Endothelial cells are specialized cells that line the interior surface of blood vessels, including arteries, veins, and capillaries. They play a crucial role in maintaining vascular health by regulating blood flow, controlling the passage of substances, and preventing blood clotting. These cells also produce various substances that help manage blood pressure and inflammation. In addition to their role in the circulatory system, endothelial cells are involved in processes such as angiogenesis, the formation of new blood vessels, and vascular permeability, which allows nutrients and waste products to pass between the blood and surrounding tissues. Their proper function is essential for overall cardiovascular health.