body temperature

Temperature deep in the tissues (core temperature). It is often measured on a thermometer. In a healthy adult it is normally 36.9°C/98.4°F. Any significant departure from this norm is potentially serious (although fever is a necessary response to many types of infection). Hyperthermia (temperature above 41°C/106°F) and hypothermia (below 35°C/95°F) are life-threatening. Excessive exposure to heat can cause heatstroke, where the body temperature rises.

Body temperature is regulated by the hypothalamus in the brain. It serves as a thermostat, initiating physiological measures to lose or gain heat. Heat is conserved by constriction of the small arteries supplying blood to tiny capillaries near the surface of the skin. This reduces blood flow in the capillaries. To lose heat, small arteries dilate, increasing blood flow in the capillaries. Heat is lost from them. As sweat is produced the evaporation of the water from the sweat cools the skin.