Maintaining body temperature
What keeps the human body at a constant temperature of 98.6?
Maintaining body temperature is very complex. It also takes a lot of energy.
About 80% of the energy from the food you eat goes to maintaining body temperature.
Basically, the chemical reactions of metabolism of stored food, especially fats,
generate heat as a by product. This heat warms the body. The brain reads temperature
and controls to some extent the rate of this metabolism. There are also many other
mechanisms triggered by the brain to keep the core of your body warm, even if the
periphery (skin) is cold. Blood vessels to the fingers and toes constrict, so that
the cold air doesn't cool the blood too much, so that cooled blood doesn't cool down
the heart and brain when it returns. In severe cases, your body will sacrifice a
finger or a toe to keep you from dying of cold core temperature (frostbite: it saves
your life!). Also the brain can order a lot of muscles to contract rapidly. This
generates a lot of heat quickly, a response called shivering. There's much more to
this exciting field of research.
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Update: June 2012