Epithelial tissues are classified by cell shape and the number of cell layers, both of which determine their function in the body. Epithelial cells can have three shapes: squamous, cuboidal, and columnar. Squamous cells look like flat, irregular pieces of a jigsaw puzzle and have disc-shaped nuclei. Cuboidal cells appear square-like with centrally located spherical nuclei. Columnar cells are tall rectangles containing elongated nuclei located near the basement membrane. All epithelial cell types are arranged either as a monolayer or in multiple layers. A simple epithelium is a thin monolayer of cells covering the basement membrane. They line the internal compartments of various organs like lungs, kidneys, and intestines, facilitating the rapid exchange of gases and nutrients. The stratified epithelia consists of several layers of cells on a basement membrane. They are present in the skin surface, esophagus, mouth lining, or anus lining, where they overcome extreme mechanical abrasions and chemical stresses of the environment without losing their integrity.