The skin contains a network of small blood vessels containing muscle fibers in their tunica media. These muscles are under the control of the sympathetic nervous system and provide an efficient means of thermoregulation through vasoconstriction and vasodilation.
When vasoconstricted, blood flow through the skin is reduced, so less core heat is lost. With restricted blood flow, the skin appears paler. When vasodilated, blood flow through the skin is increased, meaning more core heat can be lost through radiation. With increased blood flow, the skin appears red.
Arteriovenous anastomoses can be found in areas of the body exposed to maximal cooling, such as the hands, feet, nose, lips and ears. These richly innervated areas are called apical structures. The anastomoses connect cutaneous arterioles and venules directly, playing an important role in the reduction of blood flow in a cold environment.