Homeostasis

Homeostasis, any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival. If homeostasis is successful, life continues; if unsuccessful, disaster or death ensues. The stability attained is actually a dynamic equilibrium, in which continuous change occurs yet relatively uniform conditions prevail. The general idea of this self-regulating process was explored by French physiologist Claude Bernard in 1849 and the word homeostasis coined by American neurologist and physiologist Walter Bradford Cannon in 1926.

Any system in dynamic equilibrium tends to reach a steady state, a balance that resists outside forces of change. When such a system is disturbed, built-in regulatory devices respond to the departures to establish a new balance; such a process is one of feedback control. All processes of integration and coordination of function, whether mediated by electrical circuits or by nervous and hormonal systems, are examples of homeostatic regulation.

A familiar example of homeostatic regulation in a mechanical system is the action of a room-temperature regulator, or thermostat. The heart of the thermostat is a bimetallic strip that responds to temperature changes by completing or disrupting an electric circuit. When the room cools, the circuit is completed, the furnace operates, and the temperature rises. At a preset level the circuit breaks, the furnace stops, and the temperature drops. Biological systems are more complex and have regulators only very roughly comparable to such mechanical devices. The two types of systems are alike, however, in their goal—to sustain activity within a prescribed range, whether to control the thickness of rolled steel or the pressure within the circulatory system.