Question

What special structures the epithelial cells bear at their free surface? Also mention the site where cells with such structures occur.

Answer 1

Epithelium is made up of one or more layers of cells that covers or lines the external and internal surfaces of various body parts. It consists of variously shaped cells closely arranged in one or more layers. It is of two types - simple and compound epithelium. Simple epithelium consists of a single layer of cells on a basement membrane. It is further divided into six types on the basis of structural modification of the cells. 1. Squamous epithelium consists of a single thin layer of flattened cells with irregular boundaries present in the walls of blood vessels, air sac of the lungs, wall of Bownman's capsule. 2. Cuboidal epithelium consists of a single layer of cube-like cells lying on the basement membrane present in the tubular parts of nephrons, ducts of glands, thyroid follicles. 3. Columnar epithelium consists of a single layer of tall and slender cells lying on the basement membrane present in the lining of stomach and intestine. 4. Ciliated epithelium consists of cilia on the free surface of columnar and cuboidal cells present in respiratory system. 5. Pseudostratified epithelium consists of single layer of cells are columnar but unequal in size present in urethra of human male. 6. Glandular epithelium consists of columnar or cuboidal cells present in glands for secretions. Compound epithelium consists of more than one layer of cells present on the moist surface of buccal cavity, pharynx, inner lining of ducts of salivary glands and of pancreatic ducts.