The term "endothelial" refers to the cells that line the interior surface of blood vessels, lymphatic vessels, and the heart. These cells form a thin layer known as the endothelium, which plays a crucial role in maintaining vascular health by regulating blood flow, preventing blood clotting, and controlling the exchange of substances between the bloodstream and surrounding tissues. Endothelial cells are involved in various physiological processes, including inflammation and the formation of new blood vessels, a process called angiogenesis. Dysfunction of the endothelium can lead to various health issues, such as atherosclerosis and other cardiovascular diseases, highlighting its importance in overall health.