Question

Describe the structure and function of different types of epithelial tissues. Draw diagram of each type of epithelial tissue.

Answer 1

Types of Epithelial Tissue: Depending upon the shape and function of the constituent cells, epithelial tissues are of the following types:

• Squamous (cells flattened)
• Columnar (cells tall, columnar or pillar¬like)
• Cuboidal (cells cube-like)
• Ciliated (cells with cilia)
• Glandular (cells secretory in nature)
• Stratified (cells many-layered)

Squamous epithelium: The cells in this epithelium are extremely thin and flat and are arranged edge to edge forming a delicate lining or covering. It forms the lining of cavities of ducts and blood vessels, lines the chambers of the heart, covers the skin, and lining of the mouth. It also lines the pharynx, oesophagus, anal canal, vagina, and lower part of urethra. It provides protection to the underlying parts against abrasion (mechanical injury) and entry of germs or chemicals. It also helps in excretion, gas exchange and secretion of coelomic fluid.

Columnar epithelium: This epithelium consists of cells that are much longer than broad, and look like a column. It forms the lining of stomach and intestines; also found in salivary glands in the mouth, sweat glands, and oil glands of the skin. It also lines mammary gland ducts and parts of urethra. It helps in protection, absorption, and secretion. Columnar epithelium of the intestine is specialised for the absorption of water and digested food.

Cuboidal epithelium: Cells are as long as broad and appear cube-like; a centrally located nucleus is present. The cuboidal epithelium * lines the small salivary ducts, pancreatic ducts, sweat glands, salivary glands, and thyroid glands. It also covers the ovaries and lines the sperm-producing tubules. It helps in protection, secretion, absorption, excretion, and gamete formation. 

Ciliated epithelium: This epithelium, usually consisting of cuboidal or columnar cells, has numerous, thin, delicate, hair-like projections called cilia arising from the outer free surface of the cells. It is found lining the wind-pipe (trachea), kidney tubules, oviducts (Fallopian tubes), and ventricles of the brain. This epithelium helps in the movement of mucus, urine, eggs, sperms, and cerebrospinal fluid in a particular direction.

Glandular epithelium: This epithelium consists of columnar cells modified to secrete chemicals. It lines the glands such as gastric glands, pancreatic lobules, intestinal glands, etc.

Stratified epithelium: This is a compound epithelium in which cells are arranged in many layers one above the other. It is found in places where there is much wear and tear, such as the epidermis of the skin, lining of the mouth cavity.