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Thermoregulation requires the normal function of heat - production processes. Heat is produced in the body by metabolism which is the chemical reaction in all body cells. Activities requiring additional chemical reactions increase the metabolic rate.
As metabolism increases additional heat is produced. When metabolism decreases, less heat is produced. Heat production occurs during rest, voluntary movements and involuntary shivering (shivering is an involuntary body response to temperature differences in the body). Shivering can increase heat production 4 to 5 times greater than normal.
Heat is produced to equalize body temperature.
Heat production and heat loss occur simultaneously. The skin' s structure and exposure to the environment result in constant, normal heat loss through reduction, conduction, convection and evaporation.
Radiation is the transfer of heat from the surface of another without actual contact between the two. Peripheral vasodilatation increases blood flow to the skin to increase heat loss.
Peripheral vasoconstriction minimizes blood flow to the skin and inhibits heat loss.
Conduction is the transfer of heat from one object to another with direct contact.
Convection is the transfer of heat away by air movement. Heat is first conducted to air molecules directly in contact with the skin. Air current carry away the warmed air.
Evaporation is the transfer of heat energy when a liquid is changed to a gas. The body continuously losses heat by evaporation. About 600 - 900 ml of water evaporates from skin and lungs daily, resulting in water and heat loss.
By regulating sweating, the body promotes additional evaporation and heat loss. When body temperature rises, the anterior hypothalamus signals the sweat glands to release sweat to evaporate from the skin surface,
resulting in heat loss.
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