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Unit 3 - Thermoregulation

Have you ever wondered how we manage to keep cool on hot days or to stay warm when it's snowing? The answer is thermoregulation. Thermoregulation is the control of the internal body temperature in warm blooded animals (birds and mammals - including humans) and in this GCSE Biology quiz we find out exactly how thermoregulation works.

The body temperature of a warm blooded animal must be kept within precise limits so that the organism can still function. In humans, if the body temperature is too high, for example during a fever, dehydration and heatstroke can occur. If the fever is not reduced, eventually the patient will die. The same happens with a low body temperature and is more commonly referred to as hypothermia or exposure. So, how does the body manage to control its temperature?

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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.

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  1. Receptors inside the thermoregulatory centre detect blood...
    The blood flowing through the thermoregulatory centre has been heated by passing through the body
  2. What is the normal core body temperature for humans?
    It is the core body temperature that matters
  3. Temperature receptors are found in the brain and also in the...
    Skin temperature is constantly monitored
  4. Which process cools the skin during sweating?
    Sweat contains a lot of water and this evaporates, turning from a liquid into a gas. This takes heat energy away from the body and cools us down
  5. Information about skin temperature is sent to the brain by...
    Nerves are the fast messaging system of the body, so the thrmoregulatory centre can respond quickly if needed
  6. Thermoregulation is the control of body...
    Thermoregulation is an example of homeostasis
  7. The part of the brain which is involved with temperature control is called the...
    'Thermo' indicates something to do with temperature and 'regulatory' indicates the centre is something to do with control
  8. During sweating, body temperature...
    Sweating cools us down, therefore body temperature is decreased back to normal
  9. This happens when it is cold in order to generate heat from respiration.
    Muscles are made to vibrate and this extra work that they do releases more heat and warms up the blood passing through the muscles
  10. When we are too cold, these trap a layer of air for insulation.
    The idea is that they trap a layer of air against the skin for insulation. Humans have a lot less skin hair than most mammals and so this is not particularly effective

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