25 - The control of body temperature

Abstract

This chapter discusses the physiological aspects of the temperature control mechanism of body. Mammalian enzymes operate efficiently within a narrow range of temperature. All chemical reactions proceed more rapidly at higher temperatures, roughly doubling in rate with each increase of 10°C. The body is constantly producing heat because the oxidation of foodstuffs yields energy that appears as heat. The maintenance of a constant body temperature implies, therefore, a continuing loss of heat. Temperature sensors can be classed as peripheral and central. Changes in body temperature may be achieved by varying heat gain or heat loss. Nonshivering thermogenesis, an increase in basal metabolic rate, plays a very minor part in the correction of lowered deep body temperatures in adult humans. An increase in sympathetic activity, both nervous and via the adrenal medulla, may increase liver metabolism. The body does not respond to an increase in core temperature by reducing metabolic heat production. Indeed, above a certain critical temperature, there is an increase in metabolic heat production probably because of the work done in sweating. The presence in the bloodstream of pyrexins from bacteria or damaged cells raises the hypothalamic set point for temperature.