People are mammals, and mammals are warm-blooded creatures, capable of maintaining a relatively constant internal temperature regardless of the environmental temperature. Body temperature control is one example of homeostasis—an organism’s self-regulating process that tends to maintain internal stability while adjusting to conditions in ways that are optimal for survival.
The optimal temperature of the human body is 37 °C (98.6 °F), but various factors can affect this value, including exposure to the elements in the environment, hormones, an individual’s metabolism, and disease, which can lead to excessively high or low body temperatures. Body temperature is regulated mainly by the hypothalamus in the brain. Feedback about body temperature is carried through the nervous system and circulatory system (whose pressure-sensitive receptors in the blood vessels work with the nervous system to collect and communicate information on blood pressure) to the brain, where the breathing rate, blood sugar levels, and metabolic rate are adjusted to compensate for temperature changes. Heat loss is promoted by reduction of muscular activity, by perspiration, and by heat-exchange mechanisms that allow blood to circulate near the skin surface. Heat loss is reduced by the body’s insulation mechanisms, including reduction of blood flow to the skin and the fat beneath the skin, and by use of clothing, shelter, and external heat sources. In addition, the body can generate heat through shivering, a response regulated by the hypothalamus. The range between high and low body temperatures constitutes the homeostatic plateau—the "normal" range that sustains life. As either of the two extremes is approached, corrective action (through negative feedback) returns the system to the normal range.