The principle of homeostasis is controlling the heating system with a simple thermostat in a house. These components are essentials thermometer, source of heat turning it on or off the thermometer is controlled by a switch, when the temperature drops below a certain level the heating is switched on and when the temperature rises above a certain level the heating is switched off. There are many systems in the body that contribute to homeostasis the obvious, are the kidneys which regulates water and salt and remove substances that might poison the enzymes. The liver which regulates the level of glucose in the blood etc also the lungs regulate oxygen and carbon dioxide, the skin regulates temperature and the brain has the overall control of the homeostatic processes in the body. It checks the composition of the blood flowing through it and if it is too warm, too cold, too concentrated or has too little glucose, nerve impulses or hormones are sent to the organs concerned, causing them to make necessary adjustment.

Negative feedback is a control mechanism in which a change from the norm triggers off a response this allows the norm to re set. If the internal factor in question rose above its norm value, the corrective action taken by the body would cause the opposite (negative) effect. Therefore if the factor fell below its norm the corrective action would again have the opposite negative effect, causing it to rise to normal value. This is the process in which departure from a set level is detected by receptors. These convey information to effectors which bring about a return to the original value see diagram below.