Blood Functions. Temperature regulation
Heat is produced in large amounts by physiological
oxidative reactions, and the blood is essential for
its distributing and disposing of this heat. The circulation
assures relative uniformity of temperature throughout
the body and also carries the warm blood to the surface,
where heat is lost to the external environment. A heat-regulating
centre in the hypothalamus of the brain functions much
like a thermostat. It is sensitive to changes in temperature
of the blood flowing through it and, in response to
the changes, gives off nerve impulses that control the
calibre of the blood vessels in the skin and thus determine
blood flow and skin temperature. A rise in skin temperature
increases heat loss from the body surface. Heat is continuously
lost by evaporation of water from the lungs and skin,
but this loss can be greatly increased when more water
is made available from the sweat glands. The activity
of the sweat glands is controlled by the nervous system
under direction of the temperature-regulating centre.
Constancy of body temperature is achieved by control
of the rate of heat loss by these mechanisms.
