Literally meaning: " internal epithelium”
Origin: Anc Greek
ενδο-/endo-(= compining form for “inside”, “internal”, “within”)
θηλή/theli(=nipple) literally meaning “on nipple” because originally this word meant only the skin on the breast which is not identical to the epidermis and in literal translation it is a misnomer.
The term was coined in 1865 by the Swiss embryologist and anatomist Wilhelm Hirsch for cell layer lining the lumen of the vscular system and inner cavities of the body . Some years later the term was restricted to its modern usage.
The endothelium is the thin layer of cells that lines the interior surface of blood and lymph vessels.