What Is Meant By Heat Production And Heat Loss In An Organism?

Heat is produced within the body as a result of metabolic activities e.g. tissue respiration. Tissue respiration is most active in the muscles and to a lesser extent in the liver and large amounts of heat is set free in these organs. The heat is distributed to all parts of the body by the blood. In man extra heat is gained by eating hot food, from the sun's radiation or from the warmed air on very hot days. If this heat were not lost then we would die by overheating. Heat is lost:
• Through the skin by convection, radiation and to a extent by conduction.
• By evaporation of sweat from the surface of the skin.
• In the faeces and urine.
• In the expired air.
Fish, amphibians, reptiles and invertebrates are unable to balance the amount of heat produced with the amount of heat lost. Hence their body temperature is not constant. It varies according to the surroundings and to some degree their activities. They are said to be cold blooded or poikilothermic animals.
Mammals and birds are termed warm blooded or homoeothermic animals. They can maintain a constant body temperature irrespective of the temperature of the surrounding medium or atmosphere. In man the normal body temperature is about 37 Celsius.