Vasodilation, also known as vasorelaxation, is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. Vasodilation increases blood flow to the skin and helps the animal lose some of its extra heat to the environment. Vasodilation is the opposite of vasoconstriction, which is the narrowing of blood vessels.
