Epithelium Tissue and Its Types | Zoology – Biology Class 12

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Epithelium tissueBiology – Zoology | Animal Tissue
Epithelium Tissue and Its Types
For: Science Class 12

The word epithelium is composed of two words epi and thelis which mean on and grows respectively. Thus epithelium is a kind of tissue which grows upon another kind of tissue. Therefore it is also called covering tissue. The cells of epithelium are compactly arranged and form thin cover of single layer or multi layer. The epithelium tissue remains connected to another tissue by means of basement membrane which is permeable for exchanging useful and harmful substances.

Types of Epithelium
Depending on number of cells layers, epithelium is divided into two types simple and compound.

a) Simple Epithelium
Simple epithelium is single layered epithelium which is located in the organs that take part in absorption, filtration and secretion. According to the shape of the cells, simple epithelium is divided into squamous, cuboidal columnar and Pseudo stratified. The epithelium which is composed of flattened cells with centrally placed nucleus is called squamous epithelium. It looks like tile on the floor hence also known as permanent epithelium. It is distributed in blood ressels and in the linings of alveoli.

The epithelium which is composed of cube shaped cells is called cuboidal epithelium. The cells have centrally wetted nucleus and are distributed in the organs which take part in the excretion, absorption and secretion. If the epithelium is composed of column shaped cells then it is called columnar epithelium. The cells are cylindrical and may contain cilia at the tree part. This kind of columnar epithelium is called ciliated columnar epithelium which is located in the organs which take part in bringing movement absorption. The Pseudo stratified epithelium is composed of cylindrical cells but the nuclei in the cells are at different level. These epithelia are found in the trachea, renal tubules, vas deference etc.

b) Compound Epithelium
The epithelium which is composed of several layers of cell is called compound epithelium. It is of two types, stratified and transitional. The stratified epithelium is founded in the places where much wear and tear takes place. They are located in the skin, lining of mouth cavity, tongue, oesophagus, ragina and stomach. The lowermost cells are attached to the basement membrane produce new cells by mitosis division.

The transitional epithelium is also called plastie epithelium because it is stretchable inresponse to tension. This epithelium is found in the urinary bladder, uretar and urethra.

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