-thelium

A layer of body tissue.

Greek thēlē, teat.

The first term in this ending, on which others are modelled, was epithelium (Greek epi, upon), the thin tissue that forms the outer layer of a body's surface or which lines a cavity, that on a teat being taken as the model. Other examples include endothelium (Greek endon, within) is the tissue which forms a single layer of cells lining various organs and cavities of the body, especially the blood vessels, heart, and lymphatic vessels; mesothelium (Greek mesos, middle)is the epithelium that lines the pleurae, peritoneum, and pericardium; the urothelium (Greek ouron, urine) is similarly the epithelium that lines the urinary tract, especially that of the bladder.