ANIMAL TISSUES

We learnt about the distinctive features of an animal cell in the previous section. Now, we shall discuss about the tissues, organs, and organ systems, their structure and function.

   Tissues are broadly classified into four major types which show division of labour in multicellular organisms.

EPITHELIAL TISSUES

Epithelial tissues form sheet of cells that either covers the external surface or lines the internal structure. It can be further subdivided into

     (i)   Simple,  which is one-layer thick e.g; epidermis of skin

     (ii)  Stratified, which have two or more layers e.g., esophagus lining, and

     (iii)  Ciliated e.g., lung alveoli

     (iv)  Pseudpstratifed contains only a single layer of cells, but it appears to have multiple layers because the cell nuclei lie at different levels and not all cells reach the apical surface, e.g., upper respiratory tract.

Simple and stratified epithelial tissues are also classified o the basis of shape into following types:

·         Squamous   -These are thin plate-like cells arranged like tiles on the floor e.g., lining of mouth, nose, blood vessel, etc.

·         Cuboidal-These cells are cube like e.g., kidney tubules, thyroid vesicles, etc,

·         Columnar – these cells are cube like e.g. lining of intestine

·         Transitional – These cells change shape, as organs stretch and relax. E.g., urinary bladder.

·         Function: Protection, Transport Secretion, Sensory reception, etc.