Q. A young hiker has been on a long walk. He is now sitting in front of a small campfire, drinking a hot cup of soup. It is dark and a frost is beginning to form on his tent. Explain the hiker’s heat gains and losses, and what mechanisms would come into effect to keep his temperature at the desired 37ºC.
Humans are subject to vast changes in environmental temperatures, but our complex biochemical systems have a major limitation in that enzymes only operate within a relatively narrow temperature range. Accordingly the human body have anatomical and physiological mechanisms that keep body temperatures within acceptable limits, regardless of environmental conditions. This homeostatic process is called thermoregulation and it involves constantly balancing heat-producing and heat-losing mechanisms. If the body temperature is not maintained within these acceptable limits serious physiological changes can occur. If the body temperature falls below 36ºC or goes above 40ºC this can cause disorientation, and a temperature above 42ºC can cause convulsions and permanent cell damage.
We continuously produce heat as a by-product of metabolism. When energy use increases due to physical activity, or when our cells are more active metabolically, additional heat is generated. The heat produced by biochemical reactions is retained by water, which accounts for nearly two thirds of body weight. Water is a very effective conductor of heat, so the heat produced in one region of the body is rapidly distributed by diffusion, as well as through the blood stream. If the body temperature is to be remain constant, that heat must be lost to the environment at the same rate it is generated. When environmental conditions rise above or fall below ‘ideal’ the body must control the gains and losses to maintain homeostasis.
In the example of the hiker his system responds to the varying temperature changes that occur in his environment and his body. The heat loss centre and the heat gain...
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