The core temperature of a normal human body should be maintained at 37°C. When the external temperature falls below or goes above the afore-mentioned temperature range, a negative feedback mechanism is initiated to return the body to its normal range. This mechanism is initiated by the nervous system and executed mainly by the muscles, blood vessels and sweat glands.
There are thermo receptors in the hypothalamus which detect temperature changes in the blood flowing to the brain, and thermo receptors in the skin which detect changes in external temperatures. The hypothalamus relays this information to effector organs which adjust the body temperature.
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When the temperatures are low, the hypothalamus is stimulated to initiate heat conservation in various effector organs. The effector smooth muscles of arterioles under the skin contract resulting in vasoconstriction. This reduces the heat carried to the skin surface thereby conserving heat. The erector pili muscles in the skin are stimulated to contract. This raises the hairs on the skin to trap a layer of still, warm air near the skin providing insulation. The skeletal muscles contract and relax repeatedly to generate heat. The adrenal and thyroid glands are stimulated to secrete adrenaline and thyroxin. These increase the metabolic rate in tissues such as the liver and generate heat.
In case of a spike temperature, the hypothalamus initiates temperature loss through the effector organs. The erector pili muscles in the skin relax. This lowers the hairs on the skin letting air circulate freely over the skin, thereby, encouraging heat loss by evaporation and convection. Sweat glands begin secreting sweat to the skin surface, which evaporates resulting in cooling by losing its latent heat of evaporation taken from the body. The arteriole smooth muscles relax resulting in vasodilation. Heat carried to the surface of the skin increases. There, it is lost through convection and radiation and sometimes conduction when under water.
Conclusion
The end result is stable temperature of 37°C regardless of change in environmental condition. This is necessary to enable us survive in harsh conditions and still achieve optimum functionality. It is important to note that sometimes in very cold weather, vasoconstriction can lead to damage of extremities by frostbite.
References
N. K., Taylor, N. A., M. S., K. A., & Muhamed, A. M. (2009, February 9). Thermoregulatory adaptation in humans and its modifying factors. Global Environmental Research, (13), 1st ser., 35-41. Retrieved from http://ro.uow.edu.au/asdpapers/226
