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Homeostasis and hormones

Conditions in the body are controlled, to provide a constant internal environment. This is called homeostasis. The conditions that must be controlled include body temperature, water content, carbon dioxide level, and blood sugar level.

Hormones are chemicals secreted by glands. They travel through the bloodstream and affect target organs. Sexual development, the menstrual cycle and fertility in women, and blood sugar levels, are all controlled by hormones.


It is important that the body’s internal environment is controlled. For example, the amount of carbon dioxide in the bloodstream is carefully controlled.

Maintaining a constant internal environment is called homeostasis. The nervous system and hormones are responsible for this. Here are some of the other internal conditions that are controlled:

Blood sugar level

This is controlled to provide cells with a constant supply of energy. The blood sugar level is controlled by the release and storage of glucose, which is in turn controlled by a hormone called insulin.

Body temperature

This is controlled to maintain the temperature at which enzymes work best, which is 37°C. Body temperature is controlled by:

  • controlling blood flow to the skin
  • sweating
  • shivering

The body’s water content

This is controlled to protect cells by stopping too much water from entering or leaving them. Water content is controlled by water loss from:

  • the lungs when we exhale
  • the skin by sweating
  • the body, in urine produced by the kidneys

Feedback mechanisms - higher

Homeostasis is achieved by negative feedback mechanisms. The animation shows how this works when controlling the body’s water content.

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