Tissue level of organization.ppt

P r e s e n t e d b y : A b h i s h e k D a b ra ( A s s t . P r o f. )
B. PHARMACY-IST SEMESTER,
UNIT-I, CHAPTER-III
TISSUE LEVEL OF ORGANIZATION
Guru Gobind Singh College of Pharmacy,
Yamunanagar

Tissue
The tissues of the body consist of large numbers of cells and they
are classified according to the size, shape and functions of these
cells. There are four main types of tissue, each of which has
subdivisions.
They are:
A. Epithelial tissue or epithelium
B. Connective tissue
C. Muscle tissue
D. Nervous tissue

A. Epithelial Tissue
This group of tissues is found covering the body and lining cavities
and tubes. It is also found in glands. The structure of epithelium is
closely related to its functions which include:
 protection of underlying structures from, for example,
dehydration, chemical and mechanical damage
 secretion
 Absorption
The cells are very closely packed and the intercellular substance,
called the matrix, is minimal. The cells usually lie on a basement
membrane, which is an inert connective tissue.
Epithelial tissue may be:
1. Simple epithelium: a single layer of cells
2. Stratified epithelium: several layers of cells.

1. Simple Epithelium
 Simple epithelium consists of a single layer of identical cells and
is divided into four types. It is usually found on absorptive or
secretory surfaces, where the single layer enhances these
processes, and not usually on surfaces subject to stress.
 The types are named according to the shape of the cells, which
differs according to their functions. The more active the tissue,
the taller are the cells.
a. Squamous (Pavement) epithelium
b. Cuboidal epithelium
c. Columnar epithelium
d. Ciliated epithelium

a. Squamous (Pavement) epithelium:
 This is composed of a single layer of flattened cells. The cells fit
closely together like flat stones, forming a thin and very smooth
membrane.
 Diffusion takes place freely through this thin, smooth, inactive
lining of the following structures:
where it is
also known as
endothelium
Heart
Blood vessels
Lymph vessels
Alveoli of the lungs.

b. Cuboidal epithelium:
 This consists of cube-shaped cells fitting closely together lying on
a basement membrane.
 It forms the tubules of the kidneys and is found in some glands.
Cuboidal epithelium is actively involved in secretion, absorption
and excretion.
c. Columnar epithelium:
 This is formed by a single layer of cells, rectangular in shape, on a
basement membrane. It is found lining the organs of the
alimentary tract and consists of a mixture of cells; some absorb
the products of digestion and others secrete mucus.

 Mucus is a thick sticky substance secreted by modified columnar
cells called goblet cells.
d. Ciliated epithelium:
 This is formed by columnar cells each of which has many fine,
hair-like processes, called cilia.
 The wave-like movement of many cilia propels the contents of
the tubes, which they line in one direction only.

 Ciliated epithelium is found lining the uterine tubes and most of
the respiratory passages. In the uterine tubes, the cilia propel
ova towards the uterus and in the respiratory passages they
propel mucus towards the Throat.

2. Stratified Epithelium
 Stratified epithelia consist of several layers of cells of various
shapes. The superficial layers grow up from below. Basement
membranes are usually absent.
 The main function of stratified epithelium is to protect
underlying structures from mechanical wear and tear. There are
two main types: stratified squamous and transitional.
a) Stratified squamous epithelium:
 This is composed of a number of layers of cells of different
shapes representing newly formed and mature cells.
 In the deepest layers the cells are mainly columnar and, as they
grow towards the surface, they become flattened and are then
shed

i. Non-Keratinised stratified epithelium.
 This is found on wet surfaces that may be subjected to wear and
tear but are protected from drying, e.g. the conjunctiva of the
eyes, the lining of the mouth, the pharynx, the oesophagus and
the vagina.
ii. Keratinised stratified epithelium:
 This is found on dry surfaces that are subjected to wear and tear,
i.e. skin, hair and nails.
 The surface layer consists of dead epithelial cells to which the
protein keratin has been added.
 This forms a tough, relatively waterproof protective layer that
prevents drying of the underlying live cells. The surface layer of
skin is rubbed off and is replaced from below.

b. Transitional epithelium:
This is composed of several
layers of pear-shaped cells
and is found lining the urinary
bladder. It allows for
stretching as the bladder fills.

B. Connective Tissue
 Connective tissue is the most abundant tissue in the body. The
cells forming the connective tissues are more widely separated
from each other than those forming the epithelium, and
intercellular substance (matrix) is present in considerably larger
amounts.
 There may or may not be fibres present in the matrix, which may
be of a semisolid jelly-like consistency or dense and rigid,
depending upon the position and function of the tissue.
 Major functions of connective tissue are:
 binding and structural support
 protection
 transport
 insulation.

Cells of connective tissue:
Connective tissue, excluding blood, is found in all organs
supporting the specialized tissue. The different types of cell
involved include:
i. fibroblasts
ii. fat cells
iii. macrophages
iv. leukocytes
v. mast cells
i. Fibroblasts:
 Fibroblasts are large flat cells with irregular processes. They
produce collagen and elastic fibres and a matrix of extracellular
material.
 Very fine collagen fibres, sometimes called reticulin fibres, are
found in very active tissue, such as the liver and lymphoid
tissue.

 Fibroblasts are particularly active in tissue repair (wound
healing) where they may bind together the cut surfaces of
wounds or form granulation tissue following tissue destruction.
ii. Fat cells:
 Also known as adipocytes these cells occur singly or in groups in
many types of connective tissue and are especially abundant in
adipose tissue. They vary in size and shape according to the
amount of fat they contain.
iii. Macrophages:
 These are irregular-shaped cells with granules in the cytoplasm.
Some are fixed, i.e. attached to connective tissue fibres, and
others are motile.
 They are an important part of the body's defense mechanisms
as they are actively phagocytic, engulfing and digesting cell
debris, bacteria and other foreign bodies.

 Their activities are typical of those of the
macrophage/monocyte defense system e.g. monocytes in
blood, phagocytes in the alveoli of the lungs Kupffer cells in
liver sinusoids, fibroblasts in lymph nodes and spleen and
microglial cells in the brain.
iv. Leukocytes:
 White blood cells are normally found in small numbers in
healthy connective tissue but migrate in significant numbers
during infection when they play an important part in tissue
defense.
 Lymphocytes synthesize and secrete specific antibodies into the
blood in the presence of foreign material, such as microbes.
v. Mast cells:
These cells are similar to basophil leukocytes. They are found in
loose connective tissue and under the fibrous capsule of some
organs, e.g. liver and spleen, and in considerable numbers round
blood vessels.

 They produce granules containing heparin, histamine and other
substances, which are released when the cells are damaged by
disease or injury.
 Histamine is involved in local and general inflammatory
reactions, it stimulates the secretion of gastric juice and is
associated with the development of allergies and
hypersensitivity states.
 Heparin prevents coagulation of blood, which may aid the
passage of protective substances from blood to affected tissues.

Types of connective tissue:
a) Loose (areolar) connective tissue
b) Adipose tissue
c) Dense connective tissue
d) Blood
e) Cartilage
f) Bone
a) Loose (areolar) connective tissue:
This is the most generalized of all connective tissue. The matrix is
described as semisolid with many fibroblasts and some fat cells,
mast cells and macrophages widely separated by elastic and
collagen fibres. It is found in almost every part of the body
providing elasticity and tensile strength. It connects and supports
other tissues, for example:
 under the skin
 between muscles

 supporting blood vessels and nerves
 in the alimentary canal
 in glands supporting secretory cells.
Loose (areolar) connective tissue
b. Adipose tissue:
Adipose tissue consists of fat cells (adipocytes), containing large
fat globules, in a matrix of areolar tissue. There are two types:
white and brown.

i. White adipose tissue.
 This makes up 20 to 25% of body weight in well-nourished
adults. The amount of adipose tissue in an individual is
determined by the balance between energy intake and
expenditure.
 It is found supporting the kidneys and the eyes, between muscle
fibres and under the skin, where it acts as a thermal insulator.
ii. Brown adipose tissue:
 This is present in the newborn. It has a more extensive capillary
network than white adipose tissue.
 When brown tissue is metabolized, it produces less energy and
considerably more heat than other fat, contributing to the
maintenance of body temperature.
 In adults it is present in only small amounts.

c. Dense connective tissue:
i. Fibrous tissue:
This tissue is made up mainly of closely packed bundles of collagen
fibres with very little matrix. Fibrous tissue is found:
 forming the ligaments, which bind bones together
 as an outer protective covering for bone, called periosteum
 as an outer protective covering of some organs, e.g. the kidneys,
lymph nodes and the brain
 forming muscle sheaths, called muscle fascia, which extend
beyond the muscle to become the tendon that attaches the
muscle to bone.
ii. Elastic tissue:
 Elastic tissue is capable of considerable extension and recoil.
There are few cells and the matrix consists mainly of masses of
elastic fibres secreted by fibroblasts. It is found in organs where
alteration of shape is required, e.g. in large blood vessel walls,
the epiglottis and the outer ears.

d. Blood:
Blood is a connective tissue. It provides one of the means of
communication between the cells of different parts of the body
and the external environment, e.g. it carries:
i. oxygen from the lungs to the tissues and carbon dioxide from
the tissues to the lungs for excretion
ii. nutrients from the alimentary tract to the tissues and cell
wastes to the excretory organs, principally the kidneys
iii. hormones secreted by endocrine glands to their target glands
and tissues
iv. heat produced in active tissues to other less active tissues
v. protective substances, e.g. antibodies, to areas of infection
vi. clotting factors that coagulate blood, minimizing its loss from
ruptured blood vessels.

e. Lymphoid tissue:
This tissue has a semisolid matrix with fine branching reticulin
fibres. It contains white blood cells (monocytes and lymphocytes).
They are found in blood and in lymphoid tissue in the:
 lymph nodes
 spleen
 palatine and pharyngeal tonsils
 vermiform appendix
 solitary and aggregated nodes in the small intestine
 wall of the large intestine.
f. Cartilage:
Cartilage is a much firmer tissue than any of the other connective
tissues; the cells are called chondrocytes and are less numerous.
They are embedded in matrix reinforced by collagen and elastic
fibres.

There are three types:
i. hyaline cartilage
ii. fibrocartilage
iii. elastic fibrocartilage
i. hyaline cartilage:
Hyaline cartilage appears as a smooth bluish-white tissue. The
chondrocytes are in small groups within cell nests and the matrix is
solid and smooth. Hyaline cartilage is found:
 on the surface of the parts of the bones that form joints
 forming the costal cartilages, which attach the ribs to the
sternum
 forming part of the larynx, trachea and bronchi.
ii. Fibrocartilage:
This consists of dense masses of white collagen fibres in a matrix
similar to that of hyaline cartilage with the cells widely dispersed.
It is a tough, slightly flexible tissue found:

 as pads between the bodies of the vertebrae, called the
intervertebral discs
 between the articulating surfaces of the bones of the knee
joint, called semilunar cartilages
 on the rim of the bony sockets of the hip and shoulder joints,
deepening the cavities without restricting movement
 as ligaments joining bones.
iii. Elastic cartilage:
This flexible tissue consists of yellow elastic fibres lying in a solid
matrix. The cells lie between the fibres. It forms the pinna or lobe
of the ear, the epiglottis and part of the tunica media of blood
vessel walls

g. Bone:
 Bone is a connective tissue with cells (osteocytes) surrounded
by a matrix of collagen fibres that is strengthened by inorganic
salts, especially calcium and phosphate.
 This provides bones with their characteristic strength and
rigidity. Bone also has considerable capacity for growth in the
first two decades of life, and for regeneration throughout life.

C. Muscle tissue
There are three types of muscle tissue, which consists of
specialised contractile cells:
a. Skeletal muscle
b. Smooth muscle
c. Cardiac muscle
a. Skeletal muscle:
 This may be described as skeletal, striated, striped or voluntary
muscle. It is called voluntary because contraction is under
conscious control.
 When skeletal muscle is examined microscopically the cells are
found to be roughly cylindrical in shape and may be as long as
35 cm.
 Each cell, commonly called a fibre, has several nuclei situated
just under the sarcolemma or cell membrane of each muscle
fibre.

 The muscle fibres lie parallel to one another and, when viewed
under the microscope, they show well-marked transverse dark
and light bands, hence the name striated or striped muscle.

b. Smooth muscles:
Smooth muscle may also be described as non-striated or
involuntary. It is not under conscious control. It is found in the
walls of hollow organs:
 regulating the diameter of blood vessels and parts of the
respiratory tract
 propelling contents of the ureters, ducts of glands and
alimentary tract
 expelling contents of the urinary bladder and uterus.
When examined under a
microscope, the cells are seen to
be spindle shaped with only one
central nucleus. There is no
distinct sarcolemma but a very
fine membrane surrounds each
fibre.
Smooth muscle fibre

Cardiac muscle tissue:
 This type of muscle tissue is found exclusively in the wall of the
heart.
 It is not under conscious control but, when viewed under a
microscope, cross-stripes characteristic of voluntary muscle can
be seen.
 Each fibre (cell) has a nucleus and one or more branches. The
ends of the cells and their branches are in very close contact
with the ends and branches of adjacent cells.
 This arrangement gives cardiac muscle the appearance of a sheet
of muscle rather than a very large number of individual fibres.
 The end-to-end continuity of cardiac muscle cells has
significance in relation to the way the heart contracts.
 A wave of contraction spreads from cell to cell across the
intercalated discs which means that cells do not need to be
stimulated individually.

D. Nervous tissue
 The nervous system detects and responds to changes inside and
outside the body.
 Together with the endocrine system it controls important
aspects of body function and maintains homeostasis.
 The nervous system consists of the brain, the spinal cord and
peripheral nerves.
 Organization of nervous tissue within the body enables rapid
communication between different parts of the body.
 Response to changes in the internal environment maintains
homeostasis and regulates involuntary functions, e.g. blood
pressure and digestive activity.
 Response to changes in the external environment maintains
posture and other voluntary activities.

Neuron
For descriptive purposes the parts of the nervous system are
grouped as follows:
 the central nervous system (CNS), consisting of the brain and
the spinal cord.
 the peripheral nervous system (PNS) consisting of all the nerves
outside the brain and spinal cord.
 The nervous system consists of a vast number of cells called
neurons, supported by a special type of connective tissue,
neuroglia.
 Each neuron consists of a cell body and its processes, one axon
and many dendrites.
 Neurons are commonly referred to simply as nerve cells.
Bundles of axons bound together are called nerves.
 Neurons cannot divide and for survival they need a continuous
supply of oxygen and glucose

 The physiological 'units' of the nervous system are nerve
impulses, or action potentials, which are akin to tiny electrical
charges.
 However, unlike ordinary electrical wires, the neurons are
actively involved in conducting nerve impulses.
 Some neurons initiate nerve impulses while others act as 'relay
stations' where impulses are passed on and sometimes
redirected.
i. Cell bodies
 Nerve cells vary considerably in size and shape but they are all
too small to be seen by the naked eye.
 Cell bodies form the grey matter of the nervous system and are
found at the periphery of the brain and in the center of the
spinal cord.
 Groups of cell bodies are called nuclei in the central nervous
system and ganglia in the peripheral nervous system.

ii. Axon and Dendrites:
 Axons and dendrites are extensions of cell bodies and form the
white matter of the nervous system.
 Axons are found deep in the brain and in groups, called tracts, at
the periphery of the spinal cord.
 They are referred to as nerves or nerve fibres outside the brain
and spinal cord.
a. Axons
Each nerve cell has only one axon, carrying nerve impulses away
from the cell body. They are usually longer than the dendrites,
sometimes as long as 100 cm.
b. Dendrites:
The dendrites are the many short processes that receive and carry
incoming impulses towards cell bodies. They have the same
structure as axons but they are usually shorter and branching. In
motor neurons they form part of synapses and in sensory neurons
they form the sensory receptors that respond to stimuli.

References
1. Waugh A., Grant A., “ Ross and Wilson Anatomy & Physiology in health and illness,
Churchill Livingstone, 12th ed., 2014, Page no. 35-42.

Tissue level of organization.ppt

Tissue level of organization.ppt

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Tissue level of organization.ppt