The functions of epithelium are protection, absorption, secretion, and sensory reception. Epithelium, covers free internal and external surfaces of the body, lines cavities, and forms glands. It is characterized by closely packed cells with very little intercellular substance between them. There is no vascular supply within epithelium. How do the cells receive nutrients?

Simple epithelium is composed of one layer of cells in contrast to stratified (multi-layered) epithelium. The latter are named according to the shape of the lumenal or surface layer of cells. The basal cells of all epithelia, although separated by a basement membrane, are, nevertheless, contiguous with the underlying connective tissue which carries the blood vessels. This connective tissue supports the epithelium physically and nutritionally.

Study the following images of tissues obtained from different organs. You should be able to identify the various types and locations of epithelium within an organ. (Do not try to learn the organ at this time.) Note characteristics of epithelium, including surface specializations, which help to distinguish epithelium from other tissues.