How anaesthesia works 159 Stomach ulcers / Mouth ulcers 160 Hair growth / Blond hair appearance 161 Correcting heart rhythms / Salt / Adam’s apple 162 Seasickness / Rumbling stomachs 163 What are moles? 164 Brain control / Laughing 165 Dandruff / Eye adjustment / Distance the eye can see 166 Allergies / Eczema 167 Bruises / Water allergy / Cholesterol 168 Alveoli 169 Migraines / Eyedrops 170 What are twins? 172 Paper cuts / Pins and needles / Funny bones 173 Aching muscles / Fat hormone 174 Raw meat / Inoculations / Upper arm and leg 175 Feet size / Gout The body at work 090 Food and the body 098 The blood-brain barrier 099 Pituitary gland up close 100 Brain electricity / Synapses 101 Adrenaline 102 Human respiration 104 Dehydration / Sweating 105 Circadian rhythm 106 The immune system 110 Bone fracture healing 111 Making protein 112 The cell cycle 114 White blood cells 116 The science of genetics 121 Burns 122 Blood vessels 124 How your blood works 128 Hormones 130 The urinary system 132 Tracheotomy surgery 133 Hayfever 134 Exploring the sensory system 138 Chickenpox 139 Why we cry 165 Explaining eye adjustment 110 Healing bone fractures ©SPL 080 The hand revealed WorldMags.netWorldMags.net WorldMags.net
- 8. The human hand 038 Anatomy of the neck Impressive anatomical design 040 The human skeleton A bounty of boney facts 042 How muscles work Muscle power revealed 044 Skin colour / Skin grafts Skin facts explained 045 Under the skin Anatomy of our largest organ 046 Rheumatoid arthritis How is inflammation caused? 047 Bone marrow Why is this jelly vital to us? 048 The human spine 33 vertebrae explained 027 Vocal cords See how they help us talk 028 Brain power The human brain explored 032 The science of vision Inside the eye 034 How ears work Sound and balance explained 036 All about teeth Dental anatomy and more HUMAN ANATOMY 008 Inside the eye 032 080 ©DKImages 028 How we think ©SPL 010 50 amazing body facts From head to toe 018 Human cells How are they structured? 020 Illuminating cells Making cells glow 021 Inside a nucleus Dissecting a cell’s control centre 022 Stem cells Building block bring new life 024 How do we smell? A look at your nose 025 Taste / Taste buds The science of taste explained 026 The tonsils What are these fleshy lumps? 010 50 fantastic facts about the body Taste buds 025 WorldMags.netWorldMags.net WorldMags.net
- 9. 009 022 Stem cells 050 Heart attacks Why do they happen? 051 Heart bypasses How are blockages bypassed? 052 Blood transfusions This vital procedure explained 053 Strokes / Blood clotting Why do these occur? 054 Human kidneys How do your kidneys function? 056 Kidney transplants The body’s natural filters 058 Vestigial organs Are they really useless? 059 How the spleen works Learn how it staves off infections 060 Human digestion How does food get processed? 062 How the liver works The ultimate multitasker 064 The small intestine How does this organ work? 066 The human ribcage Offering essential protection 068 How the pancreas works The body’s digestive workhorse 070 How your bladder works Waste removal facts 072 Human pregnancy Nine months of growth explained 074 Embryo development The core processes revealed 076 Inside the human stomach How does this organ digest food? 078 How does angioplasty work? Inside the medical procedure 080 The human hand Our most versatile body part 082 Nails / Knee-jerk reactions A look at fingernails and more 083 Inside the knee See how it allows us to walk 084 How your feet work Feet facts and stats 086 Achilles’ tendon / Smelly feet Are they our weak spot? 087 Blisters / Cramp Why do blisters form? How your feet work 084 024 How do we smell? WorldMags.netWorldMags.net WorldMags.net
- 10. HUMANANATOMY 010 Top 50 body facts 50 Therearelotsofmedical questionseverybodywants toaskbutwejustnever getthechance…untilnow! Thehumanbodyisthemostcomplex organismweknowandifhumanstried tobuildoneartificially,we’dfail abysmally.There’smorewedon’t knowaboutthebodythanwedoknow.This includesmanyofthequirksandseemingly uselesstraitsthatourspeciescarry.However, notallofthesetraitsareasbizarreasthey mayseem,andmanyhaveanevolutionary talebehindthem. Askingthesequestionsisonlynatural butmostofusaretooembarrassedor nevergettheopportunity–sohere’sa chancetoclearupallthoseniggling queries.We’lltakeahead-to-toetour ofthequirksofhumanbiology, lookingateverythingfromtongue rollingandwhyweareticklish throughtopulledmuscles andwhywedream. Amazing facts about the human body WorldMags.netWorldMags.net WorldMags.net
- 11. 011 Useless body parts include the appendix, the coccyx and wisdom teethDID YOU KNOW? Whatarethoughts?Thisquestionwill keepscientists,doctorsand philosophersbusyfordecadesto come.Italldependshowyouwantto definetheterm‘thoughts’.Scientists maytalkaboutsynapseformation, patternrecognitionandcerebral activationinresponsetoastimulus (suchasseeinganappleand recognisingitassuch).Philosophers, andalsomanyscientists,willargue thatanetworkofneuronscannot possiblyexplainthemanythousands ofthoughtsandemotionsthatwe mustdealwith.Asportsdoctormight statethatwhenyouchoosetorun,you activateaseriesofwell-trodden pathwaysthatleadfromyourbrainto yourmusclesinlessthanasecond. Therearesomespecificswedoknow though–suchaswhichareasofyour brainareresponsibleforvarioustypes ofthoughtsanddecisions. 1How do we think? Althoughwe’reoftentaughtinschoolthat tonguerollingisduetogenes,thetruthis likelytobemorecomplex.Thereislikely tobeanoverlapofgeneticfactorsand environmentalinfluence.Studieson familiesandtwinshaveshownthatit cannotbeacaseofsimplegenetic inheritance.Askaround–thefactthat somepeoplecanlearntodoitsuggests thatinatleastsomepeopleit’s environmental(iealearnedbehaviour) ratherthangenetic(inborn). Onlyasmallamount –hencewhybabies appearsobeautiful,as theireyesareslightly outofproportionand soappearbigger. 5Why can some people roll their tongues but others can’t? 3Do eyeballs grow like the rest of the body? Frontal lobe The frontal lobe is where your personality is, and where your thoughts and emotions form. Removing this or damaging it can alter your persona. Broca’s area Broca’s area is where you form complex words and speech patterns. Pre-motor cortex The pre-motor cortex is where some of your movements are co-ordinated. Parietal lobe The parietal lobe is responsible for your complex sensory system. Occipital lobe The occipital lobe is all the way at the back, but it interprets the light signals in your eyes into shapes and patterns. Wernicke’s area Wernicke’s area is where you interpret the language you hear, and then you will form a response via Broca’s area. Primary auditory complex The primary auditory complex is right next to the ear and is where you interpret sound waves into meaningful information. Temporal lobe The temporal lobe decides what to do with sound information and also combines it with visual data. Primary motor cortex The primary motor cortex and the primary somatosensory cortex are the areas which receive sensory innervations and then co-ordinate your whole range of movements. Whenyoufeelyour ownpulse,you’re feelingthedirect transmissionofyour heartbeatdownan artery.Youcanfeela pulsewhereyoucan compressanartery againstabone,eg theradialarteryat thewrist.The carotidarterycanbe feltagainstthe vertebralbodybut beware–a)presstoo hardandyoucan faint,b)pressbothat thesametimeand you’llcutoffthe bloodtoyourbrain and,asaprotective mechanism,you’ll definitelyfaint! 6What is a pulse? Sleepisagiftfromnature,whichis morecomplexthanyouthink.There arefivestagesofsleepwhichrepresent theincreasingdepthsofsleep–when you’resuddenlywideawakeandyour eyesspringopen,it’softenanatural awakeningandyou’recomingoutof rapideyemovement(REM)sleep;you maywellrememberyourdreams.If you’recomingoutofadifferentphase, egwhenyouralarmclockgoesoff,it willtakelongerandyoumightnot wanttoopenyoureyesstraightaway! 2In the mornings, do we wake up or open our eyes first? Thisisabehaviouralresponse– somepeopleplaywiththeirhair whenthey’renervousorbored.For thevastmajorityofpeoplesuch traitsareperfectlynormal;ifthey begintointerferewithyourlife, behaviouralpsychologistscanhelp –butit’sextremelyrarethatyou’ll endupthere. 4Why do we fiddle subconsciously? I’m constantly playing with my hair ©DoraPete ©SPL WorldMags.netWorldMags.net WorldMags.net
- 12. HUMANANATOMY 012 Top 50 body facts Thehumanfieldofvisionisjustabout180 degrees.Thecentralportionofthis (approximately120degrees)isbinocularor stereoscopic–iebotheyescontribute, allowingdepthperceptionsothatwecan seein3D.Theperipheraledgesare monocular,meaningthatthereisno overlapfromtheothereyesoweseein2D. Thetonsilsarecollectionsof lymphatictissueswhichare thoughttohelpfightoff pathogensfromtheupper respiratorytract.However, theythemselvescan sometimesbecomeinfected– leadingtotonsillitis.Theones youcanseeatthebackofyour throatarejustpartofthering oftonsils.Youwon’tmissthem ifthey’retakenoutfor recurrentinfectionsasthe restofyourimmunesystem willcompensate. It’sdifferentforeverybody–your age,nutrition,healthstatus,genes andgenderallplayarole.Interms oflength,anywherebetween 0.5-1inch(1.2-2.5cm)amonth mightbeconsideredaverage, butdon’tbesurprisedifyou’re outsidethisrange. Aburpisanatural releaseofgasfrom thestomach.Thisgas haseitherbeen swallowedoristhe resultofsomething you’veingested–such asafizzydrink.The soundcomesfromthe vibrationofthe oesophageal sphincteratthe oesophago-gastric junction,whichisthe narrowestpartofthe gastrointestinaltract. 7What’s my field of vision in degrees? 8What is the point of tonsils? 13How many inches of hair does the average person grow from their head each year? 12Why do we burp? You’reactuallyhittingtheulnarnerveasitwrapsaroundthebony prominenceofthe‘humerus’bone,leadingtoa‘funny’sensation. Althoughnotsofunnyasthebraininterpretsthissuddentrauma aspaintoyourforearmandfingers! 10Why does it feel so weird when you hit your funny bone? 3D field The central 120-degree portion is the 3D part of our vision as both eyes contribute – this is the part we use the most. 2D field The areas from 120 to 180 degrees are seen as 2D as only one eye contributes, but we don’t really notice. Yourtotal‘circulatingvolume’isaboutfivelitres.Each redbloodcellwithinthishastogofromyourheart, downthemotorway-likearteries,throughthe back-roadcapillarysystem,andthenbackthroughthe rush-hourveinstogetbacktoyourheart.Theprocess typicallytakesaboutaminute.Whenyou’reinarush andyourheartrateshootsup,thetimereducesasthe blooddivertsfromtheless-importantstructures(eg largebowel)tothemoreessential(egmuscles). 11How fast does blood travel round the human body? ©SPL 1. The most important organ The brain has its own special blood supply arranged in a circle. 4. The inferior vena cava This massive vein sits behind the aorta but is no poor relation – without it, blood wouldn’t get back to your heart. 5. The furthest point These arteries and veins are the furthest away from your heart, and blood flow here is slow. As you grow older, these vessels are often the first to get blocked by fatty plaques. 2. Under pressure Blood is moving fastest and under the highest pressure as it leaves the heart and enters the elastic aorta. 3. The kidneys These demand a massive 25 per cent of the blood from each heart beat! ©SPL Lipsarepredominantlyusedasatactilesensoryorgan, typicallyforeating,butalsoforpleasurewhenkissing.They arealsousedtohelpfine-tuneourvoiceswhenwespeak. 9What are lips for? ©Frettie ©MattWillman ULNAR NERVE WorldMags.netWorldMags.net WorldMags.net
- 13. Mostofitisdowntothegenesthatresult fromwhenyourparentscometogetherto makeyou.Somehaircolourswinout (typicallythedarkones)whereassome(eg blonde)arelessstronginthegeneticrace. 17Why do we all have different coloured hair? 1While great apes such as gorillas, chimps and orang-utans use facial expressions to show their feelings, human beings are the only animals known to cry as a result of their emotions. Emotions 2A sneeze is typically expelled at around 161km/h (100mph). Sneezing helps protect the body by keeping the nose free of bacteria and viruses. There’s a video on our website. Sneeze fast! 3Red blood cells – also known as erythrocytes – live on average for 120 days. There are approximately 25 trillion red blood cells in your body at any given moment. Red blood cells 4The heart beats on average 100,000 times per day. Of course this will greatly vary depending on your level of activity and your environmental conditions. Hard worker 5Humans are made up of 70 per cent water, which is essential for body growth and repair. The NHS suggests drinking 1.2 litres of water a day to avoid growing dehydrated. Liquid5 TOP FACTS BODY ROUNDUP 013 The average person breaks wind between 8-16 times per dayDID YOU KNOW? Yourfingerprintsarefineridgesof skininthetipsofyourfingersand toes.Theyareusefulforimproving thedetectionofsmallvibrations andtoaddfrictionforbettergrip. Notwofingerprintsarethesame –eitheronyourhandsorbetween twopeople–andthat’sdownto youruniquesetofgenes. Hairfolliclesindifferentpartsofyour bodyareprogrammedbyyourgenesto dodifferentthings,egthefollicleson yourarmproducehairmuchslower thanthoseonyourhead.Mencango baldduetoacombinationofgenesand hormonalchanges,whichmaynot happeninotherareas(egnasalhair). It’sdifferentforeverybody! 14Why are everyone’s fingerprints different? 16Why, as we get older, does hair growth become so erratic? Researchershavespenttheirwholelivestryingto answerthisone.Yourpersonalityformsinthefront lobesofyourbrain,andthereareclearpersonality types.Mostofitisyourenvironment–thatis,your upbringing,education,surroundings.Howeversome ofitisgenetic,althoughit’sunclearhowmuch.The strongestresearchinthiscomesfromstudyingtwins –whatinfluencesonesetoftwinstogrowupandbe bestfriends,yetinanotherpair,onemightbecomea professorandtheotheramurderer. 19What gives me my personality? 20WHY DO MEN HAVE NIPPLES? Menandwomenarebuiltfrom thesametemplate,andthese arejustaremnantofaman’s earlydevelopment. 21WHAT’S THE POINT OF EYEBROWS? Biologically,eyebrowscan helptokeepsweatand rainwaterfromfallinginto youreyes.Moreimportantlyin humans,theyarekeyaidsto non-verbalcommunication. 22WHAT IS A BELLY BUTTON? Theumbilicusiswherea baby’sbloodflowsthroughto gettotheplacentatoexchange oxygenandnutrientswiththe mother’sblood.Onceout,the umbilicalcordisclamped severalcentimetresawayfrom thebabyandlefttofalloff.No onequiteknowswhyyou’llget an‘innie’oran‘outie’–it’s probablyalljustluck. 23WHY DO FINGERNAILS GROW FASTER THAN TOENAILS? Thelongertheboneattheend ofadigit,thefasterthegrowth rateofthenail.Howeverthere aremanyotherinfluencestoo –nutrition,sunexposure, activity,bloodsupply–and that’sjusttonameafew. 24WHY DOES MY ARM TINGLE AND FEEL HEAVY IF I FALL ASLEEP ON IT? Thishappensbecauseyou’re compressinganerveasyou’re lyingonyourarm.Thereare severalnervessupplyingthe skinofyourarmandthree supplyingyourhand(the radial,medianandulnar nerves),sodependingon whichpartofyourarmyoulie on,youmighttingleinyour forearm,handorfingers. Dreamshavefascinatedhumans forthousandsofyears.Some peoplethinktheyareharmless whileothersthinktheyarevitalto ouremotionalwellbeing.Most peoplehavefourtoeightdreams pernightwhichareinfluencedby stress,anxietyanddesires,but theyrememberveryfewofthem. Thereisresearchtoprovethatif youawakefromtherapideye movement(REM)partofyoursleep cycle,you’relikelytoremember yourdreamsmoreclearly. 15Why do we only remember some dreams? Youreyesremainshutasa defencemechanismtoprevent thesprayandnasalbacteria enteringandinfectingyour eyes.Theurbanmyththat youreyeswillpopoutifyou keepthemopenisunlikely tohappen–butkeeping themshutwillprovide someprotectionagainst nastybugsandviruses. 18Is it possible to keep your eyes open when you sneeze? ©Tristanb WorldMags.netWorldMags.net WorldMags.net
- 14. HUMANANATOMY Top 50 body facts Yourbloodtypeisdeterminedbyproteinmarkersknownasantigensonthesurfaceofyour redbloodcells.YoucanhaveAantigens,Bantigens,ornone–inwhichcaseyou’rebloodtype O.However,ifyoudon’thavetheantigen,yourantibodieswillattackforeignblood.Ifyou’re typeAandyou’regivenB,yourantibodiesattacktheBantigens.However,ifyou’rebloodtype AB,youcansafelyreceiveanytype.ThosewhoarebloodgroupOhavenoantigenssocangive bloodtoanyone,buttheyhaveantibodiestoAandBsocanonlyreceiveOback! 25What makes some blood groups incompatible while others are universal? 26What is a pulled muscle? A YouhaveAantigensandB antibodies.Youcanreceiveblood groupsAandO,butcan’treceiveB. YoucandonatetoAandAB. B YouhaveBantigensandA antibodies.Youcanreceiveblood groupsBandO,butcan’treceive A.YoucandonatetoBandAB. AB YouhaveAandBantigensandno antibodies.Youcanreceiveblood groupsA,B,ABandO(universal recipient),andcandonatetoAB. O YouhavenoantigensbuthaveAandB antibodies.Youcanreceivebloodgroup O,butcan’treceiveA,BorABandcan donatetoall:A,B,ABandO. Theheartisthemost efficient–itextracts 80percentofthe oxygenfromblood. Butthelivergetsthe mostblood–40per centofthecardiac outputcomparedto thekidneys,which get25percent,and heart,whichonly receives5percent. 27Which organ uses up the most oxygen? Theappendixisusefulincowsfor digestinggrassandkoalabearsfor digestingeucalyptus–koalascanhave a4m(13ft)-longappendix!Inhumans, however,theappendixhasnouseful functionandisaremnantofour development.Ittypicallymeasures 5-10cm(1.9-3.9in),butifitgetsblockedit cangetinflamed.Ifitisn’tquickly removed,theappendixcanburstand leadtowidespreadinfectionwhichcan belethal. 28What is the appendix? I’ve heard it has no use but can kill you… ©SPL The hamstrings These are a group of three main muscles which flex the knee. Strain A pulled muscle, or strain, is a tear in a group of muscle fibres as a result of overstretching. ©SPL Thisyellowdiscolourationoftheskin orthewhitesoftheeyesiscalled jaundice.It’sduetoabuildupof bilirubininyourbody,whennormally thisisexcretedintheurine(hence whyurinehasayellowtint).Diseases suchashepatitisandgallstonescan leadtoabuildupofbilirubindueto alteredphysiologicalprocesses, althoughtherearemanyothercauses. 29Why does people’s skin turn yellow if they contract liver disease? ©SPL Thoughwarmingupcanhelpprevent sprains,theycanhappentoanyone, fromwalkerstomarathonrunners. PulledmusclesaretreatedwithRICE: rest,ice,compressionandelevation 30What is the gag reflex? 1. Foreign bodies This is a protective mechanism to prevent food or foreign bodies entering the back of the throat at times other than swallowing. 2. Soft palate The soft palate (the fleshy part of the mouth roof) is stimulated, sending signals down the glossopharyngeal nerve. 3. Vagus nerve The vagus nerve is stimulated, leading to forceful contraction of the stomach and diaphragm to expel the object forwards. 4. The gag This forceful expulsion leads to ‘gagging’, which can develop into retching and vomiting. 014 WorldMags.netWorldMags.net WorldMags.net
- 15. 1. Human vs cheetah While the world record holder Usain Bolt can run it in 9.58 seconds, a cheetah can run 100m (328ft) in just over six seconds. 2. Human vs giraffe The average man in England is 1.7m (5.5ft) tall. The tallest man ever was 2.7m (8.8ft). A giraffe can grow up to 6m (19.7ft). 3. Human vs flea The men’s outdoor high jump world record is 2.45m (less than twice the height of a man). A flea can jump up to 100 times its height. FAST HIGH Your brain interprets pain from the rest of the body, but doesn’t have any pain receptors itselfDID YOU KNOW? Lighttouches,byfeathers,spiders,insectsorother humans,canstimulatefinenerve-endingsintheskin whichsendimpulsestothesomatosensorycortexinthe brain.Certainareasaremoreticklish–suchasthefeet– whichmayindicatethatitisadefencemechanism againstunexpectedpredators.Itistheunexpected natureofthisstimulusthatmeansyoucanbetickled. Althoughyoucangiveyourselfgoosebumpsthrough lighttickling,youcan’tmakeyourselflaugh. Youreyelashesareformedfromhairfollicles,justlikethoseonyour head,armsandbody.Eachfollicleisgeneticallyprogrammedto functiondifferently.Youreyelashesareprogrammedtogrowtoa certainlengthandevenre-growiftheyfallout,buttheywon’tgrow beyondacertainlength,whichishandyforseeing! Theimmuneresponseleadstoinflammationandthereleaseof inflammatoryfactorsintoyourbloodstream.Theseleadtoan increasedheartrateandbloodflow,whichincreasesyourcorebody temperature–asifyourbodyisdoingexercise.Thiscanleadto increasedheatproductionandthusdehydration;forthisreason,it’s importanttodrinkplentyofclearfluidswhenyou’refeelingunwell. 31Why are we ticklish? 32Why don’t eyelashes keep growing? 34Could we survive on vitamins alone? 35Why do we get a high temperature when we’re ill? TALL 36WHY DO SOME PEOPLE HAVE FRECKLES? Frecklesareconcentrationsof thedarkskinpigmentmelanin intheskin.Theytypically occuronthefaceand shoulders,andaremore commoninlight-skinned people.Theyarealsoa well-recognisedgenetictrait andbecomemoredominant duringsun-exposure. 37WHAT IS A WART? Wartsaresmall,rough,round growthsoftheskincausedby thehumanpapillomavirus. Therearemanydifferenttypes whichcanoccurindifferent partsofthebody,andtheycan becontagious.Theycommonly occuronthehands,butcan alsocomeupanywherefrom thegenitalstothefeet! 38WHY DO I TWITCH IN MY SLEEP? Thisiscommonandknownin themedicalworldasa myoclonictwitch.Although someresearcherssaythese twitchesareassociatedwith stressorcaffeineuse,theyare likelytobeanaturalpartofthe sleepprocess.Ifithappensto you,it’sperfectlynormal. No,youneedadiet balancedin carbohydrate, protein,fat, vitaminsand mineralstosurvive. Youcan’tcutoneof theseandexpectto stayhealthy. However,it’sthe proportionsofthese whichkeepus healthyandfit.You cangetthesefrom thefivemajorfood groups.Foodcharts canhelpwiththis balancingact. 33What makes us left-handed? Onesideofthebrainis typicallydominantoverthe other.Sinceeachhemisphere ofthebraincontrolsthe oppositeside(ietheleft controlstherightsideofyour body),right-handedpeople havestrongerleftbrain hemispheres.Occasionally you’llfindanambidextrous person,wherehemispheres areco-dominant,andthese peopleareequallycapable withbothrightandlefthands! ©Loyna ©Wegmann ©shlomitg ©JeinnySolis ©KlausD.Peter,Wiehl,Germany HEAD HEAD2HUMANS VS ANIMALS 015WorldMags.netWorldMags.net WorldMags.net
- 16. HUMANANATOMY 016 Top 50 body facts Theheartkeepsitselfbeating.The sinoatrialnode(SAN)isinthewallofthe rightatriumoftheheart,andiswherethe heartbeatstarts.Thesebeatsoccurdueto changesinelectricalcurrentsascalcium, sodiumandpotassiummoveacross membranes.Theheartcanbeatatarateof 60beatsperminuteconstantlyifleftalone. However–weoftenneedittogofaster.The sympatheticnervoussystemsendsrapid signalsfromthebraintostimulatethe hearttobeatfasterwhenweneeditto–in ‘fightorflight’scenarios.IftheSANfails,a pacemakercansendartificialelectrical signalstokeeptheheartgoing. Blooddoesn’tcirculatearoundyourbodyas efficientlywhenyou’reasleepsoexcesswatercan poolundertheeyes,makingthempuffy.Fatigue, nutrition,ageandgenesalsocausebags. Abruiseformswhencapillariesundertheskinleakandallow bloodtosettleinthesurroundingtissues.Thehaemoglobinin redbloodcellsisbrokendown,andtheseby-productsgivea darkyellow,brownorpurplediscolourationdependingonthe volumeofbloodandcolouroftheoverlyingskin.Despite popularbelief,youcannotageabruise–differentpeople’s bruiseschangecolouratdifferentrates. Onionsmakeyoureyeswaterduetotheirexpulsionof anirritantgasoncecut.Thisoccursaswhenanonion iscutwithaknife,manyofitsinternalcellsarebroken down,allowingenzymestobreakdownaminoacid sulphoxidesandgeneratesulphenicacids.These sulphenicacidsarethenrearrangedbyanother enzymeand,asadirectconsequence,syn- propanethial-S-oxidegasisproduced,whichisvolatile. Thisvolatilegasthendiffusesintheairsurrounding theonion,eventuallyreachingtheeyesofthecutter, whereitproceedstoactivatesensoryneuronsand createastingingsensation.Assuch,theeyesthen followprotocolandgeneratetearsfromtheirtear glandsinordertodiluteandremovetheirritant. Interestingly,thevolatilegasgeneratedbycutting onionscanbelargelymitigatedbysubmergingthe onioninwaterpriortoormidwaythroughcutting, withtheliquidabsorbingmuchoftheirritant. 39What triggers the heart and keeps it beating? 43When we’re tired, why do we get bags under our eyes? 40Why do bruises go purple or yellow? 41Why does cutting onions make us cry? Definitions Systole=contraction; Diastole=relaxation 3. Ventricular diastole The heart is now relaxed and can refill, ready for the next beat. 1. Atrial systole The atria are the low-pressure upper chambers, and are the first to contract, emptying blood into the ventricles. 2. Ventricular systole The ventricles contract next, and they send high-pressure blood out into the aorta to supply the body. 3x©SPL ‘Simple’malepatternbaldnessisdue toacombinationofgeneticfactors andhormones.Themostimplicated hormoneistestosterone,whichmen havehighlevelsofbutwomenhave lowlevelsof,sotheywin(orlose?)in thisparticularhormonecontest! 44Why do more men go bald than women? 42What is the little triangle shape on the side of the ear? Thisisthetragus.Itserves nomajorfunctionthatwe knowof,butitmayhelpto reflectsoundsintotheear toimprovehearing. 3. Discolouration Haemoglobin is then broken down into its smaller components, which are what give the dark discolouration of a bruise. 2. Blood leaks into the skin Blood settles into the tissues surrounding the vessel. The pressure from the bruise then helps stem the bleeding. 1. Damage to the blood vessels After trauma such as a fall, the small capillaries are torn and burst. ©LaliMasriera ©DavidBenbennick WorldMags.netWorldMags.net WorldMags.net
- 17. DID YOU KNOW? 017 The hyoid is the only bone that isn’t connected to another bone – it sits at the top of your neckDID YOU KNOW? Genesworkinpairs.Somegenesare ‘recessive’andifpairedwitha ‘dominant’half,theywon’tshine through.However,iftworecessive genescombine(onefromyourmother andonefromyourfather),the recessivetraitwillshowthrough. Blinkinghelpskeepyoureyescleanandmoist.Blinking spreadssecretionsfromthetearglands(lacrimalfluids) overthesurfaceoftheeyeball,keepingitmoistandalso sweepingawaysmallparticlessuchasdust. Thegluteusmaximusisthelargestmuscleandformsthebulkofyourbuttock.Theheart(cardiacmuscle)is thehardest-workingmuscle,asitisconstantlybeatingandclearlycannevertakeabreak!Howeverthe strongestmusclebasedonweightisthemasseter.Thisisthemusclethatclenchesthejawshut–puta fingeroverthelowest,outerpartofyourjawandclenchyourteethandyou’llfeelit. 48Why do some hereditary conditions skip a generation? 45Why do we blink? 50Which muscle produces the most powerful contraction relative to its size? 1. Taking the first step Musclecontractionstartswithanimpulsereceivedfromthe nervessupplyingthemuscle–anactionpotential.This actionpotentialcausescalciumionstofloodacrossthe proteinmusclefibres.Themusclefibresareformedfromtwo keyproteins:actinandmyosin. 2. Preparation Thecalciumbindstotroponinwhichisareceptoron theactinprotein.Thisbindingchangestheshapeof tropomyosin,anotherproteinwhichisboundtoactin. Theseshapechangesleadtotheopeningofaseriesof bindingsitesontheactinprotein. 3. Binding Nowthebindingsitesarefreeonactin,themyosinheads forgestrongbondsinthesepoints.Thisleadstothe contractionofthenewlyformedproteincomplex;whenall oftheproteinscontract,themusclebulkcontracts. 4. Unbinding Whentheenergyrunsout,theproteinslosetheirstrong bondsanddisengage,andfromtheretheyreturnto theiroriginalrestingstate. It stimulates its own heartbeat, beats around 100,000 times a day and pumps about 2,000 gallons of blood per day. It’s also the most efficient of organs and extracts the highest ratio of oxygen per unit of blood that it receives. The heart has its own blood supply too that supplies its muscular wall. The heart is amazing Itchingiscausedbythereleaseofa transmittercalledhistaminefrom mastcellswhichcirculateinyourbody. Thesecellsareoftenreleasedin responsetoastimulus,suchasabee stingoranallergicreaction.Theylead toinflammationandswelling,and sendimpulsestothebrainvianerves whichcausesthedesiretoitch. 47Why do we get itchy? Thisis‘phantomlimbpain’andcanrangefromamild annoyancetoadebilitatingpain.Thebraincan sometimesstruggletoadjusttothelossofalimb,andit canstill‘interpret’thelimbasbeingthere.Sincethe nerveshavebeencut,itinterpretsthesenewsignalsas pain.Thereisn’tasurgicalcureasyet,thoughtimeand specialmedicationscanhelplessenthepain. 49Why do amputees sometimes still feel pain in their amputated limbs? Mostpeople’sfeetaredifferentsizes–infactthetwo halvesofmostpeople’sbodiesaredifferent!Weallstart fromonecell,butasthecellsmultiply,genesgivethem varyingcharacteristics. 46How come most people have one foot larger than the other? Myosin head Actin filament Actin filament is pulled Cross bridge detaches Energised myosin head WorldMags.netWorldMags.net WorldMags.net
- 18. Cellsarelifeandcellsare alive.Youareherebecause everycellinsideyourbody hasaspecificfunctionanda veryspecialisedjobtodo.Thereare manydifferenttypesofcell,eachone workingtokeepthebody’svarious systemsoperating.Asinglecellisthe smallestunitoflivingmaterialinthe bodycapableoflife.Whengrouped togetherinlayersorclusters,however, cellswithsimilarjobstodoformtissue, suchasskinormuscle.Tokeepthese cellsworking,therearethousandsof chemicalreactionsgoingonallthetime. Allanimalcellscontainanucleus, whichactslikeacontrolhubtellingthe cellwhattodoandcontainsthecell’s geneticinformation(DNA).Mostofthe materialwithinacellisawatery, jelly-likesubstancecalledcytoplasm (cytomeanscell),whichcirculates aroundthecellandisheldinbyathin externalmembrane,whichconsistsof twolayers.Withinthecytoplasmisa varietyofstructurescalledorganelles, whichallhavedifferenttasks,suchas manufacturingproteins–thecell’skey chemicals.Onevitalexampleofan organelleisaribosome;thesenumerous structurescanbefoundeitherfloating aroundinthecytoplasmorattachedto internalmembranes.Ribosomesare crucialintheproductionofproteins fromaminoacids. Inturn,proteinsareessentialto buildingyourcellsandcarryingoutthe biochemicalreactionsthebodyneedsin ordertogrowanddevelopandalsoto repairitselfandheal. Cell structure explainedTherearearound75trillioncells inthehumanbody,butwhatare theyandhowdotheywork? Cell membrane Surrounding and supporting each cell is a plasma membrane that controls everything that enters and exits. Nucleus The nucleus is the cell’s ‘brain’ or control centre. Inside the nucleus is DNA information, which explains how to make the essential proteins needed to run the cell. Mitochondria These organelles supply cells with the energy necessary for them to carry out their functions. The amount of energy used by a cell is measured in molecules of adenosine triphosphate (ATP). Mitochondria use the products of glucose metabolism as fuel to produce the ATP. Golgi body Another organelle, the Golgi body is one that processes and packages proteins, including hormones and enzymes, for transportation either in and around the cell or out towards the membrane for secretion outside the cell where it can enter the bloodstream. Ribosomes These tiny structures make proteins and can be found either floating in the cytoplasm or attached like studs to the endoplasmic reticulum, which is a conveyor belt-like membrane that transports proteins around the cell. Endoplasmic reticulum The groups of folded membranes (canals) connecting the nucleus to the cytoplasm are called the endoplasmic reticulum (ER). If studded with ribosomes the ER is referred to as ‘rough’ ER; if not it is known as ‘smooth’ ER. Both help transport materials around the cell but also have differing functions. Rough endoplasmic reticulum (studded with ribosomes) Smooth endoplasmic reticulum HUMANANATOMY 018 Cells under the microscope WorldMags.netWorldMags.net WorldMags.net
- 19. Super cells Stem cells are self-renewing cells with the potential to become any other type of cell in the body. Unlike regular cells, they do not have a specialisation, such as nerve cells. Experts have discovered that adult stem cells can be manipulated into other types with the potential to grow replacement organs. Cytoplasm This is the jelly-like substance – made of water, amino acids and enzymes – found inside the cell membrane. Within the cytoplasm are organelles such as the nucleus, mitochondria and ribosomes, each of whichperformsaspecific role, causing chemical reactions in the cytoplasm. Lysosomes This digestive enzyme breaks down unwanted substances and worn-out organelles that could harm the cell by digesting the product and then ejecting it outside the cell. Pore Cell anatomy ©SciencePhotoLibrary NERVE CELLS Thecellsthatmakeupthenervous systemandthebrainarenervecells orneurons.Electricalmessages passbetweennervecellsalong longfilamentscalledaxons.To crossthegapsbetweennerve cells(thesynapse)thatelectrical signalisconvertedintoachemical signal.Thesecellsenableustofeel sensations,suchaspain,andtheyalso enableustomove. BONE CELLS Thecellsthatmakeupbonematrix–thehard structurethatmakesbonesstrong–consistofthree maintypes.Yourbonemassisconstantlychanging andreformingandeachofthethreebonecellsplaysits partinthisprocess.Firsttheosteoblasts,whichcome frombonemarrow,buildupbonemassand structure.Thesecellsthenbecome buriedinthematrixatwhich pointtheybecomeknownas osteocytes.Osteocytesmake uparound90percentofthe cellsinyourskeletonandare responsibleformaintaining thebonematerial.Finally, whiletheosteoblastsaddto bonemass,osteoclastsarethe cellscapableofdissolvingbone andchangingitsmass. PHOTORECEPTOR CELLS Theconesandrodsontheretinaat thebackoftheeyeareknown asphotoreceptorcells.These containlight-sensitive pigmentsthatconvertthe imagethatenterstheeye intonervesignals,which thebraininterpretsas pictures.Therodsenableyou toperceivelight,darkand movement,whilethecones bringcolourtoyourworld. LIVER CELLS Thecellsinyourliverareresponsible forregulatingthecompositionof yourblood.Thesecellsfilterout toxinsaswellascontrollingfat, sugarandaminoacidlevels. Around80percentoftheliver’s massconsistsofhepatocytes, whicharetheliver’sspecialised cellsthatareinvolvedwiththe productionofproteinsandbile. MUSCLE CELLS Therearethreetypesofmusclecell– skeletal,cardiacandsmooth–and eachdiffersdependingonthe functionitperformsanditslocation inthebody.Skeletalmuscles containlongfibresthatattachto bone.Whentriggeredbyanerve signal,themusclecontractsand pullsthebonewithit,makingyou move.Wecancontrolskeletalmusclesbecausethey arevoluntary.Cardiacmuscles,meanwhile,are involuntary,whichisfortunatebecausethey areusedtokeepyourheartbeating.Foundin thewallsoftheheart,thesemusclescreate theirownstimulitocontractwithoutinput fromthebrain.Smoothmuscles,whichare prettyslowandalsoinvoluntary,makeup theliningsofhollowstructuressuchasblood vesselsandyourdigestivetract.Their wave-likecontractionaidsthetransportofblood aroundthebodyandthedigestionoffood. FAT CELLS Thesecells–alsoknownas adipocytesorlipocytes– makeupyouradipose tissue,orbodyfat,which cancushion,insulate andprotectthebody. Thistissueisfound beneathyourskinand alsosurroundingyour otherorgans.Thesizeofafat cellcanincreaseordecrease dependingontheamountof energyitstores.Ifwegainweightthecellsfillwith morewateryfat,andeventuallythenumberoffatcells willbegintoincrease.Therearetwotypesofadipose tissue:whiteandbrown.Thewhiteadiposetissue storesenergyandinsulatesthebodybymaintaining bodyheat.Thebrownadiposetissue,ontheother hand,canactuallycreateheatandisn’tburnedfor energy–thisiswhyanimalsareabletohibernatefor monthsonendwithoutfood. EPITHELIAL CELLS Epithelialcellsmakeuptheepithelialtissuethat linesandprotectsyourorgans andconstitutetheprimary materialofyourskin. Thesetissuesforma barrierbetweenthe preciousorgansand unwantedpathogensor otherfluids.Aswellas coveringyourskin,you’ll findepithelialcellsinside yournose,aroundyourlungs andinyourmouth. RED BLOOD CELLS Unlikealltheothercellsinyour body,yourredbloodcells(also knownaserythrocytes)do notcontainanucleus.You aretoppedupwith around25trillionred bloodcells–that’sathird ofallyourcells,making themthemost commoncellin yourbody.Formed inthebonemarrow, thesecellsareimportant becausetheycarryoxygentoallthe tissuesinyourbody.Oxygeniscarriedin haemoglobin,apigmentedproteinthat givesbloodcellstheirredcolour. Types of human cell Sofararound200differentvarietiesofcellhavebeen identified,andtheyallhaveaveryspecificfunctionto perform.Discoverthemaintypesandwhattheydo… ©SPL ©SPL ©SPL ©SPL 019 DID YOU KNOW? Bacteria are the simplest living cells and the most widespread life form on EarthDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 20. HUMANANATOMY Making cells glow 020 FindouthowGFPandquantumdotsareshedding lightonmedicalresearch… Illuminating cells Formillionsofyears,theAequorea victoriajellyfishheldthesecretto greenfluorescentprotein(GFP)–a proteinthatabsorbstheenergyfrom theblueandultraviolet(UV)rangeandre-emitsitasa greenlight.Biologistsgottheirhandsontheglowing jellyfishintheSixties,extractingtheproteinand thenuncoveringthegenethatcodesforit. Byinsertingthissequenceintolivingorganisms, scientistsequipthemwiththeinstructionsthatare requiredtomanufactureGFP,highlightinghow genesareexpressedineverythingfrombacteria tohumancells.Specificproteinsandcelltypes canbetaggedwithGFP,allowingresearchersto tracktheirmovementandinteraction.Taggingthe HIVviruswithGFP,forinstance,showshowthe infectionspreads. Asimilareffectcanbeachievedwithquantum dots–nanoscalesemi-conductorcrystalswhich alsofluoresceunderUVlight.Thedotscanbe madeinmanydifferentcoloursandboundto proteins,allowingscientiststoobservecomplex biologicalinteractions. Recently,surgeonswearingspecialgoggles identifiedandremovedcancerouscellshighlighted withquantumdots.Thesegogglescouldalsobe usedtodevelopdiagnostictestsandtherapiesfor otherconditions. Hundreds of living organisms produce light, although most do not fluoresce, instead getting their glow from chemical reactions. Most of these are marine creatures and bacteria, although terrestrial invertebrates (eg fireflies, inset) and fungi can also glow. Bioluminescence serves a variety of functions. In many marine animals, it provides camouflage by allowing its bearer to blend in with the surrounding light when viewed from below. In other species it is used as a form of communication or, like the anglerfish, to draw in prey. Researchers aren’t certain what the Aequorea victoria jellyfish uses its eerie GFP glow for, but some believe it may be to evade predators. Bioluminescence in nature Green fluorescent protein and quantum dots are helping us understand cells’ inner workings WorldMags.netWorldMags.net WorldMags.net
- 21. Prokaryotic cells are much more basic than their eukaryotic counterparts. Up to 100 times smaller and mainly comprising species of bacteria, prokaryotic cells have fewer functions than other cells, so they do not require a nucleus to act as the control centre for the organism. Instead, these cells have their DNA moving around the cell rather than being housed in a nucleus. They have no chloroplasts, no membrane-bound organelles and they don’t undertake cell division in the form of mitosis or meiosis like eukaryotic cells do. Prokaryotic cells divide asexually with DNA molecules replicating themselves in a process known as binary fission. How do cells survive without a nucleus? Take a peek at what’s happening inside the ‘brain’ of a eukaryotic cell Central command Explore the larger body that a nucleus rules over and meet its ‘cellmates’ Nucleus in context ©Alamy Surrounded by cytoplasm, the nucleus contains a cell’s DNA and controls all of its functions and processes such as movement and reproduction. There are two main types of cell: eukaryotic and prokaryotic. Eukaryotic cells contain a nucleus while prokaryotic do not. Some eukaryotic cells have more than one nucleus – called multinucleate cells – occurring when fusion or division creates two or more nuclei. At the heart of a nucleus you’ll find the nucleolus; this particular area is essential in the formation of ribosomes. Ribosomes are responsible for making proteins out of amino acids which take care of growth and repair. Being so important, the nucleus is the most-protected part of the cell. In animal cells it is always located near its centre and away from the membrane to ensure it has the maximum cushioning. As well as the jelly-like cytoplasm around it, the nucleus itself is filled with nucleoplasm, a viscous liquid which maintains its structural integrity. Conversely, in plant cells, the nucleus is more sporadically placed. This is due to the larger vacuole in a plant cell and the added protection that is granted by a cell wall. Dissectingthecontrolcentreofacell Inside a nucleus 1 Nuclear pore These channels control the movement of molecules between the nucleus and cytoplasm. 3 Nucleolus Made up of protein and RNA, this is the heart of the nucleus which manufactures ribosomes. 2 Nuclear envelope Acts as a wall to protect the DNA within the nucleus and regulates cytoplasm access. 4 Nucleoplasm This semi-liquid, semi-jelly material surrounds the nucleolus and keeps the organelle’s structure. 5 Chromatin Produces chromosomes and aids cell division by condensing DNA molecules. Ribosomes Made up of two separate entities, ribosomes make proteins to be used both inside and outside the cell. Nucleus Golgi apparatus Named after the Italian biologist Camillo Golgi, they create lysosomes and also organise the proteins for secretion. Mitochondrion Double membraned, this produces energy for the cell by breaking down nutrients via cellular respiration. 1 2 3 4 5 Lysosome Small and spherical, this organelle contains digestive enzymes that attack invading bacteria. Ribosomes are responsible for making proteins out of amino acidsDID YOU KNOW? 021WorldMags.netWorldMags.net WorldMags.net
- 22. 022 Stemcellsareincredibly specialbecausethey havethepotentialto becomeanykindofcell inthebody,fromredbloodcellsto braincells.Theyareessentialtolife andgrowth,astheyrepairtissues andreplacedeadcells.Skin,for example,isconstantlyreplenished byskinstemcells. Stem cells begin their life cycle as generic, featureless cells that don’t contain tissue-specific structures, such as the ability to carry oxygen. Stem cells become specialised through a process called differentiation. This is triggered by signals inside and outside the cell. Internal signals come from strands of DNA that carry information for all cellular structures, while external signals include chemicals from nearby cells. Stem cells can replicate many times – known as proliferation – while others such as nerve cells don’t divide at all. There are two stem cell types, as Professor Paul Fairchild, co-director of the Oxford Stem Cell Institute at Oxford Martin School explains: “Adult stem cells are multipotent, which means they are able to produce numerous cells that are loosely related, such as stem cells in the bone marrow can generate cells that make up the blood,” he says. “In contrast, pluripotent stem cells, found within developing embryos, are able to make any one of the estimated 210 cell types that make up the human body.” This fascinating ability to transform and divide has made stem cells a rich source for medical research. Once their true potential has been harnessed, they could be used to treat a huge range of diseases and disabilities. What are stem cells? Understandhowthesebuildingblocksbringnewlife Cloning cells Scientists can reprogram cells to forget their current role and become pluripotent cells again – indistinguishable from early embryonic stem cells. These are called induced pluripotent stem cells (IPSCs) and can be used in areas of the body where they are needed, taking on the characteristics of nearby cells. IPSCs are more reliable than stem cells grown from a donated embryo because the body is more likely to accept stem cells generated by itself. IPSCs can treat degenerative conditions such as Parkinson’s disease and baldness, which are caused by cells dying without being replaced. The IPSCs fill those gaps, restoring the body’s systems. Professor Fairchild says IPSCs could help find a cure for certain disorders: “By deriving these cells from individuals with rare conditions, we are able to model the condition in the laboratory and investigate the effects of new drugs on that disease.“ A stem cell surrounded by red blood cells. Soon it could become one of them HUMANANATOMY Stem cells explained WorldMags.netWorldMags.net WorldMags.net
- 23. 023 ©Corbis;Alamy;Dreamstime How to grow a stem cell Fertilised human embryos that have been donated for research have plenty of stem cells inside them as the cells are yet to fully form. Scientists extract the cells and put them into a culture dish. This is filled with a culture medium, which is a mixture of nutrients that encourages the cells to divide and grow. As the cells divide they are placed into multiple dishes, each trying to complete an embryonic stem cell line. If a line is completed, it can then be used for further research and development. Eosinophils and neutrophils These are essential for stopping infections from spreading in the body. Platelets If you cut yourself, these blood cells clump together, stopping the blood flowing out of your body. Multipotent This stem cell in an adult is multipotent, so can become any blood- related cell. Chemical exchange When needed, chemicals from surrounding cells alter DNA strands inside the stem cell. Haematopoietic stem cell Stem cells inside the bone marrow are called haematopoietic stem cells. Bone marrow The bone marrow contains both active cells and stem cells that are waiting to develop. Myeloid progenitor cells These are the stem cells that become red blood cells, among others. Lymphoid progenitor cells These are the stem cells that turn into white blood cells, responsible for battling disease. STRANGE BUTTRUE A LIFE DIVIDED What happens if you halve a flatworm? Answer: Flatworms have the ability to regenerate organs, which is an invaluable skill for survival. Therefore, if you cut one in half, its pluripotent stem cells activate and create two flatworms. We’d rather you didn’t try this, though!A It dies B It becomes two flatworms C One half lives while the other dies Stem cells have been used to restore the sight of patients suffering from certain forms of blindnessDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 24. Theabilitytosmellisoneofour mostcrucialsensesandcan influencethefoodweeatand thepeoplewedate… Smell,orolfactiontousetheproper terminology,isaverydirectsense, inthatweactuallybreathein microscopicbitsofthe substancethatwesmell.Thesehitthe olfactoryepithelium,amucus membraneinthenasalcavity,which containsmillionsofolfactoryreceptor neuroncells.Eachofthesesensory cellsiscoveredinsmallhair-like structures,calledcilia,whichreacttothe odourandsendsignalstotheolfactorynerve, whichrelaysthisinformationtothebrainsoitisthen perceivedassmell.Humanscanrecognisearound 10,000differentodoursandnotwoindividualscan senseanythingexactlythesame. How do we smell? Nasal cavity This is where air and microscopic molecules of substances we are to smell enter. Air is pulled into this area to pass through into the lungs by the body’s diaphragm movements.1Women smell better Consistently, women out-perform men in smelling ability tests, and research has shown that women can recognise the smell of their baby only days after birth. 2Smell affects taste The human nose is actually the main organ involved in perceiving taste. Taste buds can only distinguish sweet, sour, bitter and salt, everything else perceived comes from smell! 3Blind people can’t smell better It’s a common myth that blind people can smell better than sighted. However, this has never been proven and most studies refute the fact. 4Smelling ability doesn’t improve after childhood At about eight, sense of smell reaches its full potential. Smelling ability reduces as you age. 5Sense of smell improves throughout the day When you first wake up, your sense of smell is far less acute than in the evening. 5 TOP FACTSSMELL Olfactory epithelium This is where the olfactory nerve cells are located. In a human, this area is around 10cm squared. Thepatchofsensorycellslocatedinthenasal cavityaremadeupofseveraldifferentparts Cells that smell Mucosa Mucosa lines the epithelium inside the nasal cavity and catches the odour particles to be sensed by the receptor neuron cells. Olfactory bulb This area of the brain is where signals are processed and smell is perceived. Other animals have a much larger area as they can perceive wider ranges of smells and use their sense of smell more. Olfactory nerves The olfactory nerves pass information about the particles sensed in the nasal cavity to the brain, where these signals are perceived as a certain smell. Olfactory cilia These sense the particles in air. There are 8-20 of these on each olfactory nerve cell which line the epithelium. Olfactory receptor neuron cells These are odour-sensitive cells that are stimulated by the cilia. They then send messages through to the brain. ©Chabacano,2007 HUMANANATOMY Human smell 024 WorldMags.netWorldMags.net WorldMags.net
- 25. 025 DID YOU KNOW? Buildinganin-depthmapofthetongue Thereisgeneralagreementthathumanshavefivebasictastes, althoughthefifthtaste‘primary’hasonlybeenrecentlyofficially recognised.Sweetness,bitterness,sournessandsaltinesswerejoined bysavourinessin2002.Severalothersensationsthatthetonguecan recognisehavebeenidentifiedbutarenotclassifiedastastes. Sweetnessisassociatedprimarilywithsimplecarbohydrates–ofwhichsugaris oneofthemostcommon.Thewaysweetnessisdetectediscomplexandonly recentlyhasthecurrentmodelofmultiplebindingsitesbetweenthereceptors andsweetsubstanceitselfbeenproposedandaccepted.Asweettasteinfersthat thesubstanceishighinenergyandstudieshaveshownthatnewbornsin particular,whoneedahighcalorieintaketogrow,demonstrateapreferencefor sugarconcentrationssweeterthanlactose,whichisfoundinbreastmilk. Bitternesscanbedetectedinverylowlevelsandisgenerallyperceivedtobean unpleasantorsharptaste.Manytoxicsubstancesinnatureareknowntobebitter andthereisanargumentproposedbyevolutionaryscientiststhatbitterness sensitivityisanevolutionarydefencemechanism.Humans,however,havenow developedvarioustechniquestomakepreviousinediblebittersubstancesedible throughreducingtheirtoxicity,oftenthroughcooking. Thetasteofsaltinessisproducedbythepresenceofsodiumions,orother closelyrelatedalkalimetalions.Potassiumandlithiumproduceasimilartasteas theyaremostcloselyrelatedtosodium. Sournessdetectsacidity.Thewaywemeasurethedegreeofsournessisthrough ratingsoursubstancesagainstdilutehydrochloric.Themechanisminvolvedin detectingsournessissimilartosaltinessinthattasteiscausedbyaconcentration ofions–inthiscasehydrogenions.Savourinessisthenewestoftherecognised basictastesandthetasteisproducedbyfermentedoragedfoods.Glutamateisa commoncompoundthatcancausethistasteandconsequentlysavourinessis consideredfundamentaltoEasterncuisine. The five basic human tastes Taste qualities are found in all areas of the tongue, although some regions are more sensitive than others. Your taste buds have very tiny, sensitive hairs called microvilli which send messages to your brain about how something tastes. 5TOP FACTS TASTE 1Things taste different to some because they are supertasters and experience taste significantly more intensely than ‘normal’ people. Around 25% of people are ‘supertasters’ Other factors contribute to flavour 3As well as having around 8,000 taste buds on the human tongue, humans also have them on the roof of their mouth and oesophagus. Taste buds are not only on the tongue You can lose your sense of taste 5Not all species taste things in the same way as humans. Butterflies’ taste sensors, for example, are actually located in their feet! Butterflies taste with their feet How do taste buds work? Tastebudsaresensoryorgansthatarefoundinthelittle bumps(orpapillae)onthetongue.Thetonguecontains about8,000tastebudsandthey’rereplacedapproximately everytwoweeks.Sensitivemicroscopichairsonthetaste buds(microvilli)pickupdissolvedchemicalsfromfoodandsend electricalsignalstothebrainthatdistinguishesbetweenfivedifferent tastes:sweet,bitter,savoury(umami),saltyandsour.Varying sensitivitytothesetastesoccursacrossthewholeofthetongue.But tastebudsalonecannottellustheexactflavouroffood.Otherfactors suchassmell,spiciness,temperatureandtexturealsocontributetothe eventualtaste.Soifyouholdyournosewhileyoueatthenyourbrain won’tgetthefulltastestory! Discoverhowwedistinguish betweenflavours “Factors such as smell, spiciness and texture also contribute to taste” The tongue contains about 8,000 taste budsDID YOU KNOW? 2It’s not all about just taste buds. Factors such as temperature, smell and even hearing can contribute to a thing’s flavour alongside taste. 4If you happen to suffer a serious head injury, neurological disorder or even dental problems, then these can severely affect your ability to taste things properly. WorldMags.netWorldMags.net WorldMags.net
- 26. Where you can find the three pairs of tonsils in your head Tonsil locations ©Thinkstock;DKImages Tonsils are the small masses of flesh found in pairs at the back of the throats of many mammals. In humans the word is actually used to describe three sets of this spongy lymphatic tissue: the lingual tonsils, the pharyngeal tonsils and the more commonly recognised palatine tonsils. The palatine tonsils are the oval bits that hang down from either side at the back of your throat – you can see them if you open your mouth wide in the mirror. Although the full purpose of the palatine tonsils isn’t yet understood, because they produce antibodies and because of their prominent position in the throat, they’re thought to be the first line of defence against potential infection in both the respiratory and digestive tracts. The pharyngeal tonsils are also known as the adenoids. These are found tucked away in the nasal pharynx and serve a similar purpose to the palatine tonsils but shrink in adulthood. The lingual tonsils are found at the back of the tongue towards the root and, if you poke your tongue right out, you should spot them. These are drained very efficiently by mucous glands so they very rarely get infected. Whatpurposedothesefleshylumps inthebackofourthroatsserve? What are tonsils for? Tonsillitis is usually caused by certain bacteria (eg group A beta-haemolytic streptococci) and sometimes viral infections that result in a sore and swollen throat, a fever, white spots at the back of the throat and difficulty swallowing. Usually rest and a course of antibiotics will see it off, but occasionally the infection is very severe and can potentially cause serious problems, or reoccurs very frequently. In these cases a tonsillectomy may be considered – a surgical procedure where the tonsils are removed. The adenoids are less commonly infected but, when they are, they become inflamed and swell to obstruct breathing through the nose and interfere with drainage from the sinuses, which can lead to further infections. In younger people, constant breathing through the mouth can stress the facial bones and cause deformities as they grow, which is why children will sometimes have their adenoid glands removed. Tonsillitis in focusLots of bed rest, fluids and pain relief like paracetamol are all recommended for treating tonsillitis Palatine tonsils These are the best-known pair of tonsils, as they’re clearly visible at the back of your throat. Lingual tonsils The lingual tonsils are found at the rear of your tongue – one at either side in your lower jaw. Pharyngeal tonsils These are otherwise known as the adenoids and are located at the back of the sinuses. HUMANANATOMY Human tonsils explained 026 WorldMags.netWorldMags.net WorldMags.net
- 27. 027 How do humans speak? Vocalcords,alsoknownas vocalfolds,aresituatedin thelarynx,whichisplaced atthetopofthetrachea. Theyarelayersofmucousmembranes thatstretchacrossthelarynxandcontrol howairisexpelledfromthelungsin ordertomakecertainsounds.The primaryusageofvocalcordswithin humansistocommunicateanditis hypothesisedthathumanvocalcords actuallydevelopedtotheextentwesee nowtofacilitateadvancedlevelsof communicationinresponsetothe formationofsocialgroupingsduring phasesofprimate,andspecifically human,evolution. Asairisexpelledfromthelungs,the vocalfoldsvibrateandcollidetoproduce arangeofsounds.Thetypeofsound emittediseffectedbyexactlyhowthe foldscollide,moveandstretchasair passesoverthem.Anindividual ‘fundamentalfrequency’(theirstandard pitch)isdeterminedbythelength,size andtensionoftheirvocalcords. Movementofthevocalfoldsiscontrolled bythevagusnerve,andsoundisthen furtherfine-tunedtoformwordsand soundsthatwecanrecognisebythe larynx,tongueandlips.Fundamental frequencyinmalesaveragesat125Hz, andat210Hzinfemales.Childrenhavea higheraveragepitchataround300Hz. Thevocalcordsandlarynxinparticular haveevolvedovertimetoenablehumansto produceadramaticrangeofsoundsinorder tocommunicate–buthowdotheywork? Vocal cords These layers of mucous membranes stretch across the larynx and they open, close and vibrate to produce different sounds. Trachea The vocal cords are situated at the top of the trachea, which is where air from the lungs travels up through from the chest. Tongue This muscle, situated in the mouth, can affect and change sound as it travels up from the vocal cords and out through the mouth. Epiglottis This is a flap of skin that shuts off the trachea when an individual is swallowing food. It stops food and liquids ‘going down the wrong way’. Oesophagus This tube, situated behind the trachea, is where food and liquid travels down to the stomach. Larynx Known as the voice box,thisprotectsthetrachea and is heavily involved in controlling pitch and volume. The vocal cords are situated within the larynx. Lips Lips are essential for the production of specific sounds, like ‘b’ or ‘p’. Differences between male and female vocal cords Malevoicesareoftenmuchlowerthan femalevoices.Thisisprimarilydueto thedifferentsizeofvocalfoldspresent ineachsex,withmaleshavinglarger foldsthatcreatealowerpitchedsound, andfemaleshavingsmallerfoldsthat createahigherpitchsound.The averagesizeformalevocalcordsare between17and25mm,andfemales arenormallybetween12.5and17.5mm. Fromtherangeinsize,however,males canbeseentohavequitehighpitch voices,andfemalescanhavequitelow pitchvoices. Theothermajorbiological differencethateffectspitchisthat malesgenerallyhavealargervocal tract,whichcanfurtherlowerthetone oftheirvoiceindependentofvocal cordsize.Thepitchandtoneofmale voiceshasbeenstudiedinrelationto sexualsuccess,andindividualswith lowervoiceshavebeenseentobe moresuccessfulinreproduction.The reasonproposedforthisisthatalower tonevoicemayindicateahigherlevel oftestosteronepresentinamale. Theepiglottisstopsfood enteringthetrachea Vocalcordsopenwhen breathing,butarepulled togetherwhenspeaking The vocal cords remain open when you breathe, but close completely when you hold your breathDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 28. 028 It’sacomputer,athinkingmachine,apinkorgan,andavast collectionofneurons–buthowdoesitwork?Thehumanbrainis amazinglycomplex–infact,morecomplexthananythinginthe knownuniverse.Thebraineffortlesslyconsumespower,stores memories,processesthoughts,andreactstodanger. Insomeways,thehumanbrainislikeacarengine.Thefuel–whichcould bethesandwichyouhadforlunchorasugardoughnutforbreakfast–causes neuronstofireinalogicalsequenceandtobondwithotherneurons.This combinationofneuronsoccursincrediblyfast,butthechainreactionmight helpyoucomposeasymphonyorrecallentirepassagesofabook,helpyou pedalabikeorwriteanemailtoafriend. Scientistsarejustbeginningtounderstandhowthesebrain neuronswork–theyhavenotfiguredouthowtheytriggerareaction whenyoutouchahotstove,forexample,orwhyyoucanre-generate braincellswhenyouworkoutatthegym. Theconnectionsinsideabrainareverysimilartotheinternet–the connectionsareconstantlyexchanginginformation.Yet,eventheinternet israthersimplisticwhencomparedtoneurons.Therearetento100neurons, andeachonemakesthousandsofconnections.Thisishowthebrain processesinformation,ordetermineshowtomoveanarmandgripasurface. Thesecalculations,perceptions,memories,andreactionsoccuralmost instantaneously,andnotjustafewtimesperminute,butmillions.According toJimOlds,researchdirectorwithGeorgeMasonUniversity,iftheinternet wereascomplexasoursolarsystem,thenthebrainwouldbeascomplexas ourgalaxy.Inotherwords,wehavealottolearn.Sciencehasnotgivenup trying,andhasmaderecentdiscoveriesabouthowweadapt,learnnew information,andcanactuallyincreasebraincapability. Inthemostbasicsense,ourbrainisthecentreofallinputandoutputsinthe humanbody.DrPaulaTallal,aco-directorofneuroscienceatRutgers University,saysthebrainisconstantlyprocessingsensoryinformation–even frominfancy.“It’seasiesttothinkofthebrainintermsofinputsandoutputs,” saysTallal.“Inputsaresensoryinformation,outputsarehowourbrain organisesthatinformationandcontrolsourmotorsystems.” Tallalsaysoneoftheprimaryfunctionsofthebrainisinlearningtopredict whatcomesnext.InherresearchforScientificLearning,shehasfoundthat youngchildrenenjoyhavingthesamebookreadtothemagainandagain becausethatishowthebrainregistersacousticcuesthatformintophonemes (sounds)tobecomespokenwords. “Welearntoputthingstogethersothattheybecomesmoothsequences,” shesays.Thesesmoothsequencesareobservableinthebrain,interpreting Thehumanbrainisthemost mysterious–andcomplex– entityintheknownuniverse Hypothalamus Controls metabolic functions such as body temperature, digestion, breathing, blood pressure, thirst, hunger, sexual drive, pain relays, and also regulates some hormones. Parts of the brainSowhatarethepartsofthebrain?According toOlds,therearealmosttoomanytocount –perhapsahundredormore,dependingon whoyouask.However,therearesomekey areasthatcontrolcertainfunctionsandstore thoughtsandmemories. Your brain Basal ganglia (unseen) Regulates involuntary movements such as posture and gait when we walk, and also regulates tremors and other irregularities. This is the section of the brain where Parkinson’s Disease can develop. The most fascinating organ of all HUMANANATOMY The most fascinating organ of all WorldMags.netWorldMags.net WorldMags.net
- 29. ©Marshmallow2008 Sperm whale The sperm whale has evolved the largest brain ever to exist on our planet, weighing as much as nine kilograms or 20 pounds. LARGEST 029 Cerebellum Consists of two cerebral hemispheres that controls motor activity, the planning of movements, co-ordination, and other body functions. This section of the brain weighs about 200 grams (compared to 1,300 grams for the main cortex). “In a sense, the main function of the brain is in ordering information – interpreting the outside world and making sense of it” Limbic system The part of the brain that controls intuitive thinking, emotional response, sense of smell and taste. theoutsideworldandmakingsenseofit.Thebrain isactuallyaseriesofinterconnected ‘superhighways’orpathwaysthatmove‘data’from onepartofthebodytoanother. Tallalsaysanotherwaytothinkaboutthebrain isbylowerandupperareas.Thespinalcordmoves informationuptothebrainstem,thenupintothe cerebralcortexwhichcontrolsthoughtsand memories.Interestingly,thebrainreallydoeswork likeapowerfulcomputerindeterminingnotonly movementsbutregisteringmemoriesthatcanbe quicklyrecalled. AccordingtoDrRobertMelillo,aneurologist andthefounderoftheBrainBalanceCenters (www.brainbalancecenters.com),thebrain actuallypredeterminesactionsandcalculatesthe resultsaboutahalf-secondbeforeperforming them(orevenfasterinsomecases).Thismeans thatwhenyoureachouttoopenadoor,your brainhasalreadypredeterminedhowtomove yourelbowandclaspyourhandaroundthedoor handle–maybeevensimulatedthismovement morethanonce,beforeyouevenactuallyperform theaction. Anotherinterestingaspecttothebrainisthat therearesomevoluntarymovementsandsome involuntary.Somesectionsofthebrainmight controlavoluntarymovement–suchaspatting yourkneetoabeat.Anothersectioncontrols involuntarymovements,suchasthegaitofyour walk–whichispasseddownfromyourparents. Reflexes,long-termmemories,thepainreflex– theseareallaspectsthatarecontrolledbysections inthebrain. Functions of the cerebral cortex Prefrontal cortex Executive functions such as complex planning, memorising, social and verbal skills, and anything that requires advanced thinking and interactions. In adults, helps us determine whether an action makes sense or is dangerous. Parietal lobe Where the brain senses touch and anything that interactswiththesurface of the skin, makes us aware of the feelings of our body and where we are in space. Frontal lobe Primarily controls senses such as taste, hearing, and smell. Association areas might help us determine language and the tone of someone’s voice. Temporal lobe What distinguishes the human brain – the ability to process and interpret what other parts of the brain are hearing, sensing, or tasting and determine a response. Thecerebralcortexisthewrinkling partofourbrainthatshowsupwhen youseepicturesofthebrain Complex movements Problem solving Skeletal movement Analysis of sounds Cerebral cortex The ‘grey matter’ of the brain controls cognition, motor activity, sensation, and other higher level functions. Includes the association areas which help process information. These association areas are what distinguishes the human brain from other brains. Elephant At 10.5 pounds (4.78kg) it’s certainly a big one. The brain of the elephant makes up less than 0.1 per cent of its body weight. LARGEST ON LAND The average human brain is 140mm wide x 167mm long x 93mm highDID YOU KNOW? BIG BRAINS Mouse lemur The smallest primate brain is owned by the pygmy mouse lemur of Madagascar and weighs in at just 0.004 pounds (2g). SMALLEST HEAD HEAD2 ©SPL Touch and skin sensations Language Receives signals from eyes Analysis of signal from eyes Speech Hearing WorldMags.netWorldMags.net WorldMags.net
- 30. Neurons, nerves and the spinal cord Neurons explained Neuronsfirelikeelectricalcircuits Neuronsareakindofcellinthebrain(humanshavemanycellsin thebody,includingfatcells,kidneycells,andglandcells).Aneuron isessentiallylikeahubthatworkswithnearbyneuronstogenerate anelectricalandchemicalcharge.DrLikoskyoftheSwedish MedicalInstitutesaysanotherwayofthinkingaboutneuronsis thattheyarelikeabasketballandtheconnections(calledaxons) arelikeelectricalwiresthatconnecttootherneurons.Thiscreates akindofcircuitinthehumanbody.Tallalexplainedthatinput fromthefivesensesinthebodycauseneuronstofire. “Themoreoftenacollectionofneuronsarestimulatedtogether intime,themorelikelytheyaretobindtogetherandtheeasierand easieritbecomesforthatpatternofneuronstofireinsynchronyas wellassequentially,”saysTallal. Neuron A neuron is a nerve cell in the brain that can be activated (usually by glucose) to connect with other neurons and form a bond that triggers an action in the brain. Neurotransmitter A neurotransmitter is the electro-chemical circuit that carries the signal from one neuron to another along the axon. A thin synapse A thin synapse (measuring just a few nanometres) between the neurotransmitter, carried along the axon in the brain, forms the electro-chemical connection. Inpictures,thehumanbrainoftenlookspinkandspongy. AccordingtoDrWilliamLikosky,aneurologistattheSwedish MedicalInstitute(www.swedish.org),thebrainisactually quitedifferentfromwhatmostpeoplethink.Likosky describedthebrainasbeingnotunlikefetacheesein appearance–afragileorganthatweighsabout1,500grams andsagsalmostlikeabagfilledwithwater.Intheskull,the brainishighlyprotectedandhashardtissue,butmostofthe fattytissueinthebrain–whichhelpspasschemicalsand othersubstancesthroughmembranes–isconsiderably moredelicate. What is my brain like?Ifyoucouldholditinyourhand… 030 Brain maps TrackVisgeneratesuniquemapsofthebrain TrackVisisafreeprogramusedbyneurologiststoseeamapofthebrainthatshows thefibreconnections.Oneverybrain,theseneuralpathwayshelpconnectonepartof thebraintoanothersothatafeelingyouexperienceinonepartofthebraincanbe transmittedandprocessedbyanotherpartofthebrain(onethatmaydecidethetouch isharmfulorpleasant).TrackVisusesfMRIreadingsonactualpatientstogeneratethe colourfulandeye-catchingimages.Toconstructthemaps,theprogramcantake severalhourstodetermineexactlyhowthefibresarepositioninginthebrain. The computers used to generate the TrackVis maps might use up to 1,000 graphics processors that work in tandem to process the data. ©DKImages HUMANANATOMY “The brain - a fragile organ that weighs about 1,500 grams” WorldMags.netWorldMags.net WorldMags.net
- 31. 031 The adult human brain weighs about 1.4kg (or three pounds)DID YOU KNOW? How do nerves work?Nervescarrysignalsthroughoutthe body–achemicalsuperhighway Nervesarethetransmissioncablesthatcarrybrainwavesinthe humanbody,saysSolDiamond,anassistantprofessorattheThayer SchoolofEngineeringatDartmouth.AccordingtoDiamond,nerves communicatethesesignalsfromonepointtoanother,whetherfrom yourtoenailuptoyourbrainorfromthesideofyourhead. Nerve transmissions Some nerve transmissions travel great distances through the human body, others travel short distances – both use a de-polarisation to create the circuit. De-polarisation is like a wound-up spring that releases stored energy once it is triggered. Myelinated and un-mylinated Some nerves are myelinated (or insulated) with fatty tissue that appears white and forms a slower connection over a longer distance. Others are un-myelinated and are un-insulated. These nerves travel shorter distances. What does the spinal cord do? Thespinalcordactually ispartofthebrainand playsamajorrole Scientistshaveknownforthe past100yearsorsothatthe spinalcordisactuallypartof thebrain.Accordingto Melillo,whilethebrainhas greymatterontheoutside (protectedbytheskull)and protectedwhitematteron theinside,thespinalcordis thereverse:thegreymatteris insidethespinalcordandthe whitematterisoutside. Grey matter cells Grey matter cells in the spinal cord cannot regenerate, which is why people with a serious spinal cord injury cannot recover over a period of time. White matter cells can re-generate. White matter cells White matter cells in the spinal cord carry the electro-chemical pulses up to the brain. For example, when you are kicked in the shin, you feel the pain in the shin and your brain then tells you to move your hand to cover that area. Neuroplasticity In the spinal cord and in the brain, cells can rejuvenate over time when you exercise and become strengthened. This process is called neuroplasticity. Neurogenesis According to Tallal, by repeating brain activities such as memorisation and pattern recognition, you can grow new brain cells in the spinal cord and brain. Neuronal fibre tracts Spinal nerve Nerve root ©DKImages THE BRAIN 1There are a staggering 100,000 miles of blood vessels in the brain, that is enough to wrap around Earth four times. 100,000 miles of blood vessels 2A headache actually occurs in blood vessels around the brain, not around the brain itself. The brain cannot feel any pain whatsoever. Headache not in the brain? 3Your brain is 60 per cent fat – which helps carry water and protein through membranes to brain cells, keeping everything ticking over. The brain consists of 60% fat 4The brain is quite greedy; it uses about 20 per cent of the power in your body that is generated from food consumption and processing. Your brain uses 20% of power 5The brain has trillions of connections – much more than the internet, and more than can currently be counted. The brain has trillions of connections5TOP FACTS Spinal cord core In the core of the spinal cord, grey matter – like the kind in the outer layer of the brain – is for processing nerve cells such as touch, pain and movement. Nerve triggers When many neurons are activated together at the same time, the nerve is excited – this is when we might feel the sensation of touch or a distinct smell. WorldMags.netWorldMags.net WorldMags.net
- 32. 032 The structure of the human eye is so complex that it’s hard to believe that it’s not the product of intelligent design, but by looking at the eyes of other animals, scientists have shown that it evolved very gradually from a simple light-dark sensor over the course of around 100 million years. It functions in a very similar way to a camera, with an opening through which the light enters, a lens for focusing and a light- sensitive membrane at the back. Theamountoflightthatenterstheeyeis controlledbythecircularandradialmusclesin theiris,whichcontractandrelaxtoalterthesize ofthepupil.Thelightfirstpasses throughatoughprotectivesheet calledthecornea,andthenmovesinto thelens.Thisadjustablestructure bendsthelight,focusingitdowntoa pointontheretina,atthebackoftheeye. The retina is covered in millions of light-sensitive receptors known as rods and cones. Each receptor contains pigment molecules, which change shape when they are hit by light, triggering an electrical message that travels to the brain via the optic nerve. Science of visionUncoveringoneofthemostcomplex constructsinthenaturalworld Seeing in three dimensions Our eyes are only able to produce two-dimensional images, but with some clever processing, the brain is able to build these flat pictures into a three-dimensional view. Our eyes are positioned about five centimetres (two inches) apart, so each sees the world from a slightly different angle. The brain compares the two pictures, using the differences to create the illusion of depth. Each eye sees a slightly different image, allowing the brain to perceive depth Individual image Due to the positioning of our eyes, when objects are closer than about 5.5m (18ft) away, each eye sees a slightly different angle. Combined image The incoming signals from both eyes are compared in the brain, and the subtle differences are used to create a three-dimensional image. Try it for yourself By holding your hand in front of your face and closing one eye at a time, it is easy to see the different 2D views perceived by each eye. Iris This circular muscle controls the size of the pupil, allowing it to be closed down in bright light, or opened wide in the dark. Retina The retina is covered in receptors that detect light. It is highly pigmented, preventing the light from scattering and ensuring a crisp image. Optic nerve Signals from the retina travel to the brain via the optic nerve, a bundle of fibres that exits through the back of the eye. Blind spot At the position where the optic nerve leaves the eye, there is no space for light receptors, leaving a natural blind spot in our vision. Fovea This pit at the centre of the back of the eye is rich in light receptors and is responsible for sharp central vision. HUMANANATOMY Inside the human eye WorldMags.netWorldMags.net WorldMags.net
- 33. Tarsier The eyes of these tiny primates are as big as their brains, so as a result, they have developed extremely good night vision. Ostrich Ostriches are the largest living birds and also have the largest eyes of any living land animal, measuring an incredible 5cm (2in) in diameter. Colossal squid Little is known about these mysterious creatures, but they have eyes the size of footballs – the largest known in the animal kingdom. HEAD HEAD2AN EYE FOR SIZE 1. BIG 2. BIGGER 3. BIGGEST 033 Protection The most common problems with our eyesight Pupil The pupil is a hole that allows light to reach the back of the eye. Lens The lens is responsible for focusing the light, and can change shape to accommodate objects near and far from the eye. Ciliary body This tissue surrounds the lens and contains the muscles responsible for changing its shape. Cornea The pupil and iris are covered in a tough, transparent membrane, which provides protection and contributes to focusing the light. Eyelashes Eyelashes not only catch dust before it enters the eye, they are also sensitive, like whiskers, and the slightest unexpected touch triggers a protective blink. Lachrymal gland Tears are produced here and wash across to the inner corner of the eye, helping to clean and nourish the surface. Sclera A tough white membrane known as the sclera helps to maintain the eye’s spherical shape. Vision problems Farsightedness (hyperopia) If the eye is too short, the cornea is too flat, or if the lens sits too far back, incoming light is focused behind the retina, making nearby objects appear blurry, particularly in the dark. Nearsightedness (myopia) If the eye is too long, or the cornea and lens are too curved, the light is focused before it hits the back of the eye, and then starts to defocus again as it reaches the retina, making distant objects difficult to see. Colour-blindness This rare condition is often linked to a gene on the X-chromosome and occurs more commonly in men than in women. A defect in the cone cells of the eye reduces the number of colours that can be detected. The eyes are shielded by several layers of protection. They are almost completely encased in bone at the back and insulated from shock by layers of muscle and connective tissue. The front is kept moist with tears and constantly wiped by the eyelids, while the hairs of the eyebrows and eyelashes catch any debris that might fall in. Eyebrows The arch of the eyebrows helps to keep sweat and rain away from the eyes, channelling it down the sides of the face. 285 million people in the world are estimated to be visually impaired and 39 million of them are blindDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 34. Thethingtorememberwhenlearning aboutthehumanearisthatsoundisall aboutmovement.Whensomeone speaksorbangsadrumormakesany kindofmovement,theairaroundthemis disturbed,creatingasoundwaveofalternating highandlowfrequency.Thesewavesaredetected bytheearandinterpretedbythebrainaswords, tunesorsounds. Consistingofair-filledcavities,labyrinthine fluid-filledchannelsandhighlysensitivecells,the earhasexternal,middleandinternalparts.The outerearconsistsofaskin-coveredflexiblecartilage flapcalledthe‘auricle’,or‘pinna’.Thisfeatureis shapedtogathersoundwavesandamplifythem beforetheyentertheearforprocessingand transmissiontothebrain.Thefirstthingasound waveenteringtheearencountersisthesheetof tightlypulledtissueseparatingtheouterand middleear.Thistissueistheeardrum,ortympanic membrane,anditvibratesassoundwaveshitit. Beyondtheeardrum,intheair-filledcavityofthe middleear,arethreetinybonescalledthe‘ossicles’. Thesearethesmallestbonesinyourentirebody. Soundvibrationshittingtheeardrumpasstothe firstossicle,themalleus(hammer).Nextthewaves proceedalongtheincus(anvil)andthenontothe (stapes)stirrup.Thestirruppressesagainstathin layeroftissuecalledthe‘ovalwindow’,andthis membraneenablessoundwavestoenterthe fluid-filledinnerear. Theinnerearishometothecochlea,which consistsofwateryductsthatchannelthevibrations, asripples,alongthecochlea’sspiralingtubes. Runningthroughthemiddleofthecochleaisthe organofCorti,whichislinedwithminutesensory haircellsthatpickuponthevibrationsand generatenerveimpulsesthataresenttothebrainas electricalsignals.Thebraincaninterpretthese signalsassounds. How ears workThehumanearperformsa rangeoffunctions,sending messagestothebrainwhena soundismadewhilealso providingyourbodywitha senseofbalance Structure of the ear Auricle (pinna) This is the visible part of the outer ear that collects sound wave vibrations and directs them into the ear. External acoustic meatus (outer ear canal) This is the wax-lined tube that channels sound vibrations from the outer pinna through the skull to the eardrum. Tympanic membrane (eardrum) The slightly concave thin layer of skin stretching across the ear canal and separating the outer and middle ear. Vibrations that hit the eardrum are transmitted as movement to the three ossicle bones. Malleus (hammer) One of the three ossicles, this hammer-shaped bone connects to the eardrum and moves with every vibration bouncing off the drum. Scala vestibuli (vestibular canal) Incoming vibrations travel along the outer vestibular canal of the cochlea. Cochlear duct The cochlear duct separates the tympanic and vestibular canals. The organ of Corti is found here. 034 HUMANANATOMY Ears explained WorldMags.netWorldMags.net WorldMags.net
- 35. The vestibular systemInsidetheinnereararethevestibule andsemicircularcanals,which featuresensorycells.Fromthe semicircularcanalsand maculae,informationabout whichwaytheheadis movingispassedto receptors,whichsend electricalsignals tothebrainas nerveimpulses. Thinkofsoundsas movements,or disturbancesofair, thatcreatewaves A sense of balance Thevestibularsystemfunctionstogive youasenseofwhichwayyourheadis pointinginrelationtogravity.Itenables youtodiscernwhetheryourheadis uprightornot,aswellashelpingyouto maintaineyecontactwithstationary objectswhileyourheadisturning. Alsolocatedwithintheinnerear,but lesstodowithsoundandmore concernedwiththemovementofyour head,arethesemicircularcanals.Again filledwithfluid,theseloopingductsact likeinternalaccelerometersthatcan detectacceleration(ie,movementofyour head)inthreedifferentdirectionsdueto thepositioningoftheloopsalong differentplanes.LiketheorganofCorti, thesemicircularcanalsemploytinyhair cellstosensemovement.Thecanalsare connectedtotheauditorynerveatthe backofthebrain. Yoursenseofbalanceissocomplex thattheareaofyourbrainthat’s dedicatedtothisoneroleinvolvesthe samenumberofcellsastherestofyour braincellsputtogether. Semicircular canal These three loops positioned at right angles to each other arefulloffluidthattransports sound vibrations to the crista. Crista At the end of each semicircular canal there are tiny hair-filled sensory receptors called cristae. Vestibule Inside the fluid-filled vestibules are two chambers (the utricle and saccule), both of which contain a structure called a macula, which is covered in sensory hair cells. Macula A sensory area covered in tiny hairs. Vestibular nerve Sends information about equilibrium from the semicircular canals to the brain. ©DKImages ©SciencePhotoLibrary Thesurfer’ssemicircularcanals areascrucialashisfeetwhenit comestostayingonhisboard Incus (anvil) Connected to the hammer, the incus is the middle ossicle bone and is shaped like an anvil. Stapes (stirrup) The stirrup is the third ossicle bone. It attaches to the oval window at the base of the cochlea. Movements transferred from the outer ear to the middle ear now continue their journey through the fluid of the inner ear. Cochlea A bony snail-shaped structure, the cochlea receives vibrations from the ossicles and transforms them into electrical signals that are transmitted to the brain. There are three fluid-filled channels – the vestibular canal, the tympanic canal and the cochlea duct – within the spiral of the cochlea. Scala tympani (tympanic canal) The vestibular canal and this, the tympanic canal, meet at the apex of the cochlear spiral (the helicotrema). Organ of Corti The organ of Corti contains rows of sensitive hair cells, the tips of which are embedded in the tectorial membrane. When the membrane vibrates, the hair receptors pass information through the cochlear nerve to the brain. Cochlear nerve Sends nerve impulses with information about sounds from the cochlea to the brain. 035 The eardrum needs to move less than the diameter of a hydrogen atom in order for us to perceive soundDID YOU KNOW? 5TOP FACTS HUMAN EARS 1Human ears can hear sounds with frequencies between 20Hz and 20,000Hz. The ability to hear frequencies above and below this is linked to the size of the cells and sensitivity. Hearing range 2Humans can hear much higher-pitched sounds (200,000Hz) when under water, because we can ‘hear’ with our bones, bypassing the outer ear and ossicles. Underwater hearing 3The most common causes of hearing loss are ageing and noise. As we age, our ability to hear sounds with higher frequencies deteriorates – this is known as ‘presbycusis’. Hearing loss 4Wax cleans and lubricates the outer auditory canal, transporting dirt and dead skin away from the ear. If excessive wax is a problem, consult your doctor. Wax essential 5Inflammation of the inner ear due to viral/bacterial conditions such as labyrinthitis can cause dizziness and nausea. When balance is affected, sufferers may not be able to walk or stand. Making me dizzy WorldMags.netWorldMags.net WorldMags.net
- 36. 036 Theprimaryfunctionof teethistocrunchandchew food.Forthisreason,teeth aremadeofstrong substances–namelycalcium, phosphorusandvariousmineralsalts. Themainstructureofthetoothis dentine,thisitselfisenclosedinashiny substancecalledenamel.Thisstrong whitecoatingisthehardestmaterial foundinthehumanbody. Humanshavedifferenttypesofteeth thatfunctioninvariousways.Incisors tearatfood,suchastheresiduefound onbones,whilebicuspidshavelong sharpstructuresthatarealsousedfor ripping.Bicuspidstearandcrushwhile molars,whichhaveaflattersurface, grindthefoodbeforeswallowing.This aidsdigestion.Becausehumanshavea variedarrayofteeth(calledcollective dentition)weareabletoeatacomplex dietofbothmeatandvegetables.Other species,suchasgrazinganimals,have specifictypesofteeth.Cows,forexample, havelargeflatteeth,whichrestrictsthem toasimplediet. Teethhavemanyfunctions,insome casestheyaidhuntingbuttheyalsohave strongpsychologicalconnotations.Both animalsandhumansbaretheirteeth whenfacedwithanaggressivesituation. Teetharethemostenduringfeaturesof thehumanbody.Mammalsare describedas‘diphyodont’,whichmeans theydeveloptwosetsofteeth.Inhumans theteethfirstappearatsixmonthsold andarereplacedbysecondaryteethafter sixorsevenyears.Someanimalsdevelop onlyonesetofteeth,whilesharks,for instance,growanewsetofteethevery twoweeks. Withhumans,toothlosscanoccur throughaccident,gumdiseaseoroldage. Fromancienttimeshealershavesought totreatandreplacetheteethwithfalse ones.Examplesofthispracticecanbe seenfromancientEgyptiantimesand today,weseerevolutionarynew techniquesintheformofdental implants,whicharesecureddeepwithin theboneofthejaw. Enamel The white, outer surface of the tooth. This can be clearly seen when looking in the mouth. Cementum The root coating, it protects the root canal and the nerves. It is connected to the jawbone through collagen fibres. Pulp The pulp nourishes the dentine and keeps the tooth healthy – the pulp is the soft tissue of the tooth, which is protected by the dentine and enamel. Blood vessels and nerves The blood vessels and nerves carry important nourishment to the tooth and are sensitive to pressure and temperature. Bone The bone acts as an important anchor for the tooth and keeps the root secure within the jawbone. The trouble with teeth Toothdecay,alsooften knownasdentalcaries, affectstheenameland dentineofatooth,breaking downtissueandcreating fissuresintheenamel.Two typesofbacteria–namely Streptococcusmutansand Lactobacillus–are responsiblefortoothdecay. Toothdecayoccursafter repeatedcontactwithacid- producingbacteria. Environmentalfactorsalso haveastrongeffectondental health.Sucrose,fructoseand glucosecreatelargeproblems withinthemouth,anddiet canbeanimportantfactorin maintaininggoodoralhealth. Themouthcontainsan enormousvarietyofbacteria, whichcollectsaroundthe teethandgums.Thisisvisible intheformofastickywhite substancecalledplaque. Plaqueisknownasabiofilm. Aftereating,thebacteriain themouthmetabolisessugar, whichsubsequentlyattacks theareasaroundtheteeth. HUMANANATOMY Your teeth Thebiological structuresthatareso versatiletheyenableus toeatawellvarieddiet All about teeth WorldMags.netWorldMags.net WorldMags.net
- 37. 037 Tooth anatomyThetoothisacomplexstructure.The enamelatthesurfaceofthetoothishighly visiblewhilethedentineisahardbut poroustissuefoundundertheenamel. Thegumsprovideasecureholdforthe tooth,whiletherootisanchoredright intothejawbone.Inthecentreofthetooth thereisasubstancecalled‘pulp’which containsnervesandbloodvessels,the pulpnourishesthedentineandkeepsthe toothhealthy. Toothformationbeginsbeforebirth. Normallythereare20primaryteeth (humanbabyteeth)andlater,28to32 permanentteeth,whichincludesthe wisdomteeth.Oftheprimaryteeth,ten arefoundinthemaxilla(theupperjaw) andteninthemandible(lowerjaw),while thematureadulthas16permanentteeth inthemaxillaand16inthemandible. 1. Hippopotamus A hippopotamus has an enormous mouth that can measure up to 1.2 metres wide. They are equipped with a pair of huge and very dangerous incisors. BIG 2. Piranha Piranha teeth are very small but can be extremely sharp and are often used by the local populations of South America to create a variety of tools and weapons. SMALL 3. Hamster A member of the rodent family, the hamster has teeth that grow continuously. They therefore need to grind their teeth on a hard substance to prevent overgrowth. SHARP ©ArtG07 ©Andrewself08 ©KeithPomakis Wisdom teeth Usually appear between the ages of 17 and 25, and often erupt in a group of four. Inside your mouthTheupperandlowerareasofthemouth areknownasthemaxillaandthe mandible.Theupperareaofthemouth isattachedtotheskullboneandisoften calledtheupperarchofthemouth, whilethemandibleisthev-shapedbone thatcarriesthelowersetofteeth. Canine teeth Long, pointed teeth that are used for holding and tearing at the food within the mouth. First and second premolar teeth The premolar or bicuspids are located between the canine and molar teeth. They are used for chewing. Lateral and central incisors Incisor comes from the Latin word ‘to cut’, they are used to grip and bite. ©SciencePhotoLibrary©SciencePhotoLibrary Regularcheck- upshelpkeep teethhealthy MaxillaAlayoutoftheupperarea ofyourmouth MandibleAlookinsideyourlowerjawbone 3rd molar or wisdom tooth 3rd molar or wisdom tooth 2nd molar 1st molar 1st bicuspid 2nd bicuspid Canine Central incisors Lateral incisors 2nd molar 1st molar 1st premolar 2nd premolar Canine Lateral incisors Central incisors Eruption of teethTheapproximate agesatwhichthe permanentteeth begintoerupt Age 6 Firstmolar Age 7 Centralincisor Age 9 Firstpremolar Age 10 Secondpremolar Age 11 Canine Age 12 Secondmolar Age 17 to 21 or not at all Thirdmolar (wisdomteeth) The ancient Egyptians had severe problems with their teeth. They invented the world’s first dental bridgeDID YOU KNOW? HEAD HEAD2ANIMAL TEETH WorldMags.netWorldMags.net WorldMags.net
- 38. HUMANANATOMY Neck anatomy 038 The human neck is a perfect blend of form and function. It has several specific tasks (eg making it possible to turn our heads to see), while serving as a conduit for other vital activities (eg connecting the mouth to the lungs). The anatomical design of the neck would impress modern engineers. The flexibility of the cervical spine allows your head to rotate, flex and tilt many thousands of times a day. The muscles and bones provide the strength and flexibility required, however the really impressive design comes with the trachea, oesophagus, spinal cord, myriad nerves and the vital blood vessels. These structures must all find space and function perfectly at the same time. They must also be able to maintain their shape while the neck moves. These structures are all highly adapted to achieve their aims. The trachea is protected by a ring of strong cartilage so it doesn’t collapse, while allowing enough flexibility to move when stretched. Above this, the larynx lets air move over the vocal cords so we can speak. Farther back, the oesophagus is a muscular tube which food and drink pass through en route to the stomach. Within the supporting bones of the neck sits the spinal cord, which transmits the vital nerves allowing us to move and feel. The carotid arteries and jugular veins, meanwhile, constantly carry blood to and from the brain. Exploreoneofthemostcomplexandfunctionalareasofthehumanbody Anatomy of the neck They are connected at the bottom of the skull and at the top of the spinal column. The first vertebra is called the atlas and the second is called the axis. Together these form a special pivot joint that grants far more movement than other vertebrae. The axis contains a bony projection upwards, upon which the atlas rotates, allowing the head to turn. The skull sits on top of slightly flattened areas of the atlas, providing a safe platform for it to stabilise on, and allowing for nodding motions. These bony connections are reinforced with strong muscles, adding further stability. Don’t forget that this amazing anatomical design still allows the vital spinal cord to pass out of the brain. The cord sits in the middle of the bony vertebrae, where it is protected from bumps and knocks. It sends out nerves at every level (starting right from the top) granting control over most of the body. How does the head connect to the neck? We show the major features that are packed into this junction between the head and torso Get it in the neck Larynx This serves two main functions: to connect the mouth to the trachea, and to generate your voice. Cartilage This tough tissue protects the delicate airways behind, including the larynx. Carotid artery These arteries transmit oxygenated blood from the heart to the brain. There are two of them (right and left), in case one becomes blocked. Vertebra These bones provide support to prevent the neck collapsing, hold up the skull and protect the spinal cord within. Spinal cord Shielded by the vertebrae, the spinal cord sends motor signals down nerves and receives sensory information from all around the body. Phrenic nerve These important nerves come off the third, fourth and fifth neck vertebrae, and innervate the diaphragm, which keeps you breathing (without you having to think about it). Sympathetic trunk These special nerves run alongside the spinal cord, and control sweating, heart rate and breathing, among other vital functions. Oesophagus This pipe connects the mouth to the stomach, and is collapsed until you swallow something, when its muscular walls stretch. WorldMags.netWorldMags.net WorldMags.net
- 39. Human The longest human neck ever recorded was 40 centimetres (15.8 inches) long. The average neck is closer to 10-12 centimetres (3.9-4.7 inches) in length. Sauropod These dinosaurs probably had the longest necks of all, with up to 19 vertebrae. Extinction means they don’t win the prize as the longest any more though. Giraffe The giraffe has the longest neck of any land animal today. However, amazingly, it has the same number of neck vertebrae as we do – seven. HEAD HEAD2LONG NECKS 1. LONG 2. LONGER 3. LONGEST 039 The hyoid bone at the front of the neck is the only one in the body not connected to another bone The human neck relies on a wide array of bones and muscles for support, as we see here The neck in context ©SPL;Thinkstock DID YOU KNOW? The physiology that lets us shake our heads Just say no… Axis In the spinal column, this is the second vertebra, which provides the stability for the required upwards bony projection. Odontoid process This bony projection is parallel with the longitudinal axis of the spine. Atlas This section articulates (moves) around the odontoid process which projects through it. Rotation The movement of the atlas around the odontoid peg allows for rotation of the skull above it. Atlas The first neck (cervical) vertebra is what permits the nodding motion of the head. Axis The second cervical vertebra allows rotation of the head. So when you’re shaking your head to say no, you have got this bone to thank. Cervical plexus These nerves provide sensation to the skin and also control the fine movements of the neck. Spinal cord Vertebrae create a cage of bones to protect the critical spinal cord within. Seventh cervical vertebra This is the bony protuberance at the bottom of your neck, which you can feel; doctors use it as a kind of landmark so they can locate the other vertebrae. Splenius capitis This muscle is an example of one of the many strap-like muscles which control the multitude of fine movements of the head and neck. Trapezius When you shrug your shoulders this broad muscle tenses up between your shoulder and neck. Sternocleidomastoid Turn your head left and feel the right of your neck – this is the muscle doing the turning. Jugular vein These vessels drain blood from the neck, returning it to the heart. WorldMags.netWorldMags.net WorldMags.net
- 40. Thehumanskeletoniscrucial forustolive.Itkeepsourshape andmuscleattachedtothe skeletonallowsustheabilityto movearound,whilealsoprotectingcrucial organsthatweneedtosurvive.Bonesalso producebloodcellswithinbonemarrow andstoremineralsweneedreleasedona dailybasis. Asafullygrownadultyouwillhave around206bones,butyouarebornwith over270,whichcontinuetogrow, strengthenandfuseafterbirthuntil around18infemalesand20inmales. Humanskeletonsactuallydovarybetween sexesinstructurealso.Oneofthemost obviousareasisthepelvisasafemalemust beabletogivebirth,andthereforehipsare comparativelyshallowerandwider.The craniumalsobecomesmorerobustin malesduetoheavymuscleattachmentand amale’schinisoftenmoreprominent. Femaleskeletonsaregenerallymore delicateoverall.However,althoughthere areseveralmethods,sexingcanbedifficult becauseofthelevelofvariationwesee withinthespecies. Bonesaremadeupofvariousdifferent elements.Inutero,theskeletontakes shapeascartilage,whichthenstartsto calcifyanddevelopduringgestationand followingbirth.Theprimaryelementthat makesupbone,osseoustissue,is actuallymineralisedcalcium phosphate,but otherformsoftissuesuch asmarrow,cartilageandbloodvesselsare alsocontainedintheoverallstructure. Manyindividualsthinkthatbonesare solid,butactuallyinnerboneisporousand full oflittleholes. Asweage,sodoourbones.Eventhough cellsareconstantlybeingreplaced,and thereforenocellinourbodyismorethan 20yearsold,theyarenotreplacedwith perfect,brand-newcells.Thecellscontain errorsintheirDNAandultimatelyour bonesthereforeweakenasweage. Conditionssuchasarthritisand osteoporosiscanoftenbecausedbyageing andcauseissueswithweakeningofbones andreducedmovementability. Withoutaskeleton,wewouldnot beabletolive.Itiswhatgivesus ourshapeandstructureandits presenceallowsustooperate onadailybasis.Italsoisa fascinatingevolutionarylink toallotherlivingand extinctvertebrates How the human skeleton works Phalanges Tarsals Carpals Scapula Sternum Patella Collarbone 4. Radius/Ulna The radius and ulna are the bones situated in the forearm. They connect the wrist and the elbow. 5. Rib cage This structure of many single rib bones creates a protective barrier for organs situated in the chest cavity. They join to the vertebrae in the spine at the back of the body, and the sternum at the front. HUMANANATOMY The human skeleton 040 WorldMags.netWorldMags.net WorldMags.net
- 41. Ifyousimplyfracturethebone,youmayjustneedtokeepit straightandkeeppressureoffituntilitheals.However,if youbreakitintomorethanonepiece,youmayneedmetal pinsinsertedintothebonetorealignitorplatestocoverthe breakinorderforittohealproperly.Thebonehealsby producingnewcellsandtinybloodvesselswherethe fractureorbreakhasoccurredandthesethenrejoinup.For mostbreaksorfractures,acastexternaltothebodywillbe putonaroundthebonetotakepressureofftheboneto ensurethatnomoredamageisdoneandthebreakcanheal. Whetherit’sacompletebreakor justafracture,bothcantaketime tohealproperly Skull development Whenweareborn,manyofour bonesarestillsomewhatsoftand arenotyetfused–thisprocess occurslaterduringourchildhood Theprimaryreasonsforthecraniuminparticularnottobe fullyfusedatbirthistoallowtheskulltoflexasthebabyis bornandalsotoallowtheextremerateofgrowththat occursinthefirstfewyearsofchildhoodfollowingbirth. Theskullisactuallyinsevenseparateplateswhenweare bornandoverthefirsttwoyearsthesepiecesfusetogether slowlyandossify.Theplatesstartsuturingtogetherearly on,buttheanteriorfontanel–commonlyknownasthesoft spot–willtakearound18monthstofullyheal.Someother bones,suchasthefiveboneslocatedinthesacrum,don’t fullyfuseuntillateteensorearlytwenties,butthecranium becomesfullyfusedbyaroundagetwo. 1. Cranium The cranium, also known as the skull, is where the brain and the majority of the sensory organs are located. 3. Vertebrae There are three main kinds of vertebrae (excluding the sacrum and coccyx) – cervical, thoracic and lumbar. These vary in strength and structure as they carry different pressure within the spine. 6. Pelvis This is the transitional joint between the trunk of the body and the legs. It is one of the key areas in which we can see the skeletal differences between the sexes. 7. Femur This is the largest and longest single bone in the body. It connects to the pelvis with a ball and socket joint. 8. Fibula/Tibia These two bones form the lower leg bone and connect to the knee joint and the foot. 9. Metatarsals These are the five long bones in the foot that aid balance and movement. Phalanges located close to the metatarsals are the bones which are present in toes. 2. Metacarpals The long bones in the hands are called metacarpals, and are the equivalent of metatarsals in the foot. Phalanges located close to the metacarpals make up the fingers. Inside our skeleton How the human skeleton works and keeps us upright 1. Snails Exoskeletons are often seen in animals. These are bulky, tough outer layers that protect the individual, instead of the endoskeletons we have. 2. Snake The skeleton of a snake is one of the strangest. Because of how it moves, it has more joints in the body, primarily vertebrae, and has no limbs. 3. Giraffe Considering the size of a giraffe’s neck, you’d expect it to have more cervical vertebrae than a human, but it only has seven – the same as us! EXOSKELETONS STRANGE SKELETONS NUMBERS OF VERTEBRAE How our joints workThe types of joints in our body explained 3. Skull sutures Although not generally thought of as a ‘joint’, all the cranial sutures present from where bones have fused in childhood are in fact immoveable joints. 1. Ball and socket joints Both the hip and the shoulder joints are ball and socket joints. The femur and humerus have ball shaped endings, which turn in a cavity to allow movement. 4. Hinged joints Both elbows and knees are hinged joints. These joints only allow limited movement in one direction. The bones fit together and are moved by muscles. 5. Gliding joints Some movement can be allowed when flat bones ‘glide’ across each other. The wrist bones – the carpals – operate like this, moved by ligaments. 6. Saddle joints The only place we see this joint in humans is the thumb. Movement is limited in rotation, but the thumb can move back, forward and to the sides. Breaking bones3skulls©DKImages Adult skull Six year old skull Baby skull Around five per cent of all animals have backbones and are therefore classified as vertebratesDID YOU KNOW? 041 HEAD HEAD2SKELETONS “The skull is actually seven separate plates when we are born, which fuse together” 2. Vertebrae Vertebrae fit together to support the body and allow bending movements. They are joined by cartilage and are classified as semi-mobile joints. WorldMags.netWorldMags.net WorldMags.net
- 42. HUMANANATOMY Amuscleisagroupoftissuefibresthat contractandreleasetocontrol movementswithinthebody.Wehave threedifferenttypesofmusclesinour bodies–smoothmuscle,cardiacmuscleand skeletalmuscle.Skeletalmuscle,alsoknownas striatedmuscle,iswhatwewouldcommonly perceiveasmuscle,thisbeingexternalmusclesthat areattachedtotheskeleton,suchasbicepsand deltoids.Thesemusclesareconnectedtothe skeletonwithtendons.Cardiacmuscleconcernsthe heart,whichiscrucialasitpumpsbloodaroundthe body,supplyingoxygenandultimatelyenergyto muscles,whichallowsthemtooperate.Smooth muscle,whichisnormallysheetmuscle,is primarilyinvolvedinmusclecontractionssuchas bladdercontrolandoesophagusmovements.These areoftenreferredtoasinvoluntaryaswehavelittle ornocontroloverthesemuscles’actions. Musclescontrolmostfunctionswithinour bodies;releaseofwasteproducts,breathing, seeing,eatingandmovementtonamebutafew. Actualmusclestructureisquitecomplex,andeach muscleismadeupofnumerousfibreswhichwork togethertogivethemusclestrength.Muscles increaseineffectivenessandstrengththrough exerciseandgrowthandthemainwaythisoccurs isthroughsmalldamagecausedbyeachrepetition ofamusclemovement,whichthebodythenrepairs andimproves. Morethan640musclesareactuallypresent acrossyourentirebodytoenableyourlimbsto work,controlbodilyfunctionsandshapethebody asawhole. Musclesareessentialforusto operateonadailybasis,buthow aretheystructuredandhowdo theykeepusmoving How do muscles work? 6. Abdominal muscles ‘Abs’ are often built up by body builders and support the body core. They are also referred to as core muscles and are important in sports such as rowing and yoga. 7. Quadriceps The large fleshy muscle group covering the front and sides of the thigh. 9. Hamstrings Refers to one of the three posterior thigh muscles, or to the tendons that make up the borders of the space behind the knee. 8. Gluteus maximus The biggest muscle in the body, this is primarily used to move the thighs back and forth. “More than 300 individual muscles are present across your body to enable your limbs to work” 042 Muscles explained WorldMags.netWorldMags.net WorldMags.net
- 43. 043 1. Gluteus maximus The gluteus maximus, the buttock, is the largest muscle. It is a superficial muscle that helps control thigh movement. 2. Stapedius The smallest muscle in the body is the stapedius, which is situated in the middle ear and helps move the tiny bones which aide our hearing. 3. Masseter muscle This is very much dependant on how you define strength. The masseter (jaw) muscle can exert the highest direct force on an object. SMALLEST MUSCLE STRONGEST MUSCLE 3. Pectoralis major Commonly known as the ‘pecs’, this group of muscles stretch across the chest. 2. Trapezius Large, superficial muscle at the back of the neck and the upper part of the thorax, or chest. 1. Deltoids These muscles stretch across the shoulders and aid lifting. 4. Biceps/triceps These arm muscles work together to lift the arm up and down. Each one contracts, causing movement in the opposite direction to the other. Musclestrengthreferstotheamountofforcethatamuscle canproduce,whileoperatingatmaximumcapacity,inone contraction.Sizeandstructureofthemuscleisimportant formusclestrength,withstrengthbeingmeasuredin severalways.Consequently,itishardtodefinitivelystate whichmuscleisactuallystrongest. Wehavetwotypesofmusclefibre–onethatsupports long,constantusageexertinglowlevelsofpressure,and onethatsupportsbrief,highlevelsofforce.Thelatteris usedduringanaerobicactivityandthesefibresrespond bettertomusclebuilding. Geneticscanaffectmusclestrength,ascanusage,diet andexerciseregimes.Contractionsofmusclescause injuriesinthemusclefibresanditisthehealingofthese thatactuallycreatemusclestrengthastheinjuriesare repairedandoverallstrengthenthemuscle. What affects our muscle strength? Musclesaremadeupofnumerouscylindrical fibres,whichworktogethertocontractand controlpartsofthebody.Musclefibresare boundtogetherbytheperimysiumintosmall bundles,whicharethengroupedtogetherby theepimysiumtoformtheactualmuscle. Bloodvesselsandnervesalsorunthrough theconnectivetissuetogiveenergytothe muscleandallowfeedbacktobesenttothe brain.Tendonsattachmusclessuchasbiceps andtricepstobones,allowingmusclesto moveelementsofourbodyaswewish. What are muscles made up of? Bicepsandtricepsareapairofmusclesthatworktogether tomovethearmupanddown.Asthebicepcontracts,the tricepswillrelaxandstretchoutandconsequentlythearm willmoveupwards.Whenthearmneedstomovedown, theoppositewilloccur–withthetricepscontractingand thebiceprelaxingandbeingforciblystretchedoutbythe triceps.Thebicepissonamedaflexorasitbendsajoint, andtricepswouldbetheextensorasitstraightensthejoint out.Neitherofthesemusclescanpushthemselvesstraight, theydependontheothertoopposetheirmovementsand stretchthemout.Manymusclesthereforeworkinpairs, so-calledantagonisticmuscles. How does the arm flex? Apulledmuscleisbasicallyatearinmusclefibres.Sudden movementscommonlycausepulledmuscles,andoften, whenanindividualhasnotwarmedupappropriately beforeexerciseorisunfit,atearcanoccurasthemuscleis notpreparedforusage.Themostcommonmuscletobe pulledisthehamstring, whichstretchesfrom thebuttocktotheknee. Apulledmusclemay resultinswellingand paincanlastforseveral daysbeforethefibres repairthemselves.To preventpulling muscles,warmingup isrecommended beforeanykindof physicalexertion. What is a pulled muscle, and how does it happen? Theyhurtlikecrazysohere’swhy it’simportanttowarmup Blood vessel This provides oxygen and allows the muscle to access energy for muscle operation. Epimysium The external layer that covers the muscle overall and keeps the bundles of muscle fibres together. Tendon These attach muscle to bones, which in turn enables the muscles to move parts of the body around (off image). Perimysium This layer groups together muscle fibres within the muscle. 3. Arm curls 2. Bicep contracts 1. Tricep relaxes 3. Arm extends 1. Bicep relaxes 2. Tricep contracts 5. Latissmus dorsi Also referred to as the ‘lats’, these muscles are again built up during weight training and are used to pull down objects from above. Howstrongweareisacombination ofnatureandnurture Go…run… gettothe chopper! “Tendons attach muscles such as biceps to bones, allowing muscles to move elements of our body” Endomysium This layer surrounds each singular muscle fibre and keeps the myofibril filaments grouped together. Filaments Myofibrils are constructed of filaments, which are made up of the proteins actin and myosin. LARGEST MUSCLE HUMAN MUSCLES Skeletal muscles account for around 40 per cent of your total body massDID YOU KNOW? HEAD HEAD2 Myofibril Located within the single muscle fibres, myofibrils are bundles of actomyosin filaments. They are crucial for contraction. WorldMags.netWorldMags.net WorldMags.net
- 44. Melanin and skin colour Surface Basal skin cells manufactured in the lower layers of the epidermis grow through the skin to the surface, where they are eventually sloughed away. Dendrite These branching cells pass melanin to keratinocytes. Melanocyte Those with lighter skin have fewer dendrites in their lower layers and their melanocytes are also less active. Keratinocytes The keratinocytes of lighter- skinned people take up fewer melanosomes. Melanosomes The melanosomes in lighter skin release far fewer melanin granules. Keratinocytes These protective cells are produced in the lower layers of the epidermis. They take up the melanosomes produced by the melanocytes. Melanosomes These packets of melanin release melanin granules into the keratinocytes. The light-absorbing pigment melanin is a chemical substance that gives your skin its natural colouring. Skin can vary from very dark brown to almost completely white due to a combination of your genes and inherited traits and the amount of sunlight to which you’re exposed. Skin colour differs from person to person depending on the concentration of melanin present in their skin and its distribution throughout the skin’s layers. Basically, those with less melanin have lighter skin, while those with more of the pigment have darker skin. Melanin is produced by specialised skin cells called melanocytes in the lower layers of the epidermis and is contained inside a melanosome by a very thin membrane. Exposure to sunlight stimulates the production of melanin granules. The melanosomes containing the melanin then move out towards the skin’s protective keratinocyte cells along branch cells called dendrites. Melanin is then stored in the nuclei of the keratinocytes where it acts as a natural protector against the effects of the Sun’s ultraviolet rays. Keratinocytes make up the bulk – around 95 per cent – of the outer layers of the skin and form the barrier between the body and the outside world. They take up melanin which can absorb cancer-causing UV radiation so it doesn’t get into the body’s internal tissues. Whatismelaninandhowdoes itaffectthetoneofourskin? Skin colour explained LIGHTDARK Melanocyte Melanin is made in the melanocytes. People with darker skin, or those who live in regions with greater sunlight exposure, have more active melanocytes. Skin grafting is a medical procedure where a portion of skin is removed and stitched onto another part of the body. There are many cosmetic and medical reasons why this might be necessary: serious burns, surgery, tattoo removal and some medical conditions (skin cancer or diabetes, for example) might all necessitate skin grafting. Autografts are skin grafts taken from the patient’s own body, usually the buttocks, neck or back of the arm. Depending on the size of the area that it’s removed from, it’s then stitched or stapled closed again and the new skin applied to the injured area. Allografts and xenografts, meanwhile – taken from other humans and animals, respectively – are temporary grafts. But perhaps most interesting is the artificial ‘skin’ called Integra, made of animal collagen that gives the damaged part an organic scaffolding for new skin to grow into. This is usually used in cases of extreme burns where there isn’t enough healthy skin for an autograft. Whenourbody’slargestorganisdamaged, sometimesitneedsahelpinghandtoheal How skin grafts work Skin graft surgery Donor skin The donor skin is removed and then applied to the injured area. Stitching Small skin grafts are stitched while bigger areas require stapling. Gauze A sterile gauze is applied while the skin attaches and a new blood supply establishes. ©Alamy HUMANANATOMY Skin colour / Skin grafts 044 WorldMags.netWorldMags.net WorldMags.net
- 45. 045 Under the skinOurskinisthelargestorganinourbodieswithan averageindividualskin’ssurfaceareameasuring aroundtwosquaremetresandaccountingforup to16percentoftotalbodyweight.Itismadeupof threedistinctlayers.Thesearetheepidermis,thedermisand thehypodermisandtheyallhavedifferingfunctions. Humansarerareinthatwecanseetheselayersdistinctly. Theepidermisisthetop,waterproofinglayer.Alongside helpingtoregulatetemperatureofthebody,theepidermis alsoprotectsagainstinfectionasitstopspathogensentering thebody.Althoughgenerallyreferredtoasonelayer,itis actuallymadeupoffive.Thetoplayersareactuallydead keratin-filledcellswhichpreventwaterlossandprovide protectionagainsttheenvironment,butthelowerlevels, wherenewskincellsareproduced,arenourishedbythe dermis.Inotherspecies,suchasamphibians,theepidermis consistsofonlyliveskincells.Inthesecases,theskinis generallypermeableandactuallymaybeamajor respiratoryorgan. Thedermishasthe connectivetissueandnerve endings,containshair follicles,sweatglands, lymphaticandblood vessels.Thetoplayerofthe dermisisridgedand interconnectssecurely withtheepidermis. Althoughthe hypodermisisnotactually consideredpartofthe skin,itspurposeisto connecttheupperlayers ofskintothebody’s underlyingboneand muscle.Bloodvesselsand nervespassthroughthis layertothedermis.This layerisalsocrucialfor temperature regulation,asit contains50percent ofahealthyadult’s bodyfatin subcutaneous tissue.Thesekindsof layersarenotoften seeninotherspecies, humansbeingoneoffew thatyoucanseethedistinct layerswithintheskin.Notonly doestheskinofferprotectionfor muscle,boneandinternalorgans,butitis ourprotectivebarrieragainstthe environment.Temperatureregulation, insulation,excretionofsweatandsensationarejusta fewmorefunctionsofskin. Findoutmoreaboutthelargestorganinyourbody… The skin is made of many more elements than most people imagine How your skin works ©DKImages 1Every square inch of an normal human’s skin has an average of 32 million bacteria on it… no matter how many baths or showers you have a day! Bacteria thrive on human skin 2Every 24 hours, you will lose your uppermost layer of dead skin cells, helping to keep your skin fresh and clean and able to breathe. You shed skin every day! 3Skin is around 1mm thick on your eyelids, but on your feet this thickness increases to 3mm, giving you much more protection where needed. Skin varies drastically in thickness 4Skin thins over time and begins to loosen, which is where wrinkles come from, and why people opt for plastic surgery in later life. As we age, skin thins 5Each square inch of healthy skin contains close to 650 sweat glands, which are essential for keeping you cool. We have billions of sweat glands All mammals have hair on their skin, including marine mammals which appear hairlessDID YOU KNOW? 5TOP FACTS SKIN 2. Dermis The layer that nourishes and helps maintain the epidermis, the dermis houses hair roots, nerve endings and sweat glands. 1. Epidermis This is the top, protective layer. It is waterproof and protects the body against UV light, disease and dehydration among other things. 3. Nerve ending Situated within the dermis, nerve endings allow us to sense temperature, pain and pressure. This gives us information on our environment and stops us hurting ourselves. 4. Pore Used for temperature regulation, this is where sweat is secreted to cool the body down when it is becoming too hot. 5. Subcutaneous tissue The layer of fat found in the hypodermis that is present to prevent heat loss and protect bone and muscle from damage. It is also a reserve energy source. WorldMags.netWorldMags.net WorldMags.net
- 46. Rheumatoidarthritisisa chronicandprogressive diseasethateffectsmany peoplearoundtheworld. Throughinflammationthroughout theconnectivetissuesofthebody,it causesirreversibledamageto individuals’joints.Thediseasedevelops whenaperson’sbodygeneratesan autoimmuneresponse–amistaken immunesystemreactionagainstthe body’sowntissues–thatattacksitsjoint componentsratherthanthehostile invadingorganisms. Asofnow,scientistsareunsureof whatinstigatestheautoimmune response,butitisthoughtthatit involvesabody’sgeneticsusceptibility tocertainviruses.Regardlesshowever, onceactivatedbysuchacause,aseries ofimmunesystemreactionsproceedto causeunwanted/abnormallevelsof inflammationandtissue/bone destructionwithinthebody. Inflammationiscausedbyaheavily abnormalinteractionbetweenB-cells andT-cells(see‘Cellular-level development’boxoutbelow),acomplex processthatcausesavarietyofproteins, antibodiesandothercellstobereleased whichbreakdownjointcartilage amongotherdamagingactivities. Howdoesthisconditioncauseintense inflammationofjointsandtheeventual destructionofcartilagetissue? Thecellularmechanisms,proteinsandantibodies involvedinthedevelopmentofrheumatoidarthritis Development of the condition Rheumatoid arthritis explained Plasma cells Plasma cells develop when B-cells are activated under stimulation by T-cells. They are a larger and more specialised antibody-producing cell. Macrophages The role of the macrophage is to engulf and digest cellular debris and pathogens, stimulate B-cells and release enzymes and proteins. Osteoclasts Osteoclasts are terminally differentiated cells of the macrophage lineage that re-absorb bone matrix. In rheumatoid arthritis, they aid joint destruction. T-cells Similar to B-cells, T-cells differ in the fact that they have special receptors on their surface. They assist the maturation of B-cells into plasma cells. Synovial membrane The synovial membrane is the soft tissue that lines the non-cartilaginous surfaces within joints. With rheumatoid arthritis, the synovium becomes irritated and enlarged. ©SciencePhotoLibrary B-cells B-cells are lymphocytes (white blood cells) that make antibodies to combat antigens. These cells internalise antigens before presenting them to T-cells. Extremeswellingand inflammationcausedby rheumatoidarthritis 046 ©JamesHeilman HUMANANATOMY Rheumatoid arthritis WorldMags.netWorldMags.net WorldMags.net
- 47. ©Alamy The skeleton is not only used as the body’s main structural support, it is also home to the largest collective reserve of adult stem cells within us. Bone marrow is a soft tissue present inside all the long bones of the limbs, and inside flat bones such as the pelvis, skull and ribs and it is jam-packed with haematopoietic stem cells. These cells are only partly committed to their development pathway, so depending on the signals they receive, can become any of the cells in the blood, from oxygen-carrying red blood cells to bacteria-munching macrophages. The majority of these stem cells are contained in the red marrow, which gains its colour from a rich network of blood vessels. The stem cells are supported by a range of other cells collectively known as stroma. The stromal cells provide the right microenvironment for the development of stem cells into the blood’s components, making a range of growth factors to encourage cells to differentiate down the correct path. In an adult human, most of the long bones are filled with yellow bone marrow – mostly made up of fat cells – however this can be converted to red marrow for blood cell production should an emergency arise. Bone marrow also contains a second, less-studied population of stem cells known as mesenchymal stem cells (MSCs). These are able to produce the basic elements that make up the connective tissues of the body, including fat cells, bone cells and fibroblasts. Learnhowbonemarrowcantransformcellsintowhateverthebodyneeds Inside our bones What is going on inside one of the long bones in our legs? Bone marrow in context Compact bone Compressedlayersof mineralisedboneon theoutsideprovide structuralsupport. Medullary cavity Ourlongbonesare mostlyhollow,andthe bonemarrowisstored insideacentralcavity. Blood supply Thestemcellsare generallyunabletoleave thebonemarrow;only fullydevelopedcellscan enterthebloodstream. Endosteum Theinnersurfaceofthe boneislinedwith bone-generatingcells calledosteoblasts, whichalsohelpto supportthestemcells. Bone marrow Inanadult,mostofthe medullarycavityisfilled withyellowmarrow, whiletheredmarrowis restrictedtotheendsof thebones. Osteon Thecompactbone thatsupportsthelegis madeupofseveral concentricsystems, constructedfrom layersofbone. See how bone marrow is a factory capable of producing all of the components which make up our blood… The origins of blood all of the components which make up our blood… 1. Haematopoietic stem cell Thisstemcellinredbone marrowisabletodevelop intoseveraldifferenttypes ofcelldependingonthe signalsitreceives. 2. Common myeloid progenitor TheHSCgraduallycommits tobecomingaparticular typeofcell.Eachstepin developmentnarrowsdown theoptions. 3. Common lymphoid progenitor OnceanHSCbecomesa lymphoidprogenitor,itis committedtobecominga lymphocyte(egB-cellswhich makeantibodies). 4. Erythrocyte Redbloodcellsare themostcommon typeofbloodcelland carryoxygenaround thebody. 4. Platelet Thesearesmallcellfragmentsinvolvedinblood clotting,andarecreatedbyfragmentationofhuge cellscalledmegakaryocytes. 4. Macrophage Whichcellthecommon myeloidprogenitor becomesdependson whatthebodyneeds. 4. Dendritic cell Theseplayavitalrolein theimmunesystem, capturingantigensand flaggingotherimmune cellstotakeaction. 047 Bone marrow constitutes approximately 4% of the total body mass of humansDID YOU KNOW? ©Alamy WorldMags.netWorldMags.net WorldMags.net
- 49. 049 Lumbar vertebrae Lumbar vertebraearethe largestofthe vertebraeand thestrongest, primarily becausethey withstandthe largest pressures. Comparedwith othervertebrae theyaremore compact,lacking facetsonthe sidesofthe vertebrae. Sacral vertebrae Wehavefivesacral vertebraeatbirth,butby maturitytheywillhavefused toformasolidbone,which helpssupportthelumbarvertebrae andconnectthecoccyxtothespine. Coccyx(tailbone) Thecoccyxcandisplaybetweenthreeandfive vertebrae.They’recommonlythoughttobefused, butoftenarenot.Althoughthesevertebraearea vestigialremnantofatail,theyhaveseveraluses, suchassupportingweightwhensitting. Howistheskull attachedtothe spine? Theskullisconnectedtothespinebythe atlanto-occipitaljoint,whichiscreated byC1(atlas)andtheoccipitalbone situatedatthebaseofthecranium (skull).Thisuniquevertebrahasno ‘body’andactuallylooksmorelikearing thananyothervertebra.Itsitsatthetop ofthecervicalvertebraeandconnects withtheoccipitalboneviaanellipsoidal joint,allowingmovementsuchas noddingorrotationofthehead.An ellipsoidaljointiswhereanovoid connection(inthiscasetheoccipital bone)isplacedintoanellipticalcavity(C1 vertebrae).Therestofthecervical vertebraealsoworktosupporttheweight ofthehead. ©SPL Skull Thevertebrae surroundthe spinalcord, whichconnects thebraintothe nervous system. Neck Thebones oftheneck (cervical vertebrae) arepartof thespine. © SPL © DKImages Spinalcolumncross-section 1.Spinalcord Thisisanimmenselyimportant pathwayforinformationto transferbetweenthebrainand thebody’snervoussystem.Itis heavilyprotectedbytissueand vertebrae,asanydamagetoit canbefatal. 2.Epiduralspace Thisisthespacebetweenthe outerprotectivetissuelayer, duramaterandthebone.Itis filledwithadiposetissue(fat), whilealsoplayinghostto numerousbloodvessels. 3.Duramater Thisisthetoughouterlayerof tissuethatprotectsthespinal cord.Thethreelayersof protectionbetweenthe vertebraeandthespinalcordare calledthespinalmeninges. 4.Arachnoidmater Namedforitsspiderweb appearance,thisisthesecond layerofthetissueprotection providedforthespinalcord. 5.Piamater Thisthin,delicatelayersits immediatelynexttothe spinalcord. 6.Subarachnoidspace Thisisthespacebetweenthepia materandthearachnoidmater, whichisfilledwith cerebrospinalfluid. 7.Bloodvessels Fourarteries,whichforma networkcalledtheCircleof Willis,deliveroxygen-richblood tothebrain.Thebrain’s capillariesformaliningcalled the‘blood-brainbarrier’,which controlsbloodflowtothebrain. 8.Dorsaland ventralroots Theseconnectthespinalnerves tothespinalcord,allowing transitionofinformation betweenthebrainandthebody. 9.Spinalnerves Humanshave31pairsofspinal nervesallalignedwith individualvertebrae,and thesecommunicateinformation fromaroundthebodytothe spinalcord.Theycarryall typesofinformation–motor, sensoryandsoon–andare commonlyreferredtoas‘mixed spinalnerves’. 10.Greymatter Withinthehorn-likeshapesin thecentreofthespinalcord,sit mostoftheimportantneuralcell bodies.Theyareprotectedin manyways,includingbythe whitematter. 11.Whitematter Thisareathatsurroundsthe greymatterholdsaxontrails,but isprimarilymadeupoflipid tissue(fats)andbloodvessels. 1 2 3 4 5 6 8 910 11 7 Articulatedvertebraeenable maximumflexibility 1. Swan With their long thin necks, swans have 25 cervical vertebrae. Such a high number helps to ensure maximum flexibility. 2. Amphibians Some amphibians, such as frogs, only have one neck vertebrae! Their size and structure means they don’t need the flexibility that most mammals need. 3. Giraffe Despite how incredibly long giraffe’s necks are, they only actually have the same number of cervical vertebrae as humans – just seven. MOST FEWEST SURPRISING Cartilage (intervertebral discs) actually makes up 25% of the spine’s lengthDID YOU KNOW? CERVICAL VERTEBRAE HEAD HEAD2 WorldMags.netWorldMags.net WorldMags.net
- 50. Whatcausesheartattacksand howdotheykill? Aheartattack,alsoknownasa myocardialinfarction,occurs whenablockagestopsblood oxygenatingtheheartmuscle.If thisisnotcorrectedquickly,themuscle tissuethatislackingoxygencanbecome damaged,orindeeddie.Thescaleofimpact ontheindividual’shealthaftertheattackis dependantonhowlongtheblockageoccurs for,whatarteryitaffectedandwhat treatmentwasreceived.Followingthe initialattack,heartfailureorarrhythmias canoccur,bothofwhichmayprovefatalto thevictim.However,giventheright treatmentmanysufferersgoontomake goodrecoveriesandcaneventuallyreturn totheirnormalactivities. Themostcommonreasonforheart attacks worldwideinhumansisthe generationofcoronaryarterydisease(CAD). Thisiswherearteriesareconstricteddueto plaquebuild-upsandthislayerthen ruptures.Bloodplateletsmaketheirwayto thesiteofruptureandstarttoformblood clots.Iftheseclotsbecometoolarge,the narrowedarterywillblockandaheart attackoccurs.Heartattackscanalsobe causedbycoronaryarteryspasms, butthesearerare. Althoughsomepeople willbegenetically predisposedtoheart attacks,individuals canreduceriskby keepingtheirweight down,watchingwhat theyeat,notsmokingand exercisingregularly. Heart attacks 1. Coronary arteries These are the arteries that supply the heart with blood. They are crucial to keeping the heart working effectively. 2. Plaque build-up Plaque, made up of inflammatory cells, proteins, fatty deposits and calcium, narrows the artery and means that only a reduced blood flow can get through. 3. Plaque rupture Plaque becomes hardened as it builds up, and it can rupture. If it ruptures, platelets gather to clot around the rupture, which can cause a blockage to occur. 4. Blockage occurs Either through excess clotting or further deposit build-up, a blockage can occur. This meansblood flow cannot get through at all and the lack of oxygen results in heart tissue dying. 5. Dead tissue Due to a lack of oxygen, some sections of heart muscle can die off. This can reduce effectiveness of the muscle as a whole following recovery. Heart muscle Dead heart muscle Blocked blood flow Plaque buildup in artery Healthy heart muscle Blood clot blocks artery Coronary artery Coronary artery (supplies blood and oxygen to heart muscle) HUMANANATOMY Heart attacks explained 050 WorldMags.netWorldMags.net WorldMags.net
- 51. 051 Althoughtheheartpumps oxygenatedbloodaroundthe body,theheart’smuscular wallsneedtheirownblood supply.Oxygen-richbloodisdeliveredto thesetissuesviasmallvesselsonits surface–thecoronaryarteries.These arteriescangetnarrowedorblockedup withcholesterolcausingfattyplaques whichslowbloodflow.Attimesof exercise,notenoughbloodgetstothe heartmuscles,leadingtopainduetolack ofoxygen–angina.Ifavesselbecomes completelyblocked,nobloodgets through,causingaheartattackwhere theheartmuscledies. Thefirstwaytotreatthistypeof coronaryarterydiseaseiswith medicines.Secondly,angioplastycanbe used,wherenarrowingswithinthe arteriesarestretchedusingaballoon, withorwithoutplacingastenttokeep thevesselopen.Finally,aheartbypass operationisanoptionforsomepatients. Thesurgeonuseshealthyvesselsfrom otherpartsofthepatient’sbodyto bypasstheblockage,allowinganew routeforbloodtoflow.Thisdelivers highervolumesoftheoxygen-richblood totheheartmusclesbeyondthe blockage,preventingthepain. Mostbypassesareperformedby stoppingtheheartandusingaheart- lungbypassmachinetodeliver oxygenatedbloodtothebody.Thenew vesselsarethensewnintoplace. Whentoolittlebloodisgettingtothemusclesoftheheart,a surgeoncanbypasstheblockagesusingthebody’sownvessels How heart bypasses work Heart bypass What happens in surgery? Stopping the heartCardiopulmonarybypass (whereamachinetakes overtheheart’spumping actionandthegas exchangefunctionofthe lungs)isestablishedto provideoxygenated bloodtotherestofthe body.Next,theheartis stopped.Thisisachieved usingapotassium-rich solution,pumpeddown thecoronaryarteries. Thisstopstheheart contracting.Thesurgeon cannowcarefullyattach thefreshvesselsto bypasstheblockages. 1. The problem Fatty plaques narrow and eventually block the coronary arteries, preventing oxygen-rich blood flowing to the heart muscle. 2. Getting to the heart The chest is opened through a cut down the middle of the breastbone (sternum). A special bone saw is used to cut through the sternum, which doesn’t damage the heart below. 3. Bypassing the heart Blood is removed by pumping it out of the body, oxygen is added to it in a bypass machine and the blood pumped back in. This allows oxygenated blood to continually flow while the heart is stopped. 4. Stopping the heart The aorta, the main vessel out of the heart, is clamped. The heart is then cooled and stopped using a potassium- rich solution. 5. Attaching the new vessels The new vessels are tested and then sewn into place. The opening is sewn to one of the large arteries carrying oxygen-rich blood. The end of the bypass graft is sewn beyond the fatty plaque, allowing blood to freely flow to the affected heart muscles. 6. Restarting the heart Once the new vessels have been secured, the aorta is unclamped which washes the potassium-rich solution from the heart. The patient is warmed and the heart restarts. 7. Closing the chest After making sure there is no bleeding, thin metal wires are used to hold the two halves of the sternum back together. Bypass grafts Thebodyhascertain vesselswhichitcando without,andtheseactas conduitsforbypass surgery.Commonly used,thelongsaphenous veinrunsfromtheankle tothegroin.Ashallow incisionallowstheveinto bedissectedawayfrom itssurroundingtissue. Othervesselsoftenused includesmallarteries frombehindtheribcage (internalmammary artery)orthearms (radialartery). Aorta Bypass graft Coronary artery Plaque blockage The heart has four separate chambers, four valves to control blood flow and two main coronary arteriesDID YOU KNOW? 5TOP FACTS BYPASSES 1Using complex mathematical models, each individual patient is given a risk of dying from the operation, allowing them to make a decision about how risky the operation is. Risk scores 2The op is free on the NHS but in the private sector it would cost £16,000-£20,000 ($23,300-$29,000). The price varies with the risks and if it’s the first surgery or a re-do. How much does it cost? 3On average, the heart beats 70 times per minute (about 100,000 times per day) which pumps five litres of blood per minute. Five per cent flows through the coronary arteries. How much blood? 4A bypass can be performed without stopping the heart, using a special retractor. In a few places, surgery has been performed this way on patients who are awake. Beating heart bypass 5New techniques include using mini-incisions into the chest and also the use of robots. Small cameras are also used to harvest the new vessels for the bypass grafts. New techniques WorldMags.netWorldMags.net WorldMags.net
- 52. Abloodtransfusiontakes placewhenapatientisgiven componentsofbloodfroma donorwhentheirownblood levelsaretoolow.Havingenoughblood isessentialbecauseitcarriesoxygen aroundthebodyandreturnscarbon dioxidetothelungstobeexhaledasa wasteproduct. Whenadoctordecidesapatientneeds blood,theyare‘cross-matched’with donorblood.Afewmillilitresoftheir bloodiscollectedintoasmallbottle whichmustbehand-labelledtoprevent confusionbetweenpatients.Inthelab thebloodismatchedwithdonorbloodof thesamegroup(eitherA,BorO).The unitofdonorbloodisthentransfused viaadripintothepatient’sveinovertwo tothreehours. Duringthistimethenursekeeps closeobservationofthepatienttolook fortransfusionreactions.Thesecanbe mild(suchasafever,chillsorarash), whicharesolvedbyslowingdownthe rateofflow,tosevere,life-threatening allergicreactions. Noonecanget atransfusion unlessblood donorskeep ondonating Whetherit’sapatient haemorrhagingto deathora‘topup’for life-longdiseases, bloodtransfusions arevitalprocedures Blood transfusions Red blood cells Red blood cells are the most abundant cells in blood and give it a red colour. They carry oxygen from the lungs around the body, bound to a protein called haemoglobin. Plasma Plasma is a straw-coloured watery fluid that carries all of the cells and proteins in blood, including the vital clotting factors. Platelets Platelets are tiny fragments of blood that are crucial in stopping bleeding, along with clotting factors, by forming a platelet plug. White blood cells These are your infection- fighting cells; they circulate in the blood so they can quickly multiply and be transported to an area where there’s an infection flaring. Lymphocytes Lymphocytes are a type of white blood cell that directs the body’s immune system. They have a memory for invading bacteria and viruses. What’s in your blood? Receiving a blood transfusion Thepatientisattachedtoa dripandthedonorbloodis transfusedthroughthis. Typicallyanarmveinis normallyused. Blood The blood is in a sterile, clear bag containing the details of the blood group and type, and the patient’s details it is intended for. Safety first Two nurses must double check the details on the bag of blood with the patient’s identify label before administering it. Blood screening All blood transfusions are now screened for HIV, hepatitis and other infections carried in blood. The cannula The drip is a plastic sheath which is placed directly into the patient’s vein so the transfused blood joins the circulating blood. ©CourtesyofNHSBloodandTransplant The ABO blood groups We all belong to one of four blood types (below). Different antigens present on the surface of red blood cells identify to which group you belong. A patient must receive blood with the correct antigens or else their immune system will recognise that the red blood cells are foreign cells and will attack. A– A antigens on red blood cells and anti-B antibodies in plasma B– B antigens on red blood cells and anti-A antibodies in plasma AB – A and B antigens on red blood cells and no antibodies in plasma O – No antigens on red blood cells and anti-A and anti-B antibodies in plasma HUMANANATOMY The science of blood transfusions 052 WorldMags.netWorldMags.net WorldMags.net
- 53. Thelossofbloodsupplytothebrain cancauselong-termdamageordeath Strokes Strokesarecausedwhentheflowofbloodtothebrainis interrupted.Therearetwomainreasonswhythismight occur,andischaemicstrokesarethemostcommon.They occurbecauseofabloodclotthatformsinanartery (thrombosis)orabloodclotthatformsandtravelstoabrainartery(arterial embolism)thatreducesorblocksthebloodflow(ischemia). Thesecondreasonisbleeding(haemorrhaging)ofabloodvesselinthe brain.Thiscanbecausedwhenathinpartofavessel(ananeurysm) bursts.Betweenoneandsixpercentofthepopulationhavean intracranialaneurysmandeveryyearintheUnitedKingdom1,400people dieofrupturedintracranialaneurysms. Astrokeisdefinedwheniteithercausesdeathorhasalong-termeffect after24hours.Youcanexperiencesignsofaministrokethatarecalled transientischemicattacks(TIAs)thatlastonlyafewminutesorhours.The onsetofafullstrokeischaracterisedbynumbnessinthefaceandlimbs. Visioncanbeimpairedandyoucanhavetroublewalkingortalking. Theeffectsofastrokedependonwhichpartofthebrainwasmost starvedofoxygenfromthebloodsupply.Inmanycases,strokevictims willfinditdifficulttowalkoreatduetomuscleweaknessandinextreme cases,theymightexperienceparalysis. ©SciencePhotoLibrary Areas of impact Carotid arteries Carotid blood vessels, served by the internal and external carotid arteries, supply blood to the front part of the cerebrum. Vertebral arteries Vertebral arteries supply blood to the rest of the brain and enter the skull through the foramen magnum. Clot Ischaemic strokes are caused by blood clots, which can either form directly in an artery, or form and then travel to a brain artery that it then blocks, reducing blood flow. Aneurysm When part of a thin blood vessel bursts haemorrhaging can occur. The first ever successful blood transfusion was performed on a dog in 1665 by Richard LowerDID YOU KNOW? 5TOP FACTS BLOOD Through the action of the thrombin system, coagulation of the blood occurs instantly at the location where there is a cut or other injury to the skin. The blood clot, which consists of a combination of cellular platelets and sticky strings of fibrin, forms a plug in the damaged blood vessels. The clot stops blood from freely flowing out of the body and at the same time allows the blood to continue circulating. As the skin heals, plasmin enzymes break down the webs of fibrin and the clot is eventually dissolved into the body. Clots can also form in blood vessels due to inactivity, old age, obesity, smoking, poor diet or during pregnancy. This condition is known as thrombosis and can lead to an embolism. Howthebodyreactstobloodvessel damagetoaidthehealingprocess Blood clotting Formation of a blood clot 1. Skin layer Composed of a water- resistant and protective layer called the epidermis; beneath it is the dermis layer that consists of blood vessels and connective tissue. Epidermis Strands of fibrin Platelets White blood cell Red blood cell Dermis 2. Cut If skin is cut, platelets in the blood vessels of the damaged area become ‘sticky’ and clump together at the damaged site to form a white clot. Other chemical reactions create sticky web-like strands of fibrin that adhere to the damaged blood vessel wall, to form a red clot. 3. Healing The blood clot stops blood escaping from the wound, and allows the normal circulation of the red blood cells which transport oxygen around the body and the white blood cells that protect it against infection. ©SPL 053 1One quarter of blood transfusions are given to patients with anaemia, whose blood levels have been dropping slowly over time due to diseases like cancer. Anaemia 2Some patients have blood disorders where their own red blood cells are deficient, such as in sickle cell disease or red cells destroyed at a high rate called haemolysis. Haematology 3In orthopaedic surgery – such as spinal fusion and hip arthroplasty – blood is lost during the operation. This is common with large joint replacement surgery. Orthopaedics 4Blood loss from the gastrointestinal tract, such as stomach ulcers and colorectal cancer, accounts for 11 per cent of all human blood transfusions. Gastrointestinal bleeding 5The fifth most common cause of blood transfusion is during or following traumatic childbirth. Normally blood loss during childbirth is less than 600ml. Childbirth WorldMags.netWorldMags.net WorldMags.net
- 54. Howdoyourkidneysfilter wastefromthebloodto keepyoualive? Kidneysarebean-shapedorgans situatedhalfwaydowntheback justundertheribcage,oneon eachsideofthebody,andweigh between115and170gramseach,dependent ontheindividual’ssexandsize.Theleft kidneyiscommonlyalittlelargerthanthe rightandduetotheeffectivenessofthese organs,individualsbornwithonlyone kidneycansurvivewithlittleornoadverse healthproblems.Indeed,thebodycan operatenormallywitha30-40percent declineinkidneyfunction.Thisdeclinein functionwouldrarelyevenbenoticeable andshowsjusthoweffectivethekidneysare atfilteringoutwasteproductsaswellas maintainingminerallevelsandblood pressurethroughoutthebody.Thekidneys managetocontrolallofthisbyworkingwith otherorgansandglandsacrossthebody suchasthehypothalamus,whichhelpsthe kidneysdetermineandcontrolwaterlevels inthebody. Eachdaythekidneyswillfilterbetween 150and180litresofblood,butonlypass aroundtwolitresofwastedowntheureters tothebladderforexcretion.Thiswaste productisprimarilyurea–aby-productof proteinbeingbrokendownforenergy–and water,andit’smorecommonlyknownas ‘urine’.Thekidneysfilterthebloodby passingitthroughasmallfilteringunit calledanephron.Eachkidneyhasaround amillionofthese,whicharemadeupofa numberofsmallbloodcapillaries,called glomerulus,andaurine-collectingtube calledtherenaltubule.Theglomerulussift thenormalcellsandproteinsfromtheblood andthenmovethewasteproductsintothe renaltubule,whichtransportsurinedown intothebladderthroughtheureters. Alongsidethisfilteringprocess,the kidneysalsoreleasethreecrucialhormones (knownaserythropoietin,reninand calcitriol)whichencourageredbloodcell production,aidregulationofbloodpressure andaidbonedevelopmentandmineral balancerespectively. 054 Kidney function Inside your kidney Renal cortex This is one of two broad internal sections of the kidney, the other being the renal medulla. The renal tubules are situated here in the protrusions that sit between the pyramids and secure the cortex and medulla together. Asbloodentersthekidneys,itispassed throughanephron,atinyunitmadeupof bloodcapillariesandawaste-transporting tube.Theseworktogethertofiltertheblood, returningcleanbloodtotheheartandlungs forre-oxygenationandrecirculationand removingwastetothebladderforexcretion. Renal pelvis This funnel-like structure is how urine travels out of the kidney and forms the top part of the ureter, which takes urine down to the bladder. Renal artery This artery supplies the kidney with blood that is to be filtered. Renal vein After waste has beenremoved,the clean blood is passed out of the kidney via the renal vein. Ureter The tube that transports the waste products (urine) to the bladder following blood filtration. Renal medulla The kidney’s inner section, where blood is filtered after passing through numerous arterioles. It’s split into sections called pyramids and each human kidney will normally have seven of these. Renal capsule The kidney’s fibrous outer edge, which provides protection for the kidney’s internal fibres. ©DKImages HUMANANATOMY How your kidneys work WorldMags.netWorldMags.net WorldMags.net
- 55. 055 The glomerulus Thisgroupofcapillariesisthefirststepof filtrationandacrucialaspectofanephron. Asbloodentersthekidneysviatherenal artery,itispasseddownthroughaseriesof arterioleswhicheventuallyleadtothe glomerulus.Thisisunusual,asinsteadof drainingintoavenule(whichwouldlead backtoavein)itdrainsbackintoan arteriole,whichcreatesmuchhigher pressurethannormallyseenincapillaries, whichinturnforcessolublematerials andfluidsoutofthecapillaries.Thisprocess isknownasultrafiltrationandisthefirst stepinfiltrationoftheblood.Thesethen passthroughtheBowman’scapsule (alsoknowastheglomerularcapsule)for furtherfiltration. Nephrons – the filtration units of the kidney Nephronsaretheunitswhichfilterallbloodthatpasses throughthekidneys.Therearearoundamillionineach kidney,situatedintherenalmedulla’spyramidstructures.As wellasfilteringwaste,nephronsregulatewaterandmineral saltbyrecirculatingwhatisneededandexcretingtherest. Glomerulus High pressure in the glomerulus, caused by it draining into an arteriole instead of a venule, forces fluids and soluble materials out of the capillary and into Bowman’s capsule. Loop of Henle The loop of Henle controls the mineral and water concentration levels within the kidney to aid filtration of fluids as necessary. It also controls urine concentration. Collecting duct system Although not technically part of the nephron, this collects all waste product filtered by the nephrons and facilitates its removal from the kidneys. Proximal tubule Links Bowman’s capsule and the loop of Henle, and will selectively reabsorb minerals from the filtrate produced by Bowman’s capsule. Distal convoluted tubule Partly responsible for the regulation of minerals in the blood, linking to the collecting duct system. Unwanted minerals are excreted from the nephron. Bowman’s capsule Also known as the glomerular capsule, this filters the fluid that has been expelled from the glomerulus. Resulting filtrate is passed along the nephron and will eventually make up urine. Renal tubule Made up of three parts, the proximal tubule, the loop of Henle and the distal convoluted tubule. They remove waste and reabsorb minerals from the filtrate passed on from Bowman’s capsule. Renal artery This artery supplies the kidney with blood. The blood travels through this, into arterioles as you travel into the kidney, until the blood reaches the glomerulus. Renal vein This removes blood that has been filtered from the kidney. Bowman’s capsule This is the surrounding capsule that will filter the filtrate produced by the glomerulus. Proximal tubule Where reabsorption of minerals from the filtrate from Bowman’s capsule will occur. Afferent arteriole This arteriole supplies the blood to the glomerulus for filtration. Efferent arteriole This arteriole is how blood leaves the glomerulus following ultrafiltration. Glomerulus This mass of capillaries is the glomerulus. What is urine and what is it made of? Urineismadeupofarangeoforganic compoundssuchasproteinsand hormones,inorganicsaltsand numerousmetabolites.These by-productsareoftenrichinnitrogen andneedtoberemovedfromtheblood streamthroughurination.ThepH-level ofurineistypicallyaroundneutral (pH7)butvariesdependingondiet, hydrationlevelsandphysicalfitness. Thecolourofurineisalsodetermined bythesefactors,withdark-yellowurine indicatingdehydrationandgreenish urinebeingindicativeofexcessive asparagusconsumption. 94% water 6% other organic compounds Useless body parts include the appendix, the coccyx and wisdom teethDID YOU KNOW? DID YOU KNOW? Wearethoughttohavetwokidneysbecausetheyaresocrucialtooursurvival, thesecondispurelya‘backup’.Havingtwoorgansobviouslyincreasesour chancesofsurvivalandreproductivefitness. Two for the price of one WorldMags.netWorldMags.net WorldMags.net
- 56. 056 Transplantingorgansisa complexprocess,although itcangiveanewleaseoflife torecipients.Thekidneyis themostfrequentlytransplanted organ,bothintheUKandaroundthe world.However,thereisadiscrepancy betweenthenumberofpatients waitingforatransplantandthe numberofavailableorgans;only aroundonethirdofthosewaitingper yearreceivetheirtransplant.The numberofpatientsregisteredfora kidneytransplantincreaseseachyear, andhasrisenby50percentsince2000. Kidneytransplantscomefromtwo mainsources:thelivingandthe recentlydeceased.Ifahealthy, compatiblefamilymemberiswillingto donateakidney,theycansurvivewith justoneremainingkidney.Inother cases,someoneelse’stragedyis someoneelse’sfortune.Forthosewho aredeclaredbrain-dead,thebeating heartwillkeepthekidneysperfused untiltheyarereadytoberemoved.In somepatients,theventilatorwillbe switchedoffandit’saraceagainsttime toharvestorgans.Eitherway,consent fromthefamilyisneeded,evenatsuch anemotionalandpressurisedtime. Whenasuitableorganbecomes available,itismatchedviaanational registertoasuitablerecipient.A ‘retrieval’teamfromacentral transplantunit(ofwhichthereare20 basedaroundtheUK)willgoto whicheverhospitalthedonorisin. Theywillremovetheorgans,whilethe recipientisbeingpreparedinthebase hospital.Duringthetrickyoperation, thenewkidneyis‘plumbed’intothe pelvis,leavingtheold,non-functioning onesin-situ. Kidney transplants How to perform a kidney transplant Transplantingakidneyis acaseofcarefuland cleverplumbing.Thefirst stepistoharvestthe donorkidney,andthen it’sadashtotransplant thenewkidneyintothe recipient.Whenthe brain-deaddonoris transferredtothe operatingtheatrefor organharvest,theyare treatedwiththesame careandrespectasifthey werestillalive.When consenthasbeengiven formultipleorgan harvest,acutismade fromthetopofthechest tothebottomofthe pelvis.Theheartand lungsareretrievedfirst, followedbythe abdominalorgans. ©SciencePhotoLibrary 1. The donor The donor kidney is harvested, including enough length of artery, vein and ureter (which carries urine to the bladder) to allow tension-free implantation into the recipient. 2. Out with the old? As long as there’s no question of cancer, the original kidneys are left in place. 3. Into the pelvis An incision is made in the lower part of the abdomen to gain access into the pelvis. 4. Make space! The surgeon will create space in the pelvis, and identify the large vessels which run from the heart to the leg (the iliac arteries and veins). The new kidney’s vessels vwill be connected to these. 5. Plumbing it in The renal artery and vein are connected to the corresponding iliac artery and vein in the recipient’s body. Holes (arteriotomies) are created in the main arteries, and the kidney’s vessels are anastomosed (a surgical join between two tubes using sutures). 6. The final link The ureter, which drains urine from the kidney, is connected to the bladder. This allows the kidney to function in the same way as one of the original kidneys. 7. What’s that lump? The new kidney can be felt underneath the scar in the recipient. These patients are often recruited to medical student exams . 8. Catheter A catheter is left in-situ for a short while, so that the urine output of the new kidney can be measured exactly. Kidney transplants HUMANANATOMY Thekidneysarethebody’snaturalfilters.Youcansurvive onjustone,butwhenthatfailsyoumayneedatransplant WorldMags.netWorldMags.net WorldMags.net
- 57. Pack carefully!Thetransportofharvestedorgans istimecritical–thesoonerthe surgeoncanputthemintothe recipientthebetter.Assoonas bloodstopsflowingtothe harvestedtissue,thelackofoxygen damagesthesecells,whichis calledischaemia.Theretrieval teamhaveafewtricksuptheir sleevestomaximisetheviabilityof thepreciouscargotheycarry. Intheoperatingtheatre,just beforetheyremovetheharvested kidney,itisflushedcleanofblood withaspecialcold,nutrient-rich solution.Onceremoved,itis quicklyputinasterilecontainer withice.Themostmodern techniqueistouseacoldperfusion machineinsteadofice,which pumpsacooledsolutionthrough thekidneyandimprovesitslasting power.Whileheartsandlungscan onlylastaroundfourhours, kidneyscanlast24-48hours. Transferoftheaffectedorganis doneviathefastestmethod possible;thisofteninvolvesusing helicoptersorpoliceescorts. Allofthesemethodsprolongthe preservationtimeofthekidney, althoughonce‘plugged’backin,it cantakeafewdaysforthekidney tostartworkingproperly (especiallyifharvestedfromanon- heart-beatingdonor). ©SciencePhotoLibrary Timeisalwaysof theessence 057 Of the millions of people in the UK suffering from kidney disease, 50,000 will suffer end-stage renal failureDID YOU KNOW? Who is suitable? Oftheseveralmillionpeoplein theUKwithkidneydisease,only around50,000willdevelop end-stagerenalfailure(ESRF).For thesepeople,dialysisorkidney transplantationaretheonly options.Kidneydamagefrom diabetesisthemostcommon causeoftransplantation.Other causesincludedamagefromhigh bloodpressure,chronickidney scarring(chronicpyelonephritis) andpolycystickidneydisease (thenormalkidneytissueis replacedwithmultiplecysts); manyotherlesscommoncauses existalso. Patientsmustbeselected carefullyduetothescarcityof organs.Thosewithwidespread cancer,severelycalcifiedarteries, persistentsubstanceabuseand unstablementalproblemsmean thattransplantsarelikelytofail andsothesepatientsare unsuitabletoreceiveaprecious kidneytransplant. When things go wrong… Kidneysneedtobecarefullymatchedtosuitabledonors,orrejectionoftheneworgan willsetinfast.Rejectionoccurswhenthehostbody’snaturalantibodiesthinkthe newtissueisaforeigninvaderandattacks;carefulpre-operativematchinghelpslimit thedegreeofthisattack.ThemostimportantmatchisviatheABObloodgrouptype– thebloodgroupmustmatchorrejectionisfastandaggressive.Next,thebody’sHLA (humanleukocyteantigen)systemshouldbeacloseamatchaspossible,althoughit doesn’tneedtobeperfect.Incorrectmatchesherecanleadtorejectionoverlonger periodsoftime.Aftertheoperation,patientsarestartedonanti-rejectionmedicines whichsuppressthehost’simmunesystem(immunosuppressantssuchasTacrolimus, AzathioprineorPrednisolone).Patientsaremonitoredfortherestoftheirlivesfor signsofrejection.Theseimmunosuppressantsaren’twithouttheirrisks–sincethey suppressthebody’snaturaldefences,therisksofinfectionsandcancersarehigher. Antibody If the antigens are too dissimilar, the host’s existing immune system thinks the new kidney is a foreign invader and attacks it with antibodies, leading to rejection. Antigens Antigens from the recipient kidney’s ABO blood group and HLA system should be as close a match to the donor’s as possible. Domino transplantsPatient1needsanewkidneybuttheir familymemberisn’tcompatible. Patient2alsoneedsakidneyandhas anincompatiblefamilymemberas well.However,patient2’srelationis compatiblewithpatient1andvice versa.Thesurgeonarrangesaswap– a‘paired’transplant.Alongerlineof patientsandfamilymembers swappingcompatiblekidneyscanbe arranged–a‘daisy-chain’transplant. A‘goodSamaritan’donor,whoisn’t relatedtoanyoftherecipients,can starttheprocess.Thisfirstrecipient’s familymemberwillsubsequently donatetosomeoneelse–a‘domino’ transplanteffectwhichcangoonfor severalcycles. COM PATIBLE NON-COMPATIBLE NON-COMPATIBLE From patient 1 family member From patient 2 family member Patient 1 Patient 2 5TOP FACTSTRANSPLANTS 1The very first kidney transplant to take place in the UK was performed in Edinburgh, 1960. Here a surgeon transplanted a kidney from a 49-year-old into his twin brother. Pioneers 2Around 7,000 people in the United Kingdom last year were waiting for organ transplants, but only around 2,300 kidney transplants actually took place. The ‘organ gap’ 3Organs that can be transplanted include kidneys, livers, hearts, lungs, the pancreas and intestines; tissues include bones, heart valves, skin and corneas. Which other organs? 4When removing a kidney from a living donor, the most modern centres use keyhole surgery (laparoscopy) to do it – this leads to smaller scars, less pain and faster recovery. Through the keyhole 5You can register to become an organ donor at http://www. organdonation.nhs.uk/ – don’t forget to talk to your loved ones about it. Do something about it “Patients are monitored for the rest of their lives” WorldMags.netWorldMags.net WorldMags.net
- 58. ©SPL;Thinkstock Charles Darwin is one of history’s most famous naturalists. Living in the 19th Century, he became celebrated for his theories on evolution. In his seminal work On The Origin Of Species he described how similar animals were likely to be related by common ancestors, rather than be completely unrelated. As subsequent generations are born, traits and features that did not bring a survival benefit to that species were eliminated. That, in a nutshell, is the theory of evolution. As a consequence, some organs and traits left in the body lose their function and are no longer used. This applies to modern human beings as much as other creatures; some of our physical attributes and behavioural responses are functional in other animals, but they do not seem to be of any benefit to us. These evolutionary remnants that no longer serve any purpose are called vestigial organs, though this can apply as much to behaviour and other body structures as it does to actual organs. Evolution has also adapted some existing features to help us in new ways, in a process known as exaptation. For example, birds’ wings not only help them to fly but keep them warm too. These changes may take thousands of years to develop, and in some cases the original role is eventually eliminated altogether. Whyhavehumansandotheranimalsstoppedusingcertain organsandfunctionswhichwereoncecrucialforsurvival? Useless body parts 1Appendix The best known of the vestigial organs, the appendix is used in animals to help digest cellulose found in grass, but in humans it serves no clear function now. 2Tailbone The hard bone at the bottom of your spine, the coccyx, is a remnant of our evolutionary ancestors’ tail. It has no function in humans, but you could break it if you fall over. 3Goosebumps Animals use body hair for insulation from the cold, by trapping a warm layer of air around the body. Each hair can stand on end when its own tiny muscle contracts, but as human beings have lost most of their body hair, a jumper is more effective. 4Plica semilunaris The fleshy red fold found in the corner of your eye used to be a transparent inner eyelid, which is still present in both reptiles and birds. 5Wisdom teeth These teeth emerge during our late teens in each corner of the gums. Our ancestors used them to help chew dense plant matter, but they have no function today, but can cause a lot of pain. Evolution’s leftovers Blockage Ablockage,causedbyeither atinypieceofwasteor swollenlymphatictissuein thebowelwall,causes appendixswelling. Surgery Duringsurgerytoremove theappendix,thesurgeon tiesoffthebasetoprevent bowelcontentsleaking, andremovesthewhole appendixorgan Progression Theinflammationcan leadtoperforationofthe appendixand inflammationof surroundingtissues. Thepainworsensand thenlocalisestothe lowerright-handsideof theabdomen. Inflammation Beyondtheblockage, inflammationsetsin,which causesintenseabdominalpain. Whathappenswhenyourappendixgetsinflamed? Appendicitis in focus ©SPL HUMANANATOMY Vestigial organs 058 WorldMags.netWorldMags.net WorldMags.net
- 59. ~5% PERCENTAGE OF CARDIAC OUTPUT IT RECEIVES 7.6 x 12.7 x 2.5cm 25% SIZE TOTAL WHITE PULP 200gWEIGHT 75%TOTAL RED PULP The spleen’s main functions are to remove old blood cells and fight off infection. Red blood cells have an average life span of 120 days. Most are created from the marrow of long bones, such as the femur. When they’re old, it’s the spleen’s job to identify them, filter them out and then break them down. The smaller particles are then sent back into the bloodstream, and either recycled or excreted from other parts of the body. This takes place in the ‘red pulp’, which are blood vessel-rich areas of the spleen that make up about three-quarters of its structure. The remainder is called ‘white pulp’, which are areas filled with different types of immune cell (such as lymphocytes). They filter out and destroy foreign pathogens, which have invaded the body and are circulating in the blood. The white pulp breaks them down into smaller, harmless particles. The spleen is surrounded by a thin, fragile capsule and so is prone to injury. It sits beneath the lower ribs on the left-hand side of your body, which affords it some protection, but car crashes, major sports impacts and knife wounds can all rupture the organ. In the most serious cases, blood loss can endanger the person’s life, and in these situations it needs to be removed by a surgeon. Since this reduces the body’s ability to fight infections, some people will need to take antibiotics to boost their immunity for the rest of their lives. Perhapsnotaswellknownasfamousorgansliketheheart, thespleenservesvitalfunctionsthathelpkeepushealthy How the spleen works The immune system Spleen Oneofthemasterco-ordinators thatstavesoffinfectionsand filtersoldredbloodcells.It contains anumberof lymphocytesthatrecogniseand destroyinvadingpathogens presentinthebloodasitflows throughthespleen. Thymus Asmallorganthatsitsjustabove theheartandbehindthe sternum.Itteaches T-lymphocytestoidentifyand destroyspecificforeignbodies. Itsdevelopmentisdirectly relatedtohormonesinthebody soit’sonlypresentuntilpuberty ends;adultsdon’tneedone. Tonsils Thesearemassesoflymphoid tissueatthebackofthethroat andcanbeseenwhenthemouth iswideopen.Theyformthefirst lineofdefenceagainstinhaled foreignpathogens,although theycanbecomeinfected themselves,causingtonsillitis. Adenoids Thesearepartofthetonsillar systemthatareonlypresentin childrenupuntiltheageoffive; inadultstheyhavedisappeared. Theyaddanextralayerof defenceinourearlyyears. Bone marrow Thisformsthecentral,flexible partofourlongbones(egfemur). Bonemarrowisessentialasit producesourkeycirculating cells,includingredbloodcells, whitebloodcellsandplatelets. Thewhitebloodcellsmature intodifferenttypes(eg lymphocytesandneutrophils), whichserveasthebasisofthe humanimmunesystem. Lymph nodes Thesearesmall(about1cm/ 0.4in)sphericalnodesthatare packedwithmacrophagesand lymphocytestodefendagainst foreignagents.Theseareoften linkedinchainsandare prevalentaroundthehead, neck,axillae(armpits)andgroin. ©Alamy Hilum The entrance to the spleen, this is where the splenic artery divides into smaller branches and the splenic vein is formed from its tributaries. Althoughtheredbloodthatflowsthroughourbodiesgetsallthe glory,thetransparentlymphaticfluidisequallyimportant.Ithasits ownbody-widenetworkwhichfollowsbloodvesselflowcloselyand allowsforthetransportofdigestedfats,immunecellsandmore… Location The spleen sits underneath the 9th, 10th and 11th ribs (below the diaphragm) on the left-hand side of the body, which provides it with some protection against knocks. Inside the spleen Wetakeyouonatourofthe majorfeaturesinthisoften- overlookedorgan Splenic artery The spleen receives a blood supply via this artery, which arises from a branch of the aorta called the coeliac trunk. Splenic vein The waste products from filtration and pathogen digestion are returned to the main circulation via this vein for disposal. Splenic capsule The capsule provides some protection, but it’s thin and relatively weak. Strong blows or knife wounds can easily rupture it and lead to life-threatening bleeding. Sinusoid Similar to those found in the liver, these capillaries allow for the easy passage of large cells into the splenic tissue for processing. Red pulp Forming approximately three-quarters of the spleen, the red pulp is where red blood cells are filtered and broken down. White pulp Making up roughly a quarter of the spleen, the white pulp is where white blood cells identify and destroy any type of invading pathogens. Around 15 per cent of us have an extra spleen – a small sphere close to but separate from the principal organDID YOU KNOW? THE STATS THE SPLEEN 059WorldMags.netWorldMags.net WorldMags.net
- 60. Thedigestivesystemisagroupoforgansthat processfoodintoenergythatthehumanbody canusetooperate.Itisanimmenselycomplex systemthatstretchesallthewaybetweenthe mouthandtheanus. Primaryorgansthatmakeupthesystemarethemouth, oesophagus,stomach,smallintestine,largeintestineandthe anus.Eachorganhasadifferentfunctionsothatthemaximum amountofenergyisgainedfromthefood,andthewastecan besafelyexpelledfromthebody.Secondaryorgans,suchas theliver,pancreasandgallbladder,aidthedigestiveprocess alongsidemucosacells,whichlineallholloworgansand produceasecretionwhichhelpsthefoodpasssmoothly throughthem.Musclecontractionscalledperistalsisalsohelp topushthefoodthroughoutthesystem. Thewholedigestiveprocessstartswhenfoodistakeninto thebodythroughthemouth.Mastication(chewing)breaks downthefoodintosmallerpiecesandsalivastartstobreak starchinthesepiecesoffoodintosimplersugarsastheyare swallowedandmoveintotheoesophagus.Oncethefoodhas passedthroughtheoesophagus,itpassesintothestomach.It canbestoredinthestomachforuptofourhours.Thestomach willeventuallymixthefoodwithdigestivejuicesthatit produces,andthisbreaksdownthefoodfurtherintosimpler molecules.Thesemoleculesthenmoveintothesmallintestine slowly,wherethefinalstageofchemicalbreakdownoccurs throughexposuretojuicesandenzymesreleasedfromthe pancreas,liverandglandsinthesmallintestine.Nutrientsare thenabsorbedthroughtheintestinalwallsandtransported aroundthebodythroughthebloodstream. Afterallnutrientshavebeenabsorbedfromfoodthroughthe smallintestine,resultingwastematerial,includingfibreand oldmucosacells,isthenpushedintothelargeintestinewhereit willremainuntilexpelledbyabowelmovement. Howdoesfoodget turnedintoenergy? Human digestion Many different organs are involved in the digestion process How your body digests food Rectum This is where waste material (faeces) exits the digestive system. 060 HUMANANATOMY Human digestive system “Nutrients are then absorbed through the intestinal walls and transported around the body” Small intestine Nutrients that have been released from food are absorbed into the blood stream so they can be transported to where they are needed in the body through the small intestine wall. Further breaking down occurs here with enzymes from the liver and pancreas. Large intestine The colon, as the large intestine is also known, is where waste material will be stored until expelled from the digestive system through the rectum. WorldMags.netWorldMags.net WorldMags.net
- 61. 061 Thestomach’sfunctionistobreakdownfood intosimplemoleculesbeforeitmovesinto thesmallintestinewherenutrientsare absorbed.Theorganactuallysplitsintofour distinctparts,allofwhichhavedifferent functions.Theuppermostsectionisthe cardia,wherefoodisfirststored,thefundus istheareaabovethecorpusbody,which makesupthemainareaofthestomach wherefoodismixedwithstomachacid.The finalsectionistheantrum,containingthe pyloricsphincter,whichisincontrolof emptyingthestomachcontentsintothe smallintestine.Foodispasseddownintothe stomachbymucosaandperistalsisthrough theoesophagealsphincter,andthenmixed inthestomachwithacidsandjuicesby musclecontractions. How does our stomach work?Thestomachisoneofthemostcrucial organswithinthedigestivesystem Oesophageal sphincter This is the control valve for letting food into the stomach. Corpus body This is where stomach acid is situated, consequently it is where food is broken down into molecules that the small intestine can then process. Theintestinesplitsintotwodistinctparts, thesmallintestineandthelargeintestine. Thesmallintestineiswherethefoodgoes throughfinalstagesofdigestionand nutrientsareabsorbedintothebloodstream, thelargeintestineiswherewasteisstored untilexpelledthroughtheanus.Boththe smallandlargeintestinescanbefurther dividedintosections,theduodenum, jejunumandileumarethethreedistinct sectionsofthesmallintestineandthe cecum,colonandrectumarethesectionsof thelargeintestine.Aswellasstoringwaste, thelargeintestineremoveswaterandsalt fromthewastebeforeitisexpelled.Muscle contractionsandmucosaareessentialforthe intestinetoworkproperly,andweseea variationofmucosa,calledvilli,presentin thelowerintestine. How the intestine works Theintestineisacrucial partofthedigestive systemthatisheavily involvedinbreaking downandabsorbing nutrientsreleasedfrom ingestedfood Villi These cells are shaped like fingers and linethe small intestine to increase surface area for nutrient absorption. Rectum This is where waste is stored briefly until it is expelled by the body. Duodenum The area at the top of the small intestine, this is where most chemical breakdown occurs. Oesophagus The oesophagus passes the food into the stomach. At this stage, it has been broken down through mastication and saliva will be breaking down starch. Mouth This is where food enters the body and first gets broken into more manageable pieces. Salivais produced in the glands and starts to break down starch in the food. ©DKImages ©DKImages Stomach This is where food is broken down to smaller molecules which can then be passed into the small intestine. Stomach acid and enzymes produced by the stomach aid this. Mucosa These cells line all of the stomach to aid movement of food throughout the organ. The human digestive system is between 20 to 30 feet long!DID YOU KNOW? 5TOP FACTS DIGESTION 1Generally, it can take between 24 and 72 hours for the food you eat to be fully digested, meaning you’re constantly digesting food! Complete digestion takes time! 2An average human male will consume approximately 50 tons of food during his lifetime. That’s the equivalent of ten African elephants. Some food for thought… 3The stomach will normally feel full when it reaches a capacity of one litre, but ultimately it can stretch up to two litres. The stomach can hold two litres 4Up to four pints of saliva can be produced by an individual each day and it helps to digest food and protect teeth and tissue inside the mouth. We use pints of saliva a day! 5Enzymes are crucial for digestion, but as we age, enzyme production reduces – at 70 a person may produce half what they did at 20. Enzyme production declines through age WorldMags.netWorldMags.net WorldMags.net
- 62. 062 Two halves The liver is anatomically split into two halves: left and right. There are four lobes, and the right lobe is the largest. The hepatobiliary region Eight segments Functionally, there are eight segments of the liver, which are based upon the distribution of veins draining these segments. The gallbladder The gallbladder and liver are intimately related. Bile, which helps digest fat, is produced in the liver and stored in the gallbladder. The common bile duct This duct is small, but vital in the human body. It carries bile from the liver and gallbladder into the duodenum where it helps digest fat. The portal triad The common bile duct, hepatic artery and hepatic portal vein form the portal triad, which are the vital inflows and outflows for this liver. Digestion Once nutrients from food have been absorbed in the small intestine, they are transported to the liver via the hepatic portal vein (not shown here) for energy production. The biggest organ The liver is the largest of the internal organs, sitting in the right upper quadrant of the abdomen, just under the rib cage and attached to the underside of the diaphragm. Thehumanliveristhe ultimatemultitasker– itperformsmany differentfunctions allatthesametime withoutyou evenasking How the liver worksTheliveristhelargestinternalorganin thehumanbodyandamazinglyhasover500 differentfunctions.Infact,itisthesecond mostcomplexorganafterthebrainandis intrinsicallyinvolvedinalmosteveryaspectofthebody’s metabolicprocesses.Theliver’smainfunctionsare energyproduction,removalofharmfulsubstancesand theproductionofcrucialproteins.Thesetasksarecarried outwithinlivercells,calledhepatocytes,whichsitin complexarrangementstomaximisetheiroverall efficiency. Theliveristhebody’smainpowerhouse,producing andstoringglucoseasakeyenergysource.Itisalso responsibleforbreakingdowncomplexfatmoleculesand buildingthemupintocholesterolandtriglycerides,which thebodyneedsbutinexcessarebad.Thelivermakes manycomplexproteins,includingclottingfactorswhich arevitalinarrestingbleeding.Bile,whichhelpsdigestfat intheintestines,isproducedintheliverandstoredinthe adjacentgallbladder. Theliveralsoplaysakeyroleindetoxifyingtheblood. Wasteproducts,toxinsanddrugsareprocessedhereinto Feel your liver Take a deep breath in and feel just under the right lower edge of your ribs – in some people the lower edge of the liver can be felt. HUMANANATOMY The liver explained WorldMags.netWorldMags.net WorldMags.net
- 63. The gallbladder Bile,adarkgreenslimyliquid,isproducedinthe hepatocytesandhelpstodigestfat.Itisstoredina reservoirwhichsitsontheunder-surfaceoftheliver, tobeusedwhenneeded.Thisreservoiriscalledthe gallbladder.Stonescanforminthegallbladder (gallstones)andareverycommon,althoughmost don’tcauseproblems.In2009,justunder60,000 gallbladderswereremovedfrompatientswithinthe NHSmakingitoneofthemostcommonoperations performed;over90percentoftheseareremovedvia keyholesurgery.Mostpatientsdoverywellwithout theirgallbladderanddon’tnoticeanychangesatall. 063 Liver lobules Theliverisconsidereda‘chemicalfactory,’asit formslargecomplexmoleculesfromsmaller onesbroughttoitfromthegutviatheblood stream.Thefunctionalunitoftheliveristhe lobule–thesearehexagonal-shaped structurescomprisingofbloodvessels andsinusoids.Sinusoidsarethe specialisedareaswhereblood comesintocontactwiththe hepatocytes,wheretheliver’s biologicalprocessestakeplace. 1. The lobule This arrangement of blood vessels, bile ducts and hepatocytes form the functional unit of the liver. 2. The hepatocyte These highly active cells perform all of the liver’s key metabolic tasks. 3. Sinusoids These blood filled channels are lined by hepatocytes and provide the site of transfer of molecules between blood and liver cells. 4. Kupffer cells These specialised cells sit within the sinusoids and destroy any bacteria which are contaminating blood. 5. Hepatic artery branch Blood from here supplies oxygen to hepatocytes and carries metabolic waste which the liver extracts. 6. Bile duct Bile, which helps digest fat, is made in hepatocytes and secreted into bile ducts. It then flows into the gallbladder for storage before being secreted into the duodenum. 7. Portal vein This vein carries nutrient-rich blood directly from the intestines, which flows into sinusoids for conversion into energy within hepatocytes. 8. The portal triad The hepatic artery, portal vein and bile duct are known as the portal triad. These sit at the edges of the liver lobule and are the main entry and exit routes for the liver. 9. Central vein Blood from sinusoids, now containing all of its new molecules, flows into central veins which then flow into larger hepatic veins. These drain into the heart via the inferior vena cava. formswhichareeasierfortherestofthebodytouseor excrete.Theliveralsobreaksdownoldbloodcells, producesantibodiestofightinfectionandrecycles hormonessuchasadrenaline.Numerousessential vitaminsandmineralsarestoredintheliver:vitaminsA, D,EandK,ironandcopper. Suchacomplexorganisalsounfortunatelyproneto diseases.Cancers(mostoftenmetastaticfromother sources),infections(hepatitis)andcirrhosis(aformof fibrosisoftencausedbyexcessalcoholconsumption)are justsomeofthosewhichcanaffecttheliver. “The liver also breaks down old blood cells and recycles hormones such as adrenaline” Stony Gallstones are common but usually don’t cause problems. A high demand organTheliverdealswithamassiveamountofblood. Itisuniquebecauseithastwobloodsupplies.75 percentofthiscomesdirectlyfromthe intestines(viathehepaticportalvein)which carriesnutrientsfromdigestion,whichtheliver processesandturnsintoenergy.Therestcomes fromtheheart,viathehepaticartery(which branchesfromtheaorta),carryingoxygenwhich theliverneedstoproducethisenergy.Theblood flowsintinypassagesinbetweenthelivercells wherethemanymetabolicfunctionsoccur.The bloodthenleavestheliverviathehepaticveins toflowintothebiggestveininthebody–the inferiorvenacava. Thefunctionalunitwhich performstheliver’stasks ©SciencePhotoLibrary 5TOP FACTS LIVER The liver can regenerate itself. If up to 75 per cent of the liver is removed, it can grow back to restore itselfDID YOU KNOW? 1Polar bear liver is an incredibly rich source of vitamin A – so much so that Arctic explorers have actually died from eating it, as it can cause extreme vitamin A poisoning. Ice cold liver 2In the UK 600-700 liver transplants are performed each year. The donor liver can be preserved in a solution for up to 24 hours before it is transplanted. Liver transplants 3Ways around the shortage of donor livers include splitting an adult liver in half and giving it to two children, and live-donor transplantation (a portion of a relative’s liver is transplanted). Maximising numbers 4The liver is the largest internal organ in the human body and in most animals’ bodies too. It typically has the same shape as a human’s, except in snakes where it is elongated. Largest organ in the body 5Wise Titan Prometheus was chained for eternity to a rock in the Caucasus, where an eagle would eat at his liver and each day the liver would be renewed! Greek mythology WorldMags.netWorldMags.net WorldMags.net
- 64. 064 Examine the anatomy of this vital organ in the human digestive tract Mucosa The internal lining of the small intestine where the plicae circulares (mucosal folds) and villi are situated. The small intestine is one of the most important elements of our digestive system, which enables us to process food and absorb nutrients. On average, it sits at a little over six metres (19.7 feet) long with a diameter of 2.5-3 centimetres (1-1.2 inches), and it’s made up of three distinctive parts: the duodenum, jejunum and the ileum. The duodenum connects the small intestine to the stomach and is the key place for further enzyme breakdown, following the stomach turning food into an amino acid state. While the duodenum is very important in breaking food down, using bile and enzymes from the gallbladder, liver and pancreas, it is the shortest element of the small bowel, only averaging about 30 centimetres (11.8 inches). The jejunum follows the duodenum and its primary function is to encourage absorption of carbohydrates and proteins by passing the broken-down food molecules through an area with a large surface area so they can enter the bloodstream. Villi – small finger-like structures – and mucosal folds line the passage and increase the surface area dramatically to aid this process. The ileum is the final section of the small bowel and serves to catch nutrients that may have been missed, as well as absorbing vitamin B12 and bile salts. Peristalsis is the movement used by the small intestine to push the food through to the large bowel, where waste matter is stored for a short period then disposed of via the colon. This process is generated by a series of muscles which make up the organ’s outer wall. Crucialforgettingthenutrientsweneedfromthe foodweeat,howdoesthisdigestiveorganwork? Exploring the small intestine The surface area of the small intestine is huge – in fact, rolled flat it would cover a tennis court! Structure of the small intestine Mucosal folds These line the small intestine to increase surface area and help push the food on its way by creating a valve-like structure, stopping food travelling backwards. Lumen This is the space inside the small intestine in which the food travels to be digested and absorbed. Submucosa This supports the mucosa and connects it to the layers of muscle (muscularis) that make up the exterior of the small intestine. HUMANANATOMY How the small intestine works WorldMags.netWorldMags.net WorldMags.net
- 65. 6mLENGTH 2.5-3cmDIAMETER 250m2SURFACE AREA 90%AMOUNT OF BODY’S NUTRIENT ABSORPTION 1-4 hoursTIME IT TAKES FOOD TO PASS THROUGH 10-40NUMBER OF VILLI PER SQUARE MM 065 ©Corbis;Thinkstock There are three main types of nutrient that we process in the body: lipids (fats), carbohydrates and proteins. These three groups of molecules are broken down into sugars, starches, fats and smaller, simpler molecule elements, which we can absorb through the small intestine walls and that then travel in the bloodstream to our muscles and other areas of the body that require energy or to be repaired. We also need to consume and absorb vitamins and minerals that we can’t synthesise within the body, eg vitamin B12 (prevalent in meat and fish). What exactly are nutrients? Blood vessels These sit close to the small intestine to allow easy diffusion of nutrients into the bloodstream. Circular muscle layer This works in partnership with the longitudinal muscle layer to push the food down via a process called peristalsis. Longitudinal muscle layer This contracts and extends to help transport food with the circular muscle layer. Villi Villi are tiny finger-like structures that sit all over the mucosa. They help increase the surface area massively, alongside the mucosal folds. Nutrients Nutrients move through the tube-like organ to be diffused into the body, mainly via the bloodstream. Serosa This protective outer layer stops the small intestine from being damaged by other organs. What role do these little finger-like protrusions play in the bowel? A closer look at villi Epithelium (epithelial cells) These individual cells that sit in the mucosa layer are where individual microvilli extend from. Lacteal The lacteal is a lymphatic capillary that absorbs nutrients that can’t pass directly into the bloodstream. Capillary bed These absorb simple sugars and amino acids as they pass through the epithelial tissue of the villi. Microvilli These are a mini version of villi and sit on villi’s individual epithelial cells. Mucosa The lining of the small intestine on which villi are located. Fat Carbohydrate Protein THE STATS SMALL BOWEL The small intestine is actually longer than the large intestine, but is so called because of its narrower diameterDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 66. 066 The ribcage – also known as the thoracic cage or thoracic basket – is easily thought of as just a framework protecting your lungs, heart and other major organs. Although that is one key function, the ribcage does so much more. It provides vital support as part of the skeleton and, simply put, breathing wouldn’t be possible without it. All this means that the ribcage has to be flexible. The conical structure isn’t just a rigid system of bone – it’s both bone and cartilage. The cage comprises 24 ribs, joining in the back to the 12 vertebrae making up the middle of the spinal column. The cartilage portions of the ribs meet in the front at the long, flat three- bone plate called the sternum (breastbone). Or rather, most of them do. Rib pairs one through seven are called ‘true ribs’ because they attach directly to the sternum. Rib pairs eight through ten attach indirectly through other cartilage structures, so they’re referred to as ‘false ribs’. The final two pairs – the ‘floating ribs’ – hang unattached to the sternum. Rib fractures are a common and very painful injury, with the middle ribs the most likely ones to get broken. A fractured rib can be very dangerous, because a sharp piece could pierce the heart or lungs. There’s also a condition called flail chest, in which several ribs break and detach from the cage, which can even be fatal. But otherwise there’s not much you can do to mend a fractured rib other than keep it stabilised, resting and giving it time to heal. Ribsarenotmerelyarmourfortheorgans insideourtorsos,aswerevealhere… The human ribcage It may not look like it at first glance, but there are more than two dozen bones that make up the ribcage… Clavicle Also known as the collarbone, this pair of long bones is a support between the sternum and the shoulder blades. Inside the thoracic cavity True ribs Rib pairs one through seven attach to the sternum directly via a piece of cartilage. False ribs Rib pairs eight through ten connect to the sternum via a structure made of cartilage linked to the seventh true rib. Hiccupping – known medically as singultus, or synchronous diaphragmatic flutter (SDF) – is an involuntary spasm of the diaphragm that can happen for a number of reasons. Short-term causes include eating or drinking too quickly, a sudden change in body temperature or shock. However, some researchers have suggested that hiccupping in premature babies – who tend to hiccup much more than full-term babies – is due to their underdeveloped lungs. It could be an evolutionary leftover, since hiccupping in humans is similar to the way that amphibians gulp water and air into their gills to breathe. What are hiccups? HUMANANATOMY Human ribcage formation WorldMags.netWorldMags.net WorldMags.net
- 67. 067 ©Thinkstock Consciously take in a breath, and think about the fact that there are ten different muscle groups working together to make it happen. The muscles that move the ribcage itself are the intercostal muscles. They are each attached to the ribs and run between them. As you inhale, the external intercostals raise the ribs and sternum so your lungs can expand, while your diaphragm lowers and flattens. The internal intercostals lower the ribcage when you exhale. This forces the lungs to compress and release air (working in tandem with seven other muscles). If you breathe out gently, it’s a passive process that doesn’t require much ribcage movement. Most vertebrates (ie animals with backbones) have a ribcage of sorts – however, ribcages can be very different depending on the creature. For example, dogs and cats have 13 pairs of ribs as opposed to our 12. Marsupials have fewer ribs than humans, and some of those are so tiny they aren’t much more than knobs of bone sticking out from the vertebrae. Once you get into other vertebrates, the differences are even greater. Birds’ ribs overlap one another with hook-like structures called uncinate processes, which add strength. Frogs don’t have any ribs, while turtles’ eight rib pairs are fused to the shell. A snake’s ‘ribcage’, meanwhile, runs the length of its body and can comprise hundreds of pairs of ribs. Despite the variations in appearance, ribcages all serve the same basic functions for the most part: to provide support and protection to the rest of the body. Ribs in other animals Manubrium This broadest and thickest part of the sternum connects with the clavicles and the cartilage for the first pair of ribs. Sternal angle This is the angle formed by the joint between the manubrium and the body, often used as a sort of ‘landmark’ by physicians. Body The main body of the sternum (breastbone) is almost flat, with three ridges running across its surface and cavities for the cartilage attaching to rib pairs three through seven. Xiphoid process This extension from the sternum starts as cartilage, but hardens to bone and fuses to the rest of the breastbone in adulthood. Floating ribs (not shown) Pairs 11-12 are only attached to the vertebrae, not the sternum, so are often called the floating, or free, ribs. Inhalation As you inhale, the intercostal muscles contract to expand and lift the ribcage. Breathe in, breathe out… Relaxation The diaphragm relaxes, moving upward to force air out of the lungs. Exhalation The intercostal muscles relax as we exhale, compressing and lowering the ribcage. Contraction The diaphragm contracts by moving downward, allowing the lungs to fill with air. 1In normal adults, the ribcage expands by three to five centimetres (1.2 to two inches) when you inhale. In an average breath at rest, we take in about 500 millilitres (0.9 pints) of air. Flexible cage 2Snakes can have up to 400 vertebrae, with all but the tail vertebrae having a pair of ribs. Each rib is attached to a belly scale which is a key part of how snakes slither. Endless ribs 3The seventh and the tenth ribs are the ones most likely to get broken in humans, while the first pair is rarely fractured because of its location behind the clavicle. Fractures 4Pectus excavatum is a congenital deformity caused by abnormal growth of the ribcage, resulting in a caved-in appearance that can also affect the heart and lungs. Sunken chest 5Large carnivores, such as lions, often head towards the ribcages of their kills first to devour both the rib meat and rich organs, like the heart, which are encased within. Tasty ribs 5TOP FACTS RIBCAGE TRIVIA The condition known as flail chest is fatal in almost 50 per cent of casesDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 68. 068 It might not be the biggest organ but the pancreas is a key facilitator of how we absorb nutrients and stay energised Head of the pancreas The head needs to be removed if it’s affected by cancer, via a complex operation that involves the resection of many other adjacent structures. Anatomy of the pancreasThe pancreas is a pivotal organ within the digestive system. It sits inside the abdomen, behind the stomach and the large bowel, adjacent to the spleen. In humans, it has a head, neck, body and tail. It is connected to the first section of the small intestine, the duodenum, by the pancreatic duct, and to the bloodstream via a rich network of vessels. The function of the pancreas is best considered by thinking about the two types of cell it contains: endocrine and exocrine. The endocrine pancreas is made up of clusters of cells called islets of Langerhans, which in total contain approximately 1 million cells and are responsible for producing hormones. These cells include alpha cells, which secrete glucagon, and beta cells which generate insulin. These two hormones have opposite effects on blood sugar levels throughout the body: glucagon increases glucose levels, while insulin decreases them. The cells here are all in contact with capillaries, so hormones which are produced can be fed directly into the bloodstream. Insulin secretion is under the control of a negative-feedback loop; high blood sugar leads to insulin secretion, which then lowers blood sugar with subsequent suppression of insulin. Disorders of these cells (and thus alterations of hormone levels) can lead to many conditions, including diabetes. The islets of Langerhans are also responsible for producing other hormones, like somatostatin, which governs nutrient absorption among other things. The exocrine pancreas, meanwhile, is responsible for secreting digestive enzymes. Cells are arranged in clusters called acini, which flow into the central pancreatic duct. This leads into the duodenum – part of the small bowel – to come into contact with and aid in the digestion of food. The enzymes secreted include proteases (to digest protein), lipases (for fat) and amylase (for sugar/starch). Secretion of these enzymes is controlled by a series of hormones, which are released from the stomach and duodenum in response to the stretch from the presence of food. Learnhowtheworkhorseofthedigestivesystemhelps tobreakdownfoodandcontrolourbloodsugarlevels How the pancreas works Duodenum The pancreas empties its digestive enzymes into the first part of the small intestine. Common bile duct The pancreatic enzymes are mixed with bile from the gallbladder, which is all sent through the common bile duct into the duodenum. Pancreatic duct Within the pancreas, the digestive enzymes are secreted into the pancreatic duct, which joins onto the common bile duct. Body of the pancreas The central body sits on top of the main artery to the spleen. HUMANANATOMY The pancreas up-close WorldMags.netWorldMags.net WorldMags.net
- 69. 069 ©Corbis;SüleymanHabib 336 BCE The Greek anatomist who will first discover the pancreas – Herophilus – is born. 1966 The first modern human pancreatic transplant is performed in the USA on a 28-year-old female patient. 1889 German scientists remove the pancreas in a dog and induce diabetes, proving an irrefutable link. 1642 The pancreatic duct is found in Padua, Italy. It is named after its discoverer: the duct of Wirsung. 1st century CE The name ‘pancreas’ is given, meaning ‘all flesh’, as it’s believed to serve solely as a cushioning,protectivefatpad. Every vertebrate animal has a pancreas of some form, meaning they are all susceptible to diabetes too. The arrangement, however, varies from creature to creature. In humans, the pancreas is most often a single structure that sits at the back of the abdomen. In other animals, the arrangement varies from two or three masses of tissue scattered around the abdomen, to tissue interspersed within the connective tissue between the bowels, to small collections of tissue within the bowel mucosal wall itself. One of the other key differences is the number of ducts that connect the pancreas to the bowel. In most humans there’s only one duct, but occasionally there may be two or three – and sometimes even more. In other animals, the number is much more variable. However, the function is largely similar, where the pancreas secretes digestive enzymes and hormones to control blood sugar levels. Does the pancreas vary in humans and animals? Blood supply The pancreas derives its blood supply from a variety of sources, including vessels running to the stomach and spleen. Tail of the pancreas This is the end portion of the organ and is positioned close to the spleen. Diabetes is a condition where a person has higher blood sugar than normal. It is either caused by a failure of the pancreas to produce insulin (ie type 1, or insulin- dependent diabetes mellitus), or resistance of the body’s cells to insulin present in the circulation (ie type 2, or non-insulin-dependent diabetes mellitus). There are also other disorders of the pancreas. Inflammation of the organ (ie acute pancreatitis) causes severe pain in the upper abdomen, forcing most people to attend the emergency department as it can be life threatening. In contrast, cancer of the pancreas causes gradually worsening pain which can often be mistaken for other ailments. What brings on diabetes? Beta cells It is the beta cells within the islets of Langerhans which control glucose levels and amount of insulin secretion. High glucose When the levels of glucose within the bloodstream are high, the glucose wants to move down its diffusion gradient into the cells. GLUT2 This is a glucose- transporting channel, which facilitates the uptake of glucose into the cells. Calcium channels Changes in potassium levels cause voltage-gated calcium channels to open in the cell wall, and calcium ions to flow into the cell. Depolarisation The metabolism of glucose leads to changes in the polarity of the cell wall and an increase in the number of potassium ions. Insulin released The vesicle releases its stored insulin into the blood capillaries through exocytosis. Calcium effects The calcium causes the vesicles that store insulin to move towards the cell wall. In the UK, 80 per cent of acute pancreatitis cases are caused by gallstones or excessive alcohol ingestionDID YOU KNOW? KEY DATES PANCREATIC PAST WorldMags.netWorldMags.net WorldMags.net
- 70. WWW.HOWITWORKSDAILY.COM Thebladderisoneofthekeyorgansintheurinary systemanditstoresurinefollowingproductionby thekidneysuntilthebodycanreleaseit. Urineisawastesubstanceproducedbythe kidneysastheyfilterourbloodoftoxinsandotherunneeded elements.Upto150litres(40gallons)ofbloodarefilteredperday byyourkidneys,butonlyaroundtwolitres(0.5gallons)ofwaste actuallypassdowntheureterstothebladder. Urinetravelsdowntheuretersandthroughtheuretervalves, whichattacheachtubetotheorganandpreventanyliquid passingback.Thebladderwalls,controlledbythedetrusor muscles,relaxasurineentersandallowtheorgantofill.When thebladderbecomesfull,ornearlyfull,thenervesinthe bladdercommunicatewiththebrain,whichinturninducesan urgetourinate.Thissensationwillgetstrongerifyoudonotgo –creatingthe‘burstingforawee’feelingthatyoucan occasionallyexperience.Whenreadytourinate,boththe internalandexternalsphinctersrelaxandthedetrusormuscles inthebladderwallcontractinordertogeneratepressure, forcingurinetopassdowntheurethraandexitthebody. Aswellastellingyouwhenyouneedtopassfluid,theurinary systemalsohelpstomaintainthemineralandsaltbalancein yourbody.Forinstance,whensaltsandmineralsaretoohighly concentrated,youfeelthirsttoregainthebalance. 070 Asakeypartoftheurinarysystem,thebladder iscrucialtoremovingwastefromyourbody Incontinence explainedForthebladdertoworkcorrectly, severalareaswithinitmustallfunction properly.Itismostcommonlythe failureofoneofthesefeaturesthat leadstoincontinence. Acommontypeofurinary incontinenceisurgeincontinence.This iswhenanindividualfeelsasudden compulsiontourinateandwillrelease urinewithoutcontrol.Itisoftencaused byinvoluntaryspasmsbythedetrusor muscleswhichcanbearesultofeither nervoussystemproblemsorinfections. Anothertypeisstressincontinence, causedwhentheexternalsphincteror pelvicfloormusclesaredamaged.This meansurinecanaccidentallyescape, especiallyifthepelvicfloorisunder pressure(egwhilecoughing,laughing orsneezing).Thiskindofincontinence ismostcommonintheelderly. Onemodernremedyisapreventative implantthathasbeendevelopedto replacepost-eventincontinencepads. Thiscomesintheformofacollagen- basedsubstanceinjectedaroundthe urethrainordertosupportit. THE COMPLETE URINARY SYSTEM ©SPL Kidneys The kidneys turn unwanted substances in the blood into urine. Ureters Ureters carry urine from the kidneys to the bladder. Bladder This muscular bag generally holds around a pint of urine. Whenyou’vegotto go,you’vegottogo… butreallyourbodies arereactingtoour bladders’direction Urethra The urethra runs from the bottom of the bladder to the outside world. HUMANANATOMY The human bladder ©Thinkstock How your bladder works WorldMags.netWorldMags.net WorldMags.net
- 71. 071 What is urine made up of?Ahumanbladderusuallyholdsaround 350millilitres(0.7pints)ofurine,though malebladderscantypicallyholdslightly morethanthoseoffemales.Urineis madeupofurea,thewasteby-product thebodyformswhilebreakingdown proteinacrossthebody.Thekidneyswill filterthisoutandpassitwithextrawater tothebladderforexpulsion.Otherwaste productsproducedorconsumedbythe bodythatpassthroughthekidneyswill alsoexitthebodyviathisroute. Typically,urineismadeupof95percent waterand5percentdissolvedor suspendedsolidsincludingurea,plus chloride,sodiumandpotassiumions. Internal urethral sphincter This relaxes when the body is ready to expel the waste liquid. External urethral sphincter (distal sphincter) This also relaxes for the urine to exit the body. Bladder wall (controlled by detrusor muscles) These muscles contract to force the urine out of the bladder. Urethra Urine travels down this passageway to leave the body. Ureter valves These sit at the end of the ureters and let urine pass into the bladderwithoutletting it flow back. Bladder wall (detrusor muscles) The detrusor muscles make up a layer of the bladder wall. These muscles cause the wall to relax and extend as urine enters, while nerves situated in the wall measure how full the bladder is and will signal to the brain when to urinate. Internal urethral sphincter The internal sphincter is controlled by the body. It stays closed to stop urine passing out of the body. External urethral sphincter (distal sphincter) This sphincter is controlled by the individual, and they control whether to open or close the valve. Pelvic floor muscles These hold the bladder in place, and sit around the urethra stopping unintended urination. FULL BLADDER EMPTYING BLADDER 2x©DKImages Ureters These tubes link the kidneys and the bladder, transporting the urine for disposal. URINE CONTENTS Urea 25.5g Chloride ions 6.6g Sodium ions 4.1g Potassium ions 3.2g Creatinine 2.7g Bicarbonate ions 1.2g Uric acid 0.6g Inside the bladderHow this organ acts as the middleman between your kidneys and excretion Everyone’s bladder differs slightly in size. The average maximum capacity is between 600-800ml (1.3-1.7pt)DID YOU KNOW? 1Women’s urethras are much shorter than men’s due to differing genitalia. Women are consequently far more likely to get bladder/urine infections because of this. Urethras – all the same? 2The urge to urinate normally comes when the bladder reaches between 25-50% of full volume to avoid reaching 100% when involuntary urination will occur. Getting the urge 3Urine can stay in the bladder for anywhere between one to eight hours before excretion. The time it remains there will varydependingontheamount of liquid consumed. Duration 4Of course, this would not generally be recommended in normal circumstances, but yes, urine is completely sterile – it contains no bacteria, viruses or fungi. Can you drink urine? 5It’s advised to drink around 1- 1.5 litres (2.1-3.1 pints) of water a day. This will keep the urinary systemworkingmosteffectively. We lose more water than this but obtain some from food. How to keep healthy 5TOP FACTSBLADDERS WorldMags.netWorldMags.net WorldMags.net
- 72. Thisbeginsafterthelastmenstrualperiod,whenaneggis releasedandfertilised.Ittakesaboutnineweeksforthe resultingembryotodevelopintoafetus.Duringthisperiod, themotherwillbepronetosicknessandmoodswingsdueto hormonalchanges. Thefetusgrowsrapidlyanditsorgans mature.Byweek20itsmovementscan befelt.Atweek24itcansuckitsthumb andhiccup,andcanliveindependently ofthemotherwithmedicalsupport. Pregnancyisauniqueperiodinawoman’slifethatbringsaboutphysicaland emotionalchanges.Whenitoccurs,thereisanintricatechangeinthebalanceof theoestrogenandprogesteronehormones,whichcausesthecessationof menstruationandallowstheconditionsintheuterus(womb)tobecomesuitable forthegrowthofthefetus.Theliningoftheuterus,ratherthanbeingdischarged,thickens andenablesthedevelopmentof thebaby. Atfirst,itisacollectionofembryoniccellsnobiggerthanapinhead.Byweekfourthe embryoformsthebrain,spinalcordandheartinsidethenewlyfluid-filledamnioticsac. Protectedbythiscushionoffluid,itbecomesrecognisablyhumanandentersthefetalstage byweekeight. Manydemandsareputonthemother’sbodyandsheislikelytoexperiencesickness, tiredness,lower-backpain,heartburn,increasedappetiteandmusclecramps,aswellasthe enlargementofherbreastsandstretchmarks.Herbloodsugarlevels,heartrateand breathingalsoincreasetocopewiththegrowingdemandsofthefetus. Asthedateoflabourapproaches,themotherfeelssuddencontractionsknownas Braxton-Hicks,andtheneckofheruterusbeginstosoftenandthinout.Meanwhile,thelungs ofthefetusfillwithsurfactant.Thissubstanceenablesthelungstosoften,makingthemable toinflatewhenittakesitsfirstbreathofair.Finally,chemicalsignalsfromthefetustriggerthe uterustogointolabour. Ninemonthsofchangeandgrowth Human pregnancy SECOND TRIMESTER (13–27 weeks)FIRST TRIMESTER (0–12 weeks) Week 9Head Face begins to look human and the brain is developing rapidly. Heart All the internal organs are formed and the heart is able to pump blood around its body. Movement Fetus moves around to encourage muscle development. Weight 10g Length 5.5cm Week 16 Hair and teeth At 16 weeks, fine hair (lanugo) grows over the fetal body. By 20 weeks, teeth start forming in the jaw and hair grows. Movement By week 16 the eyes can move and the whole fetus makes vigorous movements. Sound and light The fetus will respond to light and is able to hear sounds such as the mother’s voice. Weight Week 16: 140g Week 20: 340g Length Week 16: 18cm Week 20: 25cm Vernix By 20 weeks, this white, waxy substance covers the skin, protecting it from the surrounding amniotic fluid. Sweating An increase in blood circulation causes mother to sweat more. Weight gain The average woman gains 12.5kg during pregnancy. This consists of… (These figures vary according to several factors including the age, race, diet and the pre-pregnancy weight and size of the person) 4xtrimesterimages©SciencePhotoLibrary HUMANANATOMY 072 “Many demands are put on the mother’s body and she is likely to experience sickness and cramps” THE BABY AT BIRTH 3.3kg 0.9kg 4.0kg AMNIOTIC FLUID SURROUNDING THE FETUS THEPLACENTA EXTRABLOODVOLUME FLUIDRETENTION LARGERBREASTS M USCLELAYEROFUTERUS STORAGEOFFAT (FORBREASTFEEDING) 0.8kg 0.7kg 1.2kg 0.4kg 1.2kg Human pregnancy explained WorldMags.netWorldMags.net WorldMags.net
- 73. 1. Seahorses The female seahorse deposits her eggs in the pouch of the male seahorse. He fertilises the eggs and carries them for the full term of three weeks. 2. Komodo dragons Female komodo dragons can give birth to male babies without fertilisation from a male partner. This is known as parthenogenesis. 3. Spotted hyenas Female spotted hyenas have genitalia like a penis. It stretches to allow the insertion of the male penis during copulation, and stretches again when giving birth through it. MEN ONLY VIRGIN BIRTH JUST PLAIN WEIRD 073 The placentaTheplacentaisanessentialinterfacebetween themotherandfetus.Whenmatureitisa22cm diameter,flatovalshapewitha2.5cmbulgein thecentre.Thethreeintertwinedblood vesselsfromthecordradiatefromthecentre totheedgesoftheplacenta.Liketreeroots, thesevillousstructurespenetratethe placentaandlinkto15to20lobeson thematernalsurface. Thefivemajorfunctionsofthe placentadealwithrespiration, nutrition,excretionofwaste products,bacterialprotection andtheproductionofhormones. Nowalmostatfullterm,thefetuscanrecogniseand respondtosoundsandchangesinlight.Fatbegins tobestoredundertheskinandthelungsarethe verylastorganstomature. ©JoanneMerriam05 ©Midori07 ©BudgieKiller05 Placenta body Is firmly attached to the inside of the mother’s uterus. Umbilical cord Consists of three blood vessels. Two carry carbon dioxide and waste from the fetus, the other supplies oxygen and nutrients from the mother. Wharton’s jelly The umbilical blood vessels are coated with this jelly-like substance and protected by a tough yet flexible outer membrane. Maternal surface Blood from the mother is absorbed and transferred to the fetal surface. Fetal surface Blood vessels radiate out from the umbilical cord and penetrate the placenta. The surface is covered with the thin amnion membrane. ©SciencePhotoLibrary THIRD TRIMESTER (28–40 weeks) Week 24 Week 32 Movement By the 28th week, due to less room in uterus, the fetus will wriggle if it feels uncomfortable. Weight Week 24: 650g Week 28: 1,250g Length Week 24: 34cm Week 28: 38cm Breathlessness The increased size of the fetus by 24 weeks causes compression of rib cage and discomfort for mother. Hands The fetus can move its hands to touch its umbilical cord at 24 weeks. Position By 28 weeks, the uterus has risen to a position between the navel and the breastbone. Head The head can move at 28 weeks and the eyes can open and see. Under pressure Pressure on the diaphragm and other organs causes indigestion and heartburn in the mother. She will find it difficult to eat a lot. Position Head positions itself downwards, in preparation for labour. Sleep patterns Fetus will sleep and wake in 20-minute cycles. Weight 1,500g Length 41cm “The three intertwined blood vessels radiate from the centre to the edges of the plancenta” ANIMAL PREGNANCIES HEAD HEAD2 200 extra calories a day are needed in mid-pregnancy, which is 10 per cent more than the usualDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 74. 074 After fertilisation, the single-celled zygote splits into two, then the two cells double to four, four to eight and so on. The journey along the Fallopian tube is quite slow, while growth continues. On its way, the zygote divides to make a clump of 32 cells, known as the morula stage. If the early embryo splits into two clumps before this, it may develop into identical twins. Every cell in the morula could still become part of the growing embryo. By the time the womb cavity is reached, the cell cluster becomes hollow and filled with fluid; it is now referred to as the blastocyst. A blastocyst is an embryo that has developed to the stage where it has two different cell types: the surface cells, or outer coat, will become, among other things, the placenta that nourishes the baby; the inner cells, known as the inner cell mass, will become the foetus itself. On contact, the blastocyst burrows into the uterine wall for nourishment; this process is known as implantation. Blastocyst formation usually occurs on the fifth day after fertilisation. The embryonic stage begins in the fifth week. From weeks five to eight, development is rapid. Major body organs and systems, including the brain, lungs, liver and stomach, will begin to emerge. At this time, the first bone cells will also appear. By the end of the eighth week, the embryo is known as a foetus and increasingly looks like a mini human. How does an embryo develop?Discoverhowafertilisedeggtransformsinto anembryoandeventuallyanewhumanbeing Ovary A woman usually has two tubes and two ovaries, one either side of her uterus. Every month one of the ovaries releases an egg, which passes slowly along its Fallopian tube towards the womb. Fertilisation and IVF explained Natural fertilisation takes place via sexual intercourse. An egg, or ovum, is released by an ovary and is fertilised by a sperm. Fertilisation occurs when the sperm and egg unite in one of the female’s Fallopian tubes. The fertilised egg, known as a single-celled zygote, then travels to the uterus, where it implants into the uterine lining. In vitro fertilisation (IVF) is a form of assisted reproductive technology, where the sperm nucleus is combined with an egg cell in a lab. The resultant embryo is manually introduced to the uterus, where it develops in the same way as a natural conception. Week 3 At the start of week 3 a groove will form towards what will become the tail end of the embryo; this is the primitive streak. A new layer of tissue – the mesoderm – will develop from the primitive streak. The spinal cord, kidneys and major tissues will all grow from this. Cells from the ectodermal tissue create the neural fold and plate, the first stages in the development of the nervous system. The neural groove will go on to form the spine. Week 5 Pharyngeal arches that develop in the face, jaws, throat and neck appear between the head and body. A complex network of nerves and blood vessels are developing. The embryo’s eyes have formed and the ears are becoming visible. The spleen and pancreas are beginning to develop in the central part of the gut. The thymus and parathyroid glands develop from the third pharyngeal arch. The arms and legs begin to emerge as paddle-shaped buds. Fallopian tube If a woman has sexual intercourse during the days of her monthly cycle, just before or after an egg has been released from the ovary, a sperm cell from her partner could travel to the Fallopian tube and fertilise the ovum. Sperm During sexual intercourse, millions of sperm are ejaculated into the vagina, with only thousands surviving to make the journey to meet the egg. Ovulated egg The sperm cells are chemically attracted to the egg and attach themselves in an attempt to break through the outer coat. Fertilised egg Only one sperm will be successful. The egg will then lose its attraction, harden its outer shell and the other sperm will let go. If eggs are not fertilised within 12 hours of release, they die. Uterus (womb) The whole process from ejaculation to fertilisation can take less than an hour. If a woman has an average 28-day menstrual cycle, fertilisation is counted as having taken place around day 14, not on day one. In vitro (‘in glass’) IVF is the process by which eggs are removed from the ovaries and mixed with sperm in a laboratory culture dish. Fertilisation takes place in this dish. HUMANANATOMY From fertilisation to foetus WorldMags.netWorldMags.net WorldMags.net
- 75. 075 Journey of an embryo Week 8 Between the fourth and eighth weeks, the brain has grown so rapidly that the head is extremely large in proportion to the rest of the body. The gonads, or sex glands, will now start to develop into ovaries or testes. The elbows, fingers, knees and toes are really taking shape. Inside the chest cavity, the lungs are developing too. At the end of the eight-week period, the embryo becomes a foetus. What is amniotic fluid? The amniotic sac is a bag of fluid in the uterus, where the unborn baby develops. It’s filled with a colourless fluid – mainly made of water – that helps to cushion the foetus and provides fluids which enable the baby to breathe and swallow. The fluid also guards against infection to either the foetus or the uterus. Amniotic fluid plays a vital role in the development of internal organs, such as the lungs and kidneys; it also maintains a constant temperature. The amniotic sac starts to form and fill with fluid within days of conception. Thebodyofthisfoetusisreallytaking shape,safewithintheamnioticsac 3x©SPL Thefirsteightweeksisanimmensetimeofchangeforajust-conceivedhuman Week 2 The inner cells of the embryo divide into two layers: the ectoderm and the endoderm. The tissues and organs of the body will eventually develop from these. The amniotic sac, which will soon form a protective bubble around the embryo, also starts to develop. The embryo, now completely embedded in the womb, is a disc-shaped mass of cells, measuring roughly 0.2mm (0.008in) in diameter. Week 4 The kidneys are forming from mesodermal tissue and the mouth is emerging. A basic spinal cord and gut now run from the head to the tail. The head and tail fold downward into a curve as a result of the embryo developing more rapidly from the front. The heart tube bends into a U shape and blood begins to circulate around the body. Week 6 42 tissue blocks have formed along the embryo’s back and the development of the backbone, ribs and muscles of the torso begins. The length of the embryo is now 7-8mm (0.3in) . The embryo’s heart has established a regular rhythm and the stomach is in place. Ears, nose, fingers and toes are just beginning to appear. Week 7 The embryo’s eyelids begin to form from a single membrane that remains fused for several days. At this stage in development, the limb muscles are beginning to form. The chest cavity will be separated from the abdominal cavity by a band of muscles; this will later develop into the diaphragm. Week 1 Within one week of conception, the fertilised egg, known as a blastocyst, will make its way to the uterus. Within days the cells will arrange themselves into two masses: the outer coat will become the placenta, while the inner cell mass becomes the foetus. All being well, the developing embryo will settle into the folds of the womb lining. In 2009, almost two per cent of all babies born in the UK were conceived as a result of IVFDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 76. HUMANANATOMY The human stomach 076 The stomach is much more than just a storage bag. Take a look at its complex microanatomy now… Lining under the microscope The stomach’s major role is as a reservoir for food; it allows large meals to be consumed in one sitting before being gradually emptied into the small intestine. A combination of acid, protein-digesting enzymes and vigorous churning action breaks the stomach contents down into an easier-to-process liquid form, preparing food for absorption in the bowels. In its resting state, the stomach is contracted and the internal surface of the organ folds into characteristic ridges, or rugae. When we start eating, however, the stomach begins to distend; the rugae flatten, allowing the stomach to expand, and the outer muscles relax. The stomach can accommodate about a litre (1.8 pints) of food without discomfort. The expansion of the stomach activates stretch receptors, which trigger nerve signalling that results in increased acid production and powerful muscle contractions to mix and churn the contents. Gastric acid causes proteins in the food to unravel, allowing access by the enzyme pepsin, which breaks down protein. The presence of partially digested proteins stimulates enteroendocrine cells (G-cells) to make the hormone gastrin, which encourages even more acid production. The stomach empties its contents into the small intestine through the pyloric sphincter. Liquids pass through the sphincter easily, but solids must be smaller than one to two millimetres (0.04-0.08 inches) in diameter before they will fit. Anything larger is ‘refluxed’ backwards into the main chamber for further churning and enzymatic breakdown. It takes about two hours for half a meal to pass into the small intestine and the process is generally complete within four to five hours. Discoverhowthisamazingdigestiveorganstretches,churnsandholds corrosiveacidtobreakdownourfood,allwithoutgettingdamaged Insidethe humanstomach Mucous cell These cells secrete alkaline mucus to protect the stomach lining from damage by stomach acid. Chief cell (yellow) Chief cells make pepsinogen; at the low pH in the stomach it becomes the digestive enzyme pepsin, which deconstructs protein. Parietal cell (blue) These cells produce hydrochloric acid, which kills off micro- organisms, unravels proteins and activates digestive enzymes. G-cell (pink) Also known as enteroendocrine cells, these produce hormones like gastrin, which regulate acid production and stomach contraction. Muscle layers The stomach has three layers ofmusclerunningindifferent orientations. These produce the co-ordinated contraction required to mix food. Gastric pits The entire surface of the stomach is covered in tiny holes, which lead to the glands that produce mucus, acid and enzymes. Mucosa Submucosa Muscularis WorldMags.netWorldMags.net WorldMags.net
- 77. 50mlVOLUME WHEN EMPTY 1-4 litresCAPACITY 2 litres/dayGASTRIC ACID PRODUCED 4-5hrsEMPTYING TIME 2.5AVERAGE pH LEVEL 25cmLENGTH THE STATS GASTRIC FIGURES 077 Stomach rumbling, also known as borborygmus, is actually the noise of air movement in the intestinesDID YOU KNOW? This major organ in the digestive system has several distinct regions with different functions, as we highlight here Gastric anatomy ©Thinkstock Body Also called the corpus, this is the largest part of the stomachandisresponsible for storing food as gastric juices are introduced. Antrum The antrum contains cells that can stimulate or shut off acid production, regulating the pH level of the stomach. Small intestine The stomach empties into the first section of the small intestine: the duodenum. Pancreas The bottom of the stomach is located in front of the pancreas, although the two aren’t directly connected. Pyloric sphincter The pyloric sphincter is a strong ring of muscle that regulates the passage of food from the stomach to the bowels. Large intestine The large intestine curls around and rests just below the stomach in the abdomen. Cardia The oesophagus empties into the stomach at the cardia. This region makes lots of mucus, but little acid or enzymes. Fundus The top portion of the stomach curves up and allows gases created during digestion to be collected. Your stomach is full of corrosive acid and enzymes capable of breaking down protein – if left unprotected the stomach lining would quickly be destroyed. To prevent this from occurring, the cells lining the stomach wall produce carbohydrate-rich mucus, which forms a slippery, gel-like barrier. The mucus contains bicarbonate, which is alkaline and buffers the pH at the surface of the stomach lining, preventing damage by acid. For added protection, the protein-digesting enzyme pepsin is created from a zymogen (the enzyme in its inactive form) – pepsinogen; it only becomes active when it comes into contact with acid, a safe distance away from the cells that manufacture it. Why doesn’t it digest itself? Vomiting is the forceful expulsion of the stomach contents up the oesophagus and out of the mouth. It’s the result of three co-ordinated stages. First, a deep breath is drawn and the body closes the glottis, covering the entrance to the lungs. The diaphragm then contracts, lowering pressure in the thorax to open up the oesophagus. At the same time, the muscles of the abdominal wall contract, which squeezes the stomach. The combined shifts in pressure both inside and outside the stomach forces any contents upwards. Vomit reflex step-by-step Produced by parietal cells in the stomach lining, gastric acid has a pH level of 1.5 to 3.5 WorldMags.netWorldMags.net WorldMags.net
- 78. Angioplastyisacutting-edge medicalprocedurethathelps yourheartlastlonger Yourheartpumpsblood-richoxygen toyourbody’stissues–buttheheart muscleneedsoxygenitself.The coronaryarteriesaresmallvessels liningyourheart’ssurfacethatdothisjob perfectly,inexactsynchronisationwiththebeats oftheheart.However,theycanbecomeblocked.A lackofexercise,smoking,poordietandunlucky genescanallleadtoplaquesoffattytissue,called atheroma,blockingthesevitalarteries.Then,if yourheartneedstopumpharder,suchasduring exercise,thereducedbloodflowcannotsupply enoughoxygen.Thisleadstopain–angina– whichisanearlywarningsignthattheheart muscleisdying.Previously,theonlywaytocure advancedcaseswastogounderthesurgeon’s knife.However,cardiacsurgeryisarisky procedure.Thenalongcameangioplasty. Viaasmallarteryinthepatient’sgroinorwrist, doctorsinsertaguidewiredirectlyintothe coronaryarteriesoftheheart.Thisistricky,and sotheyusereal-timeX-rayimagestoguidethem toexactlytherightplace.Theyfeedatiny,thin, flexiblehollowtubeoverthiswire(acatheter). Injectingdyeintothesearteries(viathehollow catheters)andlookingcarefullyattheresult showsthemexactlywheretheblockagesare. Next,theyinflatetinyballoonsattachedtotheend oftheselongcathetersattheexactspotofthe blockage.Insomecases,thisisenough.Inothers, topreventthearteryclosingagain,astentcanbe placedthroughtheaffectedarea.Theseareclever stentsandcancontaindrugsthatpreventthem blocking.AfinalcheckX-raycompletesthe angioplastyprocess. Angioplastieslikethiscanalsobeperformed onblockedarteriesinthelegs,wherethe principleisexactlythesame.Butnomatter wheretheblockageis,thisprocedurerequiresa steadyhandandadoctorwhocanthinkfastand thinkinreal-time3Dwhilelookingat2D black-and-whiteimages. 078 How does angioplasty work? Angioplastyisoneofthemostcommonly performedmedicalproceduresaround theworld–there’sagoodchancethatyou knowsomeonewho’shadone.However, theprocedurestillrequiresalotof technicalskillandasteadyhand.Evenin thebesthandstherearerisksand complications,butmostpeoplegetgood resultsfromit. The procedure 1. The blocked artery Fatty plaques can block any of the four main arteries that feed the heart, leading to pain. 2. Access Guidewires are fed into these arteries via the small arteries in the groin or wrist. Even though the patient is awake, they don’t feel it as a local anaesthetic is given. 5. Up close High blood pressure leads to tiny spots of damage on artery walls. These walls fill with cells, including fatty lipid cells. It is the combinations of all of these cells that lead to a fibrosis, stiff plaque that narrows and then blocks the artery. Real-timeX-rayimagesare agreathelptodoctors HUMANANATOMY Help for your heart WorldMags.netWorldMags.net WorldMags.net
- 79. 079 © SciencePhotoLibrary Thefirstangioplastyoftheheartwascarriedout inthe18thCenturyonahorse.Ittookawhileto perfectitforhumans,andin1929thefirst angioplastyonaperson’sheartwasperformed inGermany.Overthenext30yearsasmall numberofdoctorspioneeredtheangioplasty intoadiagnosticandtherapeutictechnique. WhileintheSixtiesandSeventiesopenheart surgerybecameestablished,intheSeventies andEightiesangioplastystartedtotakeoverasa lowerriskbutequallyeffectivetreatment. Astonishingly,inthelate-Nineties,over1million angioplastieswereperformedworldwide, makingitoneofthemostcommonmedical proceduresontheplanet. From a single horse to the whole world Theballooncatheterisoneofthekeypiecesoftheangioplasty doctor’sequipment.Oncetheguidewireisinserted,thecatheteris fedoveritandfloatedintoexactlytherightplace.Throughthis catheter,specialdyesthatcanbeseenonX-rayimages(radio-opaque contrastdye)canbeinjectedthroughthehollowcathetertoconfirm itspositionandthenconfirmthelocationoftheblockages. Atthetipofthecatheterisaballoon.Usingwater,thisballooncan beinflatedfromoutsidetoprecisepressures.Whenthisisdonefrom thecentreoftheblockage,theatheromatousplaqueisexpandedto allowmorebloodflow.Therearemanydifferentsizesofcatheterand widthsofballoons,allowingexacttailoringtothepatient’sneeds. Sometimesthedoctorwillstartwithasmallballoonwhenthe blockageisverynarrow,andthensequentiallyinsertlargerballoons toallowforthemaximumeffect.However,careisneeded–toolargea balloonortoomuchpressureandthevesselcanrupture,whichisa life-threateningcomplication.Experience,careandcontrolofthe pressurespreventthis. Balloon catheter 3. X-rays Under real-time X-ray image guidance, the guidewires and catheters are fed through the major arteries and then into the tiny coronary arteries. 4. The blockage Using dyes, the X-rays show the doctors where the exact blockages are, and then the catheters are introduced through these narrowings. 6. Widening the gap The stent is placed through the blockage, and then expanded within it. This is all done under X-ray guidance so it’s in exactly the right position. 7. The stent Once the stent is fully expanded, the catheter holding it is removed, leaving it in place to prevent reblockage. 8. Increased flow Now the artery is wider, more blood flows, delivering vital oxygen to the heart muscle and preventing the pain of angina. Itallstarted300years ago…onahorse Emergency angioplasty is the best treatment for acute heart attacksDID YOU KNOW? 1The most modern stents that are used in angioplasty procedures aren’t just bare metal, some also secrete drugs over time, which work to prevent a blockage. Drug eluting 2In the modern era, angioplasty patients stay awake during the entire procedure, as it is now performed with the patient under local anaesthetic. No napping 3Once the ballooning and stenting is done, the tech doesn’t stop. There are devices to close holes made in the groin or wrist arteries to stop them getting bigger. High tech all the way 4Although an angioplasty is mainly used on coronary arteries, there are some doctors trialing angioplasty for narrowed arteries that feed blood to the brain. All the way up? 5Recent angioplasty- related technological developments include using lasers at the end of the catheters to burn away the offending plaques. Lasers 5TOP FACTS ANGIOPLASTY WorldMags.netWorldMags.net WorldMags.net
- 80. Thehumanhandisanimportant featureofthehumanbody, whichallowsindividualsto manipulatetheirsurroundings andalsotogatherlargeamountsofdatafrom theenvironmentthattheindividualis situatedwithin.Ahandisgenerallydefined astheterminalaspectofthehumanarm, whichconsistsofprehensiledigits,an opposablethumb,andawristandpalm. Althoughmanyotheranimalshavesimilar structures,onlyprimatesandalimited numberofothervertebratescanbesaidto havea‘hand’duetotheneedforan opposablethumbtobepresentandthe degreeofextraarticulationthatthehuman handcanachieve.Duetothisextra articulation,humanshavedevelopedfine motorskillsallowingformuchincreased controlinthislimb.Consequentlywesee improvedabilitytograspandgripitemsand developmentofskillssuchaswriting. Anormalhumanhandismadeupoffive digits,thepalmandwrist.Itconsistsof27 bones,tendons,musclesandnerves,with eachfingertipofeachdigitcontaining numerousnerveendingsmakingthehanda crucialareaforgatheringinformationfrom theenvironmentusingoneofman’smost crucialfivesenses:touch.Musclesinteract togetherwithtendonstoallowfingersto bend,straighten,pointand,inthecaseofthe thumb,rotate.However,thehandisanarea thatseesmanyinjuriesduetothenumberof waysweuseit,oneinteninjuriesinA&E beinghandrelated,andtherearealso severaldisordersthatcanaffectthehand developmentinthewomb,suchas polydactyly,whereanindividualisborn withextradigits,whichareofteninperfect workingorder. Metacarpals These five bones make up the palm, and each one aligns with one of the hand’s digits. Proximal phalanges Each finger has three phalanges, and this phalange joins the intermediate to its respective metacarpal. Intermediate phalanges This is where the superficial flexors attach via tendons to allow the digit to bend. Distal phalanges A distal phalange (fingertip) is situated at the end of each finger. Deep flexors attach to this bone to allow for maximum movement. Bones in the handThehumanhandcontains27 bones,andthesedivideupinto threedistinctgroups:the carpals,metacarpalsand phalanges.Thesealsothen furtherbreakdownintothree: theproximalphalanges, intermediatephalangesand distalphalanges.Eightbones aresituatedinthewristand thesearecollectivelycalled thecarpals.Themetacarpals, whicharesituatedinthepalm ofthehandaccountfora furtherfiveoutofthe27,and eachfingerhasthree phalanges,thethumbhastwo. Intrinsicmusclesandtendons interacttocontrolmovementof thedigitsandhand,andattach toextrinsicmusclesthat extendfurtherupintothearm, whichflexthedigits. The human handWetakeourhandsforgranted,buttheyare actuallyquitecomplexandhavebeen crucialinourevolution Carpals The carpals (scaphoid, triquetral, trapezium, trapezoid, lunate, hamate, capitate and pisiform) sit between the ulna and radius and the metacarpals. HUMANANATOMY 080 How do our hands work? WorldMags.netWorldMags.net WorldMags.net
- 81. 1. Julio Cesar Soares de Espindola Having recovered from a few earlier blunders, the Brazilian keeper is now considered one of the best. 2. Gianluigi Buffon Named the ‘Serie A Goalkeeper of the Year’ a record nine times, this is one guy it would be hard to put one past. 3. Iker Casillas Fernandez Voted best goalie in the world by the International Federation of Football History and Statistics for two years running. SAFE SAFER SAFEST Muscles and other structures Themovementsandarticulationsofthehandand bythedigitsarecontrolledbytendonsandtwo musclegroupssituatedwithinthehandandwrist. Thesearetheextrinsicandintrinsicmusclegroups, sonamedastheextrinsicsareattachedtomuscles whichextendintotheforearm,whereasthe intrinsicsaresituatedwithinthehandandwrist. Theflexorsandextensors,whichmakeupthe extrinsicmuscles,useeitherexclusivelytendonsto attachtodigitstheycontrol(flexors)oramore complexmixoftendonsandintrinsicmusclesto operate(extensors).Thesemuscleswillcontractin ordertocausedigitmovement,andflexorsand extensorsworkinapairtocomplementeachto straightenandbenddigits.Theintrinsicmuscles areresponsibleforaidingextrinsicmuscleaction andothermovementsinthedigitsandhavethree distinctgroups;thethenarandhypothenar (referringtothethumbandlittlefinger respectively),theinterosseiandthelumbrical. Thenar space Thenar refers to the thumb, and this space is situated between the first digit and thumb. One of the deep flexors (extrinsic muscle) is located in here. Mid palmar space Tendons and intrinsic muscles primarily inhabit this space within the hand. Insertion of flexor tendon This is where the tendon attaches the flexor muscle to the finger bones to allow articulation. Interossei muscle (intrinsic) This interossei muscle sits between metacarpal bones and will unite with tendons to allow extension using extrinsic muscles. Arteries, veins and nerves These supply fresh oxygenated blood (and take away deoxygenated blood) to hand muscles. Hypothenar muscle (intrinsic) Hypothenar refers to the little finger and this muscle group is one of the intrinsic muscles. Ulnar nerve This nerve stretches down the forearm into the hand and allows for sensory information to be passed from hand to brain. Extensors Extensors on the back of the forearm straighten the digits. Divided into six sections, their connection to the digits is complex. Forearm musclesExtrinsicmusclesareso calledbecausetheyare primarilysituatedoutside thehand,thebodyofthe musclessituatedalongthe undersideorfrontofthe forearm.Thisbodyof musclesactuallybreaks downintotwoquitedistinct groups:theflexorsandthe extensors.Theflexorsrun alongsidetheundersideof thearmandallowforthe bendingofthedigits, whereastheextensor muscles’mainpurposeisthe reversethisaction,to straightenthedigits.There arebothdeepandsuperficial flexorsandextensors,and whichareusedatanyone timedependsonthedigitto bemoved. Increasedarticulationof thethumbhasbeen heraldedasakey factorinhuman evolution.Itallowed forincreasedgrip andcontrol,andfor toolusetodevelop amonghuman ancestorsaswellasother primates.Thishaslateralsofacilitated majorculturaladvances,suchaswriting.Alongside thefourotherflexibledigits,theopposablethumb makesthehumanhandoneofthemostdexterousin theworld.Athumbcanonlybeclassifiedas opposablewhenitcanbebroughtoppositetothe otherdigits. Opposable thumbs Left handed or right handed? Themostcommontheoryforwhysomeindividuals arelefthandedisthatofthe‘disappearingtwin’.This supposesthattheleft-handedindividualwas actuallyoneofasetoftwins,butthatintheearly stagesofdevelopmenttheother,righthanded,twin died.However,it’sbeenfoundthatdominanceofone handisdirectlylinkedwithhemispheredominance inthebrain,asinmanyotherpairedorgans. Individualswhosomehowdamagetheirdominant handforextendedperiodsoftimecanactually changetousetheotherhand,provingtheimpactand importanceofenvironmentandextenttowhich humanscanadapt. Deep flexors The digits have two extrinsic flexors that allow them to bend, the deep flexor and the superficial. The deep flexor attaches to the distal phalanges. Superficial flexors The other flexor that acts on the digits is the superior flexor, which attaches to the intermediate phalanges. Thenars The intrinsic group of muscles is used to flex the thumb and control its sideways movement. Tendons and intrinsics These attach the flexor muscles to the phalanges, and facilitate bending. Tendons also interact with the intrinsics and extensors in the wrist, palm and forearm to straighten the digits. ©Sciencephotolibrary © W ilfredor2008 ©AgênciaBrasil ©OlafNordwch ©JuanFernàndez 081 SAFE HANDS HEAD HEAD2 Skin is attached to tendons and so when you bend you fingers back, dimples appear on the back of your handDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 82. “Reflex actions are performed independently of the brain” “The half-moon shape that you can see at the bottom of your nail is called the lanula” Whydoesyourlegkickout whenthedoctortapsjust belowyourknee? Knee-jerk reactions explained 1. Quadriceps and hamstring muscles The knee-jerk reflex means that the quadriceps muscles contract at the same time the hamstring muscle relaxes. 2. Sensory neuron The sensory, or afferent neuron, receives an impulse from the femoral nerve. 3. Interneuron The interneuron provides a connection between the sensory and motor neurons. 4. Motor neuron The motor, or efferent neuron, carries the nerve impulse to the muscles. 5. Spinal cord The spinal cord has both grey matter, which contains nerve cell bodies, and white matter, which contains the nerve fibres. The knee-jerk step-by-step Sensory neuron Motor neuron Interneuron Fingernailsaremadeofatoughproteincalledkeratin(fromthe Greekword‘Kera’,meaninghorn).Keratinisalsowhatanimals hoovesandhornsaremadefrom.Mostanimalshaveasupportive bonestructureintheirhorns,althoughrhinoceroshornsaremade completelyofkeratincompactedtogether.Theonlyotherbiologicalmaterial whichhasasimilartoughnesstokeratinisedtissueischitin,themain componentofexoskeletonsbelongingtoarthropods.Thehalf-moonshape thatyoucanseeatthebottomofyournail(apartfrommaybeyourlittlefinger) iscalledthelanula.Thisisagroupofcellsthatproducekeratinandotherliving cells.Astheselivingcellsarepushedforwardbynewercells,theydieand mergewiththekeratintobecomekeritinised.Theythenbecomeflattened, stiffandknownasyourfingernails. What are our fingernails made of? HUMANANATOMY Knee-jerk reactions / Fingernails Doctorsoftentesttheknee-jerk,orpatellar reflex,tolookforpotentialneurological problems.Lightlytappingyourpatellartendon justbelowthekneecapstretchesthefemoral nervelocatedinyourthigh,whichinturncausesyour thighmuscle(quadriceps)tocontractandthelowerlegto extend.Whenstruck,impulsestravelalongapathwayin thedorsalrootganglion,abundleofnervesintheL4level ofthespinalcord.Reflexactionsareperformed independentlyofthebrain.Thisallowsthemtohappen almostinstantaneously–inabout50millisecondsinthe caseoftheknee-jerkreflex.Thisreflexhelpsyouto maintainbalanceandposturewhenyouwalk,without havingtothinkabouteverystepyoutake. 082 Andhowaretheyformed? WorldMags.netWorldMags.net WorldMags.net
- 83. Thekneeisthelargestand alsooneofthemostcomplex jointsinthebody,allowing usbipedalhumanstomove aroundandgetfrompointAtopointB. Threedifferentbonesmeetattheknee jointandworktogethertoallowfor movementandprotection.Atthetopof thekneeisthelowerpartofthe thighbone(femur).Thisrotatesontopof theshinbone(tibia)andthekneecap (patella),thelatterofwhichmovesina groovebetweenthefemurandtibia. Cartilagewithinthekneecushionsit fromshockcausedbymotion,while ligamentspreventdamageoccurringto thejointincaseofunusualorerratic motion.Musclesrunningfromthehip downtothekneejointareresponsible forworkingthekneejointandallowing ourlegstobend,stretch,andultimately allowingustowalk,runandskip. Inside the kneeHowdoourkneejoints allowustowalkandrun? The knee structureHow does everything work in tandem to allow for movement? Femur This bone runs from the hip to the knee joint. It is the thickest and the longest bone in the human body. Patella This bone slides at the front of the femur and tibia as the knee moves, protecting the knee and giving the muscles leverage. Cartilage The point at which the three bones meet is covered in tough, elastic articular cartilage, allowing smooth movement of the joint and absorbing shock. Menisci The three bones are separated with two discs of connective tissue called ‘menisci’, also acting as shock absorbers and enhancing stability. Tibia This bone connects the knee to the ankle, running parallel to the thinner fibula bone. Hamstrings Hamstring muscles running from the thigh to the knee joint are responsible for bending the leg at the knee. Quadriceps The quadriceps, made up of four muscles, are on the front of the thigh and help to straighten the leg. Tendons These tough cords of tissue attach muscle to bone, so that the muscles can bend and straighten the leg as required. Ligaments These elastic bands of tissue connect the bones together and provide stability and strength to the knee joint. Synovial membrane The soft tissue at the centre of the knee joint contains synovial fluid, providing lubrication for the moving knee. ©SciencePhotoLibrary Thepatella,seen separatedabove,isalso knownasthekneecap 083WorldMags.netWorldMags.net WorldMags.net
- 84. Feetareimmenselycomplexstructures, yetweputhugeamountsofpressureon themeveryday.Howdotheycope? Thehumanfootandankleiscrucialforlocomotion andisoneofthemostcomplexstructuresofthe humanbody.Thisintricatestructureismade upofnolessthan26bones,20muscles,33 joints–althoughonly20arearticulated–aswellasnumerous tendonsandligaments.Tendonsconnectthemusclestothe bonesandfacilitatemovementofthefoot,whileligamentshold thetendonsinplaceandhelpthefootmoveupanddownto initiatewalking.Archesinthefootareformedbyligaments, musclesandfootbonesandhelptodistributeweight,aswellas makingiteasierforthefoottooperateefficientlywhenwalking andrunning.Itisduetotheuniquestructureofthefootandthe wayitdistributespressurethroughoutallaspectsthatitcan withstandconstantpressurethroughouttheday. Oneoftheothercrucialfunctionsofthefootistoaidbalance, andtoesareacrucialaspectofthis.Thebigtoeinparticular helpsinthisarea,aswecangripthegroundwithitifwefeelwe arelosingbalance. Theskin,nervesandbloodvesselsmakeuptherestofthe foot,helpingtoholdtheshapeandalsosupplyingitwithallthe necessaryminerals,oxygenandenergytohelpkeepitmoving easilyandconstantly. 084 How do your feet work? What happens when you sprain your ankle? The structure of the foot and how the elements work together Asprainedankleisthemostcommontypeofsofttissue injury.Theseverityofthespraincandependonhowyou sprainedtheankle,andaminorsprainwillgenerally consistofastretchedoronlypartiallytornligament. However,moreseveresprainscancausetheligament totearcompletely,orevenforceapieceofboneto breakoff. Generallyasprainhappens whenyoulosebalanceorslip, andthefootbendsinwards towardstheotherleg.Thisthen overstretchestheligaments andcausesthedamage.Over aquarterofallsporting injuriesaresprains oftheankle. Tibia The larger and stronger of the lower leg bones, this links the knee and the ankle bones of the foot. Fibula This bone sits alongside the tibia, also linking the knee and the ankle. Tendons (extensor digitorum longus, among others) Fibrous bands of tissue which connect muscles to bones. They can withstand a lot of tension and link various aspects of the foot, facilitating movement. Ligaments Ligaments support the tendons and help to form the arches of the foot, spreading weight across it. Blood vessels These supply blood to the foot, facilitating muscle operation by supplying energy and oxygen and removing deoxygenated blood. Toes Terminal aspects of the foot that aid balance by grasping onto the ground. They are the equivalent of fingers in the foot structure. Muscles – including the extensor digitorum brevis muscle Muscles within the foot help the foot lift and articulate as necessary. The extensor digitorum brevis muscle sits on the top of the foot, and helps flex digits two-four on the foot. ©DKImages ©DKImages HUMANANATOMY Anatomy of the foot WorldMags.netWorldMags.net WorldMags.net
- 85. How do we walk?‘Humangait’isthetermtodescribehowwe walk.Thisgaitwillvarybetweeneach person,butthebasicsarethesame 085 Distal phalanges The bones which sit at the far end of the foot and make up the tips of the toes. Bones of the foot Proximal phalanges These bones link the metatarsals and the distal phalanges and stretch from the base of the toes. Metatarsals The five, long bones that are the metatarsals are located between the tarsal bones and the phalanges. These are the equivalent of the metacarpals in the hand. Calcaneus This bone constitutes the heel and is crucial for walking. It is the largest bone in the foot. Talus The talus is the second largest bone of the foot, and it makes up the lower part of the ankle joint. Cuboid One of five irregular bones (cuboid, navicular and three cuneiform bones) which make up the arches of the foot. These help with shock absorption in locomotion. Navicular This bone, which is so named due to its resemblance toaboat,articulates with the three cuneiform bones. Cuneiforms bones (three) Three bones that fuse together during bone development and sit between the metatarsals and the talus. 1. Heel lift The first step of walking is for the foot to be lifted off the ground. The knee will raise and the calf muscle and Achilles tendon, situated on the back of the leg, will contract to allow the heel to lift off the ground. 2. Weight transfer The weight will transfer fully to the foot still in contact with the ground, normally with a slight leaning movement of the body. 3. Foot lift After weight has transferred and the individual feels balanced, the ball of the first foot will then lift off the ground, raising the thigh. 4. Leg swing The lower leg will then swing at the knee, under the body, to be placed in front of the stationary, weight- bearing foot. 5. Heel placement The heel will normally be the part of the foot that’s placed first, and weight will start to transfer back onto this foot as it hits the ground. 6. Repeat process The process is then repeated with the other foot. During normal walking or running, one foot will start to lift as the other starts to come into contact with the ground. ©DKImages Thestructureofthefoot enablesustostaybalanced Ababyisbornwith22 outofatotal26bonesineachfoot 1This is an enlargement of the skin or tissue around the big toe. Formation is often attributed to ill-fitting shoes, though it’s suspected that genetics is the root problem. Bunions 2A fungal infection that’s often transmitted in areas where people walk around barefoot, this develops when the skin is not properly dried and aired. It displays as flaky, itchy skin. Athlete’s foot 3Warts are small, benign lumps of skin, which appear following exposure to a virus – most commonly the human papillomavirus 2 and 7. Warts 4Ingrown toenails are a form of nail disease where the nail grows into either side of the nail bed. Infection can often occur if it is not caught and treated early. Ingrown toenails 5This is the inflammation of the Achilles tendon, which occurs prior to the rupture of the tendon, and is commonly seen in athletes. Achilles tendonitis FOOT AILMENTS 5TOP FACTS In a lifetime, a person will walk the equivalent of four times around the globe – more than 100,000 miles!DID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 86. Producinguptoa pintofsweateach day,nowonderyour feetgetabitwhiffy Sweatactuallykeepsthe skinofourfeetmoistand flexibletocopewiththe constantlychanging pressurewhenwewalk.Without thismoisturetheskinwoulddryand crack,andwalkingwouldbecome extremelypainful. Despitethehugenumberofglands (250,000perfoot)andamountof sweatthatcomesfromourfeet, rememberit’sstilljustsaltandwater. Theodourcomesfromthebacteria thatliveonhumanskinwhich,while unsettling,areperfectlynatural.Our socksareadark,moist-infestedfeast forthem,astheyeatsweatanddead skin.Itisthewasteproductsthey excretefromthisconsumptionthat arewhatsmellsbad.Themorethe bacteriaeattheworseourfeetsmell. Tokeepthesmelldown,makesure youchangeyoursocksandletyour shoesairfor24hoursifyoucan.Also, washyourfeetandspraythemwith antiperspirant! Why do feet smell? Head to Head SMELLIEST ANIMAL, PLACE AND PLANT ANIMAL 1. Striped Skunk Facts: Well known for their ability to secrete a liquid with a strong, foul smelling odour which they can use as a defensive weapon. They can shoot it up to 5 metres. PLACE 2. Rotorua, New Zealand Facts: Located in the most geologically active area of New Zealand, Rotorua is surrounded by mud pools, geysers and steam vents. PLANT 3. Titan arum Facts: This monstrous, three- metre tall plant smells like a combination of rotten eggs and rotting meat to attract insects. Thewonderfulsmellof freshlycutgrass,daisies andfeet… HUMANANATOMY Achilles’ tendon / Smelly feet What does the Achilles’ tendon do? Thistendon,thestrongestinyourbody,connectsthecalfmusclesto theheel.Wheneverythingisfine,itpullsthebackofthefootup whenthecalfmusclescontract.Thisway,yourheelraisesandyour weightgoestoyourtoes.Itenablesustodosuchthingsassprinting, hoppingorjumping.Italsostoreselasticenergytodothesetasksmore efficiently.Biologicalanthropologistsbelieveallthiswasveryimportantforthe wayweevolvedtorunaroundontwolegsandsurvive. TheAchilles’tendonisseeminglynamedthusafterthemythologicalGreek characterofAchilles,whoduringtheTrojanWar-madefamousbyHomer’sepic poemTheIlliad-isshotbyapoisonedarrowinhisunprotectedheel-hencethe commonphrasedescribingaperson’sweakpoint. 086 Isitreallyaweakspotandhow importantisit? WorldMags.netWorldMags.net WorldMags.net
- 87. Though our skin is an amazing protector against the elements, it can become damaged by such factors as heat, cold, friction, chemicals, light, electricity and radiation, all of which ‘burn’ the skin. A blister is the resulting injury that develops in the upper layers of the skin as a result of such burns. The most common example of a blister, which we’ve no doubt all experienced at some time, is due to the repeated friction caused by the material of a pair of shoes rubbing against, and irritating, the skin. The resulting water blister is a kind of plasma-filled bubble that appears just below the top layers of your skin. The plasma, or serum – which is a component of your blood – is released by the damaged tissue cells and fills the spaces between the layers of skin in order to cushion the underlying skin that is being rubbed and protect it from further damage. As more and more serum pours into the space, the skin begins to inflate under the pressure, forming a small balloon full of the serous liquid. Given time to heal, the skin will reabsorb the plasma after about 24 hours. Similarly, a blood blister is a variation of the same injury where the skin has been forcefully pinched or crushed but not pierced, causing small blood vessels to rupture, leaking blood into the skin. All blisters can be tender but should never be popped in order to drain the fluid as this leaves the underlying skin unprotected and also invites infection into the open wound. Whydoburnscausebubblestodevelop belowthesurfaceoftheskin? What are blisters? Blister caused by second-degree burns Skin When any type of burn is experienced, the overlying skin expands as it receives the protective plasma/serum. Plasma Serum is released by the damaged tissues into the upper skin layers to prevent further damage below in the epidermal layer. It also aids the healing process, which is why you should avoid popping your blisters. Damage This particular example of a blister burn has caused damage to the keratinocytes in the skin. Second-degree burns are most often caused when the skin comes into contact with a hot surface, such as an iron or boiling water, or even after exposure to excessive sunlight. Fluid reabsorbed After a day or so the serum will be absorbed back into the body and the raised skin layers will dry out and flake off in their own time. Blistersshouldn’tbe burstastheyarethe body’swayofprotecting deeperskinlayers ©SPL Crampisaninvoluntarycontractionofamuscle,oftenin alimbsuchastheleg,thatcancausepainanddiscomfort forseconds,minutesor,inextremecases,forseveral hours.Theyaremostcommonafterorduringexercise, coincidingwithlowbloodsugarlevels,dehydrationandahighlossof saltfromsweating.Althoughthefullrangeofcausesissomethingofa mysteryduetolimitedresearchinthearea,crampisbelievedtobe theresultofmusclefatigue.Ifamusclehasbeenshortenedthrough prolongedusebutisrepeatedlystimulated,itisn’tabletoproperly relax.Areflexarcfromthecentralnervoussystemtothemuscle informsittocontinuecontractingwhenitisnotnecessary,leadingto apainfulspasmknownascrampasthemusclecontinuallyattempts tocontract.Thisiswhyathletespushedbeyondtheirlimits,suchas footballplayerswhohavetoplayextratimeinasoccermatch,and long-distancerunners,willoftenexperiencethiscondition. Whydoourmusclestenseup? Cramp explained Stretch When the leg is bent or stretched the calf muscle will contract, and then relax when it is not. Cramp Prolonged stretching of the leg prevents the calf muscle from relaxing, which can lead to cramp. Rest At rest the calf muscle is in its relaxed position. 087 Writers’ cramp occurs in the hands and lower arms but is actually a form of dystonia, a neurological conditionDID YOU KNOW? Duration Any generated cramp usually lasts for a few seconds, however some severe cases can last hours. WorldMags.netWorldMags.net WorldMags.net
- 88. 106 The immune system Combating viruses 110 Healing bone fractures How broken bones are mended 111 Making protein How are they manufactured? 112 The cell cycle Inside a vital process 114 White blood cells How infection is fought 116 The science of genetics How genes define who we are 121 Burns The causes and effects of burns 122 Blood vessels Our circulations system 090 Food and your body Inside the digestive system 098 The blood-brain barrier What important role does it play? 099 Pituitary gland up close The ‘master galnd’ explored 100 Brain electricity / Synapses Revealing the truth behind both 101 Adrenaline How does it effect the body? 102 Human respiration The lungs explained 104 Dehydration / Sweating Why we sweat and using fluids 105 Circadian rhythm Our body clock explored 088 124 How your blood works The miraculous fluid analysed 128 Hormones The human endocrine system 130 The urinary system How do we pass waste? 132 Tracheotomy surgery A life-saving procedure 133 Hayfever Why do people suffer? 134 Exploring the sensory system How we experience the world 138 Chickenpox How harmful can it really be? 139 Why do we cry? The different types of tears THE BODY AT WORK 104 Why do we sweat? ©DKImages How our bones heal 110 133 Hayfever explained WorldMags.netWorldMags.net WorldMags.net
- 89. ©Thinkstock Why do we cry? 139 128 The role of hormones “The cell damage from viruses causes diseases” 089 ©Corbis 116 DNA explored 132 Tracheotomy surgery ©Alamy ©DKImages The cell cycle 112 WorldMags.netWorldMags.net WorldMags.net
- 90. 090 Thedigestivetractisalong,musculartubethat runstheentirelengthofyourbody.Itisseparated intofivedistinctsections,eachwithitsown particularandspecialisedfunction. Digestion begins in the mouth. As you chew your food, saliva is released, providing a slippery lubricant and kick-starting the break down of carbohydrates with an enzyme known as amylase. Touch receptors in your mouth tell you when it is time to swallow, and as your tongue comes upward, the food is pushed to the back of your throat. As you swallow, you pass control of digestion over to your automatic motor functions. A flap of skin called the epiglottis folds down to cover the voice box, and the entrance to the lungs, and then a wave pushes the mouthful all the way down the oesophagus. When the food reaches your stomach, it passes through a ring of muscle known as the cardiac sphincter, which prevents it from coming back out the way it came in. The inside of the stomach is a hostile environment, where the cells lining the walls pump out hydrochloric acid and protein-digesting enzymes. The presence of food triggers stretch receptors in the stomach lining, which in turn trigger a series of rhythmic contractions. These churn the stomach contents, mixing in the acid and enzymes, grinding down the food. Atthebottomofthestomachthereisasecondringofmuscle calledthepyloricsphincter,whichactsasagatekeepertothe smallintestine.Thesphincterpreventsanythinglargerthan abouttwocentimetres(0.8inches)indiameterpassing through,returningittothebodyofthestomachuntilithas Food & your bodyJoinusasweunravelallnine metresofyourdigestivesystem THEBODYATWORK WorldMags.netWorldMags.net WorldMags.net
- 91. Chew Digestion begins in the mouth, where our teeth start work on grinding food into manageable chunks. Add bile As the liquid passes into the intestines, stomach acid is neutralised by alkaline bile from the liver. Ferment waste Bacteria living in the large intestine help with the breakdown of waste, releasing even more nutrients. Absorb nutrients As the enzymes begin to release nutrients, they are absorbed across the lining of the small intestine into the bloodstream. Churn The muscles of the stomach rhythmically churn its contents, mechanically breaking food down into a lumpy paste. Remove water The large intestine absorbs excess water from the food as it passes through. Get rid of waste All that is left at the end of the digestive process is a combination of indigestible material, dead cells and bacteria. Swallow Saliva makes each mouthful slippery, allowing it to slide easily down the oesophagus to the stomach. Add acid and enzymes The stomach produces hydrochloric acid, and protein-digesting enzymes. Add more enzymes The pancreas produces digestive enzymes, which are added to the mixture as it enters the small intestine. It can take up to 48 hours for a meal to travel through your body Journey of your food LENGTH OF THE SMALL INTESTINE 7metres Shellfish Shellfish allergies tend to develop during adulthood. Foods to avoid include barnacles, crabs, shrimps, lobsters, crawfish and krill. Milk Children under the age of three are the most likely to develop an allergy to milk, but they usually outgrow it by the time they reach adulthood. Peanuts By far the most common food allergy is peanuts. In the UK, as many as one in 50 children are sensitive. HEAD HEAD2FOOD ALLERGIES 1. COMMON 2. MORE COMMON 3. MOST COMMON 091 Biological washing powder uses digestive enzymes to break down the stains on dirty laundryDID YOU KNOW? beengrounddownfurther.Thisensuresthatby thetimeitreachesthesmallintestine,yourfood isarunny,slightlylumpypaste,andisreadyfor thenextstageofdigestion. The small intestine is the site of chemical digestion. Here, the pancreas adds digestive enzymes, and the liver adds a generous squirt of alkaline bile, delivered via the gall bladder. This bile not only neutralises the burning stomach acid, it also acts a little like washing-up liquid on dirty dinner dishes, helping to separate the food particles and forcing fats to disperse into tiny bubbles. Muscles in the small intestine continue to squeeze and mix the contents together, allowing the enzymes to get to work inside the paste. As the nutrients are released, they are then absorbed over the walls of the intestine and into the bloodstream. To ensure that everything keeps moving through the system, every five to ten minutes a wave of muscle contractions begins at the stomach and travels all the way down the intestines. Known as the migrating motor complex (MMC), this wave squeezes the digestive system like a tube of toothpaste, urging its contents further toward the colon. As the food progresses through the small intestine, more and more of the nutrients are released by enzyme activity, and by the time it gets to the large intestine, most of the useful material has been absorbed into the bloodstream. However, the digestive process is not over, and here, bacteria help to break down even more of the undigested food. The large intestine also absorbs most of the remaining water, leaving behind a combination of undigested material, dead cells and bacteria. When the waste has completed its journey through the large intestine it goes to the rectum for storage until there is a convenient time to get rid of it. Food chain Energy from the Sun is converted into to chemical energy by photosynthetic organisms like plants. The plants use the energy to build biological materials from nutrients in the air and soil. Herbivores then consume the plants, releasing some of the energy, and using the components to build their own bodies. Carnivores then eat the herbivores. When plants and animals die, decomposers break their bodies down, returning nutrients to the ground for reuse, and the cycle begins again. 1 The Sun On average, every minute the Sun delivers 2kcal of energy for every cm2 (0.2in2 ) of Earth. 4 Herbivore Herbivores can digest plant material, but the process is difficult, and they can only extract around ten per cent of the energy. 3 Producer Plants use the energy from the Sun to combine CO2 and water, producing chemical energy in the form of sugars. 6 Carnivore Carnivores get easy energy by digesting the tissues of other animals. 2 Inefficient conversion Less than five per cent of the available energy from the Sun is converted into chemical energy by plants. 5 Energy loss At every step up in the food chain, some of the energy is lost, mostly as heat. 1 3 5 2 4 6 WorldMags.netWorldMags.net WorldMags.net
- 92. 092 Taste tells us whether our food is safe to eat, but smell gives it flavour Sense of taste What is a taste bud? The human tongue is able to detect five different tastes: sweet, sour, salty, bitter and umami (savoury), providing us with a quick way to distinguish between different types of food. Sweet foods contain sugar and are a good source of energy. Salty foods provide sodium, which is vital for nerve function, but deadly in high quantities. Bitter foods might contain poison. Babies are born with a natural preference for sweet food and a dislike of bitter, providing a biological safeguard that encourages them to eat safe, high-calorie food. However, nutrition is not that simple. Many vegetables are bitter but not poisonous and so learning to like them comes with experience. The degree to which we can detect different tastes varies, and appears to be dictated by our individual anatomy. The population can be broadly divided into three categories based on the number of taste buds on their tongue. Those with the fewest are known as ‘non-tasters’, those with an average number are known as ‘tasters’, and those with many more taste buds than the rest if the population are ‘supertasters.’ Supertasters are especially sensitive to taste and will react much more strongly than the rest of the population. As a result, they tend to really dislike bitter foods like green vegetables and coffee, and often shy away from rich desserts and sugary sweets. Though these anatomical differences can explain some of our food preferences, most our individual likes and dislikes are not down to taste, but to flavour; the combination of taste and smell. The act of chewing food releases chemicals known as volatiles, which evaporate rapidly. As we swallow, some of the air inside the mouth is forced up toward the nose, carrying these volatiles with it. Here, they bind to receptors on olfactory cells, triggering sensory messages to the brain. Recently, scientists have found that these olfactory receptors can detect as many as 1 trillion different odours. Taste and smell are strongly linked to emotion and memory, and as a result, experience is a powerful decider in the development of our likes and dislikes. Contrary to popular belief, all five tastes can be detected almost anywhere on the tongue Anatomy of a human tongue Posterior tongue About a third of the tongue is hidden right at the back of the mouth. Papillae The tongue is covered in tiny bumps, but not all of them contain taste buds. Muscle There are eight muscles in the tongue that alter its shape and change its position. Blood supply The tongue receives blood from the lingual artery and it drains out through the lingual veins. Nerves The front and back of the tongue send taste information to the brain. Circumvallate papillae These large bumps are found at the back of the tongue, each surrounded by a dip that collects saliva. Filiform papillae Most of the tongue is covered in thin, rough bumps that contain no taste receptors. Foliate papillae These contain taste receptors and are located on the back edges of the tongue, where saliva drips down the cheeks. Anterior tongue The visible part of the tongue is responsible for the majority of taste detection. Pore A tiny gap at the top of the taste bud allows saliva to touch the taste cells. Gustatory hair Each taste cell ends with a tiny hair, covered in receptors that allow it to detect chemicals dissolved in the saliva. Basal cell Ageing or damaged taste cells are replaced by the basal cells waiting underneath. Sensory cell Each cell is sensitive to one of the five tastes, but all types are found together in a single taste bud. Nerve Messages are relayed to the brain via a nerve that exits at the bottom of the taste bud. Support cell The taste cells are surrounded by an envelope of non-tasting support cells. Synapse Taste cells do not transmit the signals to the brain themselves, instead passing the message over to a nerve cell. TASTE CELLS ARE REPLACED EVERY TEN DAYS 10 THEBODYATWORK Taste and digestion WorldMags.netWorldMags.net WorldMags.net
- 93. 093 Stomachulcerswerelongthoughtto becausedbystress,butit’snowknowntheculprit isa bacterial infection This muscular bag turns your dinner into an acidic soup Inside the stomach The stomach acts as a holding chamber, receiving food from the mouth and preparing it to be processed in the small intestine. At rest, the stomach is around the size of a fist, and its lining is curled into a convoluted network of folds known as rugae. As you eat, these folds stretch out, allowing an adult to eat around a litre (0.26 gallons) of food in one sitting. Stretching of the stomach walls triggers rhythmic contractions, mixing the food with acid and protein-digesting enzymes, grinding it to a paste in preparation for the next stage of digestion. DID YOU KNOW? Duodenum The stomach empties its contents into the first section of the small intestine. Pyloric sphincter A ring of muscle at the base of the stomach prevents the contents from leaking out before they are ready. Cardiac sphincter A ring of muscle at the top of the stomach stops the acidic contents moving back into the oesophagus. Antrum The bottom part of the stomach generates powerful grinding contractions. Oesophagus Food travels from the mouth to the stomach via a muscular tube that runs behind the windpipe. Fundus Excess gas is collected at the top of the stomach, where it can be pushed out and up by the diaphragm. Rugae The lining of the stomach is stretchy and expandable, and when relaxed, it curls up into characteristic folds. Muscle layers There are three layers of muscle in the stomach wall, each running in a different direction. Stomach lining The lining is covered in microscopic pits that produce mucus, acid and protein-digesting enzymes. Body The central portion of the stomach helps to create downward pressure, keeping food moving in the right direction. Chewing the fat Every single cell in your body is surrounded by a membrane made of fats; it insulates your nerves and it provides a valuable energy reserve. Eating fat also provides a number of vitamins and essential fatty acids the body can’t make on its own. Saturated fats (the solid fats found in meat and dairy) and trans fats (found in hydrogenated vegetable oil and many processed foods) have shown to raise cholesterol, which can lead to circulatory problems, but unsaturated fats (the liquid fats found in plants and fish) can have the opposite effect, and are considered good for your health. Fat has a bad reputation, but the truth is, your body needs it The sight, smell and even the thought of food begin to prepare the stomach for a meal, so by the time the swallowed mouthfuls start to arrive, it is already producing more acid. Stretching and irritation of the stomach trigger it to turn up acid and enzyme production and to start churning. For the first 20 to 30 minutes after eating a meal, no food is allowed to leave. To stop the stomach emptying too quickly, protein and fat are monitored in the first part of the small intestine. If too much food comes through, the intestine sends signals to slow the stomach down. How long does it take to digest food? THE STATS 9m 40 hours 1.8kg LENGTH OF DIGESTIVE SYSTEM DAILY INTAKE 1-3HOURS TIME IN STOMACH TIME IN LARGE INTESTINE 350gDAILY OUTPUT 53 hoursAVERAGE DIGESTION TIME THE JOURNEY OF FOOD WorldMags.netWorldMags.net WorldMags.net
- 94. 094 After leaving the stomach, food must pass through over 7m (23ft) of intestines The intestines Thestomachcontentsentertheintestine gradually,allowingtimefortheliquidfoodtobe processed.Firsttheacidisneutralisedbybile, providedbytheliver,andthendigestiveenzymes areaddedbythepancreas.Theenzymesactlike molecularscissors,breakingproteins, carbohydratesandfatsdownintobuildingblocks smallenoughtobecarriedoverthewallofthe smallintestine.Theremainingundigested materialpassesintothelargeintestine,which absorbswater,leavingbehindsolidwastethat canthenbepassedoutofthebody. Appendix Near the start of the large intestine is a blind-ending tube known as the appendix – its function is largely unknown. Small intestine The first part of the intestine is responsible for breaking food down and absorbing the nutrients. Rectum Before exiting the body, waste products are stored in a small pouch known as the rectum. Large intestine The second part of the intestine absorbs water and prepares waste. Villi The cells that line the walls of the small intestine are arranged into folds known as villi. Brush border The cells that make up the intestinal wall are covered in microscopic fingers known as microvilli. Small vein Nutrients travel across the wall of the intestine into the blood stream. Lymph vessel Fatty acids are transported away from the intestines via the lymphatic system. Intestinal crypt Between the villi are crypts containing mucus-producing cells. Small artery Each of the villi has a rich blood supply. Living with bacteria Bacteriaareoftenportrayedasthe‘badguys’ofthe body,buttheproportionthatcausefoodpoisoning issurprisinglysmall.Infact,bacteriastarttomove intoyourdigestivesystemfromthemomentyouare born,andahealthyadulthasaround300to500 differentresidentspecieslivingintheirlarge intestineatanyonetime. Theupperpartsofthedigestivesystemarehostile tomicroorganisms;thestomachishighlyacidicand thesmallintestineisfilledwithdigestiveenzymes, butthelargeintestineprovidestheperfect environmentforsustainingamicroscopicworld. Bythetimefoodreachesthispoint,ourdigestive enzymeshavedonetheirworkandmostofthe nutrientshavebeenabsorbed,butbacteriahavea differentsetofenzymes.Theyareabletobreak indigestiblematerialdownevenfurther,allowing ustoabsorbevenmorenutrients,mainlyintheform offattyacids. Thepresenceofthesehelpfulbacteriaalsomeans thereislittlespaceorresourcesleftfordangerous pathogens,helpingtokeepinfectionsatbay. Thegutanditsresidentbacteriaareinconstant communication,pickinguponchemicalsignals releasedintotheenvironment.Thesesignalscan havefar-reachingeffects,andthetypesofbacteria presentinyourintestineshavebeenshownto influenceotherorgans,includingthebrain. THE TOTAL ABSORPTIVE SURFACE AREA OF THE DIGESTIVE SYSTEM 4,500m2 THEBODYATWORK Taste and digestion WorldMags.netWorldMags.net WorldMags.net
- 95. 1Drinking plenty of water is beneficial for our health, but there is nothing special about drinking eight glasses. Drinking when you feel thirsty is usually more than enough. 2In trials involving over 11,000 people, it has been shown that vitamin C does not prevent or cure colds. However, washing hands regularly is effective at preventing transmission. 3Carrots contain vitamin A, vital for eye health, but the idea that they help you see in the dark is a lie from WWII to keep radar technology secret from the Germans. 4It is a popular fact among dieters that eating celery burns more calories than it provides. Although possible in theory, no foods have been found to have this effect. 5Actually, this one might be true. New research is increasingly suggesting that diet does have an impact on acne and that saturated fats and sugars might be to blame. Eight glasses of water Vitamin C stops colds Carrot night vision Celery’s minus-calories Chocolate causes acne 5TOP FACTSFOOD MYTHS DEBUNKED The first part of the digestive system prepares the food for the next stage, ensuring it is broken into a fine paste, mixed to form a homogenous fluid, and shocked with acid to limit the potential for dangerous infection. However, it is not until food reaches the small intestine that the microscopic breakdown and absorption of nutrients really begins. At the start of the small intestine, the liver injects alkaline bile into the acidic liquid food, neutralising its pH and preparing it for the introduction of digestive enzymes. Bile also helps to emulsify fats. Fats are not water soluble, so they tend to clump together in large globules to hide from and avoid the surrounding water, but bile acts a little like washing-up liquid, separating the fats out into smaller blobs. Now that the food is nicely mixed and separated, the enzymes can really get to work. The pancreas produces a cocktail of three kinds of enzyme, each used to break down a different type of molecule. Proteases clip amino acids from proteins, lipases break fats down into fatty acids and glycerol, and carbohydrases turn long chains of carbohydrate into sugars. These small blocks can be absorbed into the bloodstream, where they are distributed around the body, used to build our own biological molecules, or broken down and burnt for energy. The body requires different quantities of each of the nutrients, and can sometimes convert one into another if supplies are running low. However, there are a number of nutrients that cannot be synthesised by the body at all or in high enough quantities, and these must be obtained directly from the diet. These essential nutrients include some types of amino acids, fatty acids like omega-3 and omega-6, and all of the vitamins and minerals needed. Vitamins and minerals are organic and inorganic compounds required by the body in small amounts for various different functions. Some of these, like calcium, make up vital structural components of our bodies, while others, like vitamin C, are involved in biochemical reactions. 095 The human mouth produces 1-2 litres of saliva every dayDID YOU KNOW? MOLECULE / VITAMIN IRON-RICH FOOD GREEN LEAFY VEGETABLES OILY FISH FRUITS FOOD YOU’LL FIND IT IN WHAT THE BODY USES IT FOR Egg yolks Red meat Spinach Cauliflower Broccoli Brussels sprouts Salmon Tuna Caviar Dried apricots Avocados Bananas IRONFOLICACIDVITAMINDPOTASSIUM Iron is a key component of haemoglobin, the red pigment that carries oxygen in our blood. Without it, oxygen cannot be transported effectively, resulting in iron-deficiency anaemia. This is most often caused by blood loss, so as a result, women are much more likely to be deficient of iron than men. Folic acid is essential for the synthesis of DNA and without it the production of red blood cells starts to slow down. It is also extremely important in the formation of the central nervous system, and during the first 12 weeks of pregnancy, folic acid supplementation is recommended to pregnant women. Vitamin D is involved in bone formation in the body, so deficiency of vitamin D in children can result in bone deformity. Luckily, this vitamin is easy to obtain. Not only can vitamin D be found in oily fish, eggs and dairy products, but our bodies can also make it themselves using sunlight. Cells use a combination of potassium and sodium to maintain their internal electrical balance. Potassium is vital to ensure muscles are able to contract properly and nerves are able to transmit their messages. It is easily obtained in the diet and deficiency is incredibly rare unless there is damage to the kidneys. WorldMags.netWorldMags.net WorldMags.net
- 96. Research into food addiction is relatively new and the results are hotly debated, but there is increasing evidence that food can elicit some of the same brain responses as addictive substances like cocaine. In overweight people, overeating can become a compulsion that is difficult to control, and has been shown to activate the same reward pathway that lights up when addictive drugs are ingested. In alcoholics, cocaine addicts and heroin addicts, the number of dopamine receptors in the reward pathway is lower than in the rest of the population and the same thing is found in obesity. It is thought that people with fewer dopamine receptors might need to over- stimulate their brains to experience the same rewards as normal people, and therefore turn to alcohol, drugs, or perhaps even food. Hunger is one of the body’s most basic and fundamental sensations, and it originates in the stomach. When the stomach is empty, it begins to produce a hormone known as ghrelin. This then travels to a region of the brain known as the hypothalamus. The hypothalamus is responsible for maintaining a constant, optimum state; keeping the body at a set temperature, regulating hormones and monitoring hydration. The arrival of ghrelin is a signal that energy levels might be about to dip, so it triggers the production of a second hormone, neuropeptide Y. This hormone promotes eating. The cue to stop eating is much more subtle. The stomach has stretch receptors, and will signal to the brain that it is full. But what happens if it is empty, but there is already enough energy stored in the system? Fat stores produce a hormone known as leptin, which tells the brain exactly 096 Food addiction Placebo + Neutral Placebo + FoodRitalin + Neutral Ritalin + Food Why do we crave these foods? Food and the brain When we are feeling stressed or sad, many people turn to comfort foods such as mashed potatoes, beans on toast or macaroni cheese. Carbohydrates not only make us feel warm and full, they actually increase levels of serotonin, sometimes known as the happy hormone. Sugary foods are craved for many reasons, the simplest of which is that your body needs an energy boost. However, eating sugar is just a temporary fix, and as the sugar is rapidly cleared from the blood, the craving will quickly return. Animals have what is known as a ‘salt appetite’, similar to thirst, which drives them to seek out salt when they are running low. However, there is little evidence for an equivalent trait in humans. Men are more likely to crave salty foods than women, though. Comfort food Sweets Salty snacks how much energy the body has in reserve. When leptin levels are high, the hypothalamus makes hormones that suppress appetite. The trouble is that with high levels of fat, we can become resistant to the leptin message, similar to insulin resistance in type-II diabetes. If the brain does not know there is enough fat, we just keep eating. Cravings are slightly different. These are generated not in the stomach, but in the brain. There are three main areas of the brain implicated in food cravings, the hippocampus, the insula and the caudate. Humans have been programmed through evolution to enjoy fatty and sugary foods; eating them ensures we have enough energy to survive. The hippocampus is involved in gathering sensory information, and processing it for long-term memory storage, and with food cravings, these memories become associated with activation of the brain’s reward circuitry. The more we enjoy eating a food, the more likely we are to crave it. Mental images are thought to play an important role in food cravings and picturing food makes it much harder to resist. But thinking about other visual images can help to curb the cravings and distract your brain. Digestion happens subconsciously, but you do have a manual override, and what your brain thinks it wants isn’t always what it needs. THEBODYATWORK Taste and digestion WorldMags.netWorldMags.net WorldMags.net
- 97. STRANGE BUTTRUE A STICKY MYTH How long does chewing gum stay in your system? Answer: It is true that chewing gum cannot be digested, but as long as it is a small piece – less than 2cm (0.8in) in diameter – there is no reason it should get stuck, and it should pass out normally within a day or two.A Seven years B A day C Forever 097 The digestive system has its own dedicated nervous system, known as the enteric nervous systemDID YOU KNOW? TAKE A LOOK AT THE CHEMICALS BEHIND SOME OF OUR FAVOURITE FOODS AND DRINKS CHEMISTRY OF FOOD Chocolate Chocolate is one of the foods most commonly associated with happiness, particularly the hormone serotonin. The chocolate itself does contain the precursor to serotonin, an amino acid known as tryptophan, but this is also found in many other foods, including meat. Chocolate also contains phenylethylamine, a molecule chemically similar to amphetamine, but it is broken down in the digestive system, and does not reach the brain intact. The feel-good factor of chocolate is more likely to be down to its fat and sugar content, and a property known as mouthfeel. Chocolate is among the only foods that melts at close to body temperature. Bacon The distinctive smell of bacon is, as most of us have probably experienced, hard to resist. That fact is all down to the chemistry of cooking meat. As the bacon is heated, the amino acids that make up the muscle protein react with reducing sugars present in the bacon fat. This process, known as the Maillard reaction, occurs only at high temperatures and produces over 150 different volatile molecules, each able to interact with different smell receptors in the nose. Most of the delicious smell of bacon is attributed to a group of nitrogen- containing compounds known as pyridines and pyrazines. Coffee Coffee contains over 1,000 different aroma compounds, responsible for its unmistakable smell. Around 12 per cent of the green coffee bean is made up of a set of chemicals known as chlorogenic acids, and when the beans are roasted, most of these acids begin to break down. Some produce the brown-coloured compounds that give coffee its characteristic dark colour, while others produce the bitter-tasting chemicals responsible for its taste. Coffee also contains high quantities of caffeine, around 100 milligrams (0.0035 ounces) in every cup. It works on receptors in the heart and brain, blocking the action of a natural neurotransmitter and acting as a stimulant. ©Jynto;GregRobson;Andreadonetti/Valentyn75/Dreamstime/Cornelius20;Thinkstock;SciencePhotoLibrary;DK Tea In England, drinking tea is a national pastime. The main chemicals in tea are known as polyphenols, and each cup contains around 200 milligrams (0.007 ounces). The polyphenols are large molecules made up of smaller building blocks, which are known as catechins. When these catechins react with oxygen, they make two types of chemical; theaflavins, which make the orange-brown colour of tea, and thearubigins, which are thought to contribute to the taste. The different amounts of the chemicals present in the tea are very dependent on the life of the plants and the processing of the leaves. THE LENGTH OF AN AVERAGE STOMACH AFTER A MEAL 30CM WorldMags.netWorldMags.net WorldMags.net
- 98. The blood-brain barrier (BBB) is an essential group of cells that line the blood vessels in the central nervous system (brain and spinal cord). They allow passage of materials between the clear fluid surrounding the brain (cerebrospinal fluid) and the red blood cells in arteries, veins and capillaries. The key advantage of having such a barrier is that it prevents large micro- organisms passing into the brain and causing infections. While infections in other areas are common (such as after a cut finger, or mild chest infections), those affecting the brain are much rarer. However when they do occur (eg meningitis), they are potentially life threatening as they are very difficult to treat. The tight junctions between cells regulate the size and type of particle that pass between them, including oxygen molecules, carbon dioxide molecules, nutrients and hormones. Since it’s so effective, it also stops medications from entering the brain (such as certain antibiotics), so while they are effective in the rest of the body, they are ineffective in this vital organ. Overcoming this is a major aim of doctors in the next decade, and the battle has already started. Manipulating the blood-brain barrier’s natural transport mechanisms and delivering drugs within nanoparticles to squeeze through the tight junctions are just two examples of the modern techniques that are under development. Howdoesthisgatewaycontrolthemolecules thatpassfromthebloodintothebrain What is the blood- brain barrier? A tight squeeze The tiny gaps between cells regulate the size and type of particle that are able to fit through. This built-in gateway is the main line of defence for the central nervous system Breaking down the barrier ©Thinkstock;SPL The endothelial lining of the blood-brain barrier loves lipids (fatty molecules), but it hates particles with high electrical charges (ions) and large substances. Thus the ideal substance is small, rich in lipids and has a low electrical charge. Barbiturates are such an example, as they freely flow across the blood-brain barrier to suppress brain function; they act as sedatives and antidepressants. However this free movement comes with risks – too much of it will accumulate and slow the brain to a point where you can lose consciousness and even stop breathing. Crossing the BBB Lipophilic Substances rich in lipids can diffuse across the barrier with relative ease. Highly charged Highly charged ions are repelled, meaning that some medications are ineffective in the brain. Special transport Active and passive transporters across this membrane can overcome some of these problems, and be manipulated to deliver medications to the correct place. Astrocyte These numerous star-shaped cells provide biochemical support to the endothelial cells, and also play an important role in transportation and repair. Just passing through Some ions are transported out of the blood cells and into the astrocytes, and then out of the astrocytes and into neurons in the brain. THEBODYATWORK The blood-brain barrier 098 WorldMags.netWorldMags.net WorldMags.net
- 99. RECORD BREAKERS TALL TALE 2.72m TALLEST MAN IN HISTORY At 2.72 metres (eight foot, 11.1 inches) Robert Wadlow is the tallest man on record. A sufferer of gigantism, he was 0.9 metres (three feet) taller than his father. Sadly, he was only 22 when he died in 1940. 099 In fish, the intermediate lobe controls skin colour change, while birds have no intermediate lobe at all ©Alamy The pea-sized pituitary gland is found at the base of the brain, close to the hypothalamus. It looks a relatively insignificant part of the brain, but it plays a role in many vital systems. Often referred to as the ‘master gland’, it not only releases hormones that control various functions, but it also prompts the activity of other glands like the ovaries and testes. The pituitary gland comprises three sections called lobes: the anterior, the posterior and the intermediate – the latter of which is considered part of the anterior lobe in humans. These work together with the hypothalamus, which monitors hormones in the blood and stimulates the pituitary gland to produce/release the appropriate hormone(s) if levels fall too low. The anterior lobe produces seven important hormones, which include those that regulate growth and reproduction. Adrenocorticotropic hormone (ACTH) targets the adrenal glands to produce cortisol and controls metabolism, while luteinising hormone triggers ovulation in women and stimulates testosterone production in men. The posterior lobe, meanwhile, doesn’t generate any hormones itself, but stores two: antidiuretic hormone (ADH), which decreases urine production by making the kidneys return more water to the blood, and oxytocin, which tells the uterus to contract during childbirth and also prompts milk production. Whatdoesthishormonefactorydoandwhycouldn’twelivewithoutit? Pituitary gland up close DID YOU KNOW? The pituitary gland also produces growth hormone, which in adults controls the amount of muscle and fat in the body and plays a key role in the immune system. In children, of course, growth hormone has a very noticeable effect in increasing height and bulk until adulthood. However, sometimes the pituitary gland becomes hyperactive – often as a result of a benign tumour – and produces excess growth hormone. In these cases, a person can grow to a far-beyond-average height, with hands, feet and facial features growing proportionally. While this might not seem so bad, gigantism is nearly always accompanied by other health issues, such as skeletal problems, severe headaches and more life-threatening conditions like heart disorders. If diagnosed early, treatment such as drugs that inhibit growth hormone production and surgical removal of the tumour can help avert the more serious conditions of gigantism. Gigantism in focus Where does this vitally important hormone manufacturer sit within the human brain? The master gland in context Posterior lobe This doesn’t produce any hormones itself, but stores and releases some, like ADH, made elsewhere in the hypothalamus. Anterior lobe Subdivided into three parts, including the thin intermediate lobe, this produces seven kinds of hormone which each target specific organs. Thyroid One of the largest endocrine glands that regulates metabolism is in turn regulated by the pituitary gland. Hypothalamus The secretion of hormones from the pituitary gland is directly controlled by this part of the brain, which links the nervous and endocrine systems. Capillaries Hormones are exchanged between the anterior lobe and the hypothalamus via a network of capillaries. Pituitary stalk This is what connects the pituitary lobes to the hypothalamus. WorldMags.netWorldMags.net WorldMags.net
- 100. Thenervoussysteminvolvesacomplexcollectionofnervecells calledneurons.Nervemessagescantravelalongindividual neuronsaselectricalnerveimpulsescausedbythemovementof lotsofelectricallychargedionparticles.Inordertocrossthe minusculegapsbetweentwoneurons,thenervemessagemustbeconverted intoachemicalmessagecapableofjumpingthegap.Thesetinygapsbetween neuronsarecalledsynapses,formingthemaincontactzonebetweentwo neurons.Eachneuronconsistsofacellbodyandbranchingstructuresknown asaxonsanddendrites.Dendritesareresponsiblefortakinginformationinvia receptors,whileaxonstransmitinformationawaybypassingelectricalsignals acrossthesynapsefromoneneurontoanother. How does a synapse work? Trillionsofneuronscarrymessagesaround thebody,buthowdotheypassthemon? ©DKImages Nerve impulse A nerve impulse is initiated when a stimulus (change in the internal or external environment) alters the electrical properties of the neuron membranes. Vesicle This is the tiny membrane that stores neurotransmitter molecules. The vesicles travel from the sending neuron to the synapse, where they fuse with the presynaptic membrane and release the neurotransmitters. Presynaptic membrane Synaptic cleft Postsynaptic membrane The cell membranes of the sending neuron (presynaptic membrane) and the receiving neuron (post-synaptic membrane) are separated by a fluid-filled gap called the synaptic cleft. Ongoing message Oncetheneurotransmitters crossthegapbetweenthetwo neurons,ionchannelsinthe receivingneuronopenallowing thepositiveionstoflowintothe receivingneuron. Neuron The ‘sending’ nerve cell contains a nucleus, which holds the cell’s genes and controls its functions. Dendrite As well as a long extension called the axon, each neuron has multiple branch-like extensions called dendrites, which take in nerve messages from other neurons. Axon The nerve signals travel in one direction along the axon to the synaptic knob at the end of the axon. Ions The flow of these charged particles is the basis of the propagation of a nerve impulse. Neurotransmitter molecules When the nerve signal reaches the synapse, it is converted into neurotransmitters, which are the chemicals that bind to the receptor nerve cell, causing an electrical impulse. Does the brain produce enough energy to power a light bulb? THEBODYATWORK Brain electricity / Synapses 100 Thebrainitselfrequiresarelativelylow powertooperateonaday-to-daybasis, around20wattswhichwouldbeenoughto poweraveryweaklightbulb.20watts correspondsto20joulesofenergypersecond.The generationofelectricityinthebrainresultsfromthe movementofions(chargedatoms)throughoutthe brain,asopposedtoelectronsmovingthroughawire. Interestingly,auniquesideeffectofthebrain’s electrochemicalprocessesisthatisgenerateselectric fieldswhenitisactive.Indeed,whenlargenumbersof neuronsaresignallingandinahighlysynchronised manner,thegeneratedelectricfieldsarelargeenough tobedetectedoutsideoftheskullthrough electroencephalography(EEG)or magnetoencephalography(MEG). Thebrainisacomplexandextremelypowerfulorgan,but woulditbestrongenoughtopoweranyeverydaylightbulb? “The generation of electricity results from the movement of ions” WorldMags.netWorldMags.net WorldMags.net
- 101. Discoverthesciencebehindyourbody’s amazingchemicalcopingmechanism Nestlingonalayeroffat locatedjustaboveeach ofyourkidneysarethe body’sadrenalglands. Around8cmlong,theadrenalglands producehormonesthataffectyour body’sconsumptionofenergyaswell asyourstressresponses. Adrenalglandsconsistoftwomain layersofhormone-secretingcells:the outercortexandtheinnermedulla. Whilethecortexproducesenergy- balancinghormones,themedulla producesachemicalcalled epinephrine,whichweknowbetter asadrenaline.Identifiedin1900, adrenalineisafast-actinghormone thathelpsthebodydealwith unexpectedstresses–nottomention highlevelsofexcitement–byupping yourheartrateandtheflowofblood toyourmuscles. Theeffectofthisisthatyourblood vesselsandairpassagesdilate, meaningthatmorebloodpassesto themusclesandmoreoxygengetsto thelungsquicker,temporarily improvingthebody’sphysical performanceandpotentiallysaving yourlife. Adrenaline Medulla At the core of the adrenal gland, the adrenal medulla produces, stores and releases adrenaline. Kidney The organ that filters waste from the blood. Fat Each adrenal gland is protected by a layer of fat. Cortex At the edge of the adrenal gland, the cortex produces steroid hormones that include cortisol (for balancing blood sugar and carb metabolism) and aldosterone (for balancing the body’s salts and water). Your adrenal glands 101 5 TOP FACTS ADRENLINE 1Ababy’sstresslevelduring birthishighand,asaresult, theiradrenalinelevelisalso veryhighatthistime.This subsidespostbirthbackdown tonormallevels. Welcome to the world 2Duetoitsblood-vessel- constrictingproperties,adrenaline isalsousedtotreatbreathing difficultiesassociatedwith anaphylacticshockcausedby allergicreactions. When you need to breathe 3Afterstressfulsituations,it’s oftenagoodideatophysically workofftheadrenalineinyour bodysoitdoesn’tstayinyour system,keepingyouawakeat night,forexample. And relaaax 4Adrenalinecanbeobtainedfrom animalsorsynthesisedinthelab. Thechemicalnameforitis aminohydroxyphenylpropionic acid,whichisrepresentedwiththe chemicalformulaC9H13NO3. Amino what now? 5Thesaying‘fightorflight’is associatedwithadrenalinebecause whenwe’restressedweproducethe hormoneinorderthatwecaneither getreadytodefendourselvesor makearunforit. Fight or flight “Adrenaline is a fast-acting hormone that helps the body deal with stresses” WorldMags.netWorldMags.net WorldMags.net
- 102. 102 Theprimaryorgansused forrespirationinhumans arethelungs.Humans havetwolungs,withthe leftlungbeingdividedintotwolobes andtherightintothree.Lungshave between300–500millionalveoli, whichiswheregasexchangeoccurs. Respirationofoxygenbreaksinto fourmainstages:ventilation, pulmonarygasexchange,gas transportationandperipheralgas exchange.Eachstageiscrucialin gettingoxygentothebody’stissue, andremovingcarbondioxide. Ventilationandgastransportation needenergytooccur,asthe diaphragmandtheheartareusedto facilitatetheseactionswhereasgas exchangingispassive.Asairisdrawn intothelungsatarateofbetween10- 20breathsperminutewhileresting, througheitheryourmouthornoseby diaphragmcontraction,andtravels throughthepharynx,thenthe larynx,downthetrachea,andinto oneofthetwomainbronchialtubes. Mucusandciliakeepthelungsclean bycatchingdirtparticlesand sweepingthemupthetrachea. Whenairreachesthelungs,oxygen isdiffusedintothebloodstream throughthealveoliandcarbon dioxideisdiffusedfromtheblood intothelungstobeexhaled.Diffusion ofgasesoccursbecauseofdiffering pressuresinthelungsandblood.This isalsothesamewhenoxygen diffusesintotissuearoundthebody. Whenbloodhasbeenoxygenatedby thelungs,itistransferredaroundthe bodytowhereitismostneededinthe bloodstream.Ifthebodyis exercising,breathingrateincreases andconsequentlysodoesheartrate toensurethatoxygenreachestissues thatneedit.Oxygenisthenusedto breakdownglucosetoprovide energyforthebody.Thishappensin themitochondriaofcells.Carbon dioxideisoneofthewasteproducts ofthis,whichiswhywegetabuildup ofthisgasinourbodythatneedsto betransportedbackintothelungsto beexhaled. Thebodycanalsorespire anaerobically,butthisproducesfar lessenergyandinsteadofproducing co2asabyproduct,lacticacidis produced.Thebodythentakestime tobreakthisdownafterexertionhas finishedasthebodyhasaso-called oxygendebt. Respirationiscrucialtoanorganism’s survival.Theprocessofrespirationisthe transportationofoxygenfromtheairthat surroundsusintothetissuecellsofour bodysothatenergycanbebrokendown Human respiration 5. Alveoli The alveoli are tiny little sacs which are situated at the end of tubes inside the lungs and are in direct contact with blood. Oxygen and carbon dioxide transfer to and from the blood stream through the alveoli. How our lungs workLungs are the major respiratory organ in humans 1. Nasal passage/ oral cavity These areas are where air enters into the body so that oxygen can be transported into and around the body to where it’s needed. Carbon dioxide also exits through these areas. Pulmonary artery Pulmonary vein Capillary beds THEBODYATWORK How we breathe WorldMags.netWorldMags.net WorldMags.net
- 103. 103 4. Bronchial tubes These tubes lead to either the leftortherightlung.Airpasses through these tubes into the lungs, where they pass through progressively smaller and smaller tubes until they reach the alveoli. 6. Ribs These provide protection for the lungs and other internal organs situated in the chest cavity. Breathingisnotsomethingthatwehaveto thinkabout,andindeediscontrolledbymuscle contractionsinourbody.Breathingis controlledbythediaphragm,whichcontracts andexpandsonaregular,constantbasis. Whenitcontracts,thediaphragmpullsairinto thelungsbyavacuum-likeeffect.Thelungs expandtofilltheenlargedchestcavity andairispulledrightthrough themazeoftubesthat makeupthe lungsto thealveoliattheends,whicharethefinal branching.Thechestwillbeseentorise becauseofthislungexpansion.Alveoliare surroundedbybloodvessels,andoxygenand carbondioxidearetheninterchangedatthis pointbetweenthelungsandtheblood.Carbon dioxideremovedfromthebloodstream andairthatwasbreathedinbutnot usedisthenexpelledfromthelungs bydiaphragmexpansion.Lungs deflatebacktoareducedsize whenbreathingout. How do we breathe?Theintakeofoxygenintothebodyiscomplex 3. Trachea Air is pulled into the body through the nasal passages and then passes into the trachea. Chest cavity This is the space that is protected by the ribs, where the lungs and heart are situated. The space changes as the diaphragm moves. Rib cage This is the bone structure which protects the organs. The rib cage can move slightly to allow for lung expansion. Heart The heart pumps oxygenated blood away from the lungs, around the body to tissue, where oxygen is needed to break down glucose into a usable form of energy. Tissue Oxygen arrives where energy is needed, and a gas exchange of oxygen and carbon dioxide occurs so that aerobic respiration can occur within cells. Why do we need oxygen? Weneedoxygentoliveasitiscrucialfortherelease ofenergywithinthebody Althoughwecanreleaseenergythrough anaerobicrespirationtemporarily,thismethod isinefficientandcreatesanoxygendebtthat thebodymustrepayafterexcessexerciseor exertionhasceased.Ifoxygensupplyiscutofffor morethanafewminutes,anindividualwilldie. Oxygenispumpedaroundthebodytobeused incellsthatneedtobreakdownglucosesothat energyisprovidedforthetissue.Theequation thatillustratesthisis: C6 H12 O6 +6O2 =6CO2 +6H2 O+energy Lungs Deoxygenated blood arrives back at the lungs, where another gas exchange occurs at the alveoli. Carbon dioxide is removed and oxygen is placed back into the blood. Diaphragm This is a sheet of muscle situated at the bottom of the rib cage which contracts and expands to draw air into the lungs. ©DKImages ©DKImages ©DKImages 2. Pharynx This is part of both the respiratory and digestive system. A flap of connective tissue called the epiglottis closes over the trachea to stop choking when an individual takes food into their body. 1Dependant on sex and body size, alongside external factors such as altitude, lung capacity ranges between 4,000 and 6,000cm3 . Lung capacity varies hugely 2Interestingly, the left lung is slightly smaller than the right in the human body because the left lung has to make room for the heart to fit in. The right lung is bigger 3On average, humans only use about one-eighth of the capacity of our lungs for each breath so we have a large reserve volume. We have excess lung capacity 4If one person’s entire alveoli were laid out they would have the surface area of about 70cm2 – that’s roughly the size of half a tennis court! Alveoli have massive surface area 5On average, one individual will breathe in 11,000 litres of air in any given day. If they exercise heavily during that day, this will increase further. We breathe 11,000 litres of air per day Trained free-divers can hold their breath underwater for up to nine minutesDID YOU KNOW? LUNGS 5TOP FACTS WorldMags.netWorldMags.net WorldMags.net
- 104. Sweatisproducedbydedicatedsweat glands,andisamechanismused primarilybythebodytoreduceits internaltemperature.Therearetwo typesofsweatglandinthehumanbody,the eccrineglandandtheapocrinegland.Theformer regulatesbodytemperature,andistheprimary sourceofexcretedsweat,withthelatteronly secretingunderemotionalstresses,ratherthan thoseinvolvedwithbodydehydration. Eccrinesweatglandsarecontrolledbythe sympatheticnervoussystemand,whenthe internaltemperatureofthebodyrises,secretea salty,water-basedsubstancetotheskin’ssurface. Thisliquidthencoolstheskinandthebody throughevaporation,storingandthentransferring excessheatintotheatmosphere. Boththeeccrineandapocrinesweatglandsonly appearinmammalsand,ifactiveoverthemajority oftheanimal’sbody,actastheprimary thermoregulatorydevice.Certainmammalssuch asdogs,catsandsheeponlyhaveeccrineglandsin specificareas–suchaspawsandlips–warranting theneedtopanttocontroltheirtemperature. Why do we sweat? Asyourdoctormaytellyou,it’sglandular… Beadsofsweatfromtheporesin humanskin,takenwitha scanningelectronmicroscope Nerve fibres Deliver messages to glands to produce sweat when the body’s temp rises. Secretary part This is where the majority of the gland’s secretary cells can be located. Secretary duct Secreted sweat travels up to the skin via this duct. Pore Sweat is released directly into the dermis via the secretary duct, which then filters through the skin’s pores to the surface. Skin Once the sweat is on the skin’s surface, its absorbed moisture evaporates, transferring the heat into the atmosphere. ©DKImages ©SciencePhotoLibrary THEBODYATWORK Sweating / Dehydration Whathappensifwedon’tdrinkenough? Dehydration Hydration is all about finding the perfect balance. Too much hydration can be harmful as well as too little; this is known as water intoxication. If too much liquid is in your body, nutrients such as electrolytes and sodium are diluted and the body suffers. Your cells bloat and expand and can even burst, and it can be fatal if untreated. The best treatment is to take on IV fluids containing electrolytes. Too much H2 O? Just by breathing, sweating and urinating, the average person loses ten cups of water a day. With H2 O making up as much as 75 per cent of our body, dehydration is a frequent risk. Water is integral in maintaining our systems and it performs limitless functions. Essentially, dehydration strikes when your body takes in less fluid than it loses. The mineral balance in your body becomes upset with salt and sugar levels going haywire. Enzymatic activity is slowed, toxins accumulate more easily and even breathing can become more difficult as the lungs are having to work harder. Babies and the elderly are most susceptible as their bodies are not as resilient as others. It has been recommended to have eight glasses of water or two litres a day. More recent research is undecided as to how much is exactly needed. How does a lack of water vary from mild to fatal? Dangers of dehydration Dehydrationlevels 1% Mild Moderate Severe Fatal 12% 11% 10% 9% 8% 7% 6% 5% 4% 3% 2% ? Dizziness Fever Delirium Loss of consciousness Racing pulse Lack of sweat HeadachesDry skin Thirst is triggered by a concentration of particles in the blood, indicating a need to hydrate. Other symptoms at this level include fatigue, a dry mouth and constipation. Other symptoms include sunken eyes, low blood pressure and dark urine. Here symptoms become much more extreme and cognitive abilities may also suffer. Risk of heat exhaustion or heat stroke is prevalent and can even be fatal. Dehydration is now so severe that IV fluid replacement is necessary. 104 WorldMags.netWorldMags.net WorldMags.net
- 105. Circadianrhythmsarebiologicalchangesthatoccuratroughly24-hour intervals,whetherwe’reawareofthetimeonourwatchornot.These changes,whicharecontrolledbyinternalbiologicaltime-keeping systems,affectusphysically,mentallyandbehaviourally. Locatedbehindtheeyesinthehypothalamusisaregionofthebraincalledthe suprachiasmaticnucleus.Nolargerthanagrainofrice,theSCNisakindofmaster bodyclockthatcontrolsallourotherinternalclocks,whichinturncontrolour circadianrhythms,ordailywake-sleepcycles.Circadianrhythmsrespondmainly tolightanddarkcuesbutevenifthebodywasmonitoredunderconditionsdevoid ofdayornightsignals,ourcircadianrhythms stillcycleinaperiodofaround24 hours.Theretinaintheeyesenseslightlevelinformation,whichisrelayedtothe SCN,whichsendsasignaltothepinealgland.Thispea-sizedgland,located beneaththethalamus,isresponsibleforthesecretionofmelatonin–ahormone thattellsthebodytosleep–andsoatnightwhenlightlevelsfall,theproductionof melatoninincreases,tellingustoheadtobed… Howdoesourinternalbodyclocktelluswhentosleep? Circadian rhythms 105 06.00 NOON 12.00 00.00 MIDNIGHT 14.30 Best co-ordination 15.30 Fastest reaction time 17.00 Highest cardio- vascular efficiency and muscle strength 18.00 18.30 Highest blood pressure time 19.00 Body temperature is highest during the late afternoon 22.30 Bowel movements suppressed here 04.30 To conserve energy during sleep, body temperature drops. It is at its lowest just before waking 02.00 Deepest sleep 06.45 Steep rise in blood pressure. Heart attacks are more likely to occur in the morning than any other time due to this rise in blood pressure 07.30 Melatonin secretion ends 08.30 Bowel movement likely 09.00 Highest testosterone secretion here 10.00 High alertness The sleep- wake cycle Thevariationsintheamountof melatoninsecretedbythebodycreate adailyrhythmofrisingandfalling hormonelevels.Thesehormones, alongwiththeSNC,affectappetite, bodytemperatureandalotelse. Suprachiasmatic nucleus (SCN) Output rhythms: physiology behaviour Light ©NationalInstituteofGeneralMedicalSciences LARKS VS OWLS We all know that our genes make us different, and this also affects our individual natural rhythms. Some people have a body clock that lasts longer than 24 hours, which means they tend to stay up later: these people are referred to as owls. Other people with shorter body clocks, meanwhile, tend to rise earlier in the morning: people like this are larks. 21.00 With the fading of sunlight into the evening, melatonin secretion begins – and increases tenfold – making us sleepy 1Time zone changes can often disrupt circadian rhythms. Your body clock may be out of sync with your wristwatch, but it will reset itself after a few days. Jet lag 2Health conditions such as depression, bipolar disorder and seasonal affective disorder (SAD) are all associated with abnormalities in circadian rhythms. Mental state 3With these rhythms known to occur approximately every 24 hours, the phrase ‘circadian’ stems from Latin for ‘circa’, which means ‘about’, and ‘diem’, which means ‘day’. Latin name 4In the 18th Century, a botanist called Carolus Linnaeus is said to have invented a living clock. His garden could help him tell the time based on the flowers he planted. The living clock 5Doctors tell you to take medicine at a prescribed time because the human body clock can affect their effectiveness. Aspirins function better when taken early in the morning. Time to take your pills The pineal gland, located near the centre of the brain, is about 8mm long and shaped like a pine coneDID YOU KNOW? 5 TOP FACTS CIRCADIAN RHYTHMS WorldMags.netWorldMags.net WorldMags.net
- 107. Whenapathogenistough,wily, ornumerousenoughtosurvive non-specificdefences,it’supto theadaptiveimmunesystemto cleanupthemess.Thekeyforces intheadaptiveimmunesystem arewhitebloodcellscalled lymphocytes.Unliketheir macrophagecousins, lymphocytesareengineeredto attackonlyonespecifictypeof pathogen.Therearetwotypesof lymphocytes:B-cellsandT-cells. Thesecellsjointheaction whenmacrophagespassalong informationabouttheinvading pathogen,throughchemical messagescalledinterleukins. Afterengulfingapathogen,a macrophagecommunicates detailsaboutthepathogen’s antigens–telltalemoleculesthat characteriseaparticular pathogen.Basedonthis information,theimmunesystem identifiesspecificB-cellsand T-cellsequippedtorecogniseand battlethepathogen.Oncethey aresuccessfullyidentified,these cellsrapidlyreproduce, assemblinganarmyofcellsthat arereadyandequippedtotake downtheattacker. TheB-cellsfloodyourbody withantibodies,moleculesthat eitherdisarmaspecificpathogen orbindtoit,markingitasatarget forotherwhitebloodcells.When T-cellsfindtheirtarget,theylock onandreleasetoxicchemicals thatwilldestroyit.T-cellsare especiallyadeptatdestroying yourbody’scellsthatareinfected withavirus. Thisentireprocesstakes severaldaystogetgoingandmay takeevenlongertoconclude.All thewhile,theragingbattlecan makeyoufeelterrible. Fortunately,theimmune systemisengineeredto learnfromthepast.While yourbodyisproducingnew B-cellsandT-cellstofightthe pathogens,italsoproduces memorycells–copiesofthe B-cellsandT-cells,whichstayin thesystemafterthepathogenis defeated.Thenexttimethat pathogenshowsupinyourbody, thesememorycellshelplauncha counter-attackmuchmore quickly.Yourbodycanwipeout theinvadersbeforeanyinfection takeshold.Inotherwords,you developimmunity. Vaccinesaccomplishthesame thingbygivingyoujustenough pathogenexposureforyouto developmemorycells,butnot enoughtomakeyousick. 107 The adaptive immune system Asgoodasyourphysicaldefencesystemis,pathogens docreeppastitregularly.Yourbodyinitiallyresponds withcounterattacksknownasnon-specificdefences, sonamedbecausetheydon’ttargetaspecifictype ofpathogen. Afterabreech–bacteriarushinginthroughacut,for example–cellsreleasechemicalscalledinflammatory mediators.Thistriggersthechiefnon-specificdefence, knownasinflammation.Withinminutesofabreach, yourbloodvesselsdilate,allowingbloodandotherfluid toflowintothetissuearoundthecut. Therushoffluidininflammationcarriesvarioustypes ofwhitebloodcells,whichgettoworkdestroying intruders.Thebiggestandtoughestofthebunchare macrophages,whitebloodcellswithaninsatiable appetiteforforeignparticles.Whenamacrophagedetects abacterium’stelltalechemicaltrail,itgrabstheintruder, engulfsit,takesitapartwithchemicalenzymes,and spitsouttheindigestibleparts.Asinglemacrophagecan swallowupabout100bacteriabeforeitsowndigestive chemicalsdestroyitfromwithin. Non-specific defences Fightingthegoodfight,andwhitebloodcellsare rightonthefrontline… How B-cells attack 1. Bacterium Any bacteria that enter your body have characteristic antigens on their surface. B-cellstarget and destroyspecificbacteria and other invaders 2. Bacterium antigen These distinctive molecules allow your immune system to recognise that the bacterium is something other than a body cell. 3. Macrophage These white blood cells engulf and digest any pathogens they come across. 4. Engulfed bacterium During the initial inflammation reaction, a macrophage engulfs the bacterium. 5. Presented bacterium antigen After engulfing the bacterium, the macrophage ‘presents’ the bacterium’s distinctive antigens, communicating the presence of the specific pathogen to B-cells. 6. Matching B-cell The specific B-cell that recognises the antigen, and can help defeat the pathogen, receives the message. 7. Non- matching B-cells Other B-cells, engineered to attack other pathogens, don’t recognise the antigen. 8. Plasma cell The matching B-cell replicates itself, creating many plasma cells to fight all the bacteria of this type in the body. 9. Memory cell The matching B-cell also replicates to produce memory cells, which will rapidly produce copies of itself if the specific bacteria ever returns. 10. Antibodies The plasma cells release antibodies, which disable the bacteria by latching on to their antigens. The antibodies also mark the bacteria for destruction. 11. Phagocyte White blood cells called phagocytes recognise the antibody marker, engulf the bacteria, and digest them. 5TOP FACTS IMMUNE SYSTEM 1Sneezing, coughing, a sore throat, and fever are all common means of expelling pathogens, so as annoying as they are, each one is necessary. The cure can sometimes hurt 2A single drop of blood contains around 375,000 white blood cells, and blood constitutes for seven per cent of your total body weight. Immunity soldiers are everywhere 3Antibodies in breast milk give babies temporary immunity from diseases their mother is immune to, preventing infancy infection. You can ‘borrow’ immunity 4In addition to fighting pathogens, T-cells fight the body’s own cancerous cells and some cancer therapies boost the number of T-cells. It deals with internal troubles, too 5Unfortunately you cannot develop immunity to the flu and common cold because the viruses are always mutating. It has trouble with change Dr Karl Landsteiner first identified the major human blood groups – A, B, AB and O – in 1901DID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 108. 108 1. Tonsils Lymphoid tissue loaded with lymphocytes, which attack bacteria that get into the body through your nose or mouth. 2. Left subclavian vein One of two large veins that serve as the re-entry point for lymph returning to the bloodstream. 6. Lymph node cluster Located along lymph vessels throughout the body, lymph nodes filter lymph as it makes its way back into the bloodstream. 3. Right lymphatic duct Passageway leading from lymph vessels to the right subclavian vein. 8. Thymus gland Organ that provides area for lymphocytes produced by bone marrow to mature into specialised T-cells. 9. Thoracic duct The largest lymph vessel in the body. 5. Spleen An organ that houses white blood cells that attack pathogens in the body’s bloodstream. 11. Peyer’s patch Nodules of lymphoid tissue supporting white blood cells that battle pathogens in the intestinal tract. 12. Bone marrow The site of all white blood cell production. 10. Lymph vessels Lymph collects in tiny capillaries, which expand into larger vessels. Skeletal muscles move lymph through these vessels, back into the bloodstream. 7. Left lymphatic duct Passageway leading from lymph vessels to the left subclavian vein. 4. Right subclavian vein The second of the two subclavian veins, this one taking the opposite path to its twin. Thelymphaticsystemisanetworkof organsandvesselsthatcollectslymph –fluidthathasdrainedfromthe bloodstreamintobodilytissues–and returnsittoyourbloodstream.Italso playsakeyroleinyourimmune system,filteringpathogensfrom lymphandprovidingahome-basefor disease-fightinglymphocytes. ©DKImages Disorders of the immune system Whowatchesthe watchmen? Theimmunesystemisapowerfulsetof defences,sowhenitmalfunctions,it candoasmuchharmasadisease. Allergiesaretheresultofanoverzealous immunesystem.Inresponseto somethingrelativelybenign,like pollen,theimmunesystemtriggers excessivemeasurestoexpelthe pathogen.Ontheextremeend,allergies maycauseanaphylacticshock,a potentiallydeadlydropinblood pressure,sometimesaccompaniedby breathingdifficultyandlossof consciousness.Inautoimmune disorderssuchasrheumatoidarthritis, theimmunesystemfailstorecognise thebody’sowncellsandattacksthem. Inanallergicreaction,thebodymayresortto sneezingtoexpelafairlyharmlesspathogen The lymphatic system ©Klem2007 ©EdUthman,MD Yourtonsilscanhelp fightbacteria Lymph nodes explained Lymphnodes filterout pathogensmoving throughyour lymphvessels Yourimmunesystemdepends onthese.04-1-inchswellingsto fightallmannerofpathogens. Aslymphmakesitsway throughanetworkoffibresin thenode,whitebloodcells filterit,destroyingany pathogenstheyfind. THEBODYATWORK Human immune system WorldMags.netWorldMags.net WorldMags.net
- 109. 1. Influenza The flu kills hundreds of thousands of people in a good year. And every once in a while, a virulent form can take out tens of millions of people. MOST DEADLY 2. Measles One person infected with measles will spread the virus to just about every unvaccinated person they encounter. Luckily, the vaccine is very effective. MOST CONTAGIOUS 3. Tuberculosis Excavated Ancient Egyptian mummies show signs of tuberculosis, and the disease is still thriving today. Around 2 billion people around the world are infected. MOST COMMON 109 Bacteria anatomyInsidethese microorganisms 1. Outgoing lymph vessel Thevesselthatcarries filteredlymphoutofthe lymphnode 2. Valve Astructurethatprevents lymphfromflowingback intothelymphnode 3. Vein Passagewayforblood leavingthelymphnode 4. Artery Supplyofincomingblood forthelymphnode 5. Reticular fibres Dividesthelymphnode intoindividualcells 6. Capsule Theprotective,shielding fibresthatsurroundthe lymphnode 7. Sinus Achannelthatslowsthe flowoflymph,giving macrophagesthe opportunitytodestroyany detectedpathogens 8. Incoming lymph vessel Avesselthatcarrieslymph intothelymphnode 9. Lymphocyte TheT-cells,B-cellsand naturalkillercellsthat fightinfection 10. Germinal centre Thisisthesiteof lymphocytemultiplication andmaturation 11. Macrophage Largewhitebloodcellsthat engulfanddestroyany detectedpathogens Major points of the lymph node1 2 3 4 5 6 7 88 8 9 10 11 Bacteriaarethesmallestand,byfar,themostpopulousformoflife onEarth.Rightnow,therearetrillionsofthesingle-celledcreatures crawlingonandinyou.Infact,theyconstituteaboutfourpoundsof yourtotalbodyweight.Totheleftisalookatbacteriaanatomy… 1. Flagella Flagella swish for movement 2. Pili The pili anchor to cell surfaces 3. Capsule Protects the inner contents 4. Nucleoid The nucleoid contains genetic material 5. Ribosomes These help with protein manufacturing 6. Cell wall Provides structural integrity 7. Cell membrane The cell’s interior barrier 8. Cytoplasm Home of all material outside the nucleoid Know your enemy: Bacteria What is HIV……andhowdoesitaffectthe immunesystem? Thehumanimmunodeficiencyvirus(HIV)isaretrovirus(avirus carryingribonucleicacid,orRNAasit’sknown),transmitted throughbodilyfluids.Likeotherdeadlyviruses,HIVinvades cellsandmultipliesrapidlyinside.Specifically,HIVinfectscells withCD4moleculesontheirsurface,whichincludesinfection- fightinghelperT-cells.HIVdestroysthehostcell,andthevirus copiesgoontoinfectothercells.Asthevirusdestroyshelper T-cells,itsteadilyweakenstheimmunesystem.Ifenough T-cellsarelost,thebodybecomeshighlysusceptibletoarange ofinfections,aconditionknownasacquiredimmunedeficiency syndrome(AIDS). ScanningelectronmicrographofHIV-1budding(ingreen)fromcultured lymphocyte.Thisimagehasbeencolouredtohighlightthemost importantfeatures.Multipleroundbumpsonthecellsurfacerepresent sitesofassemblyandbuddingofvirions. GERMS AND VIRUSES HEAD HEAD2 In 2008, approximately 33 million people worldwide were living with HIV or AIDSDID YOU KNOW? ©NationalPhotoCompany WorldMags.netWorldMags.net WorldMags.net
- 110. The stages of bone repair ©Thinkstock If a bone has too much pressure put on it, there is a chance it will break. Your body has ways of repairing these breaks, but it takes time and care. There are different kinds of break, ranging from a hairline fracture to a fully shattered bone, but they all mend in a similar way. As a bone breaks, the blood vessels are also severed. Blood leaks out and forms a clot called a fracture haematoma. This stops blood flow to the area and also helps keep both pieces of bone aligned, ready for healing. The body then makes fibrous cells and cartilage, which reinforce the bond and strengthen it. This creates a callus, which is essentially a weakened bone. Over time, the callus builds up and the two parts of the bone gradually fuse together, like a bridge being constructed from either side of a river until both ends meet in the middle. Oncebothsectionsofboneareconnected again,specialisedcellscalledosteoblastsenterto producebonecells.Thesenewcellsreplacethe callus,returningthebonetoitsoriginalshape. Much like repairing a broken toy with glue, the bone needs to be kept straight and steady for the fusion to happen correctly. This is why doctors will put a cast on the broken bone. The cast provides essential support, protection and stability, ensuring the broken bone doesn’t move. A cast will generally stay on for a few weeks until the bond has become strong enough, but it could take months for a properly set bone to fully recover. Learnhowyourbodymendsbrokenbones Bone fracture healing process Most breaks on an arm or a leg will have a plaster cast put on them to prevent the bone from setting at a wonky angle or not setting at all. It will generally be made from plaster of Paris. This is a mixture of water and gypsum that sets really hard once it has dried. The broken bone is bandaged and the wet mixture is applied to the gauze. Once it has dried then it should provide safety and stability for the bone. Fibreglass is an increasingly common cast material. As with the plaster cast, the broken bone is bandaged up. Next, another bandage, made of fibreglass and layered with resin, is soaked in water. This makes it flexible enough to be wrapped around the bone before it hardens as it dries. This is much lighter than a plaster cast and the outer layer is waterproof. All-star cast Blood clot When a bone breaks, the blood vessels that run through the bone are severed. The blood forms a clot to align the bones. This creates a solid yet weak structure to prepare for mending. The clot also cuts off blood flow to the edges of the broken bone, so these cells die. Tissue growth A few days later, the blood clot – called the fracture haematoma – is gradually replaced by tougher tissue, which becomes a soft callus. Fibrous tissue and cartilage are produced that begin to bridge the gap between the fractured ends. New blood vessels begin to form and the callus usually lasts around three weeks. Remodelling Bone-forming cells called osteoblasts work in teams to build a new bone, creating a more solid structure called a hard bone callus. It takes several months to fill the cavity with harder bone, strengthened by nutrients like calcium and phosphorus. However, it may take longer for the bone to be completely healed. Blood clot forms External callus New blood vessels Healed fracture Hard bone callus Blood flow improves Internal callus (fibrous tissue and cartilage) Ruptured blood vessels Marrow THEBODYATWORK Mending bones 110 WorldMags.netWorldMags.net WorldMags.net
- 111. Proteinsarelargecomplexmoleculesmadeupofa chainofaminoacids.Everycellinourbodyneeds proteintostayaliveasitisnecessaryfortissue repairandreplacingdeadcells. Theyhavemanyotherfunctionsaswellasaidingcellrepair andproductionincludingformingantibodiestohelpfightoff disease,formingenzymeswhichspeeduportriggerchemical reactionsandco-ordinatingprocesseswithinthebody(via hormoneregulation,forinstance).Proteinsalsoprovide supportforcellsandformstructuralelementsofthebody,such asnailsandteeth,aswellasfacilitatingthetransportationof somesmallmoleculesaroundvarioussystems. Webuildproteinsusinginformationencodedinourgenetic code.DNAcodeutilisesgroupsofthreeletters(amixofA,G,C andT)andtheseshortsequences,whichareknownastriplets orcodons,thencodemRNAtemplates;thesetemplatesare ‘translated’bycellribosomesintoaminoacids. Eachproteinismadeupofhundredsofthousandsofamino acids,whichareinlongchains.Thereare20differenttypesof aminoacidthatcanbecombinedtobuildaproteinanditisthe sequenceofaminoacidsthatdetermineseachprotein’sunique three-dimensionalstructureanditsfunction. However,notallaminoacidscanbemadebythebody.The onesthatneedtobeconsumedviaourdietarecalledessential aminoacids.Ifpossible,thebodywillalsoconserveenergyby usingaminoacidsfromfoodratherthanproducingthemitself. Proteindeficiencycancausediseasessuchaskwashiorkor,a formofmalnutritioncommoninpoverty-strickenareas. How do we make protein? Proteinsarethebuildingblocksofthehumanbody, buthowdowegoaboutmanufacturingthem? ©SPL Protein production Proteinisgeneratedinthenucleusofacellusinggenetic codinginformationheldwithinourDNA.Toproduce protein,DNAunravelstoallowmessengerRNA(ormRNA)to copyitandformatemplate.Thistemplateistranslatedby ribosomesintoaminoacids,whichthenlineuptoforma protein.PartsofDNAcodewill serveaspunctuation,telling theribosomewhentostart andstop,andsomeparts willinstructthecellhow frequentlyitmustproduce thespecificprotein. Why are amino acids important? Aminoacidsarevitalto ourbodiesbeingableto operateastheyarethe buildingblocksof proteins.Eachtypeof aminoacidperformsa differentjob,whichaids proteinactivityinthe bodyanddeterminesthe protein’sprimary function(s).Withoutthese, proteinswouldnotbe abletohelpthebodywith movement,defence againstdisease, processingfoodor co-ordinatinggeneral growthanddevelopment. Therearenine essentialaminoacidsfor humansthatmustbe absorbedfromexternal proteinsources(egmeat/ fish)astheycannotbe synthesisedbythebody. Withouttherequired amountofaminoacids, thebodycanreallysuffer. 1. Cell The body is made up of millions of cells, none of which could survive without protein, for repair and replacement. 5. DNA DNA (deoxyribonucleic acid) holds the information necessary for amino acid – and ultimately protein – production in the letter sequence in its structure. 6. mRNA This type of genetic acid forms a template based on DNA sequences, which is then used to produce amino acids by the ribosome. 8. Amino acid These small molecules combine in specific string sequences to generate the different types of protein.9. Protein Proteins are made up of long chains of amino acids. Each protein has a specific function which suits its role and is crucial to our bodies being able to operate effectively. 7. Ribosome This is the ‘protein-making machine’ in the cell. It uses mRNA templates to synthesise the specific protein needed. 2. Nucleus This is the control centre of the cell where all important genetic data is stored. 3. Chromosome Most human cells have a set of 46 chromosomes and these contain our genetic information which, among other things, instructs the cell which protein to make and also how. 4. Nucleosomes These are balls formed of DNA strands and histones (spool-like proteins) which sit inside chromosomes. 1Speedy Pokémon character Pikachu had a protein named after it in 2008. The protein, pikachurin, is used in kinetic vision, which, aptly, is the detection of fast objects. Pokémon 2We get protein from meat, fish, eggs, nuts and dairy products. We digest the proteins into amino acids, which we later use to replace these proteins in our bodies. Protein from food 3Your body makes thousands of proteins every day. For each 1kg you weigh, you typically require 1g of protein. So daily a 70kg man must manufacture 70g of protein for his needs. Protein we need 4The Biuret test is a chemical form of analysis that is used to measure the amount of protein that is present in food. It works out protein levels by analysing the peptide bonds. Biuret test 5From studies into the human genomes sequenced so far, it has been discovered that the body contains over 2 million proteins, coded by just 20,000-25,000 genes. Genome studies Around half of your body’s ‘non-water’ mass is made up of proteinsDID YOU KNOW? 111 5TOP FACTS PROTEIN WorldMags.netWorldMags.net WorldMags.net
- 112. 112 Explore the key stages of mitosis now Cell duplication The continuous cycle of cell division and growth is essential to all life on Earth. Without it, no organism ont he planet would be able to reproduce or develop. The cell cycle consists of three main stages: interphase, mitosis and cytokinesis. During interphase, the cell expands and makes the new proteins and organelles it will need for division. It then makes copies of its chromosomes, doubling the amount of DNA in the cell and ensuring the conditions are right to begin the next phase. In mitosis, the membrane surrounding the nucleus breaks down, exposing the chromosomes, which are pulled to opposite sides of the cell by tiny spindle fibres. A new nuclear envelope then forms around the chromosomes at each end of the cell. During cytokinesis the cytoplasm splits in half to create two ‘daughter’ cells, each with their own nucleus and organelles. The cycle is managed by regulating enzymes known as CDKs . These act as a checkpoint between the phases of division, giving the signal for the next stage in the cycle to begin. The cell cycle of prokaryotic cells (those without a nucleus) is slightly different. Bacteria and other prokaryotes divide via a process called binary fission, in which the cell duplicates its genetic material before doubling in size and splitting in two. Meiosis is another type of cell division and is concerned with sexual reproduction as opposed to the asexual organic growth of tissue in mitosis. Insideoneofthebody’smostvitalprocesses The cell cycle If the cell cycle goes wrong, cancerous tumours are a possible consequence. It all depends on the levels of proteins in the cycle. A protein called p53 halts the process if DNA is damaged. This provides time for the protein to repair the DNA as the cells are then killed off and the cycle begins anew. On the rare occasions this process fails, cells can reproduce at a rapid rate and tumours can form. Chemo- and radiotherapy work by destroying these mutated cells. A p53 mutation is the most frequent one leading to cancer. An extreme case is Li Fraumeni syndrome, where a genetic defect in p53 leads to a high frequency of cancer in those affected. Cancer and the cycle Metaphase In this phase, all the spindle fibres are attached and the chromosomes are arranged in a line along the equator of the cell. Prometaphase The nuclear envelope breaks down and spindle fibres extend from either side of the cell to attach to the middle of each chromatid. Anaphase Now, the spindle fibres pull the chromosomes apart, with the chromatids moving to opposite ends or ‘poles’ of the cell. Prophase Chromosomes condense, becoming thicker and shorter. Sister chromatids form when the chromosomes replicate themselves. THEBODYATWORK Cell division explained WorldMags.netWorldMags.net WorldMags.net
- 113. STRANGE BUTTRUE APPETITE FOR SELF- DESTRUCTION What is apoptosis? Answer: Essentially a cell committing suicide, apoptosis is a controlled biological system that kills off unneeded or excess cells. One example is the removal of webbing in between your fingers and toes before you are born. A Another type of cell division B Programmed cell death C A new type of soft drink 113 A common theory is that every living cell is descended from a single ancestral cell from 3-4bn years ago ©Dreamstime;BBC;Thinkstock;Dr.CecilFox;Corbis DID YOU KNOW? What is the cell cycle? The cell is the basic unit of life for all living things. One of its many properties is the ability to reproduce. The cell cycle is a series of processes that occur between the birth of the cell and its division into two. What is mitosis? Mitosis describes what happens near the end of the cycle. The replicated chromosomes are separated from each other into opposite ends of the cell just before the cell divides. What are the different parts of the cycle? The other major part occurs before mitosis and is the process in which the DNA that makes up the chromosomes replicates itself. This is called the S-phase or DNA synthetic phase [which is part of interphase]. The S-phase replicates and mitosis separates and divides. What is the difference between mitosis and meiosis and does cell division occur in both? Meiosis is usually considered to be the mitotic full cycle and also leads towards cell reproduction. However, in meiosis there are two M-phases or divisions so the number of DNA and chromosomes are halved. Meiosis uses gametes for fertilisation in diploid cells in animal and plants. Does it occur in eukaryotic or prokaryotic cells? Only in eukaryotic cells. In prokaryotic cells there is a cell cycle but it is not mitosis. This [process] is simply the copying of DNA and then a much less obvious separation of the copied DNA into the two divided cells. Why did you use yeast in your experiments? Yeast is a very simple eukaryote, which reproduces in much the same way as more complex cells in us. It only has 5,000 genes compared to our 25,000. It simplifies cell division so is extremely convenient to study. It’s got fantastic genetics and genomics, which allow you to investigate complicated processes like the cell cycle. Why do skin cells divide so quickly and nerve cells so slowly? Cells change at varying rates and some nerve cells barely divide at all. This is one reason why it is difficult to regenerate the nervous system when it becomes damaged. Because the body has to deal with cuts and abrasions, it is much easier to get skin cells to divide. What is tissue culture and why is it important? It is simply a way of growing cells from animals and plants in test tubes. They will divide under these circumstances so you can study the cell cycle away from the complexities of an animal or plant. What are the differences between plant and animal cell cycles? Fundamentally, not very much. They both undergo the same processes but are subject to different overall controls. What is proteolysis and how does that mechanism help the cell cycle? It is a biochemical mechanism that breaks down protein. It takes away certain proteins as part of a regulatory system for a variety of biological process such as the cell cycle. It is used at the end of the cycle to destroy excess protein and prepare for the next cycle. You discovered CDK (Cyclin-dependent kinase). How do they contribute to the cell cycle? CDK is a type of enzyme and my research group was involved in discovering that they were the major regulators in the cycle. CDK brings about the S-phase and mitosis and controls them. How can the cycle help understand potential cures for cancer? To understand cancer, you have to be able to understand the cell cycle. Crudely blocking the cell cycle is a problem as a therapy as our body is full of other cells that have to divide. An expert’s view Paul Nurse, Nobel Prize winner and director of the Francis Crick Institute, chats about cell cycle Paul Nurse is also the former director of Cancer Research UK and president of the Royal Society Cytokinesis The cytoplasm divides and two or more daughter cells are produced. Mitosis and the cell cycle have now reached their end. Telophase The two new sets of chromosomes form groups at each pole and a new envelope forms around each as the spindle disappears. Every step of the cell division cycle is vital for life as we know it WorldMags.netWorldMags.net WorldMags.net
- 114. White blood cells, or leukocytes, are the body’s primary form of defence against disease. When the body is invaded by a pathogen of any kind, the white blood cells attack in a variety of ways; some produce antibodies, while others surround and ultimately devour the pathogens whole. In total, there are five types of white blood cell (WBC), and each cell works in a different way to fight a variety of threats. These five cells sit in two groupings: the granulocytes and the agranulocytes. The groups are determined based on whether a cell has ‘granules’ in the cytoplasm. These granules are digestive enzymes that help break down pathogens. Neutrophils, eosinophils and basophils are all granulocytes, the enzymes in which also give them a distinct colouration which the agranulocytes do not have. As the most common WBC, neutrophils make up between 55 and 70 per cent of the white blood cells in a normal healthy individual, with the other four types (eosinophils, basophils, monocytes and lymphocytes) making up the rest. Neutrophils are the primary responders to infection, actively moving to the site of infection following a call from mast cells after a pathogen is initially discovered. They consume bacteria and fungus that has broken through the body’s barriers in a process called phagocytosis. Lymphocytes – the second-most common kind of leukocyte – possess three types of defence cells: B cells, T cells and natural killer cells. B cells release antibodies and activate T cells, while T cells attack diseases such as viruses and tumours when directed, and regulatory T cells ensure the immune system returns to normal after an attack. Natural killer cells, meanwhile, aid T cell response by also attacking virus-infected and tumour cells, which lack a marker known as MHC. The remaining types of leukocyte release chemicals such as histamine, preparing the body for future infection, as well as attacking other causes of illness like parasites. Oneofthebody’smaindefencesagainstinfectionand foreignpathogens,howdothesecellsprotectourbodies? How do white blood cells work? Different kinds of WBC have different roles, which complement one another to defend the body Types of leukocyte Eosinophil Eosinophils are the white blood cells that primarily deal with parasitic infections. They also have a role in allergic reactions. They make up a fairly small percentage of the total white blood cells in our body – about 2.3 per cent. Lymphocyte These release antibodies as well as attack virus and tumour cells through three differing types of cell. As a group, they are some of the longest lived of the white blood cells with the memory cells surviving for years to allow the body to defend itself if repeat attacks occur. Monocyte Monocytes help prepare us for another infection by presenting pathogens to the body, so that antibodies can be created. Later in their life, monocytes move from the bloodstream into tissue, and then evolve into macrophages which can conduct phagocytosis. THEBODYATWORK 114 Blood cells explained “Natural killer cells aid T cell response by also attacking virus-infected and tumour cells” WorldMags.netWorldMags.net WorldMags.net
- 115. 6NEUTROPHIL LIFETIME (HOURS) 1%BLOOD COMPOSITION 80mmMACROPHAGE DIAMETER 5-20BACTERIA CONSUMED BY EACH NEUTROPHIL 4 in 1,000WBCS WHICH ARE BASOPHILS 7,000NUMBER OF WBCS IN A DROP OF BLOOD Neutrophil Neutrophils are the most common of the leukocytes. They have a short life span so need to be constantly produced by the bone marrow. Their granules appear pink and the cell has multi-lobed nuclei which make them easily differentiated from other types of white blood cell. ©SPL;Thinkstock If the immune system stops working properly, we are at risk of becoming ill. However, another problem is if the immune system actually goes into overdrive and starts attacking the individual’s cells, mistaking them for pathogens. There are a large number of autoimmune ailments seen across the world, such as Crohn’s disease, psoriasis, lupus and some cases of arthritis, as well as a large number of diseases that are suspected to have autoimmune roots. We can often treat these conditions with immunosuppressants, which deactivate elements of the immune system to stop the body attacking itself. However, there are drawbacks with this treatment as, if the person exposes themselves to another pathogen, they would not have the normal white blood cell response. Consequently, the individual is less likely to be able to fight normally low-risk infections and, depending on the pathogen, they can even be fatal. A faulty immune system Basophil Basophils are involved in allergic response via releasing histamine and heparin into the bloodstream. Their functions are not fully known and they only account for 0.4 per cent of the body’s white blood cells. Their granules appear blue when viewed under a microscope. The body has various outer defences against infection, including the external barrier of the skin, but what happens when this is breached? White blood cells at work Skin breach A foreign object breaks through the skin, introducing bacteria (shown in green) into the body. Mast cells Mast cells release cytokines and then WBCs are called into action to ensure the infection does not spread. WBCs arrive Macrophages move to the site via the bloodstream to start defending against invading bacteria. Macrophages consume bacteria Bacteria are absorbed into cytoplasm and broken down by the macrophages. Healing Following removal of the bacteria, the body will start to heal the break in the skin to prevent further infection. A microscopic illustration of a neutrophil – the most abundant WBC 115 WBCs have colour but appear white when blood is put through a centrifuge, hence their group nameDID YOU KNOW? THE STATSLEUKOCYTES WorldMags.netWorldMags.net WorldMags.net
- 116. THEBODYATWORK The science of genetics 116 Frominheritancetogeneticdiseases,whatsecretsarehidden inourgenesandhowdotheydeterminewhoweare? GENETICS THE SCIENCE OF WorldMags.netWorldMags.net WorldMags.net
- 117. RECORD BREAKERS GIANT GENOME 150bn THE LONGEST GENOME An ordinary-looking white flower, Paris japonica, has the longest known genome with 150 billion base pairs. If stretched out it would measure over 91 metres (300 feet)! 117 If all 46 human chromosomes were stitched together and stretched they would measure nearly 2m (6.6ft) Genes define who we are. They are the basic unit of heredity, each containing a coded set of instructions to make a protein. Humans have an estimated 20,500 genes, varying in length from a few hundred to more than 2 million base pairs. They affect all aspects of our physiology, providing the code that determines our physical appearance, the biochemical reactions that occur inside our cells and even, many argue, our personalities. Every individual has two copies of every gene – one inherited from each parent. Within the population there are several alleles of each gene – that is, different forms of the same code, with a number of minor alterations in the sequence. These alleles perform the same underlying function, but it is the subtle differences that make each of us unique. Inside each of our cells (except red blood cells) is a nucleus, the core which contains our genetic information: deoxyribonucleic acid (DNA). DNA is a four-letter code made up of bases: adenine (A), guanine (G), cytosine (C) and thymine (T). As molecular biologist Francis Crick once put it, “DNA makes RNA, RNA makes protein and proteins make us.” Our genes are stored in groups of several thousand on 23 pairs of chromosomes in the nucleus, so when a cell needs to use one particular gene, it makes a temporary copy of the sequence in the form of DID YOU KNOW? How is our genetic code stored? Genetic information is coded into DNA using just four nucleobases: A, C, G and T Nucleus Surrounded by a double- thickness membrane, the nucleus contains the genetic information of the cell. Chromosome Humans have 46 chromosomes – 23 pairs containing around 20,500 genes. Base pairs The bases of DNA are always found in pairs: adenine pairs with thymine, and guanine pairs with cytosine. Double helix DNA is arranged in a double helix shape, with the bases forming the ladder-like rungs in the centre. Double stranded DNA has two complementary strands – one forms a template to make the other, allowing accurate replication. We put deoxyribonucleic acid under the microscope DNA’s chemical structure Phosphate Phosphate groups link the sugars of adjacent nucleotides together, forming a phosphate backbone. Nucleotide DNA is a polymer made up of building blocks called nucleotides. Sugar Each base is attached to a five-carbon sugar called deoxyribose. Nucleobase Each nucleotide contains a base, which can be one of four: adenine (A), thymine (T), guanine (G) or cytosine (C). Hydrogen bond Two bases interact with each other by hydrogen bonds (weak electrostatic interactions that hold the strands of DNA together). T A WorldMags.netWorldMags.net WorldMags.net
- 118. THEBODYATWORK The science of genetics 118 How does our genetic makeup compare to that of other creatures? Mapping the human genome The Human Genome Project, an initiative to map the sequence of the entire human genetic code, began in 1990 and was completed in 2003. The 3.3-billion base pair sequence was broken into sections of around 150,000 base pairs in length and the sequence for each identified. These were then joined and used to map the information on to chromosomes to determine which genes were found on each – and in what order. The genome map (right) shows a human chromosome compared with other animals; the colours are a ‘heat map’ demonstrating areas where genetic information has been conserved through evolution (the more fragmented the pattern, the more differences there are in the genetic code). The Human Genome Project ribonucleic acid (RNA). This copy contains all of the information required to make a protein – the building blocks of the human body. The Human Genome Project aimed to map the entire human genome; this map is effectively a blueprint for making a human. Using the information hidden within our genetic code, scientists have been able to identify genes that contribute to various diseases. By logging common genetic variation in the human population, researchers have been able to identify over 1,800 disease- associated genes, affecting illnesses ranging from breast cancer to Alzheimer’s. The underlying genetic influences that affect complex diseases like heart disease are not yet fully understood, but having the genome available to study is making the task of identifying genetic risk factors much easier. Interestingly, the Human Genome Project discovered we have far fewer genes than first predicted; in fact, only two per cent of our genome codes for proteins. The remainder of the DNA is known as ‘non-coding’ and serves other functions. In many human genes are non-coding regions called introns, and between genes there is intergenic DNA. One proposed function is that these sequences act as a buffer to protect the important genetic information from mutation. Other non-coding DNA acts as switches, helping the cell to turn genes on and off at the right times. Genetic mutations are the source of variation in all organisms. Most genetic mutation occurs as the DNA is being copied, when cells prepare to divide. The molecular machinery responsible for duplicating DNA is prone to errors, and often makes mistakes, resulting in changes to the DNA sequence. These can be as simple as accidentally substituting one base for another (eg A for G), or can be much larger errors, like adding or deleting bases. Cells have repair machinery to correct errors as they occur, and even to kill the cell if it makes a big mistake, but despite this some errors still slip through. Throughout your life you will acquire many mutations in your cells. Many of these are completely harmless, either occurring in Human This ring represents the genes on a human chromosome, with the numbers providing a representation of scale. Chimpanzee One of our closest living relatives – the solid bands demonstrate we share a great deal of genetic information (ie 98 per cent). Mouse There is less in common between human and mouse (90 per cent), but we are sufficiently similar that mice make a good scientific model for studying human disease. Rat The mouse and rat genomes have similar patterns, demonstrating these rodents’ close evolutionary relationship. Dog Some regions of the canine genome are very different to ours, but the pink bands show an area that has been conserved. Zebrafish Divergence between fish and mammals occurred very early in evolution, so similarities in our genes are very fragmented. Chicken Despite the fact that we are not closely related to birds, the chicken still has regions of DNA that are quite similar to ours. WorldMags.netWorldMags.net WorldMags.net
- 119. KEY DATES 1865 Gregor Mendel, the father of modern genetics, observes patterns of genetic inheritance in peas grown in his garden. 2003 Completion of the Human Genome Project provides access to the human DNA blueprint. 1983 Polymerase chain reaction (PCR)isinvented,enabling small DNA samples to be amplified for testing. 1953 Francis Crick (right) and James Watson reveal the double helix structure of DNA using X-rays. 1905 William Bateson is the first person to use the term ‘genetics’ to describe the study of biological inheritance.GENETICS HISTORY 119 Humans share 98 per cent genetic similarity with chimpanzees but just seven per cent with E coliDID YOU KNOW? It’s a common misconception that we inherit entire features from our parents – eg “You have your father’s eyes.” Actually inheritance is much more complicated – several genes work together to create traits in physical appearance; even eye colour isn’t just down to one gene that codes for ‘blue’, ‘brown’ or ‘green’, etc. The combinations of genes from both of our parents create a mixture of their traits. However, there are some examples of single genes that do dictate an obvious physical characteristic all on their own. These are known as Mendelian traits, after the scientist Gregor Mendel who studied genetic inheritance in peas in the 1800s. One such trait is albinism – the absence of pigment in the skin, hair and eyes due to a defect in the protein that makes melanin. Why do we look like our parents? Carrier parents Each parent carries the albinism gene (dark pink), but they have one normal gene (light pink), so they are able to make melanin. Gametes Each child inherits one gene from the mother and one from the father. Carrier children Two out of four will be carriers, like their parents, with one normal and one faulty gene. Affected child One in four children will receive two copies of the faulty gene and as a result will be unable to produce melanin. Healthy child One in four children will receive one healthy gene from the father and one from the mother. non-coding regions of DNA, or changing the gene so nominally that the protein is virtually unaffected. However, some mutations do lead to disease (see ‘When genes go wrong’ box). If mutations are introduced into the sperm and egg cells they can be passed on to the next generation. However, not all mutations are bad, and this process of randomly introduced changes in the DNA sequence provides the biological underpinning that supports Darwin’s theory of evolution. This is most easily observed in animals. Take, for example, the peppered moth. Before the Industrial Revolution the majority of these moths had white wings, enabling them to hide against light-coloured trees and lichens. However, a minority had a mutant gene, which gave them black wings; this made them an easy target for predators and kept their numbers low. When factories began to cover the trees in soot, however, the light- coloured moths struggled to hide themselves against the newly blackened environment, so black moths flourished. They survived much longer, enabling them to pass on their mutation to their offspring and altering the gene pool. It is easy to see how a genetic change like the one that occurred in the peppered moth could give an advantage to a species, but what about genetic diseases? Even these can work to our advantage. A good example is sickle cell anaemia – a genetic disorder that’s quite common in the African population. A single nucleotide mutation causes haemoglobin, the protein involved in binding oxygen in red blood cells, to misfold. Instead of forming its proper shape, the haemoglobin clumps together, causing red blood cells to deform. They then have trouble fitting through narrow capillaries and often become damaged or destroyed. However, this genetic mutation persists in the population because it has a protective effect against malaria. The malaria parasite spends part of its life cycle inside red blood cells and, when sickle cells rupture, it prevents the parasite from reproducing. Individuals with one copy of the sickle cell gene and one copy of the healthy haemoglobin gene have few symptoms of sickle cell anaemia, Forensic scientists can use traces of DNA to identify individuals involved in criminal activity. Only about 0.1 per cent of the genome differs between individuals, so rather than sequencing the entire genome, scientists take 13 DNA regions that are known to vary between different people in order to create a ‘DNA fingerprint’. In each of these regions there are two to 13 nucleotides in a repeating pattern hundreds of bases long – the length varies between individuals. Small pieces of DNA – referred to as probes – are used to identify these repeats and the length of each is determined by a technique called polymerase chain reaction (PCR). The odds that two people will have exactly the same 13-region profile is thought to be one in a billion or even less, so if all 13 regions are found to be a match then scientists can be fairly confident that they can tie a person to a crime scene. Using genetics to convict criminals WorldMags.netWorldMags.net WorldMags.net
- 120. 120 Cancer is not just the result of one or two genetic mutations – in fact, it takes a whole series of mistakes for a tumour to form. Cells contain oncogenes and tumour suppressor genes, whose healthy function is to tell the cell when it should and should not divide. If these become damaged, the cell cannot switch off its cell division programme and it will keep making copies of itself indefinitely. Each time a cell divides there is a risk that it will make a mistake when copying its DNA, and gradually the cell makes more and more errors, accumulating mutations that allow the tumour to progress into malignant cancer. When our genes gowrong… Repairing faulty genes Target gene The healthy gene is isolated from the DNA of the donor individual. Packaging The gene is packaged into a delivery vector, like a virus, to help it get inside the target cell. Fertilised egg A fertilised human egg is a source of undifferentiated stem cells, which can become any type of cell. Transduction The new gene is introduced into the stem cells produced by the fertilised egg. Differentiation Chemical signals are added to the stem cells to force them to differentiate into the desired cell type, eg liver cells. Embryonic stem cells The fertilised egg becomes a blastocyst, which contains undifferentiated embryonic stem cells. Transplant The new cells are transplanted into the recipient, carrying with them the healthy gene. We reveal how donated cells can be used to mend any damaged genes within the human body Tumour-associated genes Genes normally involved in regulating cell behaviour can go on to cause cancer if they become mutated. Mutagens Environmental factors, or mutagens – such as radiation and chemicals – can cause damage to the DNA, leading to mutations in key genes. Localised Cancer usually starts with just one or a few mutated cells; these begin to divide uncontrollably in their local area creating a tumour. Invasion As the tumour grows in size it starts to invade the surrounding area, taking over neighbouring tissues. Metastasis Further mutations allow cells ofthetumour to break free and enter the bloodstream. From here they can be distributed throughout the body. but are protected from malaria too, allowing them to pass the gene on to their children. Genetics is a complex and rapidly evolving field and more information about the function of DNA is being discovered all the time. It is now known that environmental influences can alter the way that DNA is packaged in the cell, restricting access to some genes and altering protein expression patterns. Known as epigenetics, these modifications do not actually alter the underlying DNA sequence, but regulate how it is accessed and used by the cell. Epigenetic changes can be passed on from one cell to its offspring, and thus provide an additional mechanism by which genetic information can be modified across generations of humans. ©SPL;Alamy;Thinkstock How tumours develop THEBODYATWORK The science of genetics WorldMags.netWorldMags.net WorldMags.net
- 121. 121 Classified by their depth, each burn case requires unique treatment How burns are measured ©Thinkstock Most people associate burns with flames, but they have many other causes. A burn is medically defined as ‘coagulative destruction’ of skin, meaning any energy source can cause one. This energy damages underlying skin proteins and fat cells, causing breaks in the skin. Burns are generally classified by their depth. First-degree (superficial) burns leave painful, red skin, but without large blisters. Only the epidermis is damaged, so regrowth is fast. Second-degree burns (partial thickness) can be either superficial or deep. The skin usually blisters and can be very painful. The dermis layer is also damaged so regrowth is slow, taking several weeks or even months. In third-degree burns (full thickness) the skin is left white or pale, with no blistering and little to no sensation. The basal growth layer is destroyed so no new skin can grow. Even minor burns can cause problems if not treated properly. The first priority is to stop the burning process; cold running water is often the best first treatment. Infection, dehydration and protein loss are all problems that occur next, which our resilient skin can solve itself if the injury isn’t too severe. Burnsrangefromirritatingtolife-threatening –learnaboutthedifferenttypesnow What happens when we burn ourselves? 1 The skin Your skin is vital to your wellbeing. It has multiple important functions, including temperature control, sensation and appearance. 3 First-degree burn Only the uppermost skin layers (known as the epidermis) are affected, but the burn is painful, leaving the area red, raw and tender to the touch. 5 Blisters Blisters appear when the epidermis separates from the dermis, and are especially common in first and second-degree burns. 2 Basal layer This layer is the key to regeneration, as new skin cells grow from here. If undamaged, regrowth occurs without any need for medical assistance. 4 Second-degree burn These partial-thickness burns affect the upper or deep dermal layers, and like first-degree burns hurt a lot because the nerve endings remain active. 6 Third-degree burn Deep burns destroy the basal layer and nerve endings, so they are painless. Regrowth will not occur alone, so skin grafts are needed. 1 2 3 4 5 6 Thermal Heat can come from a flame or friction (known as dry burns), hot liquids (known as wet burns) or contact with hot surfaces. Four major causes of burns Radiation Ionising radiation burns can be cover the body due to exposure. Sunburn is a common type of radiation burn, caused by exposure to UV in sunlight. Electrical These often cause deep burns that heal slowly. A small skin defect may mask underlying damage, which can extend throughout the body. Chemical Alkalis burn for hours, whereas acids are short-lived. These require no heat to cause a burn, and can take time to develop after skin contact. A second-degree burn will heal itself over time but probably leave scars Approximately 300,000 people die from burns each year worldwideDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 122. THEBODYATWORK 122 Blood vessels Thenetworkofbloodvesselsinthe humanbodymustcopewithdifferent volumesofbloodtravellingatdifferent pressures.Thesebloodvesselscome inamultitudeofdifferentsizesandshapes,from thelarge,elasticaortadowntoverytiny,one-cell- thickcapillaries. Bloodistheultimatemultitasker.Itcarriesoxygen forvarioustissuestouse,nutrientstoprovide energy,removeswasteproductsandevenhelpsyou warmuporcooldown.Italsocarriesvitalclotting factorswhichstopusbleeding.Bloodcomesinjust twovarieties;oxygen-rich(oxygenated)bloodis whatthebodyusesforenergy,andisbrightred. Afterithasbeenused,thisoxygen-depleted (deoxygenated)bloodisreturnedforrecyclingandis darkred(notblue,asisoftenthought). Bloodiscarriedinvessels,ofwhichthereare twomaindifferenttypes–arteriesandveins. Arteriescarrybloodawayfromtheheartanddeal withhighpressures,andsohavestrongelastic walls.Veinscarrybloodbacktowardstheheartand dealwithlowerpressures,sohavethinnerwalls. Tinycapillariesconnectarteriesandveinstogether, likesmallback-roadsconnectingmotorwaysto dualcarriageways. Arteriesandveinsareconstructeddifferentlyto copewiththevaryingpressures,butworkinperfect tandemtoensurethatthebloodreachesitsfinal destinationcorrectly.However,sometimesthingsgo wrongwhichcanleadtocertainmedicalproblems: varicoseveinsfromfailingvalves;deepvein thrombosisfrombloodclotsblockingthedeep venoussystem;heartattacksfromblockedarteries; andlastlylife-threateninganeurysmsfromweak arterywalls. Arteriesandveinsformtheplumbingsystemofthehuman body,carryingbloodthroughacomplexsystemofdifferent sizedandshapedpipes.Wefindouthowtheywork… Blood vessels Veinscarrylowpressureblood.They containnumerousone-wayvalveswhich stopbackwardsflowofblood,whichcan occurwhenpressurefallsin-between heartbeats.Bloodflowsthroughthese valvestowardstheheartbutcannotpass backthroughthemintheotherdirection. Valvescanfailovertime,especiallyinthe legs.Thisleadstosaggy,unsightlyveins, knownasvaricoseveins. Arteriescopewithallofthepressure generatedbytheheartanddeliver oxygen-richbloodtowhereitneedstobe24 hoursaday.Thewallsofarteriescontain elasticmuscles,allowingthemtostretch andcontracttocopewiththewidechanges inpressuregeneratedfromtheheart.Since thepressureishigh,valvesare unnecessary,unlikethelow-pressure venoussystem. How do veins work? Arteries – under pressure! Connecting it all together Capillariesarethetinyvesselswhich connectsmallarteriesandveinstogether. Theirwallsareonlyonecellthick,sothisis theperfectplacetotradesubstanceswith surroundingtissues.Redbloodcells withinthesecapillariestradewater, oxygen,carbondioxide,nutrients,waste andevenheat.Becausethesevesselsare onlyonecellwide,thecellshavetolineup topassthrough. Connective tissue Valve Muscle Capillary wall Cell nucleus Mostoftheamyloid consistedofacellularpink globulesthateffacedand expandedthenode,but thisimageshowsthe characteristicinvolvement ofbloodvesselwalls ©EdUthman,MD Inner lining Elastic layer Muscle layer Outer protective layer WorldMags.netWorldMags.net WorldMags.net
- 123. 123 DID YOU KNOW? “Plasma carries all of the different types of cells” Vascular surgeons can bypass blocked arteries using either the patient’s own veins or synthetic graftsDID YOU KNOW? The left side The left side of the heart pumps oxygenated blood for the body to use. It pumps directly into arteries towards the brain and other body tissues. A game of two halves Inhumanbeings,theheartisadouble pump,meaningthattherearetwosides tothecirculatorysystem.Theleftsideof theheartpumpsoxygenandnutrient-rich bloodtothebrain,vitalorgansandother bodytissues(thesystemiccirculation). Therightsideoftheheartpumps deoxygenatedbloodtowardsthelungs,so itcanpickupnewoxygenmoleculestobe usedagain(thepulmonarycirculation). The right side The right side of the heart pumps deoxygenated blood to the lungs, where blood exchanges carbon dioxide for fresh oxygen. Lungs In the lungs, carbon dioxide is expelled from the body and is swapped for fresh oxygen from the air. This oxygen-rich blood takes on a bright red colour. Aorta The aorta is an artery which carries oxygenated blood to the body; it is the largest blood vessel in the body and copes with the highest pressure blood. Arteries All arteries carry blood away from the heart. They carry oxygenated blood, except for the pulmonary artery, which carries deoxygenated blood to the lungs. Veins All veins carry blood to the heart. They carry deoxygenated blood, except for the pulmonary vein, which carries oxygenated blood back to the heart. Capillaries Tiny capillaries connect arteries and veins together. They allow exchange of oxygen, nutrients and waste in the body’s organs and tissues. Different shapes and sizes Blood vessels Artery Capillary bed This is the capillary network that connects the two systems. Here, exchange of various substances occurs with surrounding tissues, through the one-cell thick walls. Arteriole Capillary sphincter muscles These tiny muscles can open and close, which can decrease or increase blood flow through a capillary bed. When muscles exercise, these muscles relax and blood flow into the muscle increases. Venule Vein What’s in blood? It’sonlytheironinredbloodcellswhich makebloodred–takethesecellsawayand whatyou’releftwithisawateryyellowish solutioncalledplasma.Plasmacarriesall ofthedifferenttypesofcellsandalso containssugars,fats,proteinsandsalts. Themaincelltypesareredbloodcells (formedfromironandhaemoglobin,which carriesoxygenaroundthebody),white bloodcells(whichfightinfectionfrom bacteria,virusesandfungi)andplatelets (tinycellfragmentswhichstopbleedingby formingclotsatthesitesofanydamage). HEART LUNG HEAD AND ARMS KIDNEY LIVER LUNG TRUNK AND LEGS WorldMags.netWorldMags.net WorldMags.net
- 124. THEBODYATWORK How your blood worksThesciencebehindthemiraculousfluid thatfeeds,healsandfightsforyourlife ©DKImages Blood vessel wall Arteries and veins are composed of three tissue layers, a combination of elastic tissue, connective tissue and smooth muscle fibres that contract under signals from the sympathetic nervous system. Red blood cell Known as erythrocytes, red blood cells are the body’s delivery service, shuttling oxygen from the lungs to living cells throughout the body and returning carbon dioxide as waste. White blood cells White blood cells, or leukocytes, are the immune system’s best weapon, searching out and destroying bacteria and producing antibodies against viruses. There are five different types of white blood cells, all with distinct functions. Granulocyte The most numerous type of white blood cell, granulocytes patrol the bloodstream destroying invading bacteria by engulfing and digesting them, often dying in the process. Platelet When activated, these sticky cell fragments are essential to the clotting process. Platelets adhere to a wound opening to stem the flow of blood, then they team with a protein called fibrinogen to weave tiny threads that trap blood cells. 124 A look inside your blood WorldMags.netWorldMags.net WorldMags.net
- 125. 1. Discovery of veins and arteries In 300 BC, Greek anatomist Herophilus of Chalcedon figured out that arteries and veins not only carry blood, but are distinct pathways. 2. First blood transfusion After a century of animal- human blood transfusions, James Blundell performed the first recorded human-to-human transfusion in 1818. 3. Discovery of blood types In 1901, Austrian physician Karl Landsteiner was the first to identify three basic blood groups, revolutionising the success of blood transfusions. 125 Bloodistheriveroflife.It feedsoxygenand essentialnutrientsto livingcellsandcarries awaywaste.Ittransportsthefoot soldiersoftheimmunesystem,white bloodcells,whichseekoutand destroyinvadingbacteriaand parasites.Anditspeedsplateletsto thesiteofinjuryortissuedamage, triggeringthebody’smiraculous processofself-repair. Bloodlookslikeathick, homogenousfluid,butit’smorelikea waterycurrentofplasma–astraw- coloured,protein-richfluid–carrying billionsofmicroscopicsolids consistingofredbloodcells,white bloodcellsandcellfragmentscalled platelets.Thedistributionisfarfrom equal.Overhalfofbloodisplasma, 45percentisredbloodcellsanda tinyfragment,lessthanonepercent, iscomposedofwhitebloodcells andplatelets. Redbloodcellsaresonumerous becausetheyperformthemost essentialfunctionofblood,whichisto deliveroxygentoeverycellinthe bodyandcarryawaycarbondioxide. Asanadult,allofyourredbloodcells areproducedinredbonemarrow,the spongytissueinthebulbousendsof longbonesandatthecentreofflat boneslikehipsandribs.Inthe marrow,redbloodcellsstartoutas undifferentiatedstemcellscalled hemocytoblasts.Ifthebodydetectsa minusculedropinoxygencarrying capacity,ahormoneisreleasedfrom thekidneysthattriggersthestemcells tobecomeredbloodcells.Becausered bloodcellsonlylive120days,the supplymustbecontinuously replenished;roughly2millionred bloodcellsareborneverysecond. Amatureredbloodcellhasno nucleus.Thenucleusisspitoutduring thefinalstagesofthecell’stwo-day developmentbeforetakingonthe shapeofaconcave,doughnut-like disc.Likeallcells,redbloodcellsare mostlywater,but97percentoftheir solidmatterishaemoglobin,a complexproteinthatcarriesfour atomsofiron.Thoseironatomshave Monocyte The largest type of white blood cell, monocytes are born in bone marrow, then circulate through the blood stream before maturing into macrophages, predatory immune system cells that live in organ tissue and bone. Plasma Composed of 92 per cent water, plasma is the protein-salt solution in which blood cells and particles travel through the bloodstream. Plasma helps regulate mineral exchange and pH, and carries the proteins necessary for clotting. Components of bloodBloodisamixofsolidsandliquids,ablendofhighlyspecialised cellsandparticlessuspendedinaprotein-richfluidcalled plasma.Redbloodcellsdominatethemix,carryingoxygento livingtissueandreturningcarbondioxidetothelungs.For every600redbloodcells,thereisasinglewhitebloodcell,of whichtherearefivedifferentkinds.Cellfragmentscalled plateletsusetheirirregularsurfacetoclingtovesselwallsand initiatetheclottingprocess. “Red blood cells are so numerous because they perform the most essential function of blood” Bonemarrowcontributes fourpercentofaperson’s totalweight ©Bobjgalindo 54% Plasma 1% White blood cellls and platelets 45% Red blood cells “1818 - first human-to- human transfusion” HEAD HEAD2LANDMARK BLOOD EVENTS If you took all of the blood vessels out of your body and laid them end to end, they would stretch for 160,000kmDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 126. 126 theabilitytoformloose,reversible bondswithbothoxygenandcarbon dioxide–thinkofthemasweak magnets–makingredbloodcellssuch aneffectivetransportsystemfor respiratorygasses.Haemoglobin, whichturnsbrightredwhen oxygenated,iswhatgivesbloodits characteristiccolour. Toprovideoxygentoeveryliving cell,redbloodcellsmustbepumped throughthebody’scirculatorysystem. Therightsideoftheheartpumps CO2 -heavybloodintothelungs,where itreleasesitswastegassesandpicks upoxygen.Theleftsideoftheheart thenpumpsthefreshlyoxygenated bloodoutintothebodythrougha systemofarteriesandcapillaries, someasnarrowasasinglecell.Asthe redbloodcellsreleasetheiroxygen, theypickupcarbondioxide molecules,thencoursethroughthe veinsbacktowardtheheart,where theyarepumpedbackintothelungs to‘exhale’theexcessCO2 andcollect somemorepreciousO2 . Whitebloodcellsaregreatly outnumberedbyredbloodcells,but theyarecriticaltothefunctionofthe immunesystem.Mostwhiteblood cellsarealsoproducedinredbone marrow,butwhitebloodcells–unlike redbloodcells–comeinfivedifferent varieties,eachwithitsown specialisedimmunefunction.The firstthreevarieties,collectivelycalled granulocytes,engulfanddigest bacteriaandparasites,andplayarole inallergicreactions.Lymphocytes, anothertypeofwhitebloodcell, produceanti-bodiesthatbuildupour immunitytorepeatintruders.And monocytes,thelargestofthewhite bloodcells,enterorgantissueand becomemacrophages,microbesthat ingestbadbacteriaandhelpbreak downdeadredbloodcellsinto reusableparts. Plateletsaren’tcellsatall,but fragmentsofmuchlargerstemcells foundinbonemarrow.Intheirresting state,theylooklikesmoothoval plates,butwhenactivatedtoforma clottheytakeonanirregularform withmanyprotrudingarmscalled pseudopods.Thisshapehelpsthem sticktobloodvesselwallsandtoeach other,formingaphysicalbarrier aroundwoundsites.Withthehelpof proteinsandclottingfactorsfoundin plasma,plateletsweaveameshof fibrinthatstemsbloodlossand triggerstheformationofnewcollagen andskincells. Buteventhesethreefunctionsof blood–oxygensupplier,immune systemdefenderandwoundhealer– onlybegintoscratchthesurfaceofthe criticalroleofbloodineachandevery bodilyprocess.Whenbloodcirculates throughthesmallintestine,itabsorbs sugarsfromdigestedfood,whichare transportedtothelivertobestoredas energy.Whenbloodpassesthrough thekidneys,itisscrubbedofexcess ureaandsalts,wastethatwillleave thebodyasurine.Theproteins transportvitamins,hormones, enzymes,sugarandelectrolytes. Life cycle of red blood cells 1. Born in the bones When the body detects a low oxygen carrying capacity, hormones released from the kidney trigger the production of new red blood cells inside red bone marrow. 2. One life to live Mature red blood cells, also known as erythrocytes, are stripped of their nucleus in the final stages of development, meaning they can’t divide to replicate. 3. In circulation Red blood cells pass from the bone marrow into the bloodstream, where they circulate for around 120 days. 4. Ingestion Specialised white blood cells in the liver and spleen called Kupffer cells prey on dying red blood cells, ingesting them whole and breaking them down into reusable components. 5. Iron ions In the belly of Kupffer cells, haemoglobin molecules are split into heme and globin. Heme is broken down further into bile and iron ions, some of which are carried back and stored in bone marrow. 6. Reuse and recycle As for the globin and other cellular membranes, everything is converted back into basic amino acids, some of which will be used to create more red blood cells. Waste product of blood cell Waste excreted from body Everysecond,roughly2millionredbloodcellsdecayanddie.The bodyiskeenlysensitivetobloodhypoxia–reducedoxygen carryingcapacity–andtriggersthekidneytoreleaseahormone callederythropoietin.Thehormonestimulatestheproductionof moreredbloodcellsinbonemarrow.Redbloodcellsenterthe bloodstreamandcirculatefor120daysbeforetheybeginto degenerateandareswallowedupbyrovingmacrophagesinthe liver,spleenandlymphnodes.Themacrophagesextractironfrom thehaemoglobinintheredbloodcellsandreleaseitbackintothe bloodstream,whereitbindstoaproteinthatcarriesitbacktothe bonemarrow,readytoberecycledinfreshredbloodcells. THEBODYATWORK A look inside your blood WorldMags.netWorldMags.net WorldMags.net
- 127. 127 7%BLOOD PERCENTAGE OF BODY WEIGHT “Platelets weave a mesh of fibrin that stems blood loss” 7,000 litresBLOOD PUMPED BY HEART PER DAY BLOOD IN HUMAN BODY 5 litres RED BLOOD CELLS MADE EVERY SECOND 2 million Blood and healingThinkofbloodasthebody’s emergencyresponseteamtoan injury.Plateletsemitsignalsthat encouragebloodvesselsto contract,stemmingbloodloss. Theplateletsthencollectaround thewound,reactingwitha proteininplasmatoformfibrin,a tissuethatweavesintoamesh. Bloodflowreturnsandwhite bloodcellsbegintheirhuntfor bacteria.Fibroblastscreatebeds offreshcollagenandcapillaries tofuelskincellgrowth.Thescab beginstocontract,pullingthe growingskincellsclosertogether untildamagedtissueisreplaced. Morethanaone-trickpony,yourblood isavitalcoginthehealingprocess INJURY Whentheskinsurfaceiscut,torn orscrapeddeeplyenough,blood seepsfrombrokenbloodvesselsto fillthewound.Tostemtheflowof bleeding,thebloodvesselsaround thewoundconstrict. HAEMOSTASIS Activatedplateletsaggregate aroundthesurfaceofthewound, stimulatingvasoconstriction. Plateletsreactwithaproteinin plasmatoformfibrin,aweb-like meshofstringytissue. INFLAMMATORY STAGE Oncethewoundiscappedwitha dryingclot,bloodvesselsopenup again,releasingplasmaandwhite bloodcellsintothedamaged tissue.Macrophagesdigest harmfulbacteriaanddeadcells. PROLIFERATIVE STAGE Fibroblastslayfreshlayersof collageninsidethewoundand capillariesbegintosupplyblood fortheformingofnewskincells. Fibrinstrandsandcollagenpull thesidesofthewoundtogether. STAGE 1 STAGE 2 STAGE 3 STAGE 4 Anaemiaisthenameforanyblooddisorderthatresults inadangerouslylowredbloodcellcount.Insicklecell anaemia,whichafflictsoneoutofevery625childrenof Africandescent,redbloodcellselongateintoasickle shapeafterreleasingtheiroxygen.Thesickle-shaped cellsdieprematurely,leadingtoanaemia,orsometimes lodgeinbloodvessels,causingterriblepainandeven organdamage.Interestingly,peoplewhocarryonlyone geneforsicklecellanaemiaareimmunetomalaria. Sickle cell anaemia Thisraregeneticblooddisorderseverelyinhibitsthe clottingmechanismofblood,causingexcessive bleeding,internalbruisingandjointproblems.Platelets areessentialtotheclottingandhealingprocess, producingthreadsoffibrinwithhelpfromproteinsin thebloodstreamcalledclottingfactors.Peoplewho sufferfromhaemophilia–almostexclusivelymales–are missingoneofthoseclottingfactors,makingitdifficultto sealoffbloodvesselsafterevenminorinjuries. Haemophilia Anotherrareblooddisorderaffecting100,000 newbornsworldwideeachyear,thalassemia inhibitstheproductionofhaemoglobin,leading tosevereanaemia.Peoplewhoarebornwiththe mostseriousformofthedisease,alsocalled Cooley’sanaemia,sufferfromenlargedhearts, liversandspleens,andbrittlebones.Themost effectivetreatmentisfrequentblood transfusions,althoughafewluckypatientshave beencuredthroughbonemarrowtransplants fromperfectlymatchingdonors. Thalassemia Oneofthemostcommongenetic blooddisorders,hemochromatosisis themedicaltermfor“ironoverload,” inwhichyourbodyabsorbsand storestoomuchironfromfood. Severityvarieswildly, andmanypeopleexperiencefew symptoms,butotherssuffer seriousliverdamageor scarring(cirrhosis),irregular heartbeat,diabetesandevenheart failure.Symptomscanbeaggravated bytakingtoomuchvitaminC. Hemochromatosis Thrombosisisthemedicaltermforanybloodclotthatis largeenoughtoblockabloodvessel.Whenabloodclot formsinthelarge,deepveinsoftheupperthigh,it’s calleddeepveinthrombosis.Ifsuchaclotbreaksfree,it cancirculatethroughthebloodstream,passthrough theheartandbecomelodgedinarteriesinthelung, causingapulmonaryembolism.Suchablockagecan severelydamageportionsofthelungs,andmultiple embolismscanevenbefatal. Deep vein thrombosis ©SciencePhotoLibrary Lefttoright:aredbloodcell, plateletandwhitebloodcell Bloodisadelicatebalancingact,with thebodyconstantlyregulating oxygenflow,ironcontentandclotting ability.Unfortunately,thereare severalgeneticconditionsand chronicillnessesthatcandisturb thebalance,sometimeswith deadlyconsequences. Blood disorders THE STATS BLOOD Until the 23rd week of foetal development, red blood cells are produced in the liver, not red bone marrowDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 128. THEBODYATWORK 128 Controlling the human body “Amine hormones are secreted by the thyroid and adrenal medulla” Howthehumanendocrinesystem developsandcontrolsthehumanbody Theglandsintheendocrinesystem usechemicalscalledhormonesto communicatewithandcontrolthe cellsandorgansinourbodies. Theyareductlessglandsthatsecretedifferent typesofhormonedirectlyintothebloodstream andtargetspecificorgans. Thetargetorganscontainhormone receptorsthatrespondtothechemical instructionssuppliedbythehormone.There are50differenttypesofhormoneinthebody andtheyconsistofthreebasictypes:peptides, aminesandsteroids. Steroidsincludethetestosteronehormone. Thisissecretedbythecortexoftheadrenal gland,themaleandfemalereproductive organsandbytheplacentainpregnant women.Themajorityofhormonesarepeptides thatconsistofshortchainsofaminoacids. Theyaresecretedbythepituitaryand parathyroidglands.Aminehormonesare secretedbythethyroidandadrenalmedulla andarerelatedtothefightorflightresponse. Thechangesthatarecausedbythe endocrinesystemactmoreslowlythanthe nervoussystemastheyregulategrowth, moods,metabolism,reproductiveprocesses andarelativelyconstantstableinternal environmentforthebody(homeostasis).The pituitary,thyroidandadrenalglandscombine toformthemajorelementsofthebody’s endocrinesystemalongwithvariousother elementssuchasthemaletestes,thefemale ovariesandthepancreas. Hypothalamus Releases hormones to the pituitary gland to promote its production and secretion of hormones to the rest of the body. ©DKImages Hormones Adrenal glandWehavetwoadrenalglandsthatarepositionedontopofboth kidneys.Thetriangular-shapedglandseachconsistofatwo- centimetrethickoutercortexthatproducessteroidhormones, whichincludetestosterone,cortisolandaldosterone. Theellipsoidshaped,innerpartoftheglandisknownasthe medulla,whichproducesnoradrenalineandadrenaline.These hormonesincreasetheheartrate,andthebody’slevelsofoxygen andglucosewhilereducingnon-essentialbodyfunctions. Theadrenalglandisknownasthe‘fightorflight’glandasit controlshowwerespondtostressfulsituations,andpreparesthe bodyforthedemandsofeitherfightingorrunningawayasfastas youcan.Prolongedstressover-loadsthisglandandcausesillness. Pituitary gland Releases hormones to the male and female reproductive organs and to the adrenal glands. Stimulates growth in childhood and maintains adult bone and muscle mass. Thymus Is part of the immune system. It produces thymosins that control the behaviour of white blood T-cells. Adrenal glands Controls the burning of protein and fat, and regulates blood pressure. The medulla secretes adrenaline to stimulate the fight or flight response. Male testes Thesetwoglandsproduce testosteronethatis responsibleforsperm production,muscleand bonemassandsexdrive. Cortex Medulla Kidney The endocrine system Pineal gland Secretes melatonin, which controls sleep patterns and controls the production of hormones related to the reproductive organs. WorldMags.netWorldMags.net WorldMags.net
- 129. 129 When you are excited the hypothalamus and pituitary gland release opiate-like endorphinsDID YOU KNOW? Pituitary glandThepea-sizedpituitaryglandisamajor endocrineglandthatworksunderthe controlofthehypothalamus.Thetwo organsinsidethebrainworkinconcertand mediatefeedbackloopsintheendocrine systemtomaintaincontrolandstability withinthebody. Thepituitaryglandfeaturesananterior (front)lobeandaposterior(rear)lobe.The anteriorlobesecretesgrowthhormones thatstimulatethedevelopmentofthe musclesandbones;italsostimulatesthe developmentofovarianfolliclesinthe femaleovary.Inmales,itstimulatesthe productionofspermcells.Theposterior lobestoresvasopressinandoxytocinthat issuppliedbythehypothalamus. Vasopressinallowstheretentionofwaterin thekidneysandsuppressestheneedto excreteurine.Italsoraisesbloodpressure bycontractingthebloodvesselsintheheart andlungs. Oxytocininfluencesthedilationofthe cervixbeforegivingbirthandthe contractionoftheuterusafterbirth.The lactationofthemammaryglandsare stimulatedbyoxytocinwhenmothersbegin tobreastfeed. Thyroid and parathyroids Thetwolobesofthethyroidsitoneachsideofthe windpipeandarelinkedtogetherbytheisthmusthat runsinfrontofthewindpipe.Itstimulatestheamount ofbodyoxygenandenergyconsumption,thereby keepingthemetabolicrateofthebodyatthecurrent levelstokeepyouhealthyandactive. Thehypothalamusandtheanteriorpituitarygland areinoverallcontrolofthethyroidandtheyrespondto changesinthebodybyeithersuppressingorincreasing thyroidstimulatinghormones.Overactivethyroids causeexcessivesweating,weightlossandsensitivityto heat,whereasunderactivethyroidscausesensitivityto hotandcold,baldnessandweightgain.Thethyroidcan swellduringpubertyandpregnancyorduetoviral infectionsorlackofiodineinaperson’sdiet. Thefoursmallparathyroidsregulatethecalcium levelsinthebody;itreleaseshormoneswhencalcium levelsarelow.Ifthelevelofcalciumistoohighthe thyroidreleasescalcitonintoreduceit.Therefore,the thyroidandparathyroidsworkintandem. Pancreatic cells Thepancreasispositionedintheabdominalcavityabovethesmall intestine.Itconsistsoftwotypesofcell,theexocrinecellsthatdonot secretetheiroutputintothebloodstreambuttheendocrinecellsdo. Theendocrinecellsarecontainedinclusterscalledtheisletsof Langerhans.Theynumberapproximately1millioncellsand areonlyoneortwopercentofthetotalnumberofcellsin thepancreas.Therearefourtypesofendocrinecellsin thepancreas.Thebetacellssecreteinsulinandthe alphacellssecreteglucagon,bothofwhich stimulatetheproductionofbloodsugar(glucose) inthebody.IftheBetacellsdieoraredestroyed itcausestype1diabetes,whichisfatalunless treatedwithinsulininjections. Theothertwocellsarethegammaand deltacells.Theformerreducesappetite andthelatterreducestheabsorptionoffood intheintestine. Pancreas Maintains healthy blood sugar levels in the blood stream. Female ovaries Are stimulated by hormones from the pituitary gland and control the menstrual cycle. Anterior lobe Posterior lobe Hypothalamus Portal veins Hormones from the hypothalamus are carried to the anterior lobe through these veins. Hypothalamus neurons These synthesise and send hormones to the posterior lobe. Islets of Langerhans Acinar cells Thesesecrete digestiveenzymes totheintestine. Red blood cells Duct cells Secretebicarbonate totheintestine. Right lobe Left lobe Isthmus Trachea (windpipe) Thyroid cartilage (Adam’s apple) Parathyroids Parathyroid Works in combination with the thyroid to control levels of calcium. Thyroid Important for maintaining the metabolism of the body. It releases T3 and T4 hormones to control the breakdown of food and store it, or release it as energy. FRONT REAR WorldMags.netWorldMags.net WorldMags.net
- 130. THEBODYATWORK 130 “Generally, a human will produce 2.5-3 litres of urine a day” Everydaythebodyproduceswaste productsthatenterthebloodstream– buthowdowegetridofthem? Thehumanurinarysystem’s primaryfunctionistoremove by-productswhichremainin thebloodafterthebodyhas metabolisedfood.Theprocessismadeup ofseveraldifferentkeyfeatures.Generally, thissystemconsistsoftwokidneys,two ureters,thebladder,twosphincter muscles(oneinternal,oneexternal)anda urethraandtheseworkalongsidethe intestines,lungsandskin,allofwhich excretewasteproductsfromthebody. Theabdominalaortaisanimportant arterytothesystemasthisfeedstherenal arteryandvein,whichsupplythekidneys withblood.Thisbloodisfilteredbythe kidneystoremovewasteproducts,suchas ureawhichisformedthroughaminoacid metabolism.Throughcommunication withotherareasofthebody,suchasthe hypothalamus,thekidneysalsocontrol waterlevelsinthebody,sodiumand potassiumlevelsamongotherelectrolytes, bloodpressure,pHofthebloodandare alsoinvolvedinredbloodcellproduction throughthecreationandreleaseofthe hormoneerythropoietin.Consequently, theyareabsolutelycrucialtooptimum bodyoperation. Afterbloodhasbeenfilteredbythe kidneys,thewasteproductsthentravel downtheureterstothebladder.The bladder’swallsexpandout toholdthe urineuntilthebodycanexcretethewaste outthroughtheurethra.Theinternaland externalsphinctersthencontrolthe releaseofurine. Generally,ahumanwillproduce approximately2.5-3litresofurineaday, althoughthiscanvarydramatically dependantonexternalfactorssuchas waterconsumption. How does the body filter waste? Kidneys This is where liquids are filtered and nutrients are absorbed before urine exits into the ureters. Ureter These tubes link the kidneys and the bladder. Bladder This is where urine gathers after being passed down the ureters from the kidneys. Inferior vena cava This carries deoxygenated blood back from the kidneys to the right aorta of the heart. Abdominal aorta This artery supplies blood to the kidneys, via the renal artery and vein. This blood is then cleansed by the kidneys. How do the kidneys work? Thekidneyswillhavearound150-180litresofbloodtofilterperday,butonlypassaround twolitresofwastedowntheureterstothebladderforexcretion,thereforethekidneys returnmuchofthisblood,minusmostofthewasteproducts,totheheartforre- oxygenationandrecirculationaroundthebody. Thewaythekidneysdothisistopassthebloodthroughasmallfilteringunitcalleda nephron.Eachkidneyhasaroundamillionofthese,whicharemadeupofanumberof smallbloodcapillariesandatubecalledtherenaltubule.Thebloodcapillariessiftthe normalcellsandproteinsfromthebloodforrecirculationandthendirectthewaste productsintotherenaltubule.Thiswaste,whichwillprimarilyconsistofurea,mixeswith waterandformsurineasitpassesthroughtherenaltubuleandthenintotheureteronits waytothebladder. Human urinary system WorldMags.netWorldMags.net WorldMags.net
- 131. 131 Human fistAVERAGE SIZE OF KIDNEY The human urinary system 4. Urethra Urine travels down this passageway to exit the body. Urethra The urethra is the tube that urine travels through to exit the body. Renal artery and vein This supplies blood to the kidneys in order for them to operate, and then removes deoxygenated blood after use by the kidneys. Pelvis The bladder sits in the pelvis, and the urethra passes through it for urine to exit the body. How do we store waste until we’re ready to expel it? Thebladderstoreswasteproductsbyallowingtheurinetoenter throughtheuretervalves,whichattachtheuretertothebladder. Thewallsrelaxasurineentersandthisallowsthebladderto stretch.Whenthebladderbecomesfull,thenervesinthebladder communicatewiththebrainandcausetheindividualtofeelthe urgetourinate.Theinternalandexternalsphincterswillthen relax,allowingurinetopassdowntheurethra. 1. Ureters These tubes connect to the kidneys and urine flows down to the bladder through them. 5. Bladder walls (controlled by detrusor muscles) The detrusor muscles in the wall of the bladder relax to allow expansion of the bladder as necessary. 3. External urethral sphincter This secondary sphincter also remains closed to ensure no urine escapes. 2. Internal urethral sphincter This remains closed to ensure urine does not escape unexpectedly. 4. Ureter valves These valves are situated at the end of the ureters and let urine in. Bladder fills Bladder empties 3. Bladder walls (controlled by detrusor muscles) These muscles contract to force the urine out of the bladder. 2. External urethral sphincter This also relaxes for the urine to exit the body. 1. Internal urethral sphincter This relaxes when the body is ready to expel the waste. Why do we get thirsty? Maintainingthebalancebetweenthe mineralsandsaltsinourbodyandwateris veryimportant.Whenthisisoutofbalance, thebodytellsustoconsumemoreliquidsto redressthisimbalanceinorderforthebody tocontinueoperatingeffectively. Thiscraving,orthirst,canbecausedby toohighaconcentrationofsaltsinthebody, orbythewatervolumeinthebodydropping toolowforoptimaloperation.Avoiding dehydrationisimportantaslongterm dehydrationcancauserenalfailure,among otherconditions. ©DKImages 150–180 litresBLOOD FILTERED PER DAY1-8hrsTIME URINE’S IN BLADDER 400–600mlBLADDER CAPACITYTHE STATS URINARY SYSTEM On average, you make the same amount of urine in the day as in the nightDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 132. 132 ©Corbis If the upper airway is blocked, by trauma, cancer or inflammation, an alternative route must be found for air to enter the lungs. Planned tracheotomies are performed under general anaesthesia or sedation. The neck is extended backwards to allow the surgeon to easily identify the structures in the throat and to make an accurate incision (see diagram). First, a vertical cut is made in the skin, below the tracheal cartilage, and the underlying muscle and blood vessels are carefully moved out of the way to expose the trachea. The trachea is normally held open by C-shaped rings of cartilage, which prevent the airway from collapsing. A hole is made between the third and fourth rings, allowing the surgeon access to the airway without disrupting the cartilage supports. A tracheotomy tube is then inserted into the airway and secured to the neck. If the tracheal opening is going to be a permanent feature rather than temporary then a piece of cartilage may be removed to allow the tube to sit more comfortably. The vocal cords sit just behind the tracheal cartilage, above the tracheotomy incision site, but in order to talk, air must be able to pass through the vocal cords to make them vibrate. Some tracheotomy tubes contain unidirectional valves, enabling the patient to breathe in through the tube and out through their mouth, which provides good air supply to the lungs, without hampering speech. If the patient is unable to breathe unaided, a ventilator may be attached to mechanically move air in and out of the lungs. Discoverthescienceandtechbehindthislife-savingprocedure Tracheotomy surgery A tracheotomy is a complex procedure, so in life-threatening, emergency situations a faster procedure – known as a cricothyrotomy (also called cricothyroidotomy) – may be performed. A higher incision is made just below the thyroid cartilage (Adam’s apple) and then through the cricothyroid membrane, directly into the trachea. It is possible to perform this procedure with a sharp instrument and any hollow tube, such as a straw or a ballpoint pen case. However, finding the correct location to make the incision is challenging, and without medical training there is great risk of damaging major blood vessels, the oesophagus or the vocal cords. Have you got a pen? The trachea is surrounded by a minefield of major blood vessels, nerves, glands and muscles Anatomy of a tracheotomy Thyroid The thyroid gland, responsible for making numerous hormones, sits just beneath the tracheotomy site. Carotid artery Large arteries supplying blood to the brain and face run up either side of the trachea. Trachea The trachea connects the lungs to the mouth and nose; a tracheotomy bypasses them to grant direct access to the lungs. Cartilage ring The trachea is held open by stiff C-shaped rings made of cartilage. Stoma A temporary or permanent tube is inserted into the trachea through an incision between the rings of cartilage. Flanges The outer portion of the tube has flanged edges, which means it can be securely taped to the neck. Thyroid cartilage The surgeon uses the prominent Adam’s apple as a marker to locate the best incision site on the neck. Larynx The vocal cords sit behind the thyroid cartilage, above the point of the incision. Oesophagus The oesophagus lies behind the trachea, so the surgeon must take care not to puncture through from one to the other. THEBODYATWORK Tracheotomies WorldMags.netWorldMags.net WorldMags.net
- 133. We trample on lawns and mow them down, but eventually grass gets revenge. Its pollen causes many of us to suffer from hay fever, and so do trees, weeds and even some fruit. Despite being smaller than the tip of a pin, pollen is carried by the wind and lodges in the nasal lining tissues and throat, where it can cause an allergic reaction. This is when the body mistakenly thinks it has been invaded by a threat, such as a virus. To fight back, the body produces a type of antibody known as immunoglobulin E (IgE) in response to the allergen, causing nasal passages to become inflamed, producing more mucus. This is designed to help flush out the allergens but can lead to other symptoms like headaches from blocked sinuses or coughing caused by mucus dripping down the back of the throat from the nose. People genetically predisposed to hay fever are called atopics. Hay fever usually develops during childhood or teenage years, but adults can get it too. This is likely to follow repeated contact with a substance that your immune system perceives as a threat. No one knows for sure why hay fever starts affecting someone at the point in time it does. Hay-fever sufferers are in trouble when the pollen count reaches 50 pollen grains per cubic metre of air. You’ll experience it worse in the morning when plants release their pollen. Allergens collect in the air on humid days and during storms, but rain clears the pollen. Whensummerstrikes,whydosomeofussuffer? When hay fever attacks Pollen forecast GRASSPOLLEN (MAY-JULY) TREEPOLLEN(MARCH-MAY) WEEDPOLLEN(SUMMER- EARLYAUTUMN) 95 per cent of hay-fever sufferers are allergic to grass pollen. Close windows on dry, windy days. Affects 25 per cent of sufferers and instigators include ash, birch, beech, willow and oak. Cut back branches in the garden to reduce pollen. In the USA, ragweed is the biggest culprit. One plant can spew out millions of pollen grains daily. An inside look at how pollen can affect us Why do we get a runny nose? Airborne pollen Fine dusty pollen is carried by the wind and inhaled through the nasal passage. People with a genetic disposition to hay fever, known as atopics, will have an allergic reaction. Protein problem Proteins on the surface of the pollen grain irritate and inflame the cells that line your mouth, nose, eyes and throat. The body’s immune system treats the pollen like a virus and takes action to expel it. Too much histamine Histamine irritates the upper respiratory passages, making them swell and produce the typical hay fever symptoms. Histamine makes your mucus membranes work over time, producing enough mucus to flush the pollen out. Antibodies The pollen protein triggers your immune system, which creates thousands of antibodies. The antibodies attach themselves to mast cells, which release histamine – a substance the body produces to fight infection. Allergyinnumbers 15%: Of UK population get hay fever 40%: Risk if one parent suffers 80%: Risk if both parents suffer 95%: Of hay-fever sufferers are allergic to grass pollen 1 in 5: Affected by hay fever 21 million: UK adults suffer from one or more type of allergy The statistics… STRANGE BUTTRUE MISLEADING NAME Where did hay fever get its name? Answer: The term hay fever has nothing to do with hay, and everything to do with trees, grasses and ragweed. The name came about because symptons would strike during hay-harvesting season, when these pollens would be rife.A Hay allergy B Harvesting C Doctor’s name 133 DID YOU KNOW? Allergic diseases, including asthma, are the fifth most common chronic disease in all ages WorldMags.netWorldMags.net WorldMags.net
- 134. THEBODYATWORK The sensory system 134 The sensory system iswhat enablesus to experience the world. It can also warn us of danger, trigger memories and protect us from damaging stimuli, such as hot surfaces. The sensory system is highly developed, with many components detecting both physical and emotional properties of the environment. For example, it can interpret chemical molecules in the air into smells, moving molecules of sound into noises and pressure placed on theskin into touch. Indeed,some of our senses are so finely tuned they allow reactions within milliseconds of detecting a new sensation. The five classic senses are sight, hearing, smell, taste and touch. We need senses not only to interpret the world around us, but also to function within it. Our senses enable us to modify our movements and thoughts, and sometimes they directly feed signals into muscles. The sensory nervous system thatliesbehindthis is madeupof receptors, nerves and dedicated parts of the brain. There are thousands of different stimuli that can trigger our senses, including light, heat, chemicals in food and pressure. These ‘stimulus modalities’ are then detected by specialised receptors, which convert them into sensations such as hot and cold, tastes, images and touch. The incredible receptors – like the eyes, ears, nose, tongue and skin – have adapted over time to work seamlessly together and without having to be actively ‘switched on’. However, sometimes the sensory system can go wrong. There are hundreds of diseases of the senses, which can have both minor effects, or a life-changing impact. For example, a blocked ear can affect your balance, or a cold your abilityto smell – butthesethingsdon’tlastforlong. In contrast, say,after a car accident severing the spinal cord, the damage can be permanent. There are some very specific problems that the sensory system can bring as well. After an amputation, the brain can still detect signals from the nerves that used to connectto the lost limb. These sensations can causeexcruciating pain;this particular condition is known as phantom limb syndrome. Howeverthe sensory system isableto adapt to change, with thelossofoneoftenleadingtoothers being heightened. Our senses normally function to gently inhibit each other inorder to moderate individual sensations. The loss of sight from blindness is thought to lead to strengthening of signals from the ears, nose and tongue. Having saidthis,it’s certainly not universal among the blind, beingmore common in people who have been blind since a young age orfrombirth. Similarly,some people who listen to music like to close their eyes, as they claim the loss of visual input can enhance the audioexperience. Although the human sensory system is well developed, many animals out-perform us. For example, dogs can hear much higher-pitched sounds, whilesharks have a far better sense of smell – in fact, they can sniff out a single drop of blood in a million drops of water! Exploring the sensory systemThecomplexsensesofthehumanbodyandhow theyinteractisvitaltothewaywelivedaytoday Touch is the first sense to develop in the womb About 100 million photoreceptors per eye We can process over 10,000 different smells Ears feed sounds to the brain but also control balance 9,000 taste buds over the tongue and throat WorldMags.netWorldMags.net WorldMags.net
- 135. STRANGE BUTTRUE SIGHT TO BEHOLD Which creatures can have up to a hundred eyes? Answer: Scallops are an underwater mollusc that amazingly can have as many as 100 eyes! Although they can’t create as clear a picture as our eyes, they can detect enough light and movement to warn them of oncoming predators.A Scallops B Spiders C Peacocks 135 DID YOU KNOW? Taste and smell are closely linked. To test this, pinch your nose as you eat something and it will taste bland Total recall Have you ever smelt something that transported you back in time? This is known as the Madeleine effect because the writer Marcel Proust once described how the scent of a madeleine cake suddenly evoked strong memories and emotions from his childhood. The opposite type of recall is voluntary memory, where you actively try and remember a certain event. Involuntary memories are intertwined with emotion and so are often the more intense of the two. Younger children under the age of ten have stronger involuntary memory capabilities than older people, which is why these memories thrust you back to childhood. Older children use voluntary memory more often, eg when revising for exams. DID YOU KNOW? Motor neuron These fire impulses from the brain to the body’s muscles, causing contraction and thus movement. They have lots of extensions (ie they are multipolar) to spread the message rapidly. Purkinje cell These are the largest neurons in the brain and their many dendritic arms form multiple connections. They can both excite and inhibit movement. Retinal neuron These retinal bipolar cells are found in the eye, transmitting light signals from the rods and cones (where light is detected) to the ganglion cells, which send impulses into the brain. Olfactory neuron The many fine dendritic arms of the olfactory cell line the inner surface of the nasal cavity and detect thousands of different smells, or odorants. Unipolar neuron These sensory neurons transduce a physical stimulus (for example, when you are touched) into an electrical impulse. Body’s messengers The sensory system is formed from neurons. These are specialised nerve cells which transmit signals from one end to the other – for example, from your skin to your brain. They are excitable, meaning that when stimulated to a certain electrical/chemical threshold they will fire a signal. There are many different types, and they can interconnect to affect each other’s signals. Pyramidal neuron These neurons have a triangular cell body, and were thus named after pyramids. They help to connect motor neurons together. Find out how our nose and brain work together to distinguish scents How do we smell? Olfactory bulb Containing many types of cell, olfactory neurons branch out of here through the cribriform plate below. Olfactory epithelium Lining the nasal cavity, this layer contains the long extensions of the olfactory neurons and is where chemical molecules in air trigger an electric impulse. Olfactory nerve New signals are rapidly transmitted via the olfactory nerve to the brain, which collates the data with sight and taste. Cribriform plate A bony layer of the skull with many tiny holes, which allow the fibres of the olfactory nerves to pass from nose to brain. Olfactory neuron These neurons are highly adapted to detect a wide range of different odours. Anaxonic neuron Found within the retina of the eye, these cells lack an axon (nerve fibre) and allow rapid modification of light signals to and from bipolar cells. WorldMags.netWorldMags.net WorldMags.net
- 136. THEBODYATWORK The sensory system 136 Have you ever felt something scorching hot or freezing cold, and pulled your hand away without even thinking about it? This reaction is a reflex. Your reflexes are the most vital and fastest of all your senses. They are carried out by the many ‘reflex arcs’ located throughout the body. For example, a temperature-detecting nerve in your finger connects to a motor nerve in your spine, which travels straight to your biceps, creating a circular arc of nerves. By only having two nerves in the circuit, the speed of the reflex is as fast as possible. A third nerve transmits the sensation to the brain, so you know what’s happened, but this nerve doesn’t interfere with the arc; it’s for your information only. There are other reflex arcs located within your joints, so that, say, if your knee gives way or you suddenly lose balance, you can compensate quickly. Understanding lightning reflexes These transmit vital sensory information to our brain while also sending motor function signals all around the body Key nerves Trigeminal nerve This nerve is an example of a mechanoreceptor, as it fires when your face is touched. It is split into three parts, covering the top, middle and bottom thirds of your face. Olfactory nerve Starting in the nose, this nerve converts chemical molecules into electrical signals that are interpreted as distinct odours via chemoreceptors. Optic nerve The optic nerves convert light signals into electrical impulses, which are interpreted in the occipital lobe at the back of the brain. The resulting image is seen upside down and back to front, but the brain reorients the image. Eye movements The trochlear, abducent and oculomotor nerves control the eye muscles and so the direction in which we look. Facial and trigeminal motors The motor parts of these nerves control the muscles of facial expression (for example, when you smile), and the muscles of the jaw to help you chew. 1. Touch receptor When a touch receptor is activated, information about the stimulus is sent to the spinal cord. Reflex actions, which don’t involve the brain, produce rapid reactions to dangerous stimuli. 2. Signal sent to spine When sensory nerve endings fire, information passes through nerve fibres to the spinal cord. 3. Motor neurons feed back The signals trigger motor neurons that initiate their own impulses that feed back to the muscle, telling it to move the body part. WorldMags.netWorldMags.net WorldMags.net
- 137. Synaesthesia is a fascinating, if yet completely understood, condition. In some people, two or more of the five senses become completely linked so when a single sensation is triggered, all the linked sensations are activated too. For example, the letter ‘A’ might always appear red, or seeing the number ‘1’ might trigger the taste of apples. Sights take on smells, a conversation can take on tastes and music can feel textured. People with synaesthesia certainly don’t consider it to be a disorder or a disease. In fact, many do not think what they sense is unusual, and they couldn’t imagine living without it. It often runs in families and may be more common than we think. More information about the condition is available from the UK Synaesthesia Association (www.uksynaesthesia.com). Crossed senses 1There are about 9,000 taste buds on the tongue and throat. These convert chemicals found in saliva into electrical signals, split into five tastes: sweet,salt, sour, bitter and umami. 2Odours offer better memory recall than visual cues, as smell is tied to emotion. Looking at an old photograph can trigger memory, but a smell can evoke how you felt at the time. 3Human skin contains over half a million sensory receptors. These are of the highest concentrationinthefingertips, the ends of the toes and lips, where they’re most needed. 4The images formed in the occipital cortex are upside down, before the brain flips them. However babies start by seeing upside down, until the brain learns to adapt. 5Ears do more than detect sound. The fluid and fine hairs in the inner ear maintain balance. If you spin round and stop, this fluid is still moving which is why we get dizzy. A matter of taste Smell vs sight Sensitive skin Upside down Staying steady 5TOP FACTS HUMAN SENSES 137 The three smallest bones in the human body – the hammer, anvil and stirrup – are located in the middle ear ©SPL;Alamy;Thinkstock DID YOU KNOW? Our sense of balance and the position of our bodies in space are sensations we rarely think about and so are sometimes thought of as a ‘sixth sense’. There is a whole science behind them though, and they are collectively called proprioception. There are nerves located throughout the musculoskeletal system (for example, within your muscles, tendons, ligaments and joints) whose job it is to send information on balance and posture back to the brain. The brain then interprets this information rapidly and sends instructions back to the muscles to allow for fine adjustments in balance. Since you don’t have to think about it and you can’t switch it off, you don’t know how vital these systems are until they’re damaged. Sadly some medical conditions, including strokes, can affect our sense of proprioception, making it difficult to stand, walk, talk and move our limbs. Is there really a ‘sixth sense’? A patient’s sense of proprioception is being put to the test here Accessory nerve Connecting the muscles of the neck to the brain, this nerve lets us turn our heads from side to side. Vestibulocochlear nerve This nerve provides sensation to the inner part of the ear. Vagus motor This portion of the vagus nerve can slow the heartbeat and breathing rate, or increase the speed of digestion. The hypoglossal nerve This nerve controls the movements of the tongue. Vagus nerve The vagus nerve is spread all around the body. It is a mixed sensory and motor nerve, and is responsible for controlling all of the functions we don’t think about – like our heartbeat. Intermediate nerve This is a small part of the larger facial nerve. It provides the key sensation to the forward part of the tongue to help during eating. Glossopharyngeal motor The motor part of this nerve controls the pharynx, helping us to speak and breathe normally. 5 5 5 5 5 5 5 5 5 5 5 5 5 5 2 5 2 5 5 5 2 5 55 2 2 2 5555 5 5 5 5 5 5 5 5 5 5 5 5 5 5 2 5 2 5 5 5 2 5 55 2 2 2 5555 Non-synaesthetes struggle to identify a triangle of 2s among a field of number 5s. But a synaesthete who sees 2s as red and 5s as green can quickly pick out the triangle. WorldMags.netWorldMags.net WorldMags.net
- 138. Chickenpox is a strain of the Varicella zoster virus, which many of us have experienced during our youth. Most prominent in children, the virus is contracted through coughing and sneezing or transferred on shared objects, which makes schools a prime location. The most famous symptom is the appearance of small itchy red spots, which vary in size from 10-20 millimetres (0.4-0.8 inches) across. The extent can vary but in most cases they cover the face, arms, legs, stomach and back. These develop into fluid-filled blisters and are often accompanied by a fever. The blisters burst, scab over and fall off within a few days, but new waves of spots can emerge to replace them; it usually takes one to two weeks for the body to regain control. Chickenpox is rarely serious but it is important not to interfere with the scabs as infection can make it more severe. A vaccine is only offered in extreme circumstances when an individual may have a weak immune system or be particularly vulnerable to the disease. After the outbreak, chickenpox doesn’t disappear entirely. The disease lies in a dormant state within the body as your immune system keeps it under wraps. The infection can break out again later and reappear as shingles. A rash builds up on a certain point of the body and the symptoms return, most commonly in people over 50. On average, three in every 1,000 people contract shingles in the UK each year. THEBODYATWORK Chickenpox 138 ©Alamy;Thinkstock Discoverthebiologybehindtheinfamouschildhood ailmentandwhyitneverreallygoesaway… Understanding chickenpox 90 per cent of adults are immune if they’ve had the disease as a child but it still affects adults and teenagers. If you develop chickenpox at a later age, all the symptoms are more severe, with more chronic pain, headaches and sore throats; therefore, there is greater need for treatment, such as pain relief and soothing creams. The disease tends to affect adults more dramatically as it can now mutate into a variety of other strains, such as shingles or, in extreme cases, lead to encephalitis, postherpetic neuralgia or pneumonia. However, the chances of this happening are only around ten per cent. Grown-up chickenpoxGet under the skin to see how shingles can catch the body unawares When chickenpox strikes back… Low immunity The Varicella virus becomes active when the immune system is weak, overcoming the body’s natural defences. Dormancy Once the immune system regains control, the virus retreats and lies dormant in the body’s nervous system, but it can return later. Start of the illness The virus infiltrates the skin and causes inflammation and a burning sensation. Blisters emerge Blisters become visible and inflamed rashes appear on all affected areas. Don’t scratch! The blisters then harden into scabs and fall off. Scratching at the spots makes the healing process slower. Future effects In around 10-20 per cent of people who have shingles, the nerve fibres become damaged which can lead to postherpetic neuralgia (nerve pain). Deaths from chickenpox have reduced dramatically in the last 25 years WorldMags.netWorldMags.net WorldMags.net
- 139. 139 The average person will produce 140-280g (5-10oz) of basal tears per day to keep the eyes moistDID YOU KNOW? 5 TOP FACTS CRYING 1Ifyoufindthatyournoserunsa lotwhenyoucry,itisbecause excesstearsarerunningfrom youreyes,downyourtearducts andintoyournose,causing thosetearfulsniffles. Runny noses 2Babiestypicallycryforabout onetothreehoursperday.This canbeforavarietyofreasons, becausethey’rehungry,thirsty, tired,scaredorhavejustbeento thetoilet. Hush, little baby 3Syn-propanethial-S-oxideis createdbyanenzymeinacut onion.Whenitevaporates,this compoundirritatesourlacrimal glandsandtearsaretriggeredin ordertodiluteit. Onion weeping 4Whilecrocodilesareknownfor lookingtearyastheyeatfood they’vejustcaught,theyaren’t sad.Thetearsmerelylubricate theireyeswhentheyspendtime outofthewater. Crocodile tears 5Thereisaconditioncalledthe PseudoBulbarAffect(PBA)in whichpeoplecryorlaugh uncontrollably.Firstdescribedby CharlesDarwinitisoftentheresult ofbraininjuries. Darwin’s discovery ©SPL;Thinkstock Whether it’s a sad film, a joyous reunion or simply that you’ve just banged your knee on a coffee table, everyone has cried at some point in their life. But why have we evolved to do it? There’s a theory that it stems right back as far as our pre-evolved days, where tears streaming down our primitive eyes and blurring our vision was a sign of surrender, proving that we meant our aggressor no harm. But moving on to the present day, the science shows that there are a number of sound biological reasons for tearing up. There are reflex tears, the stream caused by getting smoke or sulphenic acid from a chopped onion into your eye. When this happens, sensory nerves in your cornea send a signal to the brain that the eyes need protecting. The brain then releases hormones into the lacrimal glands located behind the eyelid, which produces tears to provide a layer of protection and to water down the irritant. However, the more common form of crying is the emotional kind. When strong emotions are Findouthowourtearshavebeenhelpingto protectussincethedawnoftime The lacrimal system 1 Lacrimal gland This gland receives the message from the cerebrum to produce tears. 3 Tear ducts This is where the water flows to. If there’s too much, it flows down the face. 4 Runny nose Tears that flow through the tear ducts go down a nasal passage, which is what causes a runny nose. 2 Cornea Tears help protect the surface of the eye. While there is a stereotype that women are tearier than men, there is some science to explain the reasons behind this. Studies have shown that women cry about four times as often as men and, while there are cultural factors to be taken into consideration, there are biological factors too. Until their adolescent years, boys and girls cry fairly equally. As testosterone levels rise in boys, they are more likely to get angry than upset. Meanwhile, girls gain increased oestrogen levels, which modifies endorphin production, often leading to more emotional responses to stimuli. Battle of the sexes brought about – whether through happiness, sadness or pain – the brain’s cerebrum is aware that you are undergoing a strong emotional reaction to a stimulus. The endocrine system releases a set of hormones to the lacrimal gland, which secretes liquid onto the eye. Excess water can escapes down the nose, via the tear ducts. Studies of tears have shown there is a biochemical reason for emotional crying. While reflex tears are 98 per cent water, emotional tears contain several chemicals, including adrenocorticotropic hormones present in times of stress, and leucine- enkephalin – an endorphin that releases pain and improves your mood. Therefore, crying appears to be a way of releasing hormones and toxins that build up during times of intense emotion. Why do we cry? 1 2 3 4 139WorldMags.netWorldMags.net WorldMags.net
- 140. 142 Ageing Why do we grow old? 146 Left or right brained? The truth behind thinking 148 Brain freeze Why do we feel this cold pain? 149 Runny nose /Coma What makes your nose run? 150 Ears / Freckles / Sore throat Why do your ears pop? 151 Memory / Toothpaste / Epidurals What is a memory? 152 Blushing / Caffeine / Fainting The telltale signs of blushing 153 Eyebrows / Earwax / Self Do we need eyebrows? 154 72-hour deodorant / Modern fillings How do we combat body odour? 155 What powers your cells? Inside the mitochondria 156 Can we see thoughts? Is this science or a myth? 158 How anaesthesia works The drug that stops pain signals 159 Stomach ulcers / Mouth ulcers How do ulcers form? 160 Hair growth / Blond hair Our hair explained 161 Correcting heart rhythms / Salt / Adam’s apple Is salt bad for your heart? 162 Seasickness / Rumbling stomachs Explaining seasickness 163 What are moles? A look a mole formation 164 Brain control / Laughing Do our brains control us? 165 Dandruff / Eye adjustment / Distance the eye can see Revealing how dandruff forms 149 What makes your nose run? CURIOUS QUESTIONS 140 148 Brain freeze explained 155 173 Powering cells How do we know how much to eat? ©Thinkstock ©Alamy 168 What do alveoli do? ©SPL WorldMags.netWorldMags.net WorldMags.net
- 141. 098 166 Allergies / Eczema Why do some people suffer? 167 Bruises / Water allergy / Cholesterol How are bruises caused? 168 How do alveoli help you breathe? Inside your lungs 169 Migraines / Eye drops Discover how migraines strike 170 What are twins? What causes twins to be born? | 142 The signs of ageing 156 Can we see thoughts? ©SPL 172 Paper cuts / Pins and needles / Funny bones Why do paper cuts hurt so much? 173 Aching muscles / Fat hormone What causes muscle ache? 174 Raw meat / Inoculations / Upper arm and leg Should we eat raw meat? 175 Feet size / Gout How are feet measured? ©Thinkstock 170 164 What causes twins? Do our brains control us? Allergies explained 166 141 ©SPL WorldMags.netWorldMags.net WorldMags.net
- 143. 1When your hair turns grey has a lot to do with your genetics, but the loss of melanin associated with grey hair is due to older age. Grey hair 2The loss of skin elasticity also ages us through the creation of wrinkles, although in some cases it can be prevented or at least slowed down. Wrinkles 3Enamel on our teeth wears down over time and maintaining dental hygiene becomes more difficult, resulting in tooth loss. Missing teeth 4With ageing can come a number of vision problems that can cause a loss of sight, including cataracts, glaucoma and macular degeneration. Loss of eyesight 5Age-related hearing loss can be caused by everything from environmental factors to a degeneration of the fine hair cells in the cochlea. Loss of hearing hypothalamusinthebrainsends messagesviahormonestothepituitary gland,whichinturnstimulatesor restrictshormonesecretionsbythe thyroid,adrenalglands,ovariesand eventhetesticles. Overtimethiscomplexsystemdoes notfunctionasefficiently,leadingto everythingfromproblemssleepingto menopause(whichisanormalpartof ageingforwomen,butcanleadto additionalhealthproblems). Differenttypesofcellsinthe immunesystemdeclineinnumberas weageanddonotfunctionaswell.Some scientistspointtothefactthattheoverall riskofcontractingcancersgoesupaswe getolder;younger,moreefficient immunesystemsmayhavebeenableto fendthemoff. Oritcouldallsimplybegenetic.That is,ourDNAtellsourbodieswhenlifeisat anend.Theredoesseemtobeagenetic componenttoageingamongmost animals–theyhavepredictablelife spans.Womenalsotendtolivelonger thanmen.Ifyourparentslivedalong time,youaremorelikelytodoso yourself.Onegroupofgenes,knownas thelongevityassurancegene,habeen determinedtoinfluencelifespan.Ifyou inheritthe‘helpful’versionthenyouare morelikelytohavealongerlife. Althoughourgenesplayapartinour lifespan,obviouslytheycanbe influencedorchanged.Otherwise,we’d stillbelivingtotheripeoldageof30 insteadof80(theaveragelifespanin developedcountries).Mostresearchers believethatageingisacomplexprocess thatnosingletheorycanexplain–it’sa combinationofourgenes,ourbiological functionsandenvironmentalfactors. Wetendtofocusmoreonthevisible signsofageingatfirst,likewrinklesand greyhairs,andthesechangesareprime examplesofhowcomplicatedthe processcanbe.We’vealreadytalkeda bitaboutthecauseofwrinkles:the connectivetissuescollagenandelastin, thatkeepskinlookingsmooth,both breakdownovertime.Withoutthefirm connectionsunderneath,theskinsags. Manypeoplelosefatdepositsintheir faces,andtheskin’soilproduction decreases.Manyofthesethingshavea geneticcomponent,butoutsidefactors suchasexposuretoultravioletradiation andsmokingbothcausewrinklesand sagsfaster.TheSun’sraysbreakdown connectivetissues,whilesmoking causesbloodvesselstocontract. Greyhairiscausedbyalossof melanin,thepigmentthatisresponsible forourhaircolour.Onlyrecentlyhave scientistslearnedthatmelanin productiongetsinterruptedwhen hydrogenperoxidelevelsinthebody increaseovertime.Otherproteinsfound inhaircellsthatareresponsiblefor regrowthdiminishovertimetoo. Unlike withwrinkles,however,thereisn’tmuch youcandotoavoidgoinggreyotherthan dyeyourhair.Geneticsdoappeartoplay Subcutaneous fat layer As we age, the fat pads under the skin diminish and cause skin and muscle to sag. Age spot Sun damage, as well as the ageing process in general, can cause clumps of melanin to concentrate into spots. Epidermis The skin is kept smooth by the proteins collagen and elastin, which break down and lose their stretch over time, causing wrinkles. Ageing skinWhatlookslikespotsand wrinklesisactuallyanumberof changesgoingonundertheskin Younger Older Going grey Eachhairfollicleinourheads containsmelanin–apigmentthat givesourhairitscolour.Overtimethe melaninproductiondecreasesand unpigmentedhairbeginstogrow Shaft The hair shaft itself is composed of keratin, a fibrous protein. Papilla This specialised cell is fed by the bloodstream and is responsible for the growth of new hairs, and their number of pigment cells. Cortex Hair colour is determined through the cortex, which is part of the shaft of visible hair. Hair bulb The bulb is at the base of the root. It contains the follicle, which forms a socket for the hair. Hair root The root comprises three layers – the outer root, the inner root and the bulb – which gives hair its structure and rigidity. ©SciencePhotoLibrary ©GonzaloHaro Skin tone Decreased subcutaneous fat and elastic tissues cause sagging. Wrinkles These develop as collagen and skin cells begin to deteriorate. Greying A reduction in melanin production causes hair to grey. Hearing loss The sensory hair cells in the cochlea deteriorate, causing age-related hearing loss, known as presbycusis. Signs of ageing Hair loss A full head of hair will thin as the autoimmune system attacks the follicles. The process of ageing by a living system, or organism, is known as organismal senescenceDID YOU KNOW? 143 5TOP FACTSSIGNS OF AGEING WorldMags.netWorldMags.net WorldMags.net
- 144. CURIOUSQUESTIONS Old age explained apart,though.Ifyourparentswent greyatayoungage,itislikelythatyou willtoo. Theinternalsignsofageingare moreserious,health-wise,thanthe externalones.Whenandhowthey occurarealsobasedonawide varietyoffactors.Somegerontologists liketogeneralisethatsomepartsof thebodygetharderasweage,while othersgetsofter,buteverythingis interconnected.Aswementioned before,arteriesgetharderduetoa buildupofplaque.Theheartbuilds uppressurebecauseithastowork moretopumpbloodthroughthe harder,narrowerbloodvessels, whichresultsinhighbloodpressure. Othermuscles,likethelungs,get harderduetocalciumdeposits. Thesecanbecausedbyhormonal changesorfromhavingserious infectionssuchastuberculosis. Meanwhile,hormonalchanges causecalciumtoleechfromthe bones,makingthemsoftandbrittle andreducingtheirdensity.Knownas osteoporosis,thislossmeansthat we’reatagreaterriskofbreaking bones.Sarcopenia,orlossofmuscle mass,isanother‘soft’signofageing. Musclescontainspecialcellscalled satellites,aformofstemcell.These cellsareresponsibleformuscle growthaswellasregenerationwhen there’ssomeformofdamage.These cellsgraduallybecomelessproficient overtime,possiblyduetoa correspondingdecreaseingrowth factors(hormonesorproteinsthat stimulatecellgrowth).Lossoftonein musclessuchastheanalsphincter andthebladdercancauseoneofthe mostembarrassingsignsofageingfor manypeople:incontinence. Theageingbrainisstillvery mysteriouscomparedwithwhatwe knowabouttherestofthehuman body.Itwasoncethoughtthat age-relatedissuessuchasmemory losshadtodowithadecreasein neurons.Now,however,researchers believethatunlessyouhaveaspecific diseasethatdamagesneurons, complexchemicalprocessesare morelikelytoblame.Forexample, thebrainsofpeoplewithAlzheimer’s diseasetendtohavedepositsof fibrousproteinscalledamyloids.The exactcauseremainsunknown, althoughonecurrenttheoryisthat theamyloidsmanagetogetintothe brainbecausethesystemthat regulatestheexchangeofbloodin thebrain,knownastheblood-brain barrier,malfunctions. Whatisarguablymostfascinating abouttheageingprocessisthatit’s differentforeveryoneandit’s unpredictableinsomanyways. Thankstotheadvancesbeingmade inmedicine,we’relearningmore everydayaboutnotonlywhatcauses themostunpleasantsignsofageing, butalsowhatwecanpossiblydoto counteractthem. The seven stages of man Whataretheprincipal stagesofthevisible humanageingprocess throughoutourlives? 1. Infancy The completely dependent infant experiences rapid physical growth. 2. Childhood Tissue, muscle and bone then grow gradually until puberty. 3. Puberty This growth spurt indicates the start of sexual maturity. Girls tend to reach puberty two years earlier than boys. 4. Young adulthood A period of increasing physical maturity and body development. 6. Late adulthood After middle age tissues begin to deteriorate and weaken, while hair loses its pigmentation. 5. Adulthood Muscles are developed and strong. Organs are fully functional. Osteoporosisisadegenerativebonediseasethatresultsinlowerbonedensity, whichmakesthebonesweakandfragile.Theriskoffallingaswellasbreaking bonesincreasesasthediseaseworsens.Itiscausedbyalossofthemineralsthat makeupbone,suchascalcium.Thereisageneticfactor,andthedecreaseofsex hormonesinbothgendersincreasethelikelihoodofdevelopingosteoporosis. Bone loss 1. Healthy bone Healthy bones contain tight, strong structures and are able to easily bear body weight in most circumstances. 2. Bone with osteoporosis Bones with osteoporosis have gapped, porous structures. They are fragile and can fracture easily, as well as lead to falls. Aconditionthataffectsageingbones ©SPL 144 | HowItWorks144 WorldMags.netWorldMags.net WorldMags.net
- 145. 3. Plastic surgery The visible signs of ageing can be combated – temporarily – through surgery and other cosmetic procedures. MOST DRASTIC2. Hormone therapy The use of hormones such as human growth hormone to combat signs of ageing, such as decreased muscle mass, is very controversial. MORE DRASTIC1. Nutritional changes Antioxidants such as vitamin E and calorie-restrictive diets have both been shown to extend life span, but not without potential health risks. DRASTIC Ageing changes can be universal (happen to most people) or probabilistic (only occur in some people)DID YOU KNOW? Althoughageingitselfisinevitable(atleastcurrently), there’salotthatwecandotoslowdowntheageing process.Visiblesignsofageinglikewrinklescanbe diminishedbyavoidingSunexposureandotherrisk factorslikesmoking.Internalsignsofageingcanallbe combatedtosomeextentbylifestylechanges.Weight- bearingexercisessuchasweight-lifting,forexample, havebeenshowntohelpmaintainbonedensityand staveoffosteoporosis.Aerobicexerciselikewalkingor cyclingcanpreventweightgain–whichleadsto numerousdiseasesandconditionsthatageus–aswell asimprovecardiovascularhealth.Dietalsoplaysapart inageing–abalancedonecannotonlyreducetheriskof diseasesliketypetwodiabetesbutalsokeepour immunesystemsoperatingattheirpeakforlonger. Someresearcherstreatageinglikeadisease.Tothat end,stem-celltreatmentsandevencryogenicsare lookedtoasapotentialcure.Butatwhatcost?Others feelthatweweren’tmeanttoliveforeverandshould focusonwaystoagecomfortably. Slowing down the ageing process Allofthesensesdeclineasweage.Hearingdeclines becausethestructuresintheearbreakdownover time.Damagetotheauditorynerve,whichrelaysthe signaltothebrain,mayalsobetoblame.Visionalso lessensbecauseoldereyesarelessresponsive, sharporsensitive.Theeyemusclescanalsobecome lessresponsive,resultinginalossofperipheral visionandanarrowerdepthoffield.Tasteandsmell bothdecreasewithageaswell.The9,000tastebuds withwhichweareborndecreaseoverthecourseof ourlives.Smellmaydiminishduetoalossofnerve endingsinthenose.Decreasedbloodflowtothe areasofthebrainandnervoussystemthatreceive touchinformationmayberesponsibleforalossof sensationslikepain,cold,heatandvibration.The brainitselfgetssmallerovertimeandchemical processes(aswellasalackofstimulation)resultin age-relatedcomplaintssuchasmemoryloss. The senses Cataracts 1. Normal lens In a person with a normal lens, light from an image passes through the lens and is projected onto the tissue at the back of the eye called the retina. The retina changes the image to a nerve signal and transmits it to the brain, where it is processed. 2. Lens with cataract If protein clumps onto the lens (due to wear and tear or diseases like diabetes), it can create a cloudy area known as a cataract. Light is diffused through the lens to the retina, resulting in a blurry image. 7. Old age A more elderly appearance results from wrinkles, hair loss and decreased muscle tone. Life expectancy around the world 1. Europe MuchofEuropeenjoysa healthylifeexpectancyofmore than72years. 2. North America Canadianshaveaslightlyhigher lifeexpectancythanAmericans. 3. South America Thelargestcountryhasoneof thelowestlifeexpectancies. 4. Africa MostofAfrica,being undeveloped,hasmuchlower lifeexpectancy. 5. Asia Asiahasnearlyeveryrangeoflife expectancywithinitsborders. 6. Japan JapanistheAsiancountrywith thehighestaveragelife expectancyonthecontinent. 7. Indonesia Indonesiaisroughlyonapar withmuchofAsia. 8. Australia and New Zealand Theseindustrialisedcountries havean80+lifeexpectancy. ©SciencePhotoLibrary ©SciencePhotoLibrary ©SPL Thereareanumberofwaysto slowdowntheageingprocess 80+ 77.5-80 75-77.5 72.5-75 70-72.5 67.5-70 65-67.5 60-65 55-60 50-55 45-50 40-45 0-40 3 2 1 5 6 7 8 4 145 WAYS TO BEAT AGEING HEAD HEAD2 WorldMags.netWorldMags.net WorldMags.net
- 146. It’s true that the different sides of the brain perform different tasks, but do these anatomical asymmetries really define our personalities? Some psychologists argue that creative, artistic individuals have a more developed right hemisphere, while analytical, logical people rely more heavily on the left side of the brain, but so far, the evidence for this two-sided split has been lacking. In a study published in the journal PLOS ONE, a team at the University of Utah attempted to answer the question. They divided the brain up into 7,000 regions and analysed the fMRI scans of over 1,000 people, in order to determine whether the networks on one side of the brain were stronger than the networks on the other. Despite the popularity of the left versus right brain myth, the team found no difference in the strength of the networks in each hemisphere, or in the amount we use either side of our brains. Instead, they showed that the brain is more like a network of computers. Local nerves can communicate more efficiently than distant ones, so instead of sending every signal across from one hemisphere of the brain to the other, neurones that need to be in constant communication tend to develop into organised local hubs, each responsible for a different set of functions. Hubs with related functions cluster together, preferentially developing on the same side of the brain, and allowing the nerves to communicate rapidly on a local scale. One example is language processing – in most people, the regions of the brain involved in speech, communication and verbal reasoning are all located on the left-hand side. Some areas of the brain are less symmetrical than others, but both hemispheres are used relatively equally. There is nothing to say you can’t be a brilliant scientist and a great artist. What do the different parts of the brain actually do? Examining the human brain Occipital lobe (vision) Incoming information from the eyes is processed at the back of the brain in the visual cortex. Auditory cortex (hearing) The auditory cortex is responsible for processing information from the ears and can be found on both sides of the brain, in the temporal lobes. Frontal lobe (planning, problem solving) At the front of each hemisphere is a frontal lobe, the left side is more heavily involved in speech and verbal reasoning, while the right side handles attention. Parietal lobe (pressure, taste) The parietal lobes handle sensory information and are involved in spatial awareness and navigation. Temporal lobe (hearing, facial recognition, memory) The temporal lobes are involved in language processing and visual memory. Broca’s area (speech) Broca’s area is responsible for the ability to speak and is almost always found on the left side of the brain. Wernicke’s area (speech processing) The region of the brain responsible for speech processing is found on the left-hand side. 146 Actually,you’reneither.Discoverthetruthbehindthewaywethink Left or right brained? CURIOUSQUESTIONS How we think WorldMags.netWorldMags.net WorldMags.net
- 147. billion NEURONS THE STATS >100 trillion SYNAPSES 1.4kgNERVE IMPULSE SPEED 100 metres per second MASS 20% OXYGEN USAGE 20W POWER CONSUMPTION BRAINY NUMBERS 147 It is a myth that we only use ten per cent of our brains; even at rest, almost all brain regions are active ©Corbis;Thinkstock DID YOU KNOW? The left vs right brain personality myth is actually based on Nobel Prize-winning science. In the 1940s, a radical treatment for epilepsy was trialled; doctors severed the corpus callosum of a small number of patients, effectively splitting their brains in two. If a patient was shown an object in their right field of view, they had no difficulty naming it, but if they were shown the same object from the left, they couldn’t describe it. Speech and language are processed on the left side of the brain, but the information from the left eye is processed on the right. The patients were unable to say what they saw, but they could draw it. Psychologists wondered whether the differences between the two hemispheres could create two distinctive personality types, left-brained and right-brained. Myth-taken identity Give your brain a fun workout 1Boost your memory Look at this list of items for one minute, then cover the page and see how many you can remember: Difficult? Try again, but this time, make up a story in your head, linking the objects together in a narrative. …You get the idea. Make it as silly as you like; strange things are much more memorable than the mundane. 2Slow brain ageing Learning a new language is one of the best ways to keep your brain active. Here are four new ways to say hello: (che-sh-ch) (mar-ha-ba) (hud-yambo) ´´ It took 82,944 computer processors 40 minutes to simulate just one second of human brain activity, it’s that powerful TO DO: BANG ?!@# Planner Rational Problem solving Precise Logical Dog lovers Cat lovers Impulsive Emotional Creative Intuitive Spiritual Left Right 86 Duck Key Telephone Teacup Match Grape Bicycle Table “Duck opened his front door to find his table upturned, there were teacups everywhere” A microscopic image of the brain’s extremely complex neural network WorldMags.netWorldMags.net WorldMags.net
- 148. Thatintensepainyousometimesgetwhen youeaticecreamtoofastistechnically calledsphenopalatineganglioneuralgia, andit’srelatedtomigraineheadaches The Ophthalmic branch carries sensory messages from the eyeball, tear gland, upper nose, upper eyelid, forehead, and scalp. The Mandibular branch carries sensory signals from the skin, teeth and gums of the lower jaw, as well as tongue, chin, lower lip and skin of the temporal region. The Maxillary branch carries sensory messages from the skin, gums and teeth of the upper jaw, cheek, upper lip, lower nose and lower eyelid. CURIOUSQUESTIONS Brain freeze What is ‘brain freeze’? Thepainofabrainfreeze,alsoknowasanicecreamheadache,comesfrom yourbody’snaturalreactiontocold.Whenyourbodysensescold,itwants toconserveheat.Oneofthestepsittakestoaccomplishthisisconstricting thebloodvesselsnearyourskin.Withlessbloodflowingnearyourskin, lessheatiscarriedawayfromyourcore,keepingyouniceandwarm. Thesamethinghappenswhensomethingreallycoldhitsthebackofyourmouth. Thebloodvesselsinyourpalateconstrictrapidly.Whenthecoldgoesaway(because youswallowedtheicecreamorcoldbeverage),theyrapidlydilatebacktotheir standard,normalstate. Thisisharmless,butamajorfacialnervecalledthetrigeminalliesclosetoyour palateandthisnerveinterpretstheconstriction/dilationprocessaspain.Thelocation ofthetrigeminalnervecancausethepaintoseemlikeitscomingfromyourforehead. Doctorsbelievethissamemisinterpretationofbloodvesselconstriction/dilationisthe causeoftheintensepainofamigraineheadache. 148 “A major facial nerve called the trigeminal lies close to your palate” The trigeminal facial nerve is positioned very close to the palate. This nerve interprets palate blood vessel constriction and dilation as pain. WorldMags.netWorldMags.net WorldMags.net
- 149. 149 Discoverwhatisgoingoninsideablockednoseandwhyitgetsrunnywhenwe’reill What makes your nose run? Cilia Tinyhair-like structuresmove mucustowardsthe backofthethroatso thatitcanbe swallowed. Macrophage Cellsoftheimmune systemproducechemical mediatorslikehistamine, whichcauselocalblood vesselstobecomeleaky. Mucus Theglycoproteinsthat makeupmucusdissolvein water,formingagel-like substancethattrapsdebris. Themorewater,therunnier themucus. Epithelial cells Thenoseislined byepithelialcells, coveredincilia. Connective tissue Beneaththecells liningthenoseisa layerofconnective tissuethatisrich inbloodvessels. Goblet cell Theliningofthenose hasmanymucus- producinggobletcells. Itsurprisesmanypeoplebutthemain culpritresponsibleforablockedand runnynoseistypicallynotexcess mucusbutswellingandinflammation. Ifthenosebecomesinfected,oranallergic reactionistriggered,theimmunesystemproduces largequantitiesofchemicalmessengersthatcause thelocalbloodvesselsintheliningofthenoseto dilate.Thisenablesmorewhitebloodcellstoenter thearea,helpingtocombattheinfection,butitalso causesthebloodvesselstobecomeleaky,allowing fluidtobuildupinthetissues. Decongestantmedicinecontainsachemicalthat’s similartoadrenaline,whichcausestheblood vesselstoconstrict,stoppingthemfromleaking. Blood vessels Inflammatorychemicalsignals causebloodvesselstodilate, allowingwatertoseepintothe tissues,dilutingthemucusand makingitrunny. Whenwetalkabout‘bringing someoneoutofacoma’,weare referencingmedicallyinduced comas.Apatientwitha traumaticbraininjuryis deliberatelyputintoadeep stateofunconsciousnessin ordertoreduceswellingand allowthebraintorest.When thebrainisinjured, itbecomesinflamed.The swellingdamagesthebrain becauseitissquashedinside theskull. Doctorsinducethecoma usingacontrolleddoseof drugs.Tobringthepersonout ofthecoma,theysimplystop thetreatment.Bringingthe patientoutofthecomadoesn’t wakethemimmediately.They graduallyregainconsciousness overdays,weeksorlonger. Somepeoplemakeafull recovery,othersneed rehabilitationorlifetimecare andothersmayremain unawareoftheirsurroundings. How do we bring a person out of a coma? WorldMags.netWorldMags.net WorldMags.net
- 150. Honeyandlemoncanbe drankwarmasacomfort remedywhensuffering fromasorethroatorcold, andisapopulardrinkwithmany whoarefeelingunwell.Theideais thathoneycoatsthethroatand thereforeanyinflamedareaswillbe ‘protected’byalayerofhoney,while atthesametimesoothingpainful areas.Thismeansitwillbeless painfulwhentheseareascomeinto contactwithothersurfaceswhenyou eatorswallow. Lemonalsohelpstosettlethe stomachtoo,asitcontainsacid, which canbeparticularlyhelpful whenexperiencinganupsetstomach fromtheeffectsofacoldorother digestion-relatedillness. Why does hot honey and lemon help your throat when it’s sore? Theeardrumisathinmembranethathelpstotransmitsound.Air pressureisexertedonbothsidesoftheeardrum;withthe surroundingatmosphericpressurepushingitinwardswhileair beingdeliveredviaatubebetweenthebackofyournoseandthe eardrumpushesitoutwards.ThistubeiscalledtheEustachiantube,when youswallowotopensandasmallbubbleofairisabletomovecausinga‘pop’. Rapidaltitudechangesinplanesmakethe‘pop’muchmorenoticeable duetobiggerdifferencesinpressure.Airpressuredecreasesasaplane ascends;henceairmustexittheEustachiantubestoequalisethesepressures, againcausinga‘pop’.Conversely,asaplanedescends,theairpressurestarts toincrease;thereforetheEustachiantubesmustopentoallowthroughmore airinordertoequalisethepressureagain,causinganother‘pop’. Why do our ears ‘pop’ on planes? CURIOUSQUESTIONS Ears popping / Sore throats / Freckles 150 “Rapid altitude changes make the ‘pop’ much more noticeable” Frecklesareclustersofthepigmentmelanin.Itis producedbymelanocytesdeepintheskin,withgreater concentrationsgivingrisetodarkerskintones,and hence,ethnicity.Melaninprotectstheskinagainst harmfulultravioletsunlight,butisalsofoundinotherlocations aroundthebody,.Frecklesaremostlygeneticallyinherited,butnot always.Theybecomemoreprominentduringsunlightexposure, asthemelanocytesaretriggeredtoincreaseproductionofmelanin, leadingtoadarkercomplexion.Peoplewithfrecklesgenerallyhave paleskintones,andiftheystayintheSunfortoolongtheycan damagetheirskincells,leadingtoskincancerslikemelanoma. What are freckles? ©Thinkstock ©Thinkstock WorldMags.netWorldMags.net WorldMags.net
- 151. Liver Kidney Ureter 6. Processing Anaesthetic in the blood is filtered out by theliver and kidneys, then leaves the body in urine. The effects usually wear off a couple of hours after the initial injection. Bladder What is a memory?Memoryisthebrain’s abilitytorecall informationfromthepast anditgenerallyfallsinto threecategories–sensory,short-term andlong-term. Lookatthispagethencloseyour eyesandtrytorememberwhatit lookslike.Yourabilitytorecallwhat thispagelookslikeisanexampleof yoursensorymemory.Dependingon whetherornotthispageisimportant toyouwillbethedeterminingfactor inhowlikelyitisthatitwillgetpassed ontoyourshort-termmemory. Canyourememberthelastthing youdidbeforereadingthis?Thatis yourshort-termmemoryandisabit likeatemporarystoragefacilitywhere theless-importantstuffcandecay, whereasthemoreimportantstuffcan endupinthelong-termmemory. Oursensesareconstantlybeing bombardedwithinformation. Electricalandchemicalsignalstravel fromoureyes,ears,nose,touchand tastereceptorsandthebrainthen makessenseofthesesignals.When weremembersomething,ourbrain refiresthesameneuralpathways alongwhichtheoriginalinformation travelled.Youarealmostrelivingthe experiencebyrememberingit. Imaginejustoneofyourteeth.Ithastwo primarysections:thecrownlocatedabove thegumlineandtherootbelowit.The crowncomprisesthefollowinglayersfrom toptobottom:enamel,dentineandthepulpgum. Nervesbranchfromtheroottothepulpgum.The dentinerunstotherootandcontainsalargenumberof tubulesormicroscopicpores,whichrunfromthe outsideofthetoothrighttothenerveinthepulpgum. Peoplewithsensitiveteethexperiencepainwhen theirteethareexposedtosomethinghot,coldorwhen pressureisapplied.Theirlayerofenamelmaybe thinnerandtheymayhavearecededgumline exposingmoredentine.Therefore,theenameland gumsofferlessprotectionand,assuch,thisiswhat makestheirteethsensitive. Sensitivetoothpasteworksbyeithernumbingtooth sensitivity,orbyblockingthetubulesinthedentine. Thosethatnumbusuallycontainpotassiumnitrate, whichcalmsthenerveofthetooth.Thetoothpastes thatblockthetubulesinthedentineusuallycontaina chemicalcalledstrontiumchloride.Repeateduse buildsupastrongbarrierbypluggingthetubulesmore andmore. How does toothpaste for sensitive teeth work? 151 Thesciencebehindblockingpainexplained How epidurals work An epidural (meaning ‘above the dura’) is a form of local anaesthetic used to completely block pain while a patient remains conscious. It involves the careful insertion of a fine needle deep into an area of the spine between two vertebrae of the lower back. This cavity is called the epidural space. Anaesthetic medication is injected into this cavity to relieve pain or numb an area of the body by reducing sensation and blocking the nerve roots that transmit signals to the brain. The resulting anaesthetic medication causes a warm feeling and numbness leading to the area being fully anaesthetised after about 20 minutes. Depending on the length of the procedure, a top-up may be required. This form of pain relief has been used widely for many years, particularly post-surgery and during childbirth. 4. Absorption Over about 20 minutes the anaesthetic medication is broken down and absorbed into the local fatty tissues. 5. Radicular arteries The anterior and posterior radicular arteries run with the ventral and dorsal nerve roots, respectively, which are blocked by the drug. 3. Anaesthetic Through a fine catheter in the needle, anaesthetic is carefully introduced to the space surrounding the spinal dura. 1. Epidural space The outer part of the spinal canal, this cavity is typically about 7mm (0.8in) wide in adults. 2. Epidural needle After sterilising the area, a needle is inserted into the interspinous ligament until there is no more resistance to the injection of air or saline solution. WorldMags.netWorldMags.net WorldMags.net
- 152. CURIOUSQUESTIONS 152 | HowItWorks Caffeine / Blushing / Fainting 152 Whenweareawakethenaturally occurringbrainchemicaladenosine isdrawntofastmovingreceptorsin thebrain.Asadenosineattachesto thereceptorsitslowsthemdown,whichcausesus tofeelsleepy. Thereceptorcellsconfusecaffeinefor adenosinecellsandassuchwillinglybondtoit. Theactiondoesn’tslowdownthereceptor’s movementasadenosinewouldandasthespaceis usurpedtheyareunabletosenseadenosinesothe cellsspeedup,increasingneuronfiringinthe brain.Thepituaryglandinterpretsthisasafight orflightscenariosoreleaseshormonestoalertthe adrenalglandstoproduceadrenaline.Thisresults indilatedpupils,aracingheartandanincreasein bloodpressure.Theliveralsoreleasessugarinto thebloodstreamforaninstantenergyboost. What makes caffeine so addictive? Fainting,or‘syncope’,isa temporarylossofconsciousness duetoalackofoxygentothe brain.Itisprecededbydizziness, nausea,sweatingandblurredvision. Themostcommoncauseis overstimulationofthebody’svagusnerve. Possibletriggersofthisincludeintense stressandpain,standingupforlongperiods orexposuretosomethingunpleasant. Severecoughing,exerciseandeven urinatingcansometimesproduceasimilar response.Overstimulationofthevagus nerveresultsindilationofthebody’sblood vesselsandareductionoftheheartrate. Thesetwochangestogethermeanthatthe bodystrugglestopumpblooduptothe brainagainstgravity.Alackofbloodtothe brainmeansthereisnotenoughoxygenfor ittofunctionproperlyandfaintingoccurs. What makes us faint? Blushingoccurswhenanexcessofblood flowsintothesmallbloodvesselsjust underthesurfaceoftheskin.Facialskin hasmorecapillaryloopsandvessels,and vesselsarenearerthesurfacesoblushingismost visibleonthecheeks,butmaybeseenacrossthe wholeface.Thesmallmusclesinthevesselsare controlledbythenervoussystem. Blushingcanbeaffectedbyfactorssuchasheat, illness,medicines,alcohol,spicyfoods,allergic reactionsandemotions.Ifyoufeelguilty,angry, excitedorembarrassed,youwillinvoluntarily releaseadrenaline,whichsendstheautomatic nervoussystemintooverdrive.Yourbreathingwill increase,heartratequicken,pupilsdilate,bloodwill beredirectedfromyourdigestivesystemtoyour muscles,andyoublushbecauseyourbloodvessels dilatetoimproveoxygenflowaroundthebody;this isalltoprepareyouforafightorflightsituation.The psychologyofblushingremainselusive;some scientistsevenbelievewehaveevolvedtodisplay ouremotions,toactasapublicapology. Why and how do we blush? “Blushing can be affected by heat, illness, medicines and spicy foods” Red glow Cheeks turn red while blushing due to blood vessels being near the skin’s surface. Nervousness Being embarrassed releases adrenaline, which stimulates the nervous system. WorldMags.netWorldMags.net WorldMags.net
- 153. 153 1. Tea In a survey by the Food Standards Agency, the mean amount of caffeine found in tea was 40mg per cup. SOME CAFFEINE 2. Instant coffee The level of caffeine present in instant coffee was not much more with an average of 54mg of caffeine per regular serving. MORE CAFFEINE 3. Ground coffee Ground coffee, however, contains the most caffeine. The mean level was 105mg, in some cases ranging as high as 254mg per serving. MOST CAFFEINE Imageauthor:Pleple2000,2008 CAFFEINATED DRINKS HEAD HEAD2 Imageauthor:NaamaYm,2005 ©SciencePhotoLibrary Where is the self in the brain? Untilrecently,neuroscientistshadthoughtit fancifultospeculateaboutthephysicalsubstrates ofsuchhigh-levelphenomenaasconsciousness and‘theself’,butrecentadvancesinfunctional neuroimagingareenablingustomakesignificantin-roadsinto thesequestions.Researchershaveidentifiedacorebrain network,the‘default-modenetwork’,whichaccountsformuch ofthebrain’smetabolismandappearstosupportabackground levelofconsciousness,ofthesortassociatedwithday- dreamingormind-wandering.Crucially,thedefault-mode networkbecomesespeciallyactivatedduringself-judgments, aswellasotherhigh-level,species-specificbehaviourssuchas takinganotherperson’spointofview,orthinkingoutsideofthe momenttocontemplatethepastorfuture.Thedefault-mode networkdecreasesinactivityandconnectivityduringstatesof reducedconsciousnesssuchassleeporanaesthesia,andis knowntoexistonlyinaprimitiveformininfantsandlower primates.Usingfunctionalmagneticresonanceimaging (fMRI),werecentlyfoundthatthepsychedelicdrug,psilocybin, theactivecomponentof‘magicmushrooms’,alsodecreases activityandconnectivityinthedefault-modenetwork–ina mannerthatcorrelateswithlossofself,or‘ego-disintegration’. What is earwax? Eyebrowsareveryimportantfordiverting moisture,suchassaltysweat,awayfromour eyesduetotheirdistinctivearchshape. Thiswouldobviouslybeusefulfor allowingustoseeclearlyifitwasrainingorif weweresweatingalot.Itisquiteeasy toseehowthiscouldhavehadan evolutionaryadvantageintermsof escapingpredators.Sweatalsocauses irritationintheeyes. Why do we have eyebrows? Earwaxisasubstancethatcanbe foundintheearcanalofhumans andothermammals.Medicallyit isreferredtoascerumenand consistsofdeadskin,hairandwater-soluble secretionsfromtheouterearcanal.Itserves severalfunctions–oneofwhichisasan antibacterial,self-cleaninglubricant.Excess cerumenusuallyfindsitswayoutoftheear canalthroughthewashingofhairandjaw movement.Occasionallyitcancollectandget compactedwhichcanleadtotinnitus. WorldMags.netWorldMags.net WorldMags.net
- 154. CURIOUSQUESTIONS 72-hour deodorants / Fillings Discoverthechemistrythathelpsuscombatbodyodourforuptodaysatatime How 72-hour deodorants work Deodorants prevent the odour associated with sweating, either by masking it, or by killing the bacteria responsible. To make the effects last longer, the active ingredients are sometimes encased within microcapsules. As the capsules take up water from sweat they burst, releasing deodorising chemicals. By including capsules of a variety of sizes, each requiring a different amount of water to burst, the duration can be extended. Most deodorants also contain antiperspirants, which prevent sweating from occurring at all. These are usually aluminium- based compounds. The aluminium is taken up by the cells that line the openings of the ducts that carry sweat to the surface of the skin. As the aluminium moves into the cells, it takes water with it, causing the cells to swell and closing off the ducts. Depending on the type of aluminium compound used, the effect will last for different lengths of time. Antiperspirants cause cells to swell and the ducts to close up, preventing sweating altogether 154 | HowItWorks154 Compositeresinsarereplacingtraditional metalfillings,butwhataretheymadeof? Modern fillings Decay The decayed portion of the tooth is removed using a high-speed drill; this generates a solid platform for the filling to stick to. Base In deeper fillings, a cement base made from glass ionomer or zinc phosphate is added to insulate the nerve from temperature changes. Acid A controlled amount of acid is applied to the drilled tooth to generate micro-holes for the filling to bind to. Composite resin Dental composites are made from a resin matrix containing inorganic materials, like silica, for durability. Layering The liquid composite resin is applied in layers. After each layer, the composite is cured. Curing A light is used to trigger a chemical reaction within the resin, causing the material to harden. Primer A priming agent is brushed onto the prepared tooth surface to enable the filling to adhere properly. Finishing touches A piece of carbon paper is used to test whether the bite lines up properly, and the filling is smoothed down accordingly. Traditional silver-coloured ‘amalgam’ fillings are made from mixed metals, and are often comprised of around 50 per cent mercury. Historical evidence suggests that this type of filling has been in use since around 650 A.D, and despite the advances in composite materials, the amalgam filling is still in use to this day. There has been much controversy over the biological safety of amalgam fillings though, and concerns have been raised regarding mercury released into the body, as well as into the environment. However, as it stands, no causal link between health complaints and amalgam fillings has been proven. In fact, they still provide some advantages over composite fillings, and require significantly less repair and replacement. Is metal bad? Amalgam fillings require much less upkeep than their composite counterparts ©Thinkstock;SPL WorldMags.netWorldMags.net WorldMags.net
- 155. Phospholipid bilayer Every mitochondria has a double-layered surface composed of phosphates and lipids. Outer membrane The outer membrane contains large gateway proteins, which control passage of substances through the cell wall. ATP synthesis ATP is the basic energy unit of the cell and is produced by ATP synthase enzymes on the inner membrane at its interaction with the matrix. Mitochondrial DNA Mitochondria have their own DNA and can divide to produce copies. Inner membrane This layer contains the key proteins that regulate energy production inside the mitochondria, including ATP synthase. Inter-membrane space This contains proteins and ions that control what is able to pass in and out of the organelle via concentration gradients and ion pumps. Cristae The many folds of the inner membrane increase the surface area, allowing greater energy production for high-activity cells. Matrix The mitochondrial matrix contains the enzymes, ribosomes and DNA, which are essential to allowing the complex energy- producing reactions to occur. ©SPL Mitochondria are known as the batteries of cells because they use food to make energy. Muscle fibres need energy for us to move and brain cells need power to communicate with the rest of the body. They generate energy, called adenosine triphosphate (ATP), by combining oxygen with food molecules like glucose. However, mitochondria are true biological multi-taskers, as they are also involved with signalling between cells, cell growth and the cell cycle. Theyperform all of these functions by regulating metabolism - the processes that maintain life - by controlling Krebs Cycle which is the set of reactions that produce ATP. Mitochondria are found in nearly every cell in your body. They are found in most eukaryotic cells, which have nucleus and other organelles bound by a cell membrane. This means cells without these features, such as red blood cells, don’t contain mitochondria. Their numbers also vary based on the individual cell types, with high-energy cells, like heart cells, containing many thousands. Mitochondria are vital for most life – human beings, animals and plants all have them, although bacteria don’t. They are deeply linked with evolution of all life. It is believed mitochondria formed over a billion years ago from two different cells, where the larger cell enveloped the other. The outer cell became dependent on the inner one for energy, while the inner cell was reliant on the outer one for protection. This inner cell evolved to become a mitochondrion, and the outer cells evolved to form building blocks for larger cell structures. This process is known as the endosymbiotic theory, which is Ancient Greek for ‘living together within.’ Discoverhowmitochondriaproducealltheenergyyourbodyneeds What powers your cells? Take a tour of the cell’s energy factory Inside the mitochondria The number of mitochondria in a cell depends on how active that particular cell is and how much energy it requires to function. As a general rule, they can either be low energy without a single mitochondrion, or high energy with thousands per cell. Examples of high-energy cells are heart muscles or the busy liver cells, which are active even when you’re asleep, and are packed with mitochondria to keep functioning. If you train your muscles at the gym, those cells will develop more mitochondria as an adaptive mechanism to help provide energy. How many are in a cell? Mitochondria produce fuel for everyday activities such as exercise STRANGE BUTTRUE INHERITED AT BIRTH Who do you inherit mitochondria from? Answer: The DNA within mitochondria is only from your mother’s egg. The corresponding DNA from your father’s sperm is destroyed after fertilisation. This means researchers can track back unchanged maternal inheritance lines many hundreds of years.A Father B Mother C Grandparent 155 DID YOU KNOW? Mitochondrial disease occurs when mitochondria malfunction – there is a huge variety of symptoms WorldMags.netWorldMags.net WorldMags.net
- 156. CURIOUSQUESTIONS 156 At its most simple level, the brain is a series of interconnecting neurons that relay electrical signals between one another. They are ‘all or none’ transmitters as, like a computer, they either transmit a signal (like a binary ‘1’) or do not (‘0’). Different neurons are receptive to different stimuli, such as light, touch and pain. The complex activity of these neurons is then interpreted by various parts of the brain into useful information. For example, light images from the eye are relayed via the optic nerve to the occipital cortex located in the back of the skull, for interpretation of the scene in front of you. The generation and interpretation of thoughts is a more complex and less well understood process. In fact, it is a science of its own, where there are many definitions of what a ‘thought’ is, and of what defines consciousness. In an effort to better define these, doctors, scientists and psychologists have turned to novel imaging techniques to better understand the function of our minds. Research into understanding brain activity and function has led to some of the most advanced imaging techniques available. This has helped to treat conditions such as Alzheimer’s dementia, epilepsy and stroke, as well as mental illnesses where there is not necessarily a physical problem within the brain. It has also led to benefits for imaging other diseases in other parts of the body, including several forms of cancer. These advanced imaging techniques include scans to produce images of the anatomical structure of the brain, and interpretation of energy patterns to determine activity or abnormalities. Scientists have started to ascertain which parts of the brain function as we form different thoughts and experience different emotions. This means we are very much on the brink of seeing our own thoughts. Is it possible to see our thoughts?Thebrainisperhapsthemostvitalof thebody’svitalorgans,yetinmany waysit’salsotheleastunderstood How can we view the brain?Computed tomography (CT) This combines multiple X-rays to see the bones of the skull and soft tissue of the brain. It’s the most common scan used after trauma, to detect injuries to blood vessels and swelling. However, it can only give a snapshot of the structure so can’t capture our thoughts. Magnetic resonance imaging (MRI) MRI uses strong magnetic fields to align the protons in water molecules in various body parts. When used in the brain, it allows intricate anatomical detail to be visualised. It has formed the basis of novel techniques to visualise thought processes. Functional MRI (fMRI) This form of MRI uses blood- oxygen-level-dependent (BOLD) contrast, followed by a strong magnetic field, to detect tiny changes in oxygen-rich and oxygen-poor blood. By showing pictures to invoke certain emotions, fMRI can reveal which areas are active during particular thoughts. ©OliverStollmann ThisDTIviewofthe brainusesthehigh watercontentin neuronstoshowfine structureandactivity ThisCTscanofthebrainhasfused PETimagesoverit,showingactivity ofdifferentregionswhenthepatient isexposedtoarangeofstimuli ©SPL ©SPL Mind reading WorldMags.netWorldMags.net WorldMags.net
- 157. CT scan Fast and easily accessible 24 hours a day, these scans can identify life-threatening bleeding within the skull for neurosurgeons to stop. 3D MRI These 3D scans show intricate anatomical details of brain tumours, particularly in relation to the surrounding structures. This enables doctors to determine if they can be safely removed or not. PET scan This functional imaging is allowing researchers to test novel drugs and treatments to prevent progression of this serious brain disorder. 1. HEAD TRAUMA 2. BRAIN TUMOURS 3. ALZHEIMER’S ©ThierryGeoffroy ©Marvin101 HEAD HEAD2BRAIN SCANS CT scanning of the brain was invented in the early-SeventiesDID YOU KNOW? 157 Diffusion tensor imaging (DTI) This MRI variant relies on the direction of water diffusion within tissue. When a magnetic gradient is applied, the water aligns and, when the field is removed, the water diffuses according to a tissue’s internal structure. This allows a 3D image of activity to be built up. Positron emission tomography (PET) This bleeding-edge technology detects gamma rays emitted from biologically active tissues based on glucose. It can pick up unusual biological activity, such as that from cancer. There have been recent advances to combine PET with CT or MRI to obtain lots of data quickly. Picking apart the brain The cerebellum The cerebellum is responsible for fine movements and co-ordination. Without it, we couldn’t write, type, play musical instruments or perform any task that requires precise actions. The occipital cortex In the posterior fossa of the skull, this cortex receives impulses from the optic nerves to form images. These images are in fact seen upside down, but this area enables them to be interpreted the right way up. The sensory and motor cortexes The pre- and post-central gyri receive the sensory information from the body and then dispatch orders to the muscles, in the form of signals through motor neurons. The frontal lobes The frontal lobes of the folded cerebral cortex take care of thought, reasoning, decisions and memories. This area is believed to be largely responsible for our individual personalities. The brainstem Formed from the midbrain, pons and medulla oblongata, the brainstem maintains the vital functions without us having to think about them. These include respiration and heart function; any damage to it leads to rapid death. The pituitary gland This tiny gland is responsible for hormone production throughout the body, which can thus indirectly affect our emotions and behaviours. Imaging Alzheimer’sAlzheimer’s disease is a potentially debilitating condition, which can lead to severe dementia. The ability to diagnose it accurately and early on has driven the need for modern imaging techniques. The above image shows a PET scan. The right-hand side of the image (as you look at it) shows a normal brain, with a good volume and activity range. On the left-hand side is a patient affected by Alzheimer’s. The brain is shrunken with fewer folds, and a lower range of activity – biologically speaking, there are far fewer neurons firing. ©SPL ©Alamy WorldMags.netWorldMags.net WorldMags.net
- 158. 158 Brain activity Electroencephalograms (EEGs) show that the electrical activity in the brain drops to a state deeper than sleep, mimicking a coma. Pain neurons Unlike with local anaesthetic, pain neurons still fire under general anaesthesia, but the brain does not process the signals properly. Airway Loss of consciousness and muscle relaxation suppress breathing and prevent coughing, so a tube and ventilator are used to maintain the airway. Nil by mouth General anaesthetics suppress the gag reflex and can cause vomiting, so to prevent choking patients must not eat before an operation. Muscle relaxation A muscle relaxant is often administered with the anaesthetic; this causes paralysis and enables lower doses of anaesthetic to be used. Memory General anaesthetic affects the ability to form memories; the patient doesn’t remember the operation and often won’t recall coming to either. Heart rate The circulatory system is slowed by anaesthetic, so heart rate, blood pressure and blood oxygen are all continuously monitored. Nausea Many anaesthetics cause nausea. Often antiemetic drugs that prevent vomiting are given after surgery. What happens to various parts of the body when we’re put under? The body under general anaesthetic Anaestheticsareaformofdrugwidely usedtopreventpainassociatedwith surgery.Theyfallintotwomain categories:localandgeneral.Local anaestheticscanbeeitherapplieddirectlytothe skinorinjected.Theyareusedtonumbsmallareas withoutaffectingconsciousness,sothepatientwill remainawakethroughoutaprocedure. Localanaestheticsprovideashort-termblockade ofnervetransmission,preventingsensoryneurons fromsendingpainsignalstothebrain.Information istransmittedalongnervesbythemovementof sodiumionsdownacarefullymaintained electrochemicalgradient.Localanaestheticscut offsodiumchannels,preventingtheionsfrom travellingthroughthemembraneandstopping electricalsignalstravellingalongthenerve. Localanaesthesiaisn’tspecifictopainnerves,soit willalsostopinformationpassingfromthebrainto themuscles,causingtemporaryparalysis. Generalanaesthetics,meanwhile,areinhaled andinjectedmedicationsthatactonthecentral nervoussystem(brainandspinalcord)toinducea temporarycoma,causingunconsciousness,muscle relaxation,painreliefandamnesia. It’snotknownforsurehowgeneralanaesthetics ‘shutdown’thebrain,butthereareseveralproposed mechanisms.Manygeneralanaestheticsdissolvein fatsandarethoughttointerferewiththelipid membranethatsurroundsnervecellsinthebrain. Theyalsodisruptneurotransmitterreceptors, alteringtransmissionofthechemicalsignalsthatlet nervecellscommunicatewithoneanother. Byinterferingwithnervetransmissionthesespecialdrugsstop painsignalsfromreachingthebrainduringoperations How anaesthesia works If large areas need to be anaesthetised while the patient is still awake, local anaesthetics can be injected around bundles of nerves. By preventing transmission through a section of a large nerve, the signals from all of the smaller nerves that feed into it can’t reach the brain. For example, injecting anaesthetic around the maxillary nerve will not only generate numbness in the roof of the mouth and all of the teeth on that side, but will stop nerve transmission from the nose and sinuses too. Local anaesthetics can also be injected into the epidural space in the spinal canal. This prevents nerve transmission through the spinal roots, blocking the transmission of information to the brain. The epidural procedure is often used to mollify pain during childbirth. Comfortably numb ©Getty CURIOUSQUESTIONS Anaesthesia WorldMags.netWorldMags.net WorldMags.net
- 159. KEY DATES 1900s Stress and diet are blamed for stomach ulcers. Patients are prescribed rest and bland food, like oatmeal. 2005 Barry Marshall and Robin Warren are awarded a joint Nobel prize for their 1982 discovery. 1996 The first antibiotics are approved for treatment of the infection that causes stomach ulcers. 1982 Two Australian scientists show that H pylori causes stomach ulcers, but some are sceptical to begin with. 1970 Stomach acid is proposed as the cause of gastric ulcers and antacid treatment is introduced to counter it.STOMACH ULCERS 159 Originallythoughttobetheresultofstress,wenowknowthatbacteriaaretheculprits… What causes stomach ulcers? Normallyathicklayerof alkalinemucus effectivelyprotectsthe cellsliningthestomach fromthelowpHofstomachacid.If thismucusbecomesdisrupted, however,acidcomesintocontact withtheorgan’slining,damaging thecellsandresultinginanulcer. Around60percentofstomach ulcersarecausedbyinflammation duetochronicinfectionbythe bacteriumHelicobacterpylori. Bacterialby-productsdamagethe cellsliningthestomach,causinga breakdownofthetoplayersoftissue. Non-steroidalanti-inflammatory drugs(NSAIDs),likeibuprofenand aspirin,alsocausestomachulcersin largedoses.Theydisruptthe enzymesresponsibleformucus production,diminishingthe protectivebarrier. Enzymes Hpyloriproduceproteases andphospholipases– enzymesthatdamagethe proteinsandcell membranesofthe stomachcells. Neutralising stomach acid Hpyloribreak downureato makeammonia. Thisisusedto produce bicarbonateto neutralise dangerous stomachacid. Gastrin Theinflammatory responseincreases productionofthe hormonegastrin.This inturnstimulatesthe formationofmore stomachacid. Helicobacter pylori Bacteriaburrowthroughthe mucusinthestomachtoescape damagebyacid.Theysticktothe cellsoftheinteriorlining. The scientists who revealed bacteria caused gastric ulcers had to drink their own experiment to prove it! Ammonia Theammoniamadeby thebacteriaasadefence againstaciddamagesthe cellsliningthestomach, causinginflammation. Damage Asthecellsbecome damagedawoundopens upinthestomachwall.If thisbecomesdeepenoughit canperforatebloodvessels causingbleeding. DID YOU KNOW? Once bacteria breach the stomach lining, it can no longer protect itself from its acidic contents… An ulcer in the making Ulcersaresmalllesionsusually triggeredbyphysicaldamagetothe insideofthemouth,forexample bitingyourcheekaccidentally, eatingsharpfoodorbrushingyour teeth.Theyareveryrarely contagiousandusuallyhealwithin tendays.Recurrentulcershavea varietyofcauses,themostcommon beingstressandhormonalchanges. Inothercases,recurrentulcersmay besymptomaticofconditions includingB12orirondeficiencies, gastrointestinaldiseasesor immunosuppressantdiseasessuch asHIV.Ulcersaresometimes triggeredbysensitivitytocertain foodsincludingstrawberries, almonds,tomatoes,cheese, chocolateandcoffee. Why do we sometimes get mouth ulcers? “They are rarely contagious and usually heal in ten days” ©Alamy WorldMags.netWorldMags.net WorldMags.net
- 160. CURIOUSQUESTIONS 160 | HowItWorks Hair growth / Blond hair 160 How quickly does human hair grow? Humanhairgrowsonaverage1.25centimetres(0.5inches) permonth,whichisequivalenttoabout15centimetres (sixinches)peryear.Thereareseveralvariablesthatcan affecthair’sgrowthratesuchasage,healthandgenetics. Eachhairgrowsinthreestages,thefirstbeingtheanagenphase wheremostgrowthoccurs.Thelongeryourhairremainsinthisstage dictateshowlongandquicklyitdevelops;thiscanlastbetweentwo andeightyearsandisfollowedbythecatagen(transitional)and telogen(resting)phases.Hairgrowthratesvaryacrossdifferentareas ofthehead,withthatonthecrowngrowingthefastest. “Each hair grows in three stages, the first being the anagen phase where most growth occurs” ©Thinkstock Dryblondhairhasarough,tiledsurface–somethinglikefish scales.Whenlightrayshitthesescales,theybounceoffinall directions.Someofthelightreachesyoureyesandmakesthe hairlookbrighter;it’slikeshiningatorchonthehair. Whenyouwashyourhair,athinfilmofwaterformsaroundeachfibre. Lightrayspassintothefilmofwater,bouncearoundinside,andthere’s achancethey’llgetabsorbedbythehair.Sincethelightgetstrapped insidethewater,lessofitreachesyoureyes,sothehairactuallyappears lotdarker. Why does blond hair look darker when it’s wet? “A thin film of water forms around each fibre” WorldMags.netWorldMags.net WorldMags.net
- 161. 161 Howcanalittleelectricitybeusedtofixaheartthat’sbeatingoff-kilter? Correcting heart rhythms Atrial fibrillation Normal ECG 1. Paddles Two metallic plates are placed on the patient’s chest across the heart. 8. Low energy Resetting an abnormal heart beat uses fairly low-energy shocks of just 50-200 joules. 5. Electric shocks Low-energy electric shocks are delivered to the heart through the electrodes. 6. Natural pacemaker The heart has its own internal pacemaker known as the sinoatrial node. Delivering a small electric shock to this resynchronises the organ’s natural electrical activity. 3. Timing the shock The heart is vulnerable when it is between beats, so to prevent a cardiac arrest, the shock is timed to coincide with the pumping of the ventricles. 4. Arrhythmia If the heart beats too fast, or at an irregular pace, it becomes unable to effectively pump blood around the body. 2. Conductive gel A saltwater-based gel is used so the current can travel from the electrodes and through the skin. 7. Cardioversion machine The machine records the electrical activity of the heart and calculates the electric shocks required to restore the organ to its normal rhythm. BEFORE CARDIOVERSION AFTER CARDIOVERSION Youmaynotrealise,butactuallyeveryonehasan Adam’sapple,butmen’sareusuallyeasiertoseein theirthroat. It’sabumpontheneckthatmoves whenyouswallow,namedafterthebiblicalAdam. Supposedly,it’sachunkoftheGardenofEden’sforbiddenfruit stuckinhisdescendants’throats,butit’sactuallyabumponthe thyroidcartilagesurroundingthevoicebox.Thyroidcartilageis shield-shapedandtheAdam’sappleisthebitatthefront. Whydomen’sAdam’sapplesstickoutmore?Thisispartly becausetheyhaveboniernecks,butitisalso becausetheir larynxesgrowdifferentlyfromwomen’sduringpubertyto accommodatetheirlonger,thickervocalcords,whichgivethem deepervoices. Do women have an Adam’s apple? Simply put, too much salt is bad for you as it increases the demand on your heart to pump blood around the body. This is because when you eat salt it causes the body to retain increased quantities of water, which increases your blood pressure, and this places more strain on your heart. As such, most doctors recommend moderating daily salt intake. Why’s salt bad for the heart? WorldMags.netWorldMags.net WorldMags.net
- 162. Discoverhowthesmall intestineisreallytoblame… Wavesofinvoluntarymuscle contractionscalledperistalsischurn thefoodweeattosoftenitand transportitthroughthedigestive system.Thecontractionsarecausedbystrong musclesintheoesophaguswall,whichtakejust tensecondstopushfooddowntothestomach. Musclesinthestomachchurnfoodandgastric juicestobreakitdownfurther. Then,afterfourhours,thesemi-digested liquefiedfoodmovesontothesmallintestine whereyetmorepowerfulmusclecontractions forcethefooddownthroughtheintestine’sbends andfolds.Thisiswheretherumblingoccurs.Air fromgaseousfoodsorthatswallowedwhenweeat –oftenduetotalkingorinhalingthroughthenose whilechewingfood–alsoendsupinthesmall intestine,andit’sthiscombinationofliquidand gasinasmallspacethatcausesthegurglingnoise. Rumblingislouderthelessfoodpresentinthe smallintestine,whichispartlywhypeople associaterumblingtummieswithhunger.The otherreasonisthatalthoughthestomachmaybe clear,thebrainstilltriggersperistalsisatregular intervalstoridtheintestinesofanyremaining food.Thiscreatesahollowfeelingthatcausesyou tofeelhungry. What causes a rumbling stomach? Oesophagus Thismuscularpipe connectsthethroat tothestomach. Large intestine Foodpassesfromthe smallintestinetothe largeintestinewhere itisturnedintofaeces. Small intestine Here,liquidfood combinedwithtrapped gasescanmakeforsome embarrassingnoises. Lungs Liver Rectum CURIOUSQUESTIONS Rumbling stomach / Seasickness 162 “Then, after four hours, the semi- digested liquefied food moves to the small intestine” Stomach Foodischurnedand mixedwithgastric juicestohelpitto breakdown. Are seasickness and altitude sickness the same thing? No,they’renot–altitudesicknessisacollection ofsymptomsbroughtonwhenyou’resuddenly exposedtoahigh-altitudeenvironmentwith lowerairpressuresolessoxygenentersourbody. Thesymptomscanincludeaheadache,fatigue, dizzinessandnausea. Seasickness,ontheotherhand,isamore generalfeelingofnauseathat’sthoughttobe causedwhenyourbrainandsensesget‘mixed signals’aboutamovingenvironment–for instance,whenyoureyestellyouthatyour immediatesurroundings(suchasaship’s cabin)arestillasarock,whileyoursenseof balance(andyourstomach!)tellyousomething quitedifferent. Thisisthereasonwhyclosingyoureyesor takingaturnoutondeckwilloftenhelp,asit reconcilesthetwoopposingsensations. ©Thinkstock WorldMags.netWorldMags.net WorldMags.net
- 163. “A malignant melanoma is a rare kind of skin cancer that can occur in melanocytes” Thesesmallskinblemishesare common,butwhataretheyandwhy mustwekeepacloseeyeonthem? Amoleontheskin,ora melanocyticnaevus,isan abnormalcollectionofthe pigmentcellscalled melanocytes.Somemolescanbepresentat birth(congenitalmelanocyticnaevi)but mostdevelopspontaneouslylaterinlife, usuallyasaresultofexposuretosunlight. Molesareoftenbrownorblack(pigmented naevi)andareusuallyroundoroval,but theycanbeavarietyofdifferentshapes andsizes.Growthandchangeovertimeis quitenormal. Molessoundprettyunremarkableand areharmlessinnature,andyetwemustbe vigilantifanewoneappearsontheskinor ifanexistingmolebeginstochange.A malignantmelanomaisararekindofskin cancerthatcanoccurinmelanocytes. Althoughrare,malignantmelanomas causethemajorityofthedeathsrelatedto skincancer.Ifyou’reparticularlymoley you’remoresusceptibletomelanomaand shouldtrytoavoidtoomuchsunlight. Molestowatcharedysplasticnaevi, whicharelarge,irregularlyshapedmoles ofmixedcolouration.Theyoftenhave paler,jaggededgeswithdarkercentres andtendtobeaccompaniedbyalotof othermolesonthebody. What are moles? Dermis The dermis is the layer that consists of blood vessels, glands and nerve endings. Melanocyte The skin’s natural pigment, melanin, is a protein produced in cells called melanocytes. Melanocytes are usually spread evenly throughout the skin for even colour. Melanin also absorbs UV radiation. Melanoma People with a family history of malignant melanomas and those who have been exposed to a lot of sunlight are most at risk from this uncontrollable growth of pigment cells. Epidermis This is the outer layer of your skin and it contains tough, flat cells. Melanocytes are located in the dermis and epidermis. Amalignantmelanoma canspelltrouble 163 Hairs Hairs are made from filamentous biomaterial that grows from follicles in the dermis. WorldMags.netWorldMags.net WorldMags.net
- 164. CURIOUSQUESTIONS 164 | HowItWorks Brain control / Laughing 164 Do we control our brains or do our brains control us? AnexperimentattheMaxPlanckInstitute,Berlin,in2008 showedthatwhenyoudecidetomoveyourhand,thedecision canbeseeninyourbrain,withanMRIscanner,beforeyouare awareyouhavemadeadecision.Thedelayisaroundsix seconds.Duringthattime,yourmindismadeupbutyourconsciousness doesn’tacknowledgethedecisionuntilyourhandmoves.One interpretationofthisisthatyourconsciousness–thethingyouthinkofas ‘you’–isjustapassengerinsideadeterministicautomaton.Your unconsciousbrainandyourbodygetonwithrunningyourlife,andonly reportbacktoyourconsciousmindtopreserveasenseoffreewill.Butit’s justasvalidtosaythatwhenyoumakeadecision,there’salways backgroundprocessinggoingon,whichtheconsciousmindignoresfor convenience.Inthesameway,youreyeprojectsanupside-downimage ontoyourretina,butyourunconsciousbrainturnsittherightwayaround. Laughing can sometimes be completely involuntary and involves a complex series of muscles, which is why it’s so difficult to fake and also why an active effort is required to suppress laughter in moments of sudden hilarity at inopportune moments. In the face, the zygomaticus major and minor anchor at the cheekbones and stretch down towards the jaw to pull the facial expression upward; on top of this, the zygomaticus major also pulls the upper lip upward and outward. The sound of our laugh is produced by the same mechanisms which are used for coughing and speaking: namely, the lungs and the larynx. When we’re breathing normally, air from the lungs passes freely through the completely open vocal cords in the larynx. When they close, air cannot pass, however when they’re partially open, they generate some form of sound. Laughter is the result when we exhale while the vocal cords close, with the respiratory muscles periodically activating to produce the characteristic rhythmic sound of laughing. The risorius muscle is used to smile, but affects a smaller portion of the face and is easier to control than the zygomatic muscles. As a result, the risorius is more often used to feign amusement, hence why fake laughter is easy to detect by other humans. What happens when we laugh? Gelotologyisthestudy oflaughterandits effectsonthe humanbody ©Alamy Whichmusclesreactwhenwefind somethingfunnyandwhyis laughtersohardtofake? “Laughter is produced by the same mechanisms used for coughing and speaking” WorldMags.netWorldMags.net WorldMags.net
- 165. 165 Dust,watervapourandpollutionintheairwillrarelyletyouseemorethan 20kilometres,evenonaclearday.Often,thecurvatureoftheEarthgetsin thewayfirst–egatsealevel,thehorizonisonly4.8kmaway.OnthetopofMt Everest,youcouldtheoreticallyseefor339km,butinpracticecloudgetsin theway.Foratrulyunobstructedview,lookup.Onaclearnight,youcansee theAndromedagalaxywiththenakedeye,whichis2.25millionlightyearsaway. What is the maximum distance the human eye can see? Ourlineofsightcanbeimpededby manythings,frompollutiontothe curvatureoftheEarth Atthebackoftheeyeontheretina,there aretwotypesofphotoreceptors(cells whichdetectlight).Conesdealwith colourandfinedetailandactinbright light,whilerodsdealwithvisioninlow-light situations.Inthefirstfewminutesofmovingintoa darkroom,conesareresponsibleforvisionbut provideapoorpicture.Oncetherodsbecomemore active,theytakeoverandcreateamuchbetter pictureinpoorlight.Onceyoumovebackintolight, therodsareresetandsodark-adaptionwilltakea fewmomentsagain.Soldiersaretrainedtocloseor coveroneeyeatnightwhenmovinginandoutofa brightroom,orwhenusingatorch,toprotecttheir nightvision.Oncebackinthedark,theyreopenthe closedeyewiththerodsstillworkingand,asa result,maintaingoodvision.Thisallowsthemto keepoperatinginapotentiallyhostileenvironment atpeakoperationalefficiency.Giveitatrynexttime yougetupinthemiddleofthenight,itmayhelpyou avoidtrippingoverinthedark. Why do eyes take a while to adjust to dark? What is dandruff? Dandruffiswhendeadskincellsfalloffthescalp.This isnormal,asourskinisalwaysbeingrenewed.About halfthepopulationoftheworldsuffersfroman excessiveamountofthisshedding,whichcanbe triggeredbythingsliketemperatureortheincreasedactivityofa microorganismthatnormallylivesineveryone’sskin,knownas malasseziaglobosa.Dandruffisnotcontagiousandtherearemany treatmentsavailable,themostcommonisspecialisedshampoo. ©Horoporo WorldMags.netWorldMags.net WorldMags.net
- 166. CURIOUSQUESTIONS Allergies / Eczema ©Alamy;JKadavoor;Thinkstock The histamine increase can cause itching, leading to open sores Whatcausestheskintoreacttootherwiseharmlessmaterial? Eczema explained Eczema is a broad term for a range of skin conditions, but the most common form is atopic dermatitis. People with this condition have very reactive skin, which mounts an inflammatory response when in contact with irritants and allergens. Mast cells release histamine, which can lead to itching and scratching, forming sores open to infection. There is thought to be a genetic element to the disease and a gene involved in retaining water in the skin has been identified as a potential contributor, but there are many factors. Eczema can be treated with steroids, which suppress immune system activity, dampening the inflammation so skin can heal. In serious cases, immunosuppressant drugs – used to prevent transplant rejection – can actually be used to weaken the immune system so it no longer causes inflammation in the skin. What happens inside the body when eczema flares up? Under the skin Allergen Eczema is commonly triggered by the same things as many allergies – anything from pet hair to certain types of food. Water loss The skin is less able to retain water, leading to dryness and irritation. Inflammatory response The immune system produces a response to allergens beneath the skin, leading to redness, itching and also inflammation. Allergen entry route The cells of the skin are normally tightly bound together to prevent contaminants from entering the body, but in eczema there are gaps. Ceramides The membranes of skin cells contain waxy lipids to prevent moisture evaporation, but these are often deficient in eczema. 166 | HowItWorks166 “People who are likely to develop allergies have a condition known as ‘atopy’” Why do some people have allergies and some don’t? Allergies can be caused by two things: host and environmental factors. Host is if you inherit an allergy or are likely to get it due to your age, sex or racial group. Environmental factors can include things such as pollution, epidemic diseases and diet. People who are likely to develop allergies have a condition known as ‘atopy’. Atopy is not an illness but an inherited feature, which makes individuals more likely to develop an allergic disorder. Atopy tends to run in families. The reason why atopic people have a tendency to develop allergic disorders is because they have the ability to produce the allergy antibody called ‘Immunoglobulin E’ or ‘IgE’ when they come into contact with a particular substance. However, not everyone who has inherited the tendency to be atopic will develop an allergic disorder. ©Thinkstock WorldMags.netWorldMags.net WorldMags.net
- 167. 167 “The purple is given by haemoglobin” Why do bruises go purple? Sometimes we trip over or hurt ourselves in other ways. When it happens some of our blood vessels break, blood piles up under our skin and we can see this as a bruise. These nasty things have the familiar ‘black and blue’ or purple appearance in the beginning but gradually change into different colours. The purple colour is given by haemoglobin, a protein that carries the oxygen in our red blood cells. Our body reacts to this with some white blood cells called phagocytes ‘eating up’ the materials in the bruise. As the phagocytes degrade the haemoglobin, they turn it into other molecules. Different molecules show different colours and the bruise will change colour with time to green, yellow and brown. When everything has been cleared up by your immune system the bruise disappears and you’re ready to bump into something else. A rare condition called aquagenic urticaria is often referred to as an allergy to water. The symptoms of aquagenic urticaria are painful but generally not fatal. Contact with water- containing substances can bring out sore hives on the surface of the skin, cause a burning sensation and induce headaches. Because saliva contains water, the condition hinders intimacy. Death could occur when water is swallowed if the throat swells up, blocking the airway. The root cause is unknown. One hypothesis is that H2O generates a toxic compound in the outer layers of the skin, prompting the release of histamines. Reactions can sometimes be controlled with antihistamines. Is it possible for humans to have an allergy to water? Aquagenic urticaria mainly occurs in women and can affect parts, or the whole, of the body Is cholesterol bad for you? Blood Restriction of blood flow in the arteries can lead to angina, strokes and heart attacks. Isthissubstanceasevilaswehear? Cholesterolisafattymoleculeinthebloodand,generally speaking,havingtoomuchisbad:itcansticktothewallsof yourarteriesandincreasetheriskofheartdisease.Most foods,withtheexceptionofoffal,eggsandshellfish,don’t containanycholesterol,butmanycontainsaturatedfats,whichare turnedintocholesterolbytheliver.However,cholesterolitselfisn’t unhealthy–infact,youwouldn’tbeabletolivewithoutit.Thebodyuses cholesterolasakindofpadding,coatingtheoutermembranesofallour cellsandinsulatingnervefibres,helpingsignalstravelproperlytoand fromthebrain.It’salsoafundamentalpartoftheendocrinesystem,as allsteroidhormones(egoestrogen)aresynthesisedfromcholesterol. Importantly,agood,balanceddietandregularexercisecankeep cholesteroleasilywithinahealthyrangeformostpeople. “Cholesterol itself isn’t unhealthy – in fact, you wouldn’t be able to live without it” ©SPL Plaque Artery walls thicken with further deposits of cholesterol and connective tissue, which can lead to a deadly blockage. Artery wall Wear and tear comes with age, and a diet high in saturated fat can lead to fatty buildup on artery walls. WorldMags.netWorldMags.net WorldMags.net
- 168. Gas exchange occurs in the lungs, where toxic gases (carbon dioxide) are exchanged for fresh air with its unused oxygen content. Of all the processes in the body that keep us functioning and alive, this is the most important. Without it, we would quickly become unconscious through accumulation of carbon dioxide within the bloodstream, which would poison the brain. The two lungs (left and right) are made up of several lobes, and the fundamental building blocks of each are the tiny alveolus. They are the final point of the respiratory tract, as the bronchi break down into smaller and smaller tubes, leading to the alveoli, which are grouped together and look like microscopic bunches of grapes. Around the alveoli is the epithelial layer – which is amazingly only a single cell thick – and this is surrounded by extremely small blood vessels called capillaries. It is here that vital gas exchange takes place between the fresh air in the lungs and the deoxygenated blood within the capillary venous system on the other side of the epithelial layer. The alveoli of the lungs have evolved to become specialised structures, maximising their efficiency. Their walls are extremely thin and yet very sturdy. Pulmonary surfactant is a thin liquid layer made from lipids and proteins that coats of all the alveoli, reduces their surface tension and prevents them crumpling when we breathe out. Without them, the lungs would collapse. Thelungsarefilledwithtiny balloon-likesacsthatkeepyoualive How do alveoli help you breathe? 168 ©DKImages;Thinkstock How alveoli enable gas exchange Alveoli anatomy The alveoli function to allow gas exchange, but since they’re so small, they can’t move new air inside and out from the body without help. That’s what your respiratory muscles and ribs do, hence why your chest moves as you breathe. The diaphragm, which sits below your heart and lungs but above your abdominal organs, is the main muscle of respiration. When it contracts, the normally dome-shaped diaphragm flattens and the space within the chest cavity expands. This reduces the pressure compared to the outside atmosphere, so air rushes in. When the diaphragm relaxes, it returns to its dome shape, the pressure within the chest increases and the old air – now full of expired carbon dioxide – is forced out again. The muscles between the ribs (called intercostal muscles) are used when forceful respiration is required, such as during exercise Try taking a deep breath and observe how both your chest expands to reduce the pressure! Breathe in, breathe out Deoxygenated blood arrives The capillary veins bring deoxygenated blood from the right side of the heart, which has been used by the body and now contains toxic CO2 . One cell thick The alveolus wall is just one cell thick, separated from the blood capillaries by an equally thin basement membrane. Type I pneumocytes These large, flattened cells form 95 per cent of the surface area of an alveolus, and are the very thin diffusion barriers for gases. Type II pneumocytes These thicker cells form the remaining surface area of the alveoli. They secrete surfactant, which prevents the thin alveoli collapsing. Macrophages These are defence cells that digest bacteria and particles present in air, or that have escaped from the blood capillaries. Oxygenated blood The freshly oxygenated blood is taken away by capillaries and enters the left side of the heart, to be pumped through the body. CURIOUSQUESTIONS Alveoli anatomy WorldMags.netWorldMags.net WorldMags.net
- 169. How do dilating eye drops work? 169 A better look inside the eye Before and after Contracted pupil A contracted pupil will appear much smaller and let less light into the eye, which makes it difficult to see the retina and optic nerve inside. Ray of light The size of the pupil will determine how much light enters the eye. Dilated pupils let in more light, which means you can see a larger portion of the retina and optic nerve. Dilated pupil Dilating eye drops will temporarily paralyse the muscle that constricts the pupil, which means the pupil will remain dilated for much longer. Retina This light-sensitive tissue converts incoming light into electrical impulses. These impulses are then sent to the optic nerve. Optic nerve The optic nerve carries electrical impulses from the retina to the brain, which then interprets them as visual images. The lens It is positioned behind the pupil and helps focus light onto the retina. Some dilating eye drops relax the muscle around it to prevent the lens from focusing. Our eyes need good care to stay healthy Discoverhowthesemega-headachesstrike Why do we get migraines? 169 Those who suffer from migraines know they are a constant concern as they are liable to strike at any time. Essentially, a migraine is an intense pain at the front or on one side of the head. This usually takes the form of a heavy throbbing sensation and can last as little as an hour or two and up to a few days. Other symptoms of a migraine include increased sensitivity to light, sound and smell, so isolation in a dark and quiet room often brings relief. Nausea and vomiting is also often reported, with pain sometimes subsiding after the sufferer has been sick. It is thought that migraines occur when levels of serotonin in the brain drop rapidly. This causes blood vessels in the cortex to narrow, which is caused by the brain spasming. The blood vessels widen again in response, causing the intense headache. Emotional upheaval is often cited as a cause for the drop in serotonin in the brain, as is a diet in which blood-sugar levels rise and fall dramatically. Discoverhowtheyareusedtodiagnoseandtreateyeconditions Sight is one our most important senses, so maintaining good eye health is absolutely essential. However, eyesight problems can be difficult to detect or treat on the surface, so specialist eye doctors will often use dilating eye drops in order to get a better look inside the eye at the lens, retina and optic nerve. The drops contain the active ingredient atropine, which works by temporarily relaxing the muscle that constricts the pupil, enabling it to remain enlarged for a longer period of time so a thorough examination can be performed. Some dilating eye drops also relax the muscle that focuses the lens inside the eye, which allows an eye doctor or optometrist to measure a prescription for young children who can’t perform traditional reading tests. Dilating eye drops are not only used to help perform procedures, they may also be administered after treatment, as they can prevent scar tissue from forming. They are also occasionally prescribed to children with lazy-eye conditions, as they will temporarily blur vision in the strong eye, causing the brain to use and strengthen the weaker eye. 1People with blue eyes all share a common ancestor. A genetic mutation about 10,000 years ago gave someone blue eyes, when everyone else’s were brown. 2Your eyes will blink around 15-20 times per minute and it last for around 100 milliseconds. You also blink more when talking than when reading. 3Technically, you see with your brain and not your eyes. Poor vision sometimes stems from problems with the visual cortex of the brain and not the eye itself. 4Tears are not only an emotional response; they also help prevent your eyes from drying up and get rid of any irritating particles that could cause damage. 5On average, a human eyeball is around 2.5cm (1in) in diameter and weighs as little as 7.5g (0.25oz). A giant squid’s eyeball is ten times as big as a human’s. Blue eyes Blinking Sight Tears Measurements 5TOP FACTS IN YOUR EYES DID YOU KNOW? SAD is more common in women and people between the ages of 15 and 55 WorldMags.netWorldMags.net WorldMags.net
- 171. 1Although sadly this pregnancy did not reach full term and no babies survived, a woman in Argentina was observed to have 12 foetuses inside her womb from natural conception. 12 foetus world record 2A Malaysian mother gave birth to five boys and four girls in March 1999 – none survived over six hours. Another set of nonuplets suffered a similar fate in Sydney in 1971. Nonuplets exist 3With regard to DZ twins, there is seen to be a higher prevalence of these twins in black Africans, and a lower incidence than to be expected in Oriental mothers. Race affects conception 4The highest recorded number of children had by one woman is the first wife of Feodor Vassilyev, who lived in the 1700s. She gave birth to an incredible 69 children. Most children 5With regard to quadruplets, the average gestation period is just 32 weeks – that’s eight weeks shorter than usual, primarily due to the size restriction of the womb. Quad gestation 171 Therearemanydifficultieswithtwin pregnancies–mainlyduetothelimitedsize ofthemother’swomb.Multiplepregnancies rarelyreachfulltermduetotheselimits, twinsaveragingataround37weeks.Also, becauseofthelackofspaceandeggssplitting inthewomb,furthercomplicationssuchas conjoinedtwinscanoccur.Conjoinedtwins canbeaproblemdependantonwhere they’rejoined.Ifitisbyavitalorganorbone structure,oneorbothmaydiefollowingbirth astheygrow–orduringanoperationto separatethem. Itisalsosuspectedthatasmanyasonein eightpregnanciesmayhavestartedoutasa potentialmultiplebirth,butoneormoreofthe foetusesdoesnotprogressthrough developmenttofullterm. Multiple pregnancies, multiple problems? Monozygotic(MZ),oridentical,twinsareformedbythe eggsplittingsoonafterfertilisation,andfromthose identicalsplitgroupsofcells,twoseparatefoetuseswill starttogrow.Monozygotictwinsarethereforegenetically identicalandwillbethesamesex,exceptwhenmutations orveryraresyndromesoccurduringgestation.Noreason isknownfortheoccurrenceofthesplitoftheovum,and thefatherhasnoinfluenceoverwhetheridenticaltwins areproduced. Dizygotic(DZ)twins,however,areproducedwhenthe female’sovariesreleasetwoovumandbotharefertilised andimplantedinthewombwall.Theycanbeknownas fraternaltwinsasgeneticallytheyarelikelytoonlybeas similarassiblings.Theywillalsohaveseparateplacentas, whereMZtwinswillshareone,astheyareentirely separatetoeachother–theyarejustsharingthewomb duringgestation.Thiskindoftwinisfarmorecommon. Formation of identical and fraternal twins Monozygotic Dizygotic 1. Sperm fertilises egg In MZ twins, only one egg and one sperm are involved. 2. Fertilised egg splits At some point very early on, the fertilised egg will split and two separate foetuses will start to form. These will be genetically identical. 3. Sperm fertilise separate eggs In DZ twins, two separate eggs are fertilised by different sperm. These will implant independently in the mother’s womb wall, commonly on opposite sides. 4. Separate eggs continue to develop In DZ twins, both foetuses will continue to develop independently to each other. Fromstudyingidentical,monozygotictwins, wecanattempttodecipherthelevelofimpact environmenthasonanindividualandthe influencegeneshave.Asthegeneticsofthe individualswouldbeidentical,wecansay thatdifferencesdisplayedbetweentwo MZtwinsarelikelytobedownto environmentalinfluences. Someofthemostinterestingstudieslookat twinsthathavebeenseparatedatbirth,often whenindividualshavebeenadoptedby differentparents.OftenweseeasimilarIQ andpersonalitydisplayed,whetherornot theygrowuptogether,buteventheseand otherlifestylechoicescanvarydependant onenvironment. Ultimately,itishardtodrawfirm conclusionsfromtwinstudiesastheywillbe anunrepresentativelysmallsamplewithina muchlargerpopulationandweoftenfindthat bothenvironmentandgeneticsinteractto influenceanindividual’sdevelopment. Genetically identical, but why do twins differ? Placenta Provides a metabolic interchange between the twins and mother. Umbilical cord A rope-like cord connecting the fetus to the placenta. Uterine wall The protective wall of the uterus. Cervix The lower part of the uterus that projects into the vagina. Twins inside the womb Amniotic sac A thin-walled sac that surrounds the fetus during pregnancy. MULTIPLE BIRTHS 5TOP FACTS Female monozygotic twins are more common due to the increased likelihood of male mortality in the wombDID YOU KNOW? WorldMags.netWorldMags.net WorldMags.net
- 172. 172 | HowItWorks172 “This squeezes the insulating sheath around the nerve and ‘shorts it out’” Papercancutyourskin asitisincrediblythin and,ifyouweretolook atitunderahigh- poweredmicroscope,ithas serratededges.Criticallythough,a sheetofloosepaperisfartoosoft andflexibletoexertenough pressuretopiercetheskin,hence whytheyarenotamorefrequent occurrence.However,ifthepaper isfixedinplace–maybebybeing sandwichedwithinapackof paper–asheetcanbecomestiff enoughtoattainskin-cutting pressure.Papercutsaresopainful onceinflictedastheystimulatea largenumberofpainreceptors– nociceptorssendnervesignalsto thespinalcordandbrain–ina verysmallareaduetothe razor-typeincision.Becausepaper cutstendnottobedeep,bleeding islimited,leavingpainreceptors opentotheenvironment. Why do paper cuts hurt so much? Thenumbsensationofyourleg ‘goingtosleep’isn’tcausedby cuttingoffthebloodcirculation. It’sthepressureonthenervesthat isresponsible.Thissqueezestheinsulating sheatharoundthenerveand‘shortsitout’, blockingnervetransmission.Whenpressure isreleased,thenervesdownstreamfromthe pinchpointsuddenlyallbeginfiringatonce. Thisjumbleofunco-ordinatedsignalsisa mixtureofpainandtouch,hotandcoldall mixedtogether,whichiswhyit’sexcruciating. What is ‘pins and needles’? ©Thinkstock Pins and needles is the result of nerves that have been prevented from sending signals firing all at once ©Thinkstock CURIOUSQUESTIONS Pins and needles / Burns / Funny bones Theterm‘funnybone’ismisleading becauseitreferstothepainfulsensation youexperiencewhenyoutrapyourulnar nervebetweentheskinandthebonesof theelbowjoint.Thishappensintheso-calledcubital tunnel,whichdirectsthenerveovertheelbowbuthas littlepaddingtoprotectagainstexternalimpacts.The ulnarnervetakesitsnamefromtheulnabone,whichis oneoftwobonesthatrunsfromthewristtotheelbow; theotheristheradialbone,orradius. Nootherjointinthehumanskeletoncombinesthese conditionsandduplicatesthethiserroneouslynamed reactionsoweonlyhaveone‘funnybone’. Are there other ‘funny bones’ in the body? WorldMags.netWorldMags.net WorldMags.net
- 173. Learnwhatcausesstiffnessandpaininourmusclesfordaysafterexercise Why do our muscles ache? Discoverhowthebodymanagesto keeptrackofitsenergyreserves The fat hormone What happens to your biceps when you pump iron? Weightlifting and the bodyNormally, when our muscles contract they shorten and bulge, much like a bodybuilder’s biceps. However, if the muscle happens to be stretched as it contracts it can cause microscopic damage. The quadriceps muscle group located on the front of the thigh is involved in extending the knee joint, and usually contracts and shortens to straighten the leg. However, when walking down a steep slope, say, the quadriceps contract to support your body weight as you step forward, but as the knee bends, the muscles are pulled in the opposite direction. This tension results in tiny tears in the muscle and this is the reason that downhill running causes so much delayed-onset pain. At the microscopic level, a muscle is made up of billions of stacked sarcomeres, containing molecular ratchets that pull against one another to generate mechanical force. If the muscle is taut as it tries to contract, the sarcomeres get pulled out of line, causing microscopic damage. The muscle becomes inflamed and fills with fluid, causing stiffness and activating pain receptors – hence that achy feeling you get after unfamiliar exercise. In order to know how much food to eat, the human body needs a way of assessing how much energy it currently has in storage. Leptin – more commonly known as the ‘fat hormone’ – essentially acts as our internal fuel gauge. It is made by fat cells and tells the brain how much fat the body contains, and whether the supplies are increasing or being used up. Food intake is regulated by a small region of the brain called the hypothalamus. When fat stores run low and leptin levels drop, the hypothalamus stimulates appetite in an attempt to increase food intake and regain lost energy. When leptin levels are high, appetite is suppressed, reducing food intake and encouraging the body to burn up fuel. It was originally thought that leptin could be used as a treatment for obesity. However, although it is an important regulator of food intake, our appetite is affected by many other factors, from how full the stomach is to an individual’s emotional state or their food preferences. For this reason, it’s possible to override the leptin message and gain weight even when fat stores are sufficient. Bending Normallywhenthebiceps musclegroupcontractsit shortens,pullingtheforearm towardstheshoulder. Pain Thesorenessassociated withexerciseistheresult ofrepetitivestretchingof contractedmuscles. Straightening Asthearmstraightensout,the bicepsarestretched,butthe weightisstillpullingdownon thehand,sothemusclesremain partlycontractedtosupportit. Stretching Asthemuscletriesto contract,theweightpullsin theoppositedirection, causingmicroscopictears withinthemusclecells. The leptin (LEP) gene was originally discovered when a random mutation occurred in mice, making them put on weight ©Alamy 173WorldMags.netWorldMags.net WorldMags.net
- 174. CURIOSITIES&QUESTIONS 174 | HowItWorks Bones / Raw meat / Inoculations 174 Meatcanharbourmanydifferentbacteria,viruses andevenparasites.Cookingmeatproperly destroysthem,makingmeatmuchsaferfor consumption.Bacteriaandvirusescanmakeyou ill,whileparasitescangrowinsideyourgutandevenmigrate toyourbrain.Foodpoisoningisaveryseriousbusinessand bynotcookingmeatthoroughly,youaregreatlyincreasing yourchancesofgettingsomethingnasty.Peoplequiteoften eatrawmeatsuchassteaktartare,butitrequiresextracare inthepreparation.Besidessafety,cookingmeatalsomakesit tastebetter.Bycookingmeatandotherfoods,humanscan getmuchmoreenergythanfromchewingrawfoodalone. Why shouldn’t we eat raw meat? Themakeupofthe humanskeletonisa fantasticdisplayof evolutionthathasleftus withtheabilitytoperform incrediblycomplextaskswithout eventhinkingaboutthem.There areseveraldifferenttypesofjoint betweenbonesinyourbody,which reflecttheirfunction;someare strongandallowlittlemovement, othersareweakbutallowfree movement.Theforearmandlower leghavetwobones,whichform planejointsatthewristandankle. Thistypeofjointallowsforarange offinemovements,includinggliding androtation.Thehingejointsat yourelbowsandkneesallowforless lateralmovement,buttheyare strong.Shouldersandhips,though, areball-and-socketjoints,which allowforawiderangeofmotion. Why do the upper arm and upper leg have only one bone? “They involve introducing antigens into the body” Theterms‘inoculation’and‘vaccination’are usedinterchangeably.Theyinvolve introducingaforeignsubstance(antigens)into thebody,causingantibodyproduction.These caneitherbedead,madelessharmful,orjustcontain certainbitsthatcausedisease. WhitebloodcellscalledBlymphocytesrecognisethese antigens,andproduceantibodiestoneutralisethem. Aftertheinitialencounter,agroupofBlymphocytesare madecalled‘memorycells’,whichproduceantibodies fasterifexposedtothesameantigenagain. How do inoculations work? ©MarkWolfe ©Thinkstock WorldMags.netWorldMags.net WorldMags.net
- 175. 175 Feet,likeanyotherpartof ourbody,aremeasuredin centimetres.Ifyou’re askingaboutwhyshoe sizesareweirdnumbers,thenthere’s aninterestingstorytothis. Thestandardwaytodoshoesizes istotakethreetimesthefootsizein inches,andthentakeaway25(or12 forkids’sizes).Thereasonforthis complicatedsystemisbecauseshoes usedtobemeasurednotininchesor centimetres,butinanOldEnglish unitcalledthe‘barleycorn’,which amountstoone-thirdofaninch. Why aren’t feet measured in centimetres or inches? “Shoes used to be measured in an Old English unit called the ‘barleycorn’” ©Thinkstock Why do we develop gout? Excessivelevelsofuricacidintheblood causegout.Weproduceuricacidasawaste productfromdigestingprotein.Uricacidis removedbythekidneysandexcretedasa dilutesolution.Ifkidneyfunctionisimpaired,the concentrationrisestothepointwhereitprecipitatesas monosodiumuratecrystals. Thesenormallyforminthejointsofyourtoes, becauseyourfeetarecoolerandcoldtemperatures reducethesolubilityofuricacid.Goutispartlygenetic, butexacerbatedbyexcessivedrinking–particularly beer–andnotenoughexercise,sotherearethings thatcanbedonetohelpavoidsuffering. “Your feet are cooler and cold temperatures reduce the solubility of uric acid” ©Thinkstock WorldMags.netWorldMags.net WorldMags.net
- 176. NEW THE BODY AT WORK CURIOUS QUESTIONSHUMAN ANATOMY Anatomyof thetongue PACKED WITH AMAZING FACTS AND STUNNING ILLUSTRATIONS BOOK OF Respiration and oxygenation Uncover thescience ofDNA Understanding hormones Everything you need to know about the human body HUMAN BODY THE Explorethe sensory system Insidea humanheart Howmany bonesarein afoot? Theevolution ofthehand Alook inside theeye Foodand thebrain Howdoour muscleswork? Guidesto theessential organs Fracture healing process INCREDIBLEIMAGES 300 OVER Operating onthe brain Kidney function explained * This offer entitles new UK Direct Debit subscribers to receive their first 3 issues for £5.After these issues, subscribers will then pay £17.95 every 6 issues. Subscribers can cancel this subscription at any time. New subscriptions will start from the next available issue. Offer code‘ZGGZIN’must be quoted to receive this special subscriptions price. Direct Debit guarantee available on request. ** This is a US subscription offer.The USA issue rate is based on an annual subscription price of £50 for 13 issues, which is equivalent to $78 at the time of writing compared with the newsstand price of $9.50 for 13 issues being $123.50.Your subscription will start from the next available issue. Special trialoffer Exclusiveofferfornew Enjoyed thisbook? Try 3 issues for just £5* WorldMags.netWorldMags.net WorldMags.net
- 177. For amazing offers please visit www.imaginesubs.co.uk/hiw Quote code ZGGZIN Try 3 issues for £5 in the UK* or just $6.00 per issue in the USA** (saving 37% off the newsstand price) The magazine that feeds minds Full-colour illustrations Jam-packed with amazing visuals to really get you excited about science and technology Expert writers We commission a pool of highly intelligent and talented experts to write every article Join the community Link up with other readers with a passion for knowledge at www.howitworksdaily.com About the mag Or telephone UK 0844 815 5944 overseas +44 (0)1795 418 680 subscribersto… WorldMags.netWorldMags.net WorldMags.net
- 178. Everythingyou needtoknow BUYYOURCOPYTODAY Print edition available at www.imagineshop.co.uk Digital edition available at www.greatdigitalmags.com facebook.com/ImagineBookazines twitter.com/Books_Imagine Available on the following platforms WorldMags.netWorldMags.net WorldMags.net
- 180. Human respiration Human anatomy Discoverhowourheartsbeat,our brainsthinkandourearshearand everythinginbetween The body at work Findouthowourbodieswork,from geneticsandtheimmunesystemto respirationandwhitebloodcells Curious questions Uncoveramazingfactsthatexplainsomeof life’sbiggestquestions,suchaswhat powerscellsandhowanaesthesiaworks 170+ PAGES OF FACTS AND TRIVIA INSIDE The structure of the skeleton How do we combat viruses? The development of an embryo The importance of teeth The science behind a sprained ankle BOOK OF HUMAN BODY THE PACKED WITH AMAZING FACTS AND STUNNING ILLUSTRATIONS Inside the eye Understand our sense of taste How do we smell? The circulation system The science of genetics Functions of the liver THE BODY AT WORK CURIOUS QUESTIONSHUMAN ANATOMY 3RD REVISED EDITION WorldMags.netWorldMags.net WorldMags.net