Endothelial Cells: The Lining of Blood Vessels - Function & Importance

The lumen of all blood vessels is lined by a layer of endothelial cells. Endothelial cells are thin, flat cells that form a continuous lining over the entire inner surface of the blood vessels. They play a vital role in the regulation of blood flow, the exchange of nutrients and waste products between the blood and the tissues, and the prevention of blood clotting.