The picture below is skin, an example or epithelial tissue. Epithelial tissue is made of cells that tend to be very closely packed and cover the surface of a whole body. The tissue cells are specialized to cover all the internal and external surfaces in one or more layers. If epithelial tissue has one layer, it’s known as simple epithelium, and with two or more layers, it is known as stratified epithelium. Some functions of the epithelial tissue is protection, sensation, excretion, diffusion, absorption, and cleaning. All mammals and many other organisms have epithelial tissue that cover their bodies.