EPITHELIAL TISSUE

Epithelial tissue exists in many structural forms. In general, it either covers or lines something and typically consists of renewable sheets of cells that have surface specializations adapted for their specific roles. Usually, a basement membrane separates epithelial tissues from underlying, adjacent tissues. Epithelial tissues absorb (e.g., the lining of the small intestine), transport (e.g., kidney tubules), excrete (e.g., sweat glands), protect (e.g., the skin), and contain nerve cells for sensory reception (e.g., the taste buds in the tongue). The size, shape, and arrangement of epithelial cells are directly related to these specific functions. Epithelial tissues are classified on the basis of shape and the number of layers present. Epithelium can be simple, consisting of only one layer of cells, or stratified, consisting of two or more stacked layers . Individual epithelial cells can be flat (squamous epithelium; ), cube shaped (cuboidal epithelium;), or columnlike (columnar epithelium; . The cells of pseudostratified ciliated columnar epithelium possess cilia and appear stratified or layered, but they are not; hence, the prefix pseudo. They look layered because their nuclei are at two or more levels within cells of the tissues