Physical Heat Exchange

Abstract

In some respects the machinery of the body is like a thermodynamic engine which transforms energy from one kind to another. A fraction of the chemical energy derived from the breakdown of food is converted into work, but because of the body’s limited efficiency the greater part appears finally as heat. In the homoiothermic animal a balance is maintained between the rate at which this heat is lost to the environment and the rate at which it is produced by metabolism, so that the resulting constancy of temperature reflects a thermal steady state with a continuous flow of energy through the system. Both sides of the equation of heat balance, namely the heat production and the heat loss, are variable, and in practice the total heat content, or heat storage, of the body may fluctuate somewhat according to both physical and physiological conditions.