temperature regulation

Ability of an organism to control its internal body temperature. Animals that rely on their environment for their body temperature (and therefore have a variable temperature) are known as ectotherms or ‘cold-blooded’ animals (for example, lizards). Animals with a constant body temperature irrespective of their environment are known as endotherms or ‘warm-blooded’ animals (for example, birds and mammals). Their temperature is regulated by the hypothalamus in the brain.

Ectotherms have behavioural means of temperature control; they can warm themselves up by basking in the sun, or shivering, and can cool themselves down by sheltering from the sun under a rock or by bathing in water. In cold weather their metabolism slows and they become less active.

Endotherms too can regulate temperature by behavioural means (for example, seeking sun or shade), but also make use of physical and metabolic processes of regulation. The skin plays an important role – heat can be lost by sweating, whereby the water secreted evaporates from the skin and causes cooling. Heat can also be lost through capillaries near the surface of the skin, which flush with blood and lose heat by radiation. In the same way, heat can be retained by diverting blood from the surface capillaries, which gives the skin a paler colour in the cold. Heat can also be retained by hairs which become erect and trap an insulating layer of air next to the skin (producing ‘goose bumps’). In some animals, there is a more specialized insulating layer such as fur, feathers, or blubber. Endotherms can also gain heat metabolically through shivering, whereby involuntary muscle contractions release heat, and by an increased metabolism in the liver.