Stratified epithelium is a type of tissue found in the human body. Epithelial tissue is the lining of cells that covers most body surfaces and cavities, with an attached membrane called a basement membrane. Stratified epithelium means that this lining is more than one layer of cells thick. Simple epithelium consists of a single layer of cells. Both types of epithelium can serve many purposes in different areas of the body, such as protection from injury or pathogens, sensing different stimuli like taste, secretion of hormones or enzymes, and absorption of nutrients.
Stratified epithelium is usually classified according to the shape of the cells in the top layer, with one common type being squamous epithelium. The shape of the cells in the top layer of stratified squamous epithelium is thin and flat, with irregular, curvy, wavy edges — the cells in the layers beneath can be shaped the same or differently than those on top. Squamous is the most widespread type of stratified epithelium in the human body. It is forms the lining of the mouth, vagina, anus, and several other openings in the body, as well as the lining of the vocal cords and the cornea. The skin is also made up of stratified squamous epithelium.
Another type of stratified epithelium is stratified cuboidal epithelium. Cuboidal cells have a shape similar to that of a cube. Stratified cuboidal epithelium is not as common as the squamous type, however it can be found in several areas of the body particularly in ducts of various glands, such as sweat and mammary glands, and ducts of the salivary glands found in the tongue.
Stratified columnar epithelium has cells shaped like a rectangular prism, with a height noticeably longer than its width. This type is not very widespread, but it is found in a few areas such as very large mammary ducts, and the ducts of the large salivary glands on the bottom of the mouth under the tongue. The columnar type of stratified epithelium can also be found in some parts of the respiratory and urinary tracts, and on the tubules of the testes.
Sometimes columnar epithelium can appear to be stratified when it isn't, due to the nuclei appearing at different heights, and the cells themselves being different lengths. These factors give the appearance of layers, but in reality there's just a single layer with all cells touching the basement membrane. This variety of epithelium is called psuedostratified, and it's found in several body systems, including respiratory and reproductive.
