Cutaneous Circulation and Thermoregulation

Expansion

Skin blood flow serves thermoregulation rather than local metabolism, and is therefore under central sympathetic control rather than local metabolic control.

• Arteriovenous anastomoses in the hands, feet, nose, ears and lips shunt blood directly from arterioles to venules, bypassing capillaries. They are richly innervated by sympathetic vasoconstrictor fibres and have no vasodilator innervation
• Heat loss: withdrawal of sympathetic tone opens these shunts, flooding the skin and the venous plexuses, and flow can reach several litres per minute
• Heat conservation: sympathetic vasoconstriction reduces flow to almost nothing, and countercurrent heat exchange between deep arteries and veins limits loss further

Consequences worth remembering: cold, pale peripheries are a sensitive early sign of shock, since skin is sacrificed first; and cutaneous vasodilatation in sepsis, in a hot environment or after alcohol represents a loss of circulatory reserve and contributes to hypotension and to hypothermia in trauma.