The conditions inside our body must be very carefully controlled if the body is to function effectively. Homeostasis is the maintenance of a constant internal environment. The nervous system and hormones are responsible for this.

One example of homeostasis is the concentration of carbon dioxide in the blood being carefully controlled. Here are some of the other internal conditions that are regulated:

Body temperature

This is controlled to maintain the temperature at which the body’s enzymes work best, which is usually 37°C.

Blood sugar level

This is controlled to provide cells with a constant supply of glucose for respiration. It is controlled by the release and storage of glucose, which is in turn controlled by insulin.

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

Negative feedback

Homeostatic control is achieved using negative feedback mechanisms:

  • if the level of something rises, control systems reduce it again
  • if the level of something falls, control systems raise it again
Conditions in the body change from set point, the change is detected and corrective mechanisms are activated. Conditions then return to set point and corrective mechanisms are switched off.

Negative feedback flowchart

  1. contract A muscle tenses as fibres shorten or create tension.
  2. effectors Organ which has an effect when stimulated (eg muscles or glands).
  3. enzyme A protein which catalyses or speeds up a chemical reaction.
  4. evaporate Evaporation is the process in which a liquid turns into a gas.
  5. glucose A simple sugar made by the body from food, which is used by cells to make energy in respiration.
  6. glycogen The storage form of glucose in animal cells.
  7. hormone Chemical messengers produced in glands and carried by the blood to specific organs in the body.
  8. insulate To help maintain the temperature.
  9. insulin A hormone that regulates the level of sugar in the blood. It is produced in the islets of Langerhans in the pancreas.
  10. nerve impulses Electrical signals that travel along the nerve fibre from one end of the nerve cell to the other.
  11. obesity The medical term for being overweight. Being obese is dangerous to health.
  12. respiration The chemical change that takes place inside living cells, which uses glucose and oxygen to produce the energy organisms need to live. Carbon dioxide is a by-product of respiration.
  13. vasoconstriction The narrowing of the skin arterioles to reduce blood flow and reduce heat loss by radiation.
  14. vasodilation The increase in diameter of the skin arterioles to increase blood flow and increase heat loss by radiation.