The immediate response to acute temperature chance is mediated through the central nervous system. The physiological thermostat has been located in the hypothalamus of the mammal and the spinal cord of the bird. These are the centres of reflex action and are activated by the temperature receptors of the skin or mucous membranes or directly through the changes in the temperature of the hypothlamus (or the blood circulating through it).
The physiological thermostat through the efferent nerve fibres stimulate the muscles for panting and shivering and through the autonomic system it regulates the cutaneous blood vessels, the sweat glands and so on. In some of the amniotes, the pineal and parapineal organs influence thermoregulatory behaviour and physiology. Cardiovascular and cutaneous responses are acute reactions to temperature change. If the exposure is more prolonged, the endocrine system enters the picture and the metabolism is altered particularly by way of the thyroid and adrenal glands.