Epithelium

Epithelium, tissue covering external surfaces of the body, such as the skin, and lining various bodily tubes and cavities. It consists of one or more layers of cells variously modified to provide protection or aid in excretion of waste products and the assimilation of nutrients. The epithelium that covers the surface of the skin consists of one or more layers of adjoining cells. Often strands of cells grow from the epithelium into deeper-lying layers and differentiate to form glands. Some sensory organs are specialized forms of epithelium.