11.3 : 体温

Body temperature is the difference between the amount of heat produced by the body and the amount lost to the external environment.

The average body temperature of an adult ranges between 97 °F to 99 °F.

The hypothalamus is the brain structure responsible for thermoregulation—the balance between heat lost and heat produced.

The anterior hypothalamus controls heat loss primarily through the skin.

As the temperature rises, the anterior hypothalamus stimulates the sympathetic nervous system to open the atrioventricular shunt—a tiny connection between the arterioles and venules causing vasodilation, to allow heat to escape the skin.

Heat loss mechanisms occur through evaporation, radiation, convection, and conduction.

Similarly, the posterior hypothalamus regulates heat production, mainly through metabolism.

As temperature decreases, the posterior hypothalamus signals the sympathetic nervous system to close the atrioventricular shunt, causing vasoconstriction to prevent heat loss.

The mechanisms that allow heat production include thyroid hormones, piloerection, shivering, and exercise.