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Thermoregulation is the body’s ability to balance between heat gain and heat loss, thus maintaining a stable internal temperature of around 36 to 37.5° C or 96.8 to 99.5° F. This range is considered normal body temperature but it’s actually the average across the population. Normal body temperature can vary depending on the time of day, age of the individual, activity level, and many other factors. This normal body temperature is maintained by four mechanisms: neural and vascular control; heat production; heat loss; and behavioral control.
Okay, let’s discuss the physiology of these four mechanisms, starting with neural and vascular control. If we zoom into the brain, there's a region called hypothalamus. The hypothalamus acts like a thermometer. It has thermoreceptors that monitor the body’s internal, or core, temperature; and it also receives information about the peripheral temperature from the thermoreceptors in the skin.
Now, the hypothalamus is also the body’s thermostat, because it controls the internal temperature “set point” and when the core temperature deviates from the set point, the hypothalamus will signal the rest of the body to increase or decrease the body temperature and bring it back to the set point. So, on a hot summer day, the hypothalamus senses the core body temperature is getting too high and responds by initiating mechanisms like sweating and dilating skin blood vessels, resulting in body heat loss. On the flip side, on a cold winter day, the hypothalamus senses that the core body temperature is getting too low, and in turn, activates mechanisms like shivering which generates heat, and vasoconstriction in the skin that prevents heat loss.
Thermoregulation is the body's ability to balance between heat gain and heat loss. This is possible by four mechanisms, called neural and vascular control; heat production; heat loss; and behavioral control. Disrupted thermoregulation can manifest as hyperthermia or hypothermia. Causes of hyperthermia include heat stroke, exercise, hyperthyroidism, and infections, whereas causes of hypothermia include frostbite, diabetes, hypothyroidism, and malnutrition.
The most common cause of hyperthermia is extremely high environmental temperature. In this situation, even though the hypothalamus activates sweating and causes dilatation of superficial arteries, these mechanisms are insufficient to dissipate heat. On the other hand, the most common cause of hypothermia is extremely low environmental temperature. In this case, the hypothalamus activates shivering and causes constriction of superficial arteries, but yet again, these mechanisms are insufficient. Complications of hyperthermia include hypotension, tachycardia, and rhabdomyolysis, whereas complications of hypothermia include electrolyte imbalances, coagulopathy, and arrhythmia.
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