1) The main type of cell found in the inside lining of blood vessels, lymph vessels, and the heart.

2) Highly specialized epithelial cells that line the heart; blood vessels; and lymph vessels, forming the endothelium. They are polygonal in shape and joined together by tight junctions. The tight junctions allow for variable permeability to specific macromolecules that are transported across the endothelial layer.

3) The main type of cell forming the lining of blood and lymph vessels and the inner layer of the endocardium. SYN endotheliocyte.