Thermoregulation is an important function of the human body. The range of temperatures that a person can survive without permanant damage is not very great, about 95 °F to 105 °F. Because maintenance of a constant temperature is essential for the human body to function properly, there are several responses that humans have in order to maintain their constant internal temperature.

Responses to cold stress:

  1. Vasoconstriction: tightening of muscles surrounding the blood vessels of the skin. This retards heat loss by shunting the blood flow to the internal organs.
  2. Pilomotor response: muscles of hair follicles constrict, making hair stand up and trapping more air under the hair and next to the skin as an insulation mechanism.
  3. Shivering (rhythmic tremors): rapid periodic muscle contractions that speed up fat metabolism in muscles, generating extra heat. This works for only short periods of time at a high metabolic cost because it produces lactic acid that must be removed by the kidneys.
  4. Metabolism of brown adipose fat can also generate internal heat without shivering.
  5. Hypothermia is a condition where core temperature falls below normal. It can lead to brain damage and even death.
Responses to heat stress:
  1. Vasodilation: relaxation of muscles surrounding skin blood vessels, allowing more blood to flow close to the surface to radiate heat away.
  2. Evaporative heat loss by sweating often accompanies vasodilation. Evaporation can remove a substantial amount of heat from the body.
  3. Hyperthermia is a rise in core temperature that can result in heat exhaustion and heat stroke.

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