Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. In endotherms, warm blood from the body’s core typically loses heat to the environment as it passes near the skin. Shrinking the diameter of blood vessels that supply the skin reduces blood flow and helps retain heat. The process is the opposite of vasodilation, the widening of blood vessels.
