. Describe the structure and function of different types of epithelial tissues.


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Answer: Epithelial cells are the thin protective coverings that line most organs and cavities within the body. It also forms a barrier to keep different body systems separate. The skin, the lining of the mouth, the lining of blood vessels, lung alveoli and kidney tubules are all made of epithelial tissue. Epithelial tissue cells are tightly packed and form a continuous sheet.

They have only a small amount of cementing material between them and almost no intercellular spaces.

Obviously, anything entering or leaving the body must cross at least one layer of epithelium. As a result, the permeability of the cells of various epithelia plays an important role in regulating the exchange of materials between the body and the external environment and also between different parts of the body. Regardless of the type, all epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.

Epithelial cells are the protective coverings that line most organs and cavities of our body. Epithelial cells form a barrier that keeps different body systems separate. Skin, the lining of blood vessels, alveoli of the lung, kidney tubules etc are made of epithelial tissue. Cells in the epithelial tissue are tightly packed and form a continuous sheet.

 

Epithelial tissue has only a small amount of cementing material between them and almost no intercellular spaces. It is obvious that anything entering or leaving the body must cross at least one layer of epithelium. This results in the permeability of the cells of various epithelia to play an important role in regulating the exchange of materials between the body and the external environment and between different parts of the body.

The epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.

Depending on the shape and function, epithelial cells are classified into a) Squamous epithelial tissue b) Stratified squamous epithelial tissue c) Cuboidal epithelial tissue d) Columnar( Ciliated) epithelial tissue.

a) Squamous epithelial tissue:

In cells lining blood vessels or lung alveoli transportation of substances occurs through a selectively permeable surface, this epithelium is a flat kind of epithelium. This is called the simple squamous epithelium. Simple squamous epithelial cells are extremely thin and flat and form a delicate lining. The oesophagus and the lining of the mouth are also covered with squamous epithelium. The skin, which protects the body, is also made of squamous epithelium. Skin epithelial cells are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.

b) Stratified squamous epithelium: Skin epithelial cells are arranged in many layers to prevent wear and tear. Since they are arranged in a pattern of layers, the epithelium is called stratified squamous epithelium.

c) Columnar epithelium: Where absorption and secretion occur, as, in the inner lining of the intestine, these tall epithelial cells are present. This columnar epithelial facilitates movement across the epithelial barrier. In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair-like projections on the outer surfaces of epithelial cells. These cilia can move and their movement pushes the mucus forward to clear it. This type of epithelium is thus ciliated columnar epithelium.

d) Cuboidal epithelium: These form the lining of the kidney tubules and ducts of salivary glands where these provide mechanical support. Sometimes, a portion of the epithelial tissue folds inward and a multicellular gland is formed. This is the glandular epithelium.

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