Birds and mammals are endotherms (inside heat) they can maintain a constant body temperature by generating heat internally. Humans have several mechanisms which don’t stop working to balance heat production against heat loss. This balance is achieved by a temperature control centre in the hypothalamus, a region of the brain. As a barrier between the body and its environment the skin is also the main organ concerned with heat loss and heat conversion.
An endothermic animal maintains an ideal body temperature by balancing heat loses and heat gains.
Many biochemical reactions, especially respiration, in the liver generate heat.
Movement generates heat by respiration and friction within the muscles.
Excretion: urine and faeces are at body temperature. Heat is lost when they are expelled from the body. Heat is lost when water evaporates from the lungs and sweat evaporates from the skin.
Heat can be lost by the three processes convection, radiation and conduction.
Convection is the transfer of heat to and from the body on air currents; this can be increased by ‘fanning’ air past the body. Radiation is the transfer of heat in the form of rays, usually infra-red rays. Conduction is the transfer of heat by direct contract with another object such as a cold rock or a hot oven door.
Fat is an important compound in temperature control, each fat molecule provides about twice as much money energy in respiration as a molecule of either protein or carbohydrate. Fat stores under the heat also insulate against heat loss.
If the body is too cold it can use corrective mechanisms to try and conserve heat, these include shivering as muscular activity generates heat. Adding clothing as the insulation reduces heat loss and eating more as eating stimulates heat production by respiration. The skin can also prevent the three types of heat loss. Convection heat loss can be prevented by the hair erector muscles contracting which cause the hairs to rise which trap’s a layer of still hair. Radiation heat loss can be prevented by vasoconstriction of the surface capillaries shunts blood away from the skin. Evaporation heat loss can be prevented by the sweat glands not secreting sweat. It can also cause heat loss if the body Is too hot.
