ABSTRACT
The endothelium is the single layer of cells that lines blood and lymph vessels and the heart. Because of its location at these interfaces between tissue and blood or lymph, the endothelium serves several important physiological functions that maintain tissue homeostasis. Most importantly, the endothelium provides a barrier that regulates transport of fluid, macromolecules, proteins, and cells into and out of tissues. Second, the endothelium is a key player in autoregulation of tissue perfusion in response to changes in blood pressure, potentiating blood fl ow rate through vessels by controlling their diameters. In normal circumstances, the endothelium also prevents blood clotting.
