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:
- Vasoconstriction: tightening of muscles surrounding the blood vessels of the skin. This retards heat loss by shunting the blood flow to the internal organs.
- 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.
- 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.
- Metabolism of brown adipose fat can also generate internal heat without shivering.
- Hypothermia is a condition where core temperature falls below normal. It can lead to brain damage and even death.
Responses to heat stress:
- Vasodilation: relaxation of muscles surrounding skin blood vessels, allowing more blood to flow close to the surface to radiate heat away.
- Evaporative heat loss by sweating often accompanies vasodilation. Evaporation can remove a substantial amount of heat from the body.
- Hyperthermia is a rise in core temperature that can result in heat exhaustion and heat stroke.