Thermoregulation: A* understanding for iGCSE Biology

Homeostasis is a term that means maintaining a constant internal environment in spite of changes in the external environment.  Many variables in the body are regulated by homeostasis but the two control systems specifically mentioned in your specification for iGCSE are osmoregulation (regulation of water balance) and thermoregulation (regulating of body temperature)


Thermoregulation means to maintain the core body temperature at a set value.  This can be energetically very costly as the animal has to respire at a much higher rate to release the heat needed to warm the body, but it has allowed mammals and birds to colonise habitats that would be inaccessible to all poikilothermic (cold-blooded) animals.

Why regulate body temperature?

All metabolic reactions in the body are catalysed by enzymes.  If the body temperature falls too low below the set value, the rate of an enzyme-controlled reaction will drop, and this would be a problem as metabolic reactions would happen too slowly.  If the temperate goes much above the optimum temperature, then the enzymes that catalyse all the reactions in cells would denature.  This means they will change their shape so that the “lock and key” mechanism of catalysis cannot work at all.

In any homeostatic control system there will be three components:

• Sensors (where the variable is measured)
• Integrating Centre (where the measured value is compared to a set value)
• Effectors (which can bring about a response)

In human thermoregulation, there are two sets of sensors that measure temperature.  The skin contains hot and cold receptors which can respond if the skin gets too hot or cold respectively.  The temperature of the blood is constantly measured by a second set of thermoreceptors which are found in the hypothalamus in the brain.

The hypothalamus also acts as the integrating centre, collecting information from a variety of sensors and then initiating an appropriate response.
The main effector organ in thermoregulation is the skin.



Just check you understand the role of sweating, vasodilation in helping the body lose heat if it gets too hot and vasoconstriction and shivering if it gets to cold.