B1 - Homeostasis

Everything you need to know about homeostasis for your biology exam.

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What is homeostasis?

Homeostasis is maintaining a constant internal environment. This means that the conditions within your body need to be kept steady in order for your body cells to function properly.

Therefore, you need to control the inputs and the outputs - which are basically the things going into your body, and the things leaving your body.

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The Outputs and Inputs controlled by Homeostasis

Levels of carbon dioxide -

Respiration produces carbon dioxide all the time, and you need to get rid of that as it is poisonous to the body.

Water content -

You make water in respiration, and you can also get it from food and drink. Therefore, you need to get rid of some of this by urinating, sweating, and the moisture in your breath.

Body temperature -

If you are hot, you need to lose heat. When you are cold, you need to retain heat.

All in all, this is quite simple.

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Negative Feedback

Negative feedback is the mechanism that your body uses to counter any changes. For example, a drop in body temperature would be countered by a response that raises your body temperature.

This means that, on average, your internal environment stays the how it should.


If the change is extreme, then it may not be possible to counteract it, and your cells will stop working, resulting in death.

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How is body temperature controlled?

All enzymes have an optimum temperature. This is the temperature at which they perform best at. In the human body, the enzymes work best at 37 degrees celcius.

This means that the body needs to be kept as close to 37 degrees celcius as it can get. This is achieved by the thermoregulatory centre in the brain, which contains receptors that are sensitive to body temperature. It receives impulses from the skin to provide it with information on skin temperature. This means that the brain can then activate a response from the nervous and hormonal systems to control the temperature.

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So, what happens when you're too hot?

  • hairs lie flat
  • you sweat
  • blood vessels widen to allow more heat radiation (vasodilation)
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And what happens when you're too cold?

  • hairs stand on end
  • very little sweat is produced
  • shiver
  • blood vessels constrict to reduce heat radiation (vasoconstriction)
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What happens if you can't counteract the changes?

If you get too cold, then you can develop hypothermia, which can kill you very quickly.

If you are too hot, then you will get dehydrated and possibly suffer from heat stroke, which can kill you.

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