Homeostasis is the regulation of the internal conditions of the body to maintain a stable internal environment, despite changes in the external environment. This is essential for cells to function at optimum conditions.
Conditions that are controlled include: body temperature, blood glucose concentration, water levels, and CO2 levels.
Water levels are controlled by the kidneys, which regulate the amount of water reabsorbed into the blood, partly through the hormone ADH. CO2 levels are controlled by the lungs, which regulate the rate of gas exchange.
All control systems involve three components:
1. Receptors — detect changes (stimuli) in the environment
2. Coordination centres — (brain, spinal cord, pancreas) process information and coordinate a response
3. Effectors — muscles or glands that carry out the response