The main function of vascular smooth muscle is to control the blood flow to tissues and organs, providing the primary route of transportation for nutrients, immune cells, and signaling molecules in the body. This is achieved by regulating the resistance to flow, which in turn is the basis for a maintained blood pressure. Interactions with other cells (nerve endings, endothelia, and smooth muscle cells), with humoral (circulating hormones and nutrients) and physical factors (blood pressure, blood flow) determine if the vascular smooth muscle will contract, relax, or maintain pressure. In their contractile phenotype, the basic physiological role of vascular smooth muscle is to regulate the diameter of the vessel lumen in order to control perfusion
