Epithelium

Epithelium is a tissue that lines the surfaces of organs, blood vessels, and other body cavities. It has an important role in providing a physical barrier against invasion by infectious agents, in controlling the movement of materials into and out of the body, and in producing hormones and other substances essential for bodily functions. Epithelium forms the lining of the digestive, respiratory, and reproductive systems, and is also found in the urinary tract. It plays a crucial role in protecting the body from infection, regulating fluid and electrolyte balance, and providing lubrication. Epithelium can also differentiate into specialized cells which are able to secrete substances such as mucus and sweat. The precise structure and function of epithelial cells vary according to tissue type, but all epithelia provide protection, secretion, and absorption.