Each of these variables is controlled by one or more regulators or homeostatic mechanisms, which together maintain life.

Homeostasis is brought about by a natural resistance to change when already in its optimal conditions, and equilibrium is maintained by many regulatory mechanisms; it is thought to be the central motivation for all organic action. All homeostatic control mechanisms have at least three interdependent components for the variable being regulated: a receptor, a control center, and an effector. The receptor is the sensing