Homeostasis means "The maintenance of a constant internal environment". It's all about a living creature keeping their inside as
constant and
stable as possible, whatever may be happening on the
outside.
There are six main bodily levels that need to be controlled. CO2 and Urea need to be disposed of, and Ion content, water content, sugar content (of the blood), as well as temperature all need to be kept at a constant level.
CO2
CO
2 is breathed out through the
lungs. Co
2 levels are monitored by the
hypothalmus.
Urea
Urea is a substance produced in the
liver as a by-product of the process which breaks down amino acids. Urea is filtered out by the kidneys and also lost partly in sweat. Urea is a
poison.
Ion content
Ions are taken into the body in food, then absorbed into the
bloodstream. They are filtered out by the kidneys and also lost partly in sweat (which is why sweat tastes
salty).
Temperature
Blood temperature is monitored by the
hypothalmus, which then sends nerve impulses to the skin. If we're too hot then the hairs lie flat,
sweat is produced and
vasodilation occurs. Vasodilation is the opening up of the blood supply to the skin to remove heat, and it's why we go
red when we're hot.
If we're too cold, our hairs stand up and vasoconstriction occurs. This is when the blood supply to the skin is closed off to try and keep heat in. The body also increases liver activity and makes us shiver when we're cold, all to the end of producing more heat.
Water
Water levels in the blood are monitored by the
hypothalmus, which sends nerve impulses to the
pituitary gland, which produces
ADH (Anti-Diuretic Hormone). This instructs the kidneys as to what levels of water should be filtered from the blood.
Sugar content
The
liver and
pancreas work to control sugar levels in the blood. The pancrease produces insulin, which makes the liver turn
glucose into
glycogen.