in physiology, the transfer of heat produced by the body’s vital processes to the external environment by means of radiation, evaporation, and conduction (convection). Heat elimination is often called physical thermoregulation.
Under optimal conditions, approximately 50 percent of the heat produced in the human body is dispersed into the external environment by radiation, approximately 25 percent by the evaporation of water from the surface of the skin and mucosa, and 25 percent by convection. Retention of heat may lead to increased body temperature and to hyperthermia. There is danger of hyperthermia when thermogenesis increases sharply as a result of muscular activity or when the surrounding temperature rises owing to high humidity and the wearing of moistureproof clothing.
Heat elimination is intensified by such physiological reactions as increased blood flow to the skin, increased skin temperature, and the evaporation of perspiration. When the environmental temperature approaches that of the body surface (about 34°C), the body can eliminate heat only through the evaporation of water in the form of perspiration or through panting, as in the case of animals that do not perspire. In humans, the discharge of perspiration may reach 2 liters per hour; the body is thus able to maintain its normal temperature for a certain period of time even when the surrounding temperature is very high.
K. P. IVANOV