Classification of Epithelia

Epithelium is given two names. The first is the number of cells present and the second decries the shape of its cells. There is simple and stratified epithelial. Simple epithelial is composed of a single cell layer. Stratified epithelial consists of two or more cell layers stacked on top of each other. Epithelial cells have six sides and an apical surface. Simple squamous epithelium is when the cells are flattened and their cytoplasm is sparse. Two simple squamous epithelia are called endothelium. They provide a slick, friction-reducing lining in lymphatic vessels. They are found in capillaries. Mesothelium is epithelium found in serous membranes lining the ventral body cavity and covering its organs. Simple cuboidal epithelium consists of a single layer of cells as tall as they are wide. This epithelium forms the walls of the ducts of glands. Simple columnar epithelium is a single layer of tall closely packed cells. They are aligned in a row. It is used to line the digestive tract from the stomach through the rectum. They are used with absorption and secretion. Pseudostratified columnar epithelium has a variety of cells that differ in height. The cells of this particular type of epithelium rest on the basement membrane, but only the tallest cells reach the the free surface of the epithelium. It gives the false impression that there are several cell layers. It is used to secrete and absorb substances. The stratified epithelia is more durable than simple epithelia. This is because it's major role is protection. Stratified squamous epithelium is composed of several layers. It is found in areas of the body that are subjected to wear and tear. It's cells are constantly being replaced by basal cells. This epithelium forms the external part of the skin and extends a short distance into every body opening that is directly continuous with the skin. Stratified cuboidal epithelium is found in cuboidal cells and glands. It is not very common. This is similar with stratified columnar epithelium. It is found in the pharynx, the male urethra, and in the lining of some glandular ducts. It occurs at transition areas. Transitional epithelium forms the lining of hollow urinary organs, which stretch when filled with urine. They allow more urine to be held in the bladder.