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Figure 26-2. Methods for reducing the body surface exposed to cold water
PHYSIOLOGIC LIMITATION OF HEAT LOSS
Physiologic mechanisms for limiting heat loss are largely limited to constriction of blood
vessels in the skin, arms, and legs. (Humans evolved in a tropical climate, and the body's
mechanismsforincreasingheatlossaremuchbetterdevelopedthanthoseforreducingheat
loss.) Vasoconstriction reduces cutaneous blood flow, which allows tissues to cool. Since
the skin temperature is lower, less heat is lost by radiation and by convection.
The arms and legs, as the result of their long narrow shape, have a greater relative sur-
face area than the body and tend to lose heat more readily. Narrowing of blood vessels in
the extremities reduces blood flow and heat loss and also tends to keep the heart and brain
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