Describe the role of the skin in maintaining a constant internal body temperature when a person moves from a warm room into cold outdoor conditions.

When a person leaves a warm room for cold air the skin acts to reduce heat loss. First, the tiny muscles that attach to hairs contract, raising the hairs and trapping a layer of air that insulates the skin. Second, the blood vessels close (vasoconstriction), so less blood reaches the skin surface and less heat is carried away. Third, because the skin is cooler, less heat is radiated from the body. Finally, if the temperature falls further, the body starts shivering – rapid muscle contractions that produce heat by increasing metabolic activity.