Maintaining body temperature
The body responds to heat and cold stress by changing blood flow quantities and patterns around the body, modifying sweating, adjusting metabolism and changing behaviour. Blood flow to the superficial vessels (those just beneath the skin) is reduced in cold conditions to conserve heat, and is increased in hot conditions to aid heat loss. Sweating facilitates heat loss by evaporative cooling, and increases in response to exertion and rises in body temperature. Shivering, which can increase the body’s heat production five-fold, and muscular activity, which can increase heat production tenfold, are the main means by which the body generates metabolic heat in cold environments.
Shivering and deliberate activity to keep warm have high energy demands and are limited in duration by energy availability. People in normal states of consciousness automatically modify their behaviour to cope with heat and cold stress, for example, by seeking shelter or shade, curling up in a ball or lying spreadeagled, depending on the need to gain or lose heat.