Epithelial Tissue

Epithelial tissue (epi = above/upon, thelium = layer of cells) forms a continuous covering or lining over the outer surface of the body and over the inner surfaces of organs and cavities. Its cells are packed tightly together with very little intercellular matrix between them, and the whole sheet sits on a non-cellular basement membrane that separates it from the underlying connective tissue.

Epithelial cells may be polygonal, cuboidal or columnar in outline and typically carry a single nucleus, positioned either centrally or towards the base of the cell. The tissue is avascular (it has no blood vessels of its own and is nourished by diffusion from the connective tissue below) but has a good capacity for regeneration, since its cells divide readily to replace worn-out or damaged cells. Functionally, epithelial tissue's chief role is protection of the surface it covers, and depending on the site it also carries out absorption, transport, filtration and secretion. …