n. the tissue that covers the external surface of the body and lines hollow structures (except blood and lymphatic vessels). It is derived from embryonic ectoderm and endoderm. Epithelial cells may be flat and scalelike (squamous), cuboidal, or columnar. The latter may bear cilia or brush borders or secrete mucus or other substances (see goblet cell). The cells rest on a common basement membrane, which separates epithelium from underlying connective tissue. Epithelium may be either simple, consisting of a single layer of cells; stratified, consisting of several layers; or pseudostratified, in which the cells appear to be arranged in layers but in fact share a common basement membrane (see illustration). See also endothelium, mesothelium. —epithelialadj.
Types of epithelium.
Subjects: Medicine and Health — Science and Mathematics.