Endothelial cells are able to sense changes in their surrounding environment, and release molecules that have a powerful effect on blood pressure and blood flow, coagulation (blood clotting), inflammation and oxidation. It also controls passage of materials in and out of the bloodstream. A healthy endothelium will prevent blood from clotting while it flows inside the blood vessel. It will also keep the blood vessel dilated. These properties makes it an important defense mechanism against atherosclerosis and cardiovascular diseases