ABSTRACT
The vascular endothelium forms the lumenal surface of blood vessels and exerts an essential role as a selective barrier to the vessel lumen. A host of functions are performed by the vascular endothelium, some of which are unique in relation to the vascular bed or size of the vessel in which the endothelial cells are located. The vascular endothelium is able to regulate permeability to gases, fluids, solids, cells, macromolecules, nutrients, metabolites, and autocrine and paracrine factors, not only to the endothelial cells themselves but also to the underlying smooth muscle cells. It also exerts a profound influence on vascular tone, manipulating blood pressure and flow by adjusting the caliber of the arteries and arterioles.
