Cardiovascular System: Structure, Function, and Clinical Insights

CARDIOVASCULAR
SYSTEM
Dr. Segawa Ronald

Learning Objectives
By the end of this topic, a student must be able to;
• Describe the anatomy of the heart.
• Describe the structure of the cardiac muscle and how it contracts.
• Describe the structure, types and functions of blood vessels.
• Describe the composition and functions of blood.
• List various blood disorders.
• Discuss the various type of anaemia and their causes.
• Describe the body fluid compartments.
• Outline the differences between blood and lymph fluid.
• Discuss the pathophysiology of the heart.
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Introduction
• Cardiovascular system includes heart and blood vessels.
• Heart pumps blood into the blood vessels.
• Blood vessels circulate the blood throughout the body.
• Blood transports nutrients and oxygen to the tissues and removes
carbon dioxide and waste products from the tissues.
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THE HEART
• Heart is a muscular organ that pumps blood throughout the
circulatory system.
• It is made up of four chambers, two atria and two
ventricles.
• The musculature of ventricles is thicker than that of the
atria.
• The broad superior portion of the heart, the base, is the
point of attachment for the pulmonary trunk, pulmonary
veins, and aorta—the so-called great vessels.
• The human heart is located within the thoracic cavity,
medially between the lungs in the space known as the
mediastinum.
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Within the mediastinum, the heart is separated from the other
mediastinal structures by a tough membrane known as the
pericardium, or pericardial sac, and sits in its own space called the
pericardial cavity.
The dorsal surface of the heart lies near the bodies of the
vertebrae, and its anterior surface sits deep to the sternum and
costal cartilages.
The great veins, the superior and inferior venae cavae, and the
great arteries, the aorta and pulmonary trunk, are attached to the
superior surface of the heart, called the base.
The base of the heart is located at the level of the third costal
cartilage.

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The inferior tip of the heart, the apex, lies just to the left of the
sternum between the junction of the fourth and fifth ribs near
their articulation with the costal cartilages.
The right side of the heart is deflected anteriorly, and the left
side is deflected posteriorly.
The slight deviation of the apex to the left is reflected in a
depression in the medial surface of the inferior lobe of the left
lung, called the cardiac notch.
The normal adult heart weighs about 300 g (10 ounces) and
measures about 9 cm (3.5 in.) wide at the base, 13 cm (5 in.)
from base to apex, and 6 cm (2.5 in.) from anterior to posterior
at its thickest point.

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▪ Whatever one’s body size, the
healthy heart is roughly the
same size as the fist.
Heart anatomy

The Pericardium
• Pericardium is a triple-layered sac that surrounds and protects the
heart.
• It is made up of two main parts; the fibrous pericardium and serous
pericardium.
The fibrous pericardium
• Is composed of tough, inelastic, dense irregular connective tissue.
• It extends inferiorly over the diaphragm and superiorly over the bases
of the large vessels that enter and leave the heart.
• It prevents over stretching of the heart, provides protection and
anchors the heart to the mediastinum.
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Serous pericardium
• The serous pericardium is a thin, delicate membrane.
• It consists of two layers; the outer parietal layer and the inner visceral
layer.
• The space between the two layers is called pericardial cavity.
• It contains a thin film of fluid, called pericardial fluid, which reduces
friction between the two layers.
The Function of the Pericardium:
▪ Protects and anchors the heart
▪ Prevents overfilling of the heart with blood
▪ Allows for the heart to work in a relatively friction- free environment
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The walls of the heart
The wall of the heart consists of three layers:
• The epicardium (external layer),
• The myocardium (middle layer), and
• The endocardium (inner layer).
1. The Epicardium
• Is a thin, transparent outer layer of the heart wall,
• It is also called the visceral layer of the serous pericardium.
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2. Myocardium
• Is the middle layer which is cardiac muscle tissue.
• It makes up about 95% of the heart.
• It is responsible for its pumping action of the heart.
• Unlike the skeletal muscle, cardiac muscle is involuntary in nature.
• The thickness of the myocardium of the four chambers varies
according to each chamber’s function.
• The atria are thin-walled since, they deliver blood under low pressure
to the adjacent ventricles.
• The ventricles, because they pump blood under high pressure over
greater distances, their walls are thicker.
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Cont’n
• Much as both the left and right ventricles eject the same volume of
blood, the right ventricle has smaller workload – it pumps blood to a
short distance (to the lungs), at a lower pressure and low resistance to
blood flow, as compared to the left side which pumps blood to a longer
distance (to the rest of the body) at a high pressure and high resistance
to blood flow.
• Therefore, the wall of the left ventricle is considerably thicker than
that of the right ventricle.
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3. Endocardium
• Endocardium is the inner most layer of heart wall.
• It is a thin, smooth and glistening membrane. The smoothness of the
endocardium is an important characteristic of the endocardium
because it prevents abnormal blood clotting.
• It is formed by a single layer of endothelial cells, lining the inner
surface of the heart.
• Endocardium continues as endothelium of the blood vessels.
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Chambers of the Heart
• The heart has four chambers.
• The two superior receiving chambers are the atria , and the two
inferior pumping chambers are the ventricles.
Right Side Of The Heart
• Right side of the heart has two chambers, right atrium and right
ventricle.
Right atrium
• Is a thin walled and low-pressure chamber.
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Cont’n
• It has got the pacemaker known as sinoatrial node that produces
cardiac impulses and atrioventricular node that conducts the impulses
to the ventricles.
• The right atrium receives venous (deoxygenated) blood via two large
veins:
oSuperior vena cava that returns venous blood from the head, neck and
upper limbs
oInferior vena cava that returns venous blood from lower parts of the
body.
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The right ventricle
• Wall of right ventricle is thick.
• Right atrium communicates with right ventricle through tricuspid
valve.
• Venous blood from the right atrium enters the right ventricle through
this valve.
• From the right ventricle, pulmonary artery arises. It carries the venous
blood from the right ventricle to the lungs. In the lungs, the
deoxygenated blood is oxygenated.
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The left side of the heart
• Left side of the heart has two chambers, left atrium and left ventricle.
Left atrium
• Is a thin walled and low-pressure chamber.
• It receives oxygenated blood from the lungs through pulmonary veins.
This is the only exception in the body, where an artery carries venous
blood and vein carries the arterial blood.
The left ventricle
• Wall of the left ventricle is very thick.
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Cont’n
• Blood from left atrium enters the left ventricle through mitral valve
(bicuspid valve).
• Left ventricle pumps the arterial blood to different parts of the body
through systemic aorta.
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Septa Of The Heart
• Right and left atria are separated from one another by a fibrous septum
called interatrial septum.
• Right and left ventricles are separated from one another by
interventricular septum.
• The upper part of this septum is a membranous structure, whereas the
lower part of it is muscular in nature.
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Atrioventricular Valve Function
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Valves Of The Heart
• There are four valves in human heart these can be categorized into two
namely;
1. Atrioventricular valves (mitral valves). These are found between
the atria and ventricles of the heart.
• The Right atrioventricular valve is known as tricuspid valve and is
formed by two cusps or flaps.
• The right atrioventricular valve is known as bicuspid valve and is
formed by three cusps.
• Atrioventricular valves open only towards ventricles and prevent the
backflow of blood into atria.
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Cont’n
• The cusps of these valves are connected to tendon-like cords, called
the chordae tendineae, which in turn are connected to papillary
muscles.
• Therefore, when the ventricles are relaxed, the papillary muscles are
relaxed, the chordae tendineae are loose, and AV valves are open.
• When the ventricles contract, the pressure of the blood drives the
cusps upward until their edges meet and close the opening .
• At the same time, the papillary muscles contract, which pulls on and
tightens the chordae tendineae, preventing the valve cusps from
opening into the atria due to the high ventricular pressure.
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2. Semilunar valves
• These are present at the openings of systemic aorta and pulmonary artery
and are known as aortic valve and pulmonary valve respectively.
• Semilunar valves are made up of three moon shaped cusps.
• They open only towards the aorta and pulmonary artery and prevent the
backflow of blood into the ventricles.
• The semilunar valves open when pressure in the ventricles exceeds the
pressure in the arteries, (during ventricular systole).
• As the ventricles relax, blood starts to flow back toward the heart. This back
flowing blood fills the valve cusps, which causes the semilunar valves to
close tightly.
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Pathway of Blood Through the Heart
• The right side of the heart is the pulmonary circuit pump. Blood
returning from the body is relatively oxygen-poor and carbon dioxide-
rich.
• It enters the right atrium and passes into the right ventricle, which
pumps it to the lungs via the pulmonary trunk.
• In the lungs, the blood unloads carbon dioxide and picks up oxygen.
• The freshly oxygenated blood is carried by the pulmonary veins back
to the left side of the heart.
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Contd..
• The left side of the heart is the systemic circuit pump.
• Freshly oxygenated blood leaving the lungs is returned to the left
atrium and passes into the left ventricle, which pumps it into the
aorta.
• From there the blood is transported via smaller systemic arteries
to the body tissues, were gases and nutrients are exchanged across
the capillary walls.
• Then the blood, once again loaded with carbon dioxide and
depleted of oxygen, returns through the systemic veins to the
right side of the heart, were it enters the right atrium through the
superior and inferior venae cavae.
• This cycle repeats itself continuously.
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Pathway of Blood Through the Heart and
Lungs
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Pathway of Blood Through the Heart and
Lungs
▪ Right atrium → tricuspid valve → right ventricle
▪ Right ventricle → pulmonary semilunar valve →
pulmonary arteries → lungs
▪ Lungs → pulmonary veins → left atrium
▪ Left atrium → bicuspid valve → left ventricle
▪ Left ventricle → aortic semilunar valve → aorta
▪ Aorta → systemic circulation
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• Cardiac muscle, like skeletal muscle, is striated, and it
contracts by the sliding filament mechanism.
• Cardiac cells are short, fat, branched, and interconnected.
• Each fiber contains one or at most two large, pale, centrally
located nuclei.
• The intercellular spaces are filled with a loose connective
tissue matrix: (the endomysium) containing numerous
capillaries.
• The plasma membranes of adjacent cardiac cells interlock
like the ribs of two sheets of corrugated cardboard at dark-
staining junctions called intercalated discs

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• These discs contain anchoring desmosomes and gap
junctions .
• The desmosomes prevent adjacent cells from separating
during contraction, and the gap junctions allow ions to pass
from cell to cell, transmitting current across the entire heart.
• Because cardiac cells are electrically coupled by the gap
junctions, the myocardium behaves as a single coordinated
unit, or functional syncytium.
• Large mitochondria account for 25-35% of the volume of
cardiac cells and give cardiac cells a high resistance to
fatigue.

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• Most of the remaining volume is occupied by myofibrils
composed of fairly typical sarcomeres.
• The sarcomeres have Z discs, A bands, and I bands that
reflect the arrangement of the thick
• (myosin) and thin (actin) filaments composing them.
• The myofibrils of cardiac muscle cells vary greatly in
diameter and branch extensively, accommodating
• the abundant mitochondria that lie between them.
• The T tubules are wider and fewer than in skeletal muscle
and they enter the cells once per sarcomere at the Z discs.

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Mechanism and Events of Contraction
1. Means of stimulation. Some cardiac muscle cells are self-excitable
and can initiate their own depolarization, and that of the rest of the
heart, in a spontaneous and rhythmic way. This property, called
automaticity, or auto rhythmicity.
2. Organ contraction. In cardiac muscle, the heart either contracts as a
unit or doesn't contract at all. This is ensured by the transmission of
the depolarization wave across the heart from cell to cell via ion
passage through gap junctions, which tie all cardiac muscle cells
together into a single contractile unit.
3. Length of absolute refractory period. The absolute refractory
period, lasts approximately 250 ms in cardiac muscle cells, nearly as
long as the contraction. This prevents tetanic contractions, which
would stop the heart’s pumping action.

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About 1 % of cardiac fibers are autorhythmic ("self-rhythm")
and have the special ability to depolarize spontaneously and
thus pace the heart, the bulk of heart muscle is composed of
contractile muscle fibers responsible for the heart’s pumping
activity.
1. Depolarization opens a few voltage-gated fast Na + channels
in the sarcolemma allowing extracellular Na + to enter. This
initiates a positive feedback cycle that causes the rising phase of
the action potential (and reversal of the membrane potential
from -90 mV to nearly +30 Mv. The period of increased Na +
permeability is very brief, because the sodium channels are
quickly inactivated and the Na + influx stops.

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2. Transmission of the depolarization wave down the T
tubules (ultimately) causes the sarcoplasmic reticulum (SR) to
release Ca2+ into the sarcoplasm.
3. Excitation-contraction coupling occurs as Ca2+ provides the
signal (via troponin binding) for cross bridge activation and
couples the depolarization wave to the sliding of the
myofilaments.
Although these three steps are common to both skeletal and
cardiac muscle cells, how the SR is stimulated to release Ca2+
differs in the two muscle types.

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Physiology of the heart; Setting the Basic Rhythm:
The Intrinsic Conduction System
The independent, but coordinated, activity of the heart is a
function of (1) the presence of gap junctions, and
(2) the activity of the heart's "in-house“ conduction system
Action Potential Initiation by Autorhythmic Cells
The autorhythmic cells making up the intrinsic conduction
system have an unstable resting potential that continuously
depolarizes, drifting slowly toward threshold.
These spontaneously changing membrane potentials, called
pacemaker potentials or prepotentials, initiate the action
potentials that spread throughout the heart to trigger its
rhythmic contractions.

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Explanation about pace maker cells.
In these cells, hyperpolarization at the end of an action potential
leads to both closing of K+ channels and opening of slow Na
+ channels.
The Na + influx alters the balance between K+ loss and Na +
entry, and the membrane interior becomes less and less negative
(more positive). Ultimately, at threshold (approximately -40
mV), Ca2+ channels open, allowing explosive entry of Ca2+
from the extracellular space.
Thus, in autorhythmic cells, it is the influx of Ca2+ (rather
than Na+) that produces the rising phase of the action
potential and reverses the membrane potential.

Pacemaker andAction Potentials of the Heart
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Heart Physiology: Sequence of Excitation
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Sequence of Excitation
Autorhythmic cardiac cells are found in the following areas;
sinoatrial node, atrioventricular node, atrioventricular bundle,
right and left bundle branches, and ventricular walls (as
Purkinje fibers).
Impulses pass across the heart in the same order.
Sinoatrial node. The crescent-shaped sinoatrial (SA) node is
located in the right atrial wall, just inferior to the entrance of
the superior vena cava.
A minute cell mass with a mammoth job, the SA node
typically generates impulses about 75 times every minute.
It is the heart’s pacemaker, and its characteristic rhythm,
called sinus rhythm, determines heart rate.

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Atrioventricular node. From the SA node, the depolarization
wave spreads via gap junctions throughout the atria and via the
internodal pathway to the atrioventricular (AV) node, located
in the inferior
portion of the interatrial septum immediately above the
tricuspid valve.
At the AV node, the impulse is delayed for about 0.1 s,
allowing the atria to respond and complete their contraction
before the ventricles contract.
This delay reflects the smaller diameter of the fibers here and
the fact that they have fewer gap junctions for current flow.

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Atrioventricular bundle. From the AV node, the impulse
sweeps to the atrioventricular (AV) bundle (also called the
bundle of His) in the superior part of the interventricular
septum. The atria and ventricles abut each other, they are not
connected by gap junctions.
The AV bundle is the only electrical connection between them.
The balance of the AV junction is insulated by the non-
conducting fibrous skeleton of the heart.
Right and left bundle branches. The AV bundle persists only
briefly before splitting into two pathways-the right and left
bundle branches, which course along the interventricular
septum toward the heart apex.

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Purkinje fibers. The Purkinje fibers complete the pathway
through the interventricular septum, penetrate into the heart
apex, and then turn superiorly into the ventricular walls.
The bundle branches excite the septal cells, but the bulk of
ventricular depolarization depends on the large Purkinje fibers
and, ultimately; on cell to-cell transmission of the impulse via
gap junctions between the ventricular muscle cells.
Because the left ventricle is much larger than the right, the
Purkinje network is more elaborate in that side of the heart.

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Electrocardiography
The electrical currents generated in and transmitted through
the heart spread throughout the body and can be detected with
an electrocardiograph.
A graphic record of heart activity is called an
electrocardiogram (ECG or EKG).
A typical ECG has three distinguishable waves or deflections.
The first, the small P wave, lasts about 0.08 s and results from
movement of the depolarization wave from the SA node
through the atria.
Approximately 0.1 s after the P wave begins, the atria contract.

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The large QRS complex results from ventricular depolarization and
precedes ventricular contraction.
The time required for each ventricle to depolarize depends on its size
relative to the other ventricle. Average duration of the QRS complex is
0.08 s.
The T wave is caused by ventricular repolarization and typically lasts
about 0.16 s. Repolarization is slower than depolarization, so the T wave
is more spread out and has a lower amplitude (height) than the QRS
wave.
Because atrial repolarization takes place during the period of ventricular
excitation, the wave representing atrial repolarization is normally
obscured by the large QRS complex being recorded at the same time.

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• The P-Q interval is the time (about 0.16 s) from the beginning of
atrial excitation to the beginning of ventricular excitation.
• Sometimes called the P-R interval because the Q wave tends to be
very small, it includes atrial depolarization (and contraction) as well
as the passage of the depolarization wave through the rest of the
conduction system.
• During the S-T segment of the ECG, when the action potential is in
its plateau phase, the entire ventricular myocardium is depolarized.
• The Q-T interval, lasting about 0.38 s, is the period from the
beginning of ventricular depolarization through ventricular
repolarization.
• Changes in the pattern or timing of the ECG may reveal a diseased or
damaged heart or problems with the heart's conduction system.

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Cardiac Output
• Cardiac output (CO) is the amount of blood pumped out by each
ventricle in 1 minute.
• It is the product of heart rate (HR) and stroke volume (SV).
• Stroke volume is defined as the volume of blood pumped out by one
ventricle with each beat.
• The difference between resting and maximal CO is referred to as
cardiac reserve.
• In nonathletic people, cardiac reserve is typically four to five times
resting CO (20-25 L/min), but CO in trained athletes during
competition may reach 35 L/min (seven times resting).

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Regulation of Stroke Volume
SV represents the difference between end diastolic volume (EDV),
the amount of blood that collects in a ventricle during diastole, and
end systolic volume (ESV), the volume of blood remaining in a
ventricle after it has contracted.
FactorsAffecting Stroke V
olume
▪ Preload – amount ventricles are stretched by contained
blood
▪ Contractility – cardiac cell contractile force due to factors other
than EDV
▪ Afterload – back pressure exerted by blood in the large arteries
leaving the heart

Frank-Starling Law of the Heart
▪ Preload, or degree of stretch, of cardiac muscle cells before they
contract is the critical factor controlling stroke volume
▪ Slow heartbeat and exercise increase venous return to the heart,
increasing SV
▪ Blood loss and extremely rapid heartbeat decrease SV
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Extrinsic Factors Influencing Stroke Volume
▪ Contractility is the increase in contractile strength, independent
of stretch and EDV
▪ Increase in contractility comes from:
▪ Increased sympathetic stimuli
▪ Certain hormones
▪ Ca2+ and some drugs
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Extrinsic Factors Influencing Stroke Volume
▪ Agents/factors that decrease contractility include:
▪ Acidosis
▪ Increased extracellular K+
▪ Calcium channel blockers
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BLOOD VESSELS AND CIRCULATION
Blood vessels
• Vessels of circulatory system are the aorta, arteries, arterioles,
capillaries, venules, veins and venae cavae.
Basic Structure of a Blood Vessel
• The wall of a blood vessel consists of three layers, or tunics, of
different tissues:
• The tunica interna (intima), (innermost layer)
• Tunica media, (middle layer) and
• Tunica externa, (outermost layer)
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Structure of Blood Vessel Walls
• The walls of all blood vessels, except the very smallest,
have three distinct layers, or tunics ("coverings").
• The innermost tunic is the tunica intima (tunica interna)
and it contains the endothelium.
• It's made of simple squamous epithelium which lines the
lumen of all vessels.
• The endothelium is a continuation of the endocardial lining
of the heart, and its flat cells fit closely together, forming a
slick surface.
• In vessels larger than 1 mm in diameter, a subendothelial
layer, consisting of a basement membrane and loose
connective tissue, supports the endothelium.
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61
• The tunica media, is mostly made of circularly arranged
smooth muscle cells and sheets of elastin.
• The activity of the smooth muscle is regulated by
sympathetic vasomotor nerve fibers of the autonomic
nervous system and other chemicals.
• It can either vasoconstrict or vasodilate.
• Small changes in vessel diameter greatly influence blood
flow and blood pressure, the activities of the tunica media
are critical in regulating 'circulatory dynamics.
• The tunica media is the bulkiest layer in arteries, which
bear the chief responsibility for maintaining blood pressure
and continuous blood circulation.

• The tunica externa, is composed largely of collagen
fibers that protect and reinforce the vessel, and also
anchor it to surrounding structures.
• It is infiltrated with nerve fibers, lymphatic vessels,
and, in larger veins, a network of elastin fibers.
• In larger vessels, the tunica externa contains a system
of tiny blood vessels, (the vasa vasorum) literally,
"vessels of the vessels" that nourish the more external
tissues of the blood vessel wall.
• The innermost or luminal portion of the vessel obtains
its nutrients directly from blood in the lumen.
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THE FLOW OF BLOOD THROUGH THE BLOOD VESSEL'S ILLUSTRATION
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The cardiovascular system has three types of blood vessels:
1. Arteries and arterioles – carry blood away from the heart
2. Capillaries – where nutrient and gas exchange occur
3. Veins and venules – carry blood toward the heart
VASOCONSTRICTION is a reduction in lumen diameter as
the smooth muscle contracts.
VASODILATION is an increase in lumen diameter as the
smooth muscle relaxes.

• As the heart contracts, it forces blood into the large
arteries leaving the ventricles.
• The blood then moves into successively smaller arteries,
finally reaching their smallest branches, the arterioles,
which feed into the capillary beds of body organs and
tissues.
• Blood drains from the capillaries into venules, the smallest
veins, and then on into larger and larger veins that merge
to form the large veins that ultimately empty into the
heart.
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• Arteries carry blood away from the heart, they are said to
"branch," "diverge," or "fork" as they form smaller and
smaller divisions.
• Veins, by contrast, carry blood towards the heart and so are
said to "join," "merge," and "converge" into the successively
larger vessels approaching the heart.
• In the systemic circulation, arteries always carry oxygenated
blood and veins always carry oxygen-poor blood.

• The opposite is true in the pulmonary circulation' where
the arteries, still defined as the vessels leading away from
the heart, carry oxygen-poor blood to the lungs, and the
veins carry oxygen-rich blood from the lungs to the heart.
• Of all the blood vessels, only the capillaries have intimate
contact with tissue cells and directly serve cellular needs.
• Exchanges between the blood and tissue cells occur
primarily through the gossamer-thin capillary walls.
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The arterial system
Arterial system comprises the aorta, arteries and
arterioles
Arteries and arterioles
They vary considerably in size and their walls consist of
three layers of tissue
1. tunica adventitia or outer layer of fibrous tissue
2. tunica media or middle layer of smooth muscle and
elastic tissue
3. tunica intima or inner lining of squamous epithelium
called endothelium.
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• The amount of muscular and elastic tissue varies in the
arteries depending upon their size and function.
• Large arteries are sometimes called elastic arteries, the tunica
media contains more elastic tissue and less smooth muscle to
allow the vessel wall to stretch, and absorbing the pressure
wave generated by the heart as it beats.
• These proportions gradually change as the arteries branch
many times and become smaller until in the arterioles (the
smallest arteries) the tunica almost entirely of smooth
muscle.

• Systemic blood pressure is mainly determined by the
resistance these tiny arteries offer to blood flow.
• Arteries have thicker walls than veins to withstand the
high pressure of arterial blood.
Anastomoses and end-arteries
• An anastomosis is an area where vessels unite to form
interconnections that normally allow blood to circulate to
a region even if there may be partial blockage in another
branch.
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• This is most likely to provide an adequate blood supply
when the occlusion occurs gradually, giving the
anastomotic arteries time to dilate.
• An end-artery is an artery that is the sole source of blood to
a tissue, e.g. the branches from the circle of Willis in the
brain or the central artery to the retina of the eye.
• When an end-artery is occluded the tissues, it supplies die
because there is no alternative blood supply.

Capillaries and sinusoids
• The smallest arterioles divide up into a number of minute
vessels called capillaries.
• Capillary walls consist of a single layer of endothelial
cells sitting on a very thin basement membrane.
• Blood cells and large molecules such as plasma proteins
do not normally pass through capillary walls.
• The capillaries form a vast network of tiny vessels that
link the smallest arterioles to the smallest venules.
• Their diameter is approximately that of an erythrocyte (7
µm).
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• The capillary bed is the site of exchange of substances
between the blood and tissues.
• Entry to capillary beds is guarded by precapillary sphincters
that direct blood flow.
• Hypoxia or high levels of tissue wastes, indicating high
levels of activity, dilate the sphincters and increase blood
flow through the affected beds.
• In certain places, including the liver and bone marrow, the
capillaries are significantly wider and leakier than normal,
these capillaries are called sinusoids

Venous System
• Veins are called capacitance vessels because they are
distensible, and therefore have the capacity to hold a
large proportion of the body’s blood.
• Veins return blood at low pressure to the heart.
• The walls of the veins are thinner than arteries but have
the same three layers of tissue.
• They are thinner because there is less muscle and elastic
tissue in the tunica media, as veins carry blood at a lower
pressure than arteries.
• Some veins possess valves, which prevent backflow of
blood, ensuring that it flows towards the heart .
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• They are formed by a fold of tunica intima and strengthened
by connective tissue.
• The cusps are semilunar in shape with the concavity towards
the heart.
• Valves are abundant in the veins of the limbs, especially the
lower limbs where blood must travel a considerable distance
against gravity when the individual is standing but are absent
in very small and very large veins in the thorax and abdomen.
• Valves are assisted in maintaining one-way flow by skeletal
muscles surrounding the veins.
• The smallest veins are called venules.
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Comparison of arteries, veins and
capillaries
Arteries Veins Capillaries
Carry blood from the heart to
capillaries
Carry blood from capillaries
back to the heart.
Are a site for exchange of
materials between blood and
tissues
Have no valves except the aorta Have valves Have no valves
Carry oxygenated blood except
pulmonary artery
Carry deoxygenated blood
except pulmonary vein
Carry both oxygenated and
deoxygenated blood.
Have thick walls Have thin walls Have very thin walls (one-cell
thick)
Have narrow lumen Have large lumen Have narrow lumen
Blood flows at a high pressure Blood flows at a considerably
lower pressure, hence there is a
tendency of back flow of blood.
Blood pressure is low
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Blood Supply Through The Heart
• Blood flows through two divisions of circulatory system:
1. Systemic Circulation
• Is otherwise known as greater circulation.
• Blood pumped from left ventricle passes through the arterial system
and reaches the tissues.
• Exchange of various substances between blood and the tissues occurs
at the capillaries.
• After exchange of materials, blood enters the venous system and
returns to right atrium of the heart.
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Cont’n
• From right atrium, blood enters the right ventricle.
• Thus, through systemic circulation, oxygenated blood is supplied from
heart to the tissues and venous blood returns to the heart from tissues.
2. Pulmonary Circulation
• Pulmonary circulation is also called lesser circulation.
• Blood is pumped from right ventricle to lungs through pulmonary
artery.
• Exchange of gases occurs between blood and alveoli of the lungs at
pulmonary capillaries.
78

Cont’n
• Oxygenated blood returns to left atrium through the pulmonary veins.
• Thus, left side of the heart contains oxygenated or arterial blood and
the right side of the heart contains deoxygenated or venous blood.
Coronary circulation
• The myocardium is too thick to make diffusion a practical means of
nutrient delivery.
• The coronary circulation, the functional blood supply of the heart, is
the shortest circulation in the body.
• The coronary arteries branch from the ascending aorta and encircle the
heart.
79

Coronary Circulation:Arterial Supply
80

81
Coronary arteries supply blood to the myocardium and other
components of the heart.
There are three dilations in the wall of the aorta just above the aortic
semilunar valve;
• Two of these, the left posterior aortic sinus and anterior aortic
sinus, give rise to the left and right coronary arteries,
respectively.
• The third sinus, the right posterior aortic sinus, typically does not
give rise to a vessel.

82
• The left coronary artery distributes blood to the left side of the
heart, and the interventricular septum.
• The circumflex artery arises from the left coronary artery and it
fuses with the small branches of the right coronary artery.
• The larger anterior interventricular artery, is the second major
branch arising from the left coronary artery and it gives rise to
numerous smaller branches that interconnect with the branches of
the posterior interventricular artery, forming anastomoses.
• One or more marginal arteries arise from the right coronary
artery inferior to the right atrium and they supply blood to the
superficial portions of the right ventricle.

83
• The right coronary artery gives rise to the posterior interventricular
artery, It supplies the interventricular septum and portions of both
ventricles.
• Coronary veins drain the heart and generally parallel the large
surface arteries.
• The great cardiac vein- drains the areas supplied by the anterior
interventricular and also receives blood from several major branches,
including the posterior cardiac vein, the middle cardiac vein, and the
small cardiac vein.
• The posterior cardiac vein - drains the areas supplied by the
marginal arteries.

84
• The middle cardiac vein - drains the areas supplied by the posterior
interventricular artery.
• The small cardiac vein - drains the blood from the posterior surfaces
of the right atrium and ventricle.
• The coronary sinus is a large, thin-walled vein on the posterior
surface of the heart, emptying directly into the right atrium.
• The anterior cardiac veins - drains the anterior surface of the right
ventricle.
• Unlike these other cardiac veins, it bypasses the coronary sinus and
drains directly into the right atrium.

85
Coronary Circulation: Venous Supply

BLOOD
Definition Of Blood
• Blood is a connective tissue in fluid form.
Functions Of Blood
1.Transports oxygen, carbon dioxide, nutrients, hormones, heat, and
wastes.
2. Regulates pH, body temperature, and water content of cells.
3. Protects against blood loss through clotting, and against disease
through phagocytic white blood cells and antibodies.
86

Physical Characteristics of Blood
• Blood is denser and more viscous (thicker) than water and
feels slightly sticky.
• The temperature of blood is 38◦C (100.4◦F), about 1◦C higher
than oral or rectal body temperature.
• It has a slightly alkaline pH ranging from 7.35 to 7.45.
• The color of blood varies with its oxygen content.
• When it has a high oxygen content, it is bright red.
• When it has a low oxygen content, it is dark red.
87

Cont’n
• Blood constitutes about 20% of extracellular fluid, amounting
to 8% of the total body mass.
• The blood volume is 5 to 6 liters in an average-sized adult
male and 4 to 5 liters in an average-sized adult female.
• The difference in volume is due to differences in body size.
88

Components of Blood
• Blood has two components:
(1) Blood plasma, a watery liquid extracellular matrix that contains
dissolved substances, and
(2) Formed elements, which are cells and cell fragments.
a) Blood Plasma
• Plasma is a straw-colored clear liquid part of blood.
• Blood plasma is about 91.5% water and 8.5% solutes, most of which
(7% by weight) are proteins (called plasma proteins) namely, albumin,
globulin and fibrinogen.
89

Plasma Proteins
There are basically three types of plasma proteins namely;
1. Albumins
• Smallest and most numerous blood plasma proteins, accounting for
approximately 54 percent of the total plasma protein content (3.5–5.0
g/dL blood in clinical levels).
• They are produced by liver.
• Function as transport proteins for several steroid hormones and for
fatty acids.
• Albumin is also the most significant contributor to the osmotic
pressure of blood. 90

2. Globulins
• Globulins are the second commonest plasma proteins, making up
approximately 38 percent of the total plasma protein volume of blood
(1.0–1.5 g/dL of blood in clinical levels).
• Globulins are of three types: alpha, beta, and gamma globulins.
• They are produced by liver and by plasma cells.
• Antibodies (immunoglobulins) help attack viruses and bacteria.
• Alpha and beta globulins transport iron, lipids, and fat-soluble
vitamins A, D, E, and K to the cells.
• Like albumin, globulins also contribute to the osmotic pressure of
blood. 91

3. Fibrinogen
Fibrinogen is the least abundant accounting for about 7 percent
of the total plasma protein volume of blood, (0.2–0.45 g/dL of
blood in clinical levels).
• It is produced by liver.
• Plays essential role in blood clotting – it is converted to fibrin
(a stable clot) during blood clotting.
92

Serum
• Serum is the clear straw-colored fluid that oozes from blood clot.
• It is different from plasma only by the absence of fibrinogen, i.e.
serum contains all the other constituents of plasma except
fibrinogen.
• Fibrinogen is absent in serum because it is converted into fibrin
during blood clotting.
• Thus,
• Serum = Plasma – Fibrinogen
93

b) Formed Elements
• The formed elements of the blood include three principal components:
• Red blood cells (RBCs)
• White blood cells (WBCs)
❑granular leukocytes
oneutrophils
oeosinophils
obasophils
❑agranular leukocytes
94

Cont’n
olymphocytes - T cells, B cells, natural killer cells (N.K.C)
omonocytes
• Platelets .
-RBCs and WBCs are whole cells, whereas, platelets are cell fragments
-RBCs are larger in number compared to the other two blood cells,
namely
white blood cells and platelets.
95

1. Red Blood Cells (RBCs)
• Red blood cells (RBCs) or erythrocytes the non-nucleated formed
elements in the blood.
Anatomy of RBCs
• Normally, the RBCs are disk shaped and biconcave (dumbbell
shaped) - Central portion is thinner and periphery is thicker.
• This shape helps the RBCs to squeeze through the narrow capillaries.
It also offers the RBC a large surface area for absorption or removal of
substances.
• They have a diameter of 7.4 µm (7–8 µm.)
97

Cont’n
• RBCs lack a nucleus and other organelles such as mitochondria, golgi
apparatus etc., and can neither reproduce nor carry on extensive
metabolic activities. Because RBCs lack mitochondria and, generate
ATP anaerobically (without oxygen), they do not use up any of the
oxygen they transport.
• Each RBC contains about 280 million hemoglobin molecules.
• A hemoglobin molecule consists of a protein called globin, composed
of four polypeptide chains (two alpha and two beta chains) and a ring-
like non-protein pigment called a heme, bound to each of the four
chains.
98

Cont’n
• At the center of each heme ring is an iron ion (Fe2+) that can combine
reversibly with one oxygen molecule, allowing each hemoglobin
molecule to bind four oxygen molecules.
RBC count
• The normal RBCs count is; about 5.4 million red blood cells per micro
liter (µL) of blood in adult males and about 4.8 million in adult
females.
• An abnormally low RBC count is termed as anaemia and an
abnormally high RBC count is termed as polycythemia.
99

Life Cycle Of RBCs
• Red blood cells live only about 120 days because of the wear and tear
their plasma membranes undergo as they squeeze through blood
capillaries.
• The plasma membrane becomes more fragile with age, and the cells
are more likely to burst, especially as they squeeze through narrow
channels in the spleen.
• Ruptured red blood cells are removed from circulation and destroyed
by fixed phagocytic macrophages in the spleen and liver, and the
breakdown products are recycled, as follows;
101

Cont’n
1. Macrophages in the spleen, liver, or red bone marrow phagocytize
ruptured and worn-out red blood cells.
2. The globin and heme portions of hemoglobin are split apart.
3. Globin is broken down into amino acids, which can be reused to
synthesize other proteins.
4. Iron is removed from the heme portion in the form of Fe3+ and
carried to the liver, muscle fibers or macrophages of the spleen where
it is stored. On demand, iron (Fe3+) is again transported to the bone
marrow for use in hemoglobin synthesis.
102

Cont’n
5.When iron is removed from heme, the non-iron portion of heme is
converted to biliverdin, a green pigment, and then into bilirubin, a
yellow-orange pigment.
6. Bilirubin enters the blood and is transported to the liver.
7. Within the liver, bilirubin is released by liver cells into bile, which
passes into the small intestine and then into the large intestine.
8. In the large intestine, bacteria convert bilirubin into urobilinogen.
9.Most urobilinogen is eliminated in feces in the form of a brown
pigment called stercobilin, which gives feces its characteristic color.
103

Cont’n
10. Some urobilinogen is absorbed back into the blood, converted to a
yellow pigment called urobilin, and excreted in urine.
104

Functions of RBCs
1. Transport. Major function of RBCs is the transport of respiratory
gases - oxygen (from the lungs to tissues) and carbondioxide (from
tissues to the lungs).
2. Buffering Action in Blood. Hemoglobin functions as a good buffer.
By this action, it regulates the hydrogen ion concentration and thereby
plays a role in the maintenance of acid-base balance.
3. Blood Group Determination. RBCs carry the blood group antigens
like A antigen, B antigen and Rh factor. This helps in determination of
blood group and enables to prevent reactions due to incompatible blood
transfusion.
106

Properties of RBCs
1. Suspension Stability. During circulation, the RBCs remain
suspended uniformly in the blood. This property of the RBCs is called
the suspension stability.
2. Specific Gravity
Specific gravity of RBC is 1.092 to 1.101.
3. Rouleaux Formation. When blood is taken out of the blood vessel,
the RBCs pile up one above another like the pile of coins. This property
of the RBCs is called rouleaux formation. It is accelerated by plasma
proteins globulin and fibrinogen.
107

3. Packed Cell Volume (PCV)
Packed Cell Volume (PCV) is the proportion of blood occupied by
RBCs expressed in percentage.
It is also called hematocrit value.
It is 45% of the blood and the plasma volume is 55%.
PVC is used in the diagnosis of anaemia, polycythemia, dehydration and
making a decision for blood transfusion.
108

White blood cells (WBCs)
• White blood cells (WBCs) or leukocytes are the colorless and
nucleated formed elements of blood. They are the only formed
elements that are complete cells, possessing a nucleus and
organelles.
• They are larger than erythrocytes, with a maximum diameter of
18µm.
• WBCs are irregular in shape.
• They do not contain hemoglobin.
110

Cont’n
• They routinely leave the blood stream to perform their defensive
functions in the body’s tissues.
• The life span of WBCs varies. Most live for a few hours to a few days,
since they can be destroyed by invading organisms.
• WBCs are less numerous than RBC – are 5000 to 10,000/µL of blood.
• An abnormally low level of white blood cells (below 5000/µL) is
termed leukopenia and this may be caused by; radiation, shock, and
certain chemotherapeutic agents.
• An abnormally high count of leukocytes (above 10,000µL) is called
leukocytosis.
111

Properties of WBCs
1. Diapedesis (Emigration). Diapedesis is the process by which the
leukocytes squeeze through the narrow blood vessels.
2. Amoeboid Movement. Neutrophils, monocytes and lymphocytes
show amebic movement, characterized by protrusion of the cytoplasm
and change in the shape.
3. Chemotaxis. Chemotaxis is the attraction of WBCs towards the
injured tissues by the chemical substances released at the site of injury.
4. Phagocytosis. Neutrophils and monocytes engulf the foreign bodies
by means of phagocytosis
112

Functions of WBCs
• Generally, WBCs play an important role in defense mechanism.
These cells protect the body from invading organisms or foreign bodies,
either by destroying or inactivating them.
113

Types of WBCs
• WBCs are classified as either granulocytes or agranulocytes,
depending on whether they contain cytoplasmic granules.
Granulocytes.
• Are WBCs with granules in their cytoplasm.
• They include neutrophils, eosinophils, and basophils;
Agranulocytes
• These are WBCs without granules in their cytoplasm.
• They include lymphocytes and monocytes.
114

Neutrophils
• Neutrophils which are also known as polymorphs, comprise 50–70
percent of total leukocyte count.
• They have fine or small granules in the cytoplasm which stain violet
with leishman’s stain.
• Nucleus is multilobed, (2 to 5 lobes).
• The diameter of cell is 10 to 12 μ.
• The neutrophils are amoeboid in nature.
• Neutrophils are rapid responders and very efficient phagocytes with a
preference for bacteria.
115

Cont’n
• Their granules include lysozyme, an enzyme capable of breaking
down, bacterial cell walls; oxidants such as hydrogen peroxide.
• They also contain defensins, proteins that bind to and puncture
bacterial and fungal plasma membranes, so that the cell contents leak
out.
• Abnormally high counts of neutrophils indicate infection and/or
inflammation, particularly triggered by bacteria. They are also found
in burn patients and others experiencing unusual stress.
• Low counts may be caused by drug toxicity and other disorders, and
may increase an individual’s susceptibility to infection. 116

Eosinophils
• Eosinophils comprise 2–4 percent of total leukocyte count
• Have coarse (larger) granules in the cytoplasm, which stain pink or red
with eosin.
• Nucleus is bilobed and spectacle-shaped.
• Have a diameter of 10 to14 μ.
• The granules of eosinophils contain antihistamine molecules.
• Some eosinophils also have molecules toxic to parasitic worms.
• Eosinophils are also capable of phagocytosis.
117

Cont’n
• High counts of eosinophils are typical of patients experiencing
allergies, parasitic worm infestations, and some autoimmune diseases.
• Low counts may be due to drug toxicity and stress.
118

Basophils
• Basophils comprise less than 1 percent leukocyte count.
• Have coarse granules in the cytoplasm.
• The granules stain purple blue with methylene blue.
• Nucleus is bilobed.
• Diameter is 8 to 10 μ.
• Like mast cells, basophils intensify the inflammatory response.
• High counts of basophils are associated with allergies, parasitic
infections, and hypothyroidism.
• Low counts are associated with pregnancy, stress, and hyperthyroidism
119

Monocytes
• Monocytes are the largest leukocytes with diameter of 14 to 18 μ.
• They represent 2–8 percent of the total leukocyte count.
• Nucleus is round, oval and horseshoe shaped (bean or kidney shaped).
• Nucleus is placed either in the center of the cell or pushed to one side
and a large amount of cytoplasm is seen.
• They are very effective phagocytic cells engulfing pathogens and
worn-out cells.
• They also serve as antigen presenting cells (APCs) for other
components of the immune system.
120

Cont’n
• Macrophages are monocytes that have left the circulation and
phagocytize debris, foreign pathogens, worn-out erythrocytes, and
many other dead, worn out, or damaged cells.
• Macrophages also release chemotactic chemicals that attract other
leukocytes to the site of an infection.
• Abnormally high counts of monocytes are associated with viral or
fungal infections, tuberculosis, and some forms of leukemia and other
chronic diseases.
• Abnormally low counts are typically caused by suppression of the
bone marrow. 121

Lymphocytes
• Like monocytes, the lymphocytes also do not have granules in the
cytoplasm.
• Nucleus is oval, bean-shaped or kidney-shaped.
• Nucleus occupies the whole of the cytoplasm. A rim of cytoplasm may
or may not be seen.
122

Types of Lymphocytes
• Depending on their function, lymphocytes can be classified as;
1. T lymphocytes: Cells concerned with cellular immunity – directly
attack other cells.
2. B lymphocytes: Cells concerned with humoral immunity – release
antibodies.
123

T lymphocytes
• T lymphocytes (T cells) are processed in thymus.
Types of T Lymphocytes
• During the processing, T lymphocytes are transformed into four types:
1. Helper T cells or inducer T cells. These cells are also called CD4 cells
because of the presence of molecules called CD4 on their surface.
2. Cytotoxic T cells or killer T cells. These cells are also called CD8
cells because of the presence of molecules called CD8 on their surface.
3. Suppressor T cells.
4. Memory T cells.
124

B lymphocytes
• B lymphocytes (B cells) are processed in the liver (during fetal life)
and bone marrow (after birth).
Types of B Lymphocytes
• After processing, the B lymphocytes are transformed into two types:
1. Plasma cells.
2. Memory cells.
NB: After transformation lymphocytes are stored in the lymphoid
tissues of lymph nodes, spleen, bone marrow and the GI tract.
125

Summary of functions of lymphocytes
Cell Function
Cytotoxic T cell Kills host target cells by releasing granzymes that
induce apoptosis, perforin that forms channels to
cause cytolysis, etc.
Memory T cell Remains in lymphatic tissue and recognizes original
invading antigens, even years after the first
encounter.
Suppressor T cell Suppresses the activities of killer T cells, preventing
them from destroying the body’s own tissues.
126

Cont’n
Cell Function
Helper T cell Activates all other T and B cells
B cell Differentiates into antibody producing plasma cells.
Plasma cell Descendant of B cell that produces and secretes
antibodies.
Memory B cell Descendant of B cell that remains after an immune
response and is ready to respond rapidly and
forcefully should the same antigen enter the body in
the future.
127

Cont’n
• Abnormally high lymphocyte counts are characteristic of viral
infections as well as some types of cancer.
• Abnormally low lymphocyte counts are characteristic of prolonged
(chronic) illness or immunosuppression, including that caused by HIV
infection and drug therapies that often involve steroids.
128

3. Platelets
• Platelets, also called thrombocytes are small colorless, non-nucleated
and moderately refractive bodies.
• They are considered to be the fragments of cytoplasm.
• They have a diameter of 2.5 μ (2 to 4 μ).
• Average lifespan of platelets is 10 days, then they are phagocytized by
the macrophages.
• The normal platelet count is 150,000–160,000 per μL of blood.
• An abnormally low count of platelets is called thrombocytopenia and
an abnormally high count is called thrombocytosis.
130

Properties Of Platelets
Platelets have three important properties (three ‘A’s):
1.Adhesiveness
• This is the property of sticking to a rough surface.
2. Aggregation
This is the grouping of platelets.
3. Agglutination.
• This means clumping together of platelets. Aggregated platelets are
agglutinated by the actions of some platelet agglutinins and platelet-
activating factor.
131

Functions Of Platelets
• Platelets play an important role in blood clotting (hemostasis).
• They also take part in preventing excess blood loss.
• Release growth factors for tissue repair and healing.
• Defense.
132

FUNCTIONS OF BLOOD
❑NUTRITIVE FUNCTION
Nutritive substances like glucose, amino acids, lipids and vitamins
derived from digested food are absorbed from gastrointestinal tract and
carried by blood to different parts of the body for growth and production
of energy.
❑EXCRETORY FUNCTION
Waste products formed in the tissues during various metabolic activities
are removed by blood and carried to the excretory organs like kidney,
skin, liver, etc. for excretion.
133

❑TRANSPORT OF HORMONES AND ENZYMES
Hormones which are secreted by ductless (endocrine) glands are
released directly into the blood. The blood transports these hormones
to their target organs/tissues.
Blood also transports enzymes.
❑REGULATION OF WATER BALANCE
Water content of the blood is freely interchangeable with interstitial
fluid. This helps in the regulation of water content of the body.
❑REGULATION OF ACID-BASE BALANCE
Plasma proteins and hemoglobin act as buffers and help in the
regulation of acid-base balance
134

❑REGULATION OF BODY TEMPERATURE
Because of the high specific heat of blood, it is responsible for
maintaining the thermoregulatory mechanism in the body, i.e. the
balance between heat loss and heat gain in the body.
❑STORAGE FUNCTION
Water and some important substances like proteins, glucose, sodium
and potassium are constantly required by the tissues. Blood serves as a
readymade source for these substances. And, these substances are
taken from blood during the conditions like starvation, fluid loss,
electrolyte loss, etc.
135

❑DEFENSIVE FUNCTION
Blood plays an important role in the defense of the body. The white
blood cells are responsible for this function. Neutrophils and monocytes
engulf the bacteria by phagocytosis. Lymphocytes are involved in
development of immunity. Eosinophils are responsible for
detoxification, disintegration and removal of foreign proteins.
❑RESPIRATORY FUNCTION
Transport of respiratory gases is done by the blood. It carries oxygen
from alveoli of lungs to different tissues and carbon dioxide from tissues
to alveoli.
136

BLOOD DISODER’S
• Anemia - A condition in which the body lacks enough healthy
red blood cells to carry adequate oxygen to the body's tissues
• Lymphoma is a type of blood cancer that affects the lymphatic system,
which is part of the immune system
• Leukemia is a type of cancer that affects the blood and bone marrow,
the spongy center of bones where blood cells are made
• Myeloma - A type of blood cancer that affects plasma cells, a
type of white blood cell that produces antibodies.
• Hemophilia is a rare bleeding disorder in which the blood
doesn't clot normally
137

Blood Disorders
a) RBC disorders
1. Anaemia
Anemia is the blood disorder, characterized by the reduction in the red
blood cell (RBC) count, hemoglobin content and packed cell volume
(PVC).
General causes of anaemia
1. Decreased production of RBC
2. Increased destruction of RBC
3. Excess loss of blood from the body.
138

Types of anaemia
i). Hemorrhagic anaemia
This is a type of anaemia caused by excessive loss of RBCs due to
bleeding.
causes
• Acute loss of blood due to accidents.
• Chronic conditions like peptic ulcer, purpura, hemophilia and
menorrhagia (heavy menstruation).
140

HEMOLYTIC ANEMIA
• Hemolysis means destruction of RBCs.
• Anemia due to excessive hemolysis which is not compensated by
increased RBC production is called hemolytic anemia.
It is classified into two types:
A. Extrinsic hemolytic anemia. It is the type of anemia caused by
destruction of RBCs by external factors. Healthy RBCs are
hemolyzed by factors outside the blood cells such as antibodies,
chemicals and drugs.
B. Intrinsic hemolytic anemia. Extrinsic hemolytic anemia is also
called autoimmune hemolytic anemia.
141

ii) Hemolytic anaemia
• Hemolytic anaemia is any disorder that causes rupture of RBCs before
the end of their normal life span.
• Hemolytic anemias are often characterized by jaundice because of the
increased production of bilirubin.
Causes
i). Liver failure.
ii). Renal disorder.
iii. Hypersplenism.
iv. Burns.
142

Cont’n
v. Infections – hepatitis, malaria and septicemia.
vi. Drugs – Penicillin, antimalarial drugs and sulfa drugs.
vii. Poisoning by lead, coal and tar.
viii. Presence of isoagglutinins like anti Rh.
xi. Autoimmune diseases – rheumatoid arthritis and ulcerative colitis.
143

iii) Iron Deficiency Anemia
• Iron deficiency anemia is the most common type of anemia.
Causes of iron deficiency anemia:
i. Loss of blood
ii. Decreased intake of iron
iii. Poor absorption of iron from intestine
iv. Increased demand for iron in conditions like growth and pregnancy
144

iv) Megaloblastic anaemia
• Megaloblastic anaemia is a type of anaemia characterized by
production of large, abnormal red blood cells (megaloblasts).
Causes
oInadequate intake of vitamin B12 or folic acid.
oDrugs that alter gastric secretion or are used to treat cancer.
145

v) Pernicious Anemia.
• Pernicious anaemia is a type of anaemia caused by deficiency of
vitamin B12.
Causes
• Insufficient dietary intake of vitamin B12.
• Lack of the intrinsic factor due to autoimmune destruction of the
parietal cells of the stomach lining. This intrinsic factor is needed in
the absorption of vitamin B12 in the intestines.
146

vi) Aplastic anemia
• Aplastic anemia is suppression of the red bone marrow, with a
resultant decrease in the production of RBCs, WBCs, and platelets.
• Causes
• Exposure to radiation, certain chemicals such as benzene, or some
medications.
147

vi) Sickle cell anaemia
• Sickle cell anaemia is a type of anaemia where an individual has
abnormal hemoglobin (sickle shaped).
• Sickle-cell disease is hereditary - it is inherited from the parents.
148

viii) Thalassemia
• Thalassemia is an inherited disorder, characterized by abnormal
hemoglobin.
• Thalassemia is of two types:
i. α thalassemia. In this type αchains are less, absent or abnormal, with
excess of ß chains.
ii. β thalassemia. In this type, βchains are less in number, absent or
abnormal with an excess of α chains.
149

2. Polycythemia
• In contrast to anemia, an elevated RBC count is called polycythemia
and is detected in a patient’s elevated hematocrit.
150

b) WBC disorders
• Leukopenia is a condition in which too few leukocytes are produced.
• Leukocytosis. Is a condition in which there is excessive proliferation
of leukocytes. Although leukocyte counts are high, the cells
themselves are often nonfunctional, leaving the individual at
increased risk for disease.
• Leukemia is a cancer involving an abundance of leukocytes. It may
involve only one specific type of leukocyte.
• Lymphoma is a form of cancer in which masses of malignant T and/or
B lymphocytes collect in lymph nodes, the spleen, the liver, and other
tissues.
151

c) Platelets Disorders
1. Thrombocytosis is a condition in which there are too many platelets.
This may trigger formation of unwanted blood clots (thrombosis), a
potentially fatal disorder.
2. Thrombocytopenia is a condition in which there is insufficient
number of platelets. As a result, blood may not clot properly, leading to
excessive bleeding.
3. Hemophilia. is a group of sex-linked inherited blood disorders,
characterized by prolonged clotting time.
Because of prolonged clotting time, even a mild trauma causes excess
bleeding which can lead to death. 152

Body Fluids
Introduction
The chemical reactions of life take place in aqueous solutions.
The dissolved substances in a solution are called solutes. These include
proteins—including those that transport lipids, carbohydrates, and, very
importantly, electrolytes.
Often in medicine, a mineral dissociated from a salt that carries an
electrical charge (an ion) is called and electrolyte. For instance, sodium
ions (Na+) and chloride ions (Cl-) are often referred to as electrolytes.
Most of the human body is made up of water (50-60%) and it moves
from one compartment to another by a process called osmosis.
153

Body fluid compartments
A fluid compartment is a location that is largely separate from another
compartment by some form of a physical barrier.
Total water in the body is about 40 L.
It is distributed into two major compartments:
1. Intracellular fluid (ICF) compartment. Is the system that includes
all fluid enclosed in cells by their plasma membranes.
Its volume is 22 L and it forms 55% of the total body water
2. Extracellular fluid (ECF): Its volume is 18 L and it forms 45% of
the total body water.
154

Cont’n
Extracellular fluid (ECF): ECF surrounds all cells in the body.
Its volume is 18 L and it forms 45% of the total body water.
Extracellular fluid has two primary constituents:
• The fluid component of the blood (called plasma) and
• The interstitial fluid (IF) that surrounds all cells not in the blood.
155

Composition Of Body Fluids
• Body fluids contain water and solids. Solids are organic and inorganic
substances.
• Organic substances are glucose, amino acids and other proteins, fatty
acids and other lipids, hormones and enzymes.
• Inorganic substances present in body fluids are sodium, potassium,
calcium, magnesium, chloride, bicarbonate, phosphate and sulfate.
• ECF contains large quantity of sodium, chloride, bicarbonate, glucose,
fatty acids and oxygen.
156

Cont’n
• ICF contains large quantities of potassium, magnesium, phosphates,
sulfates and proteins.
• The pH of ECF is 7.4.
• The pH of ICF is 7.0.
157

Important Constituents of the Intracellular Fluid
• The intracellular fluid is separated from the extracellular fluid by a
cell membrane that is highly permeable to water but not to most of
the electrolytes in the body.
• In contrast to the extracellular fluid, the intracellular fluid contains
only small quantities of sodium and chloride ions and almost no
calcium ions.
• Instead, it contains large amounts of potassium and phosphate ions
plus moderate quantities of magnesium and sulfate ions, all of
which have low concentrations in the extracellular fluid.
• Also, cells contain large amounts of protein, almost four times as
much as in the plasma
158

The lymphatic system
• Lymphatic system is a closed system of lymph channels or lymph
vessels, through which lymph flows. It is a one-way system and allows
the lymph flow from tissue spaces toward the blood.
• The lymphatic system is responsible for returning tissue fluid to the
blood and for protecting the body against foreign material.
• The lymphatic system consists of a fluid called lymph, vessels called
lymphatic vessels that transport the lymph, a number of structures and
organs containing lymphatic tissue, called lymphatic organs.
160

Functions of the Lymphatic System
The lymphatic system has three primary functions:
1. Drains excess interstitial fluid. Lymphatic vessels drain excess
interstitial fluid from tissue spaces and return it to the blood.
2. Transports dietary lipids. Lymphatic vessels transport lipids and
lipid-soluble vitamins (A, D, E, and K) absorbed by the gastrointestinal
tract.
3. Carries out immune responses. Lymphatic tissue initiates highly
specific responses directed against particular microbes or abnormal
cells.
161

Lymph
Definition
Lymph is a clear and colorless fluid that flows in lymph vessels. It is formed
by 96% water and 4% solids.
Formation
Lymph is formed from interstitial fluid, due to the permeability of lymph
capillaries. When blood passes via blood capillaries in the tissues, 9/10th of
fluid passes into venous end of capillaries from the arterial end.
And, the remaining 1/10th of the fluid passes into lymph capillaries, which
have more permeability than blood capillaries.
162

Functions of lymph
1. Returns the proteins from tissue spaces into blood.
2. It is responsible for redistribution of fluid in the body.
3. Bacteria, toxins and other foreign bodies are removed from tissues via
lymph.
4. Lymph flow is responsible for the maintenance of structural and
functional integrity of tissue.
5. Lymph flow serves as an important route for intestinal fat absorption.
This is why lymph appears milky after a fatty meal.
6. It plays an important role in immunity by transporting lymphocytes.
164

Differences Between Blood And Lymph
Blood Lymph
Blood is red in colour. Lymph is colourless.
It flows in blood vessels. It flows in lymph vessels.
It is pumped by the heart It is pumped by skeletal muscle
and respiratory pumps
Blood flows in a two-way pathway
– from the heart to tissues and back
Lymph flows in one direction and
drains into the subclavian vein.
Blood transports respiratory gases,
nutrients, hormones and wastes.
Lymph returns plasma protein into
blood.
165

Lymphatic Vessels and Lymph Circulation
• Lymphatic vessels begin as lymphatic capillaries, tiny vessels with
closed ends located between cells.
• Lymphatic capillaries unite to form larger lymphatic vessels, which
resemble veins in structure but have thinner walls and more valves.
• Lymphatic vessels become larger and larger as they join together,
eventually forming two large ducts, the thoracic duct and the right
lymphatic duct.
• Right lymphatic duct opens into right subclavian vein and the
thoracic duct opens into left subclavian vein.
166

Lymphatic Organs and Tissues
• Lymphatic organs or tissues can be categorized into two;
• Primary lymphatic organs are the sites where stem cells divide and
become immunocompetent, (capable of mounting an immune
response).
• They include the red bone marrow and the thymus.
• The secondary lymphatic organs and tissues are the sites where
most immune responses occur.
• They include lymph nodes, the spleen, and lymphatic nodules
(follicles).
167

Disorders of fluid balance
Edema
• Edema is the accumulation of excess water in the tissues. It is most
common in the soft tissues of the extremities.
Causes
• Pregnancy
• Certain therapeutic drugs,
• Localized injury
• An allergic reaction.
168

Symptoms
In the limbs, the symptoms of edema include;
• Swelling of the subcutaneous tissues,
• An increase in the normal size of the limb, and
• Stretched, tight skin.
169

Assignment 1
• Describe all the diseases of the heart.
• Describe coronary circulation
• Outline the blood vessel that constitute the circle of Willis
Hand in in one week's time.
170

Cardiovascular System: Structure, Function, and Clinical Insights

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