Understanding Vascular Endothelium : Nature’s Container for Blood The entire cardiovascular system, from the chambers of the heart to the smallest capillaries of peripheral tissues, is lined by a single-cell-thick continuous layer—the vascular endothelium. For many years, this gossamer membrane was thought to function largely as an inert barrier, passively separating the reactive components of the circulating blood from the cells and connective tissue matrix of the various organs of the body....