Epithelium << `ehp` uh THEE lee uhm >> is one of the major kinds of tissue formed in the bodies of human beings and some animals. It covers the body surface and lines the channels of the body that have openings to the outside. For example, the respiratory tract, alimentary tract, and the urinary tract are lined with epithelium.
Three types of cells make up the epithelium. They are the squamous, cuboidal, and columnar cells. These cells are differentiated by their shape. The squamous cells are thin and scalelike. They have irregular edges. These cells make up the tissue that covers the body surface and lines the mouth and esophagus. Cuboidal cells look like tiny cubes. They are almost as tall as they are broad. These cells line some of the body cavities and are found in many of the glands. Columnar cells resemble columns. They are much taller than they are broad. Tissue made up of these cells lines the stomach and intestines, and the innermost layer of the epidermis (skin). A form of columnar epithelium equipped with cilia lines the respiratory passages.
See also Epithelioma.
