Unit 3 - Thermoregulation

In mammals, the thermoregulatory centre in the brain monitors and controls body temperature. This centre has receptors capable of detecting the temperature of the blood flowing through the brain. The skin also has temperature receptors which can monitor the temperature of the skin, and these send messages to the thermoregulatory centre. If the core temperature of the body is not at a normal level, the thermoregulatory centre sends messages to effectors that carry out actions which will restore it to the correct value.

If the temperature is too high, for example during heavy exercise, the thermoregulatory centre sends messages to the sweat glands which cause an increase in the volume of sweat they produce. More sweat on the surface of the skin means an increase in evaporation. This takes away more heat, cooling the skin and therefore cooling the blood flowing through the blood capillaries of the skin. It also sends nerve impulses that cause the surface blood capillaries to dilate (increase in diameter). This process is called vasodilation and it allows more blood to flow through the capillaries, thus losing more heat to the surroundings. It is vasodilation that causes your skin to redden during exercise.

If the temperature falls too low, vasoconstriction occurs, reducing the blood flow through the surface capillaries and reducing heat loss. This can cause your fingers and toes to turn white and go numb. In extreme cases, frostbite occurs. Frostbite is when cells that have no blood supply die because they are getting no oxygen - the dead flesh turns black (gangrene). This can be left to fall off of its own accord or can be removed surgically. The thremoregulatory system also sends out messages to the muscles to vibrate rapidly (shivering) which generates extra heat for the body. A third set of nerve impulses raise the surface hairs of the body in order to trap a layer of air next to the skin for extra insulation.