ABSTRACT
The tissues of the body can each be classified as one of four basic tissues: epithelium, connective tissue, muscle or nervous tissue.
An epithelium is a sheet of cells which lines a lumen of an organ or covers an organ surface. The tissue is avascular, highly cellular, and has little intercellular substance.
Epithelia protect underlying structures and function in absorption, secretion, surface transport, and sensory reception.
Each epithelium is classified by the number of cellular layers and the shape of cells in the surface layer.
