Structural Organisation In Animal
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ANIMAL TISSUES
Tissue : A group of cells in which cells are similar in structure, function and origin is called tissue.
Group of similar cells along with intercellular substance perform a specific function such organisation is called
tissue. But in a tissue, cells may be dissimilar in structure and function but they are always similar in origin.
Organ : Tissues are organised in specific proportion and pattern to form organ.
Organ system : When two or more organ perform common function by their physical &/or chemical
interaction, they together form organ system.
Division of labour: Cell, tissue, organs and organ systems splits up the work in a way that they exhibit division
of labour.
On the basis of functions & structure tissues are of four types :
1. Epithelium/Epithelial Tissue : Covering & protective tissue.
2. Connective Tissue – To connect structures, provide support to the body and transport substances in
the body.
3. Muscular Tissue – Helps in contraction & locomotion.
4. Nervous tissue – To generate and conduct nerve impulses in body
Origin of Epithelium Tissue
It is the only tissue which originated from all the three primordial germinal layers.
eg. (i) Ectodermal – Epidermis (stratified squamous Epithelium)
(ii) Mesodermal – Mesothelium (simple squamous Epithelium)
(iii) Endodermal – Inner living of gut (simple columnar Epithelium)
Simple Squamous epithelium
(i) Single layer of flat, scale like cells with
irregular boundries.
(ii) It is also called pavement
epithelium due to its tile like
appearance.
(iii) It is also called Tesselated
epithelium due to its wavy
appearance.
Functions : Forming a diffusion boundaryeg.
It is found in the lining of :
– Bowman's capsule (Podocyte)
Alveoli of lungs (Pneumocytes)
Mesothelium – Covering of coelom is called as mesothelium.(Tesselated).
(Visceral & Parietal peritonium, Visceral and parietal pleura, Visceral and Parietal
pericardium).
– Endothelium – Inner lining of blood vessels and lymph vessels. (Tesselated)
– Inner lining of heart wall (Tesselated).
Simple Cuboidal Epithelium
(i) Cells are cube like in shape.
(ii) This epithelium is also called Germinal epthelium because in gonads (testis & ovaries) cubodial cells
divide to form egg & sperm.
Simple columnar Epithelium
(i) Cells are pillar like in shape. (Tall and Slender)
(ii) Elongated nucleus is present at the base of cell
PSEUDOSTRATIFIED EPITHELIUM
(i) These cells are pillar like in shape so it is also a
modification of columnar epithelum.
(ii) In this epithelium two types of cells are present
i.e.Long cells, Short cells.
(iii) Nucleus in both cells are present on different level
so it appears bilayered because few cells are too
short to reach the top surface.But all cells are
present on single basement membrane so it is unilayered
Pseudostratified ciliated columnar glandular epithelium [PSCCGE] :
In this epithelium cillia are present of free end of long cells and goblet cells are also present in this epithelium.
eg. Trachea
Bronchioles
Respiratory epithelium of nasal chambers
COMPOUND EPITHELIUM
It is multilayered and have limited role in secretion and absorption. It provide protection against chemical &
mechanical stress.
On the basis of stretching ability it is of 2 types –
(1) Transitional epithelium :– Stretchable.
(2) Stratified epithelium :– Non-stretchable
1. Transitional Epithelium (Urothelium)
(1) In resting conditions a thin basement
membrane is present but on stretching
basement membrane almost get
disappeared.
(2) In this epithelium 4-6 layers of cells are
persent.
– Inner most layer of cell is
composed of cube like cells.
– Middle 2-4 layers are composed
of pear shaped or umbrella shaped
cells/Polyheadral cells.
– Outermost 1 or 2 layers are of oval shaped cells.
– These different shape of cells appears only in resting stage. When this tissue is stretched, all the cells
become flattened.
– At outermost layer a thin cuticle line is present which makes this tissue water proof
– Cells are interconnected by interdigitation.
Eg. Renal Pelvis, Ureter, Urinary Bladder, Proximal part of male urethra
Stratified Epithelium
On the basis of shape of the cells of outermost layer it is of three types.
(A) STRATIFIED SQUAMOUS EPITHELIUM
(i) Innermost layer of cells are of cuboidal. These cells have high mitotic index. They get their nutrition from
underlaying connective tissue.They divide to from layers of Stratified epithelium so this layer is called as
Germinativum layer.
(ii) Middle layers are made up of polygonal cells. These cells are interconnected with Desmosomes which provide
rigidity or mechanical support.
(iii) Cells of outermost layer are scale like flat cells.
On the basis of presence of keratin protein in the outer most cells this epitheluim is of two types .
1. Keratinized Stratified squamous epithelium.
If keratin protein is present in scaly cells and cells become non nucleated dead cells
Non Keratinized Stratified squamous epithelium.
If Keratin protein is absent. Cells are nucleated and Living.
eg. – Buccal cavity or oral cavity of mammals
– Inner lining of cheeks, lips, hard palate, tonsils,
– Pharynx, Oesophagus, Anal canal,
– Lining of vagina
– Cornea of eye
STRATIFIED CUBOIDAL EPITHELIUM
1. Inner most layer is cuboidal.
2. Middle layer - polygonal shaped cells.
3. Outermost layer of cells are cube like & cells are nucleated & living.
Eg. Secretory duct of sweat glands, mammary glands and sebaceous gland, pancreas, salivary glands
STRATIFIED COLUMNAR EPITHELIUM
Outermost layer is composed of pillar shaped cells, cells are nucleated. On the basis of presence of cilia this
epithelium is of 2 types
(1) Ciliated stratified columnar epithelium.
Eg. Buccopharyngeal cavity of Frog.
Larynx
(2) Non ciliated stratified columnar epithelium. Cilia absent on free end.
Eg. Epiglottis.
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