control of internal conditions

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It is important that the internal environment of the body is controlled. Maintaining a constant internal environment is called homeostasis.

The nervous system and hormones are responsible for homeostasis. The following are some of the internal conditions that are controlled.

Water content of the body

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

  • the lungs - when we exhale
  • the skin - by sweating, and
  • the body - in urine produced by the kidneys.
hormone reaction when too little water in blood   hormone reaction when too little water in blood

Ion (salts) content of the body

This is controlled to protect cells by avoiding too much water entering or leaving them. Ion content is controlled by loss of ions from:

  • the skin by sweating, and
  • the body in urine produced by the kidneys.

Temperature of the body

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

  • controlling blood flow to the skin
  • sweating
  • shivering.

Blood sugar level

This means the same as blood glucose level. The level is controlled to provide cells with a constant supply of energy. Insulin, when secreted by the pancreas, causes glucose to be absorbed from the blood by the tissues. This reduces blood glucose level.

hormone reaction when blood glucose level too high   hormone reaction when blood glucose level too low

[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science ]