Homeostasis or homoeostasis is the property of a system within the body of a living organism in which a variable, such as the concentration of a substance in solution, is actively regulated to remain very nearly constant. Examples of homeostasis include the regulation of the body temperature of an animal, the pH of its extracellular fluids, or the concentrations of sodium (Na+) and calcium (Ca2+) ions or of glucose in the blood plasma, despite changes in the animal’s environment, or what it has eaten, or what it is doing (for example, resting or exercising). Each of these variables is controlled by a separate “homeostat” (or regulator), which, together, maintain life. Homeostats are energy-consuming physiological mechanisms.
The concept was described by French physiologist Claude Bernard in 1865 and the word was coined by Walter Bradford Cannon in 1926.
The concept of homeostasis is sometimes also applied to technological control systems such as thermostats, which function in an analogous way.
The word homeostasis (/ˌhoʊmioʊˈsteɪsᵻs/) uses combining forms of homeo- and -stasis, New Latin from Greek: ὅμοιος homoios, "similar" and στάσις stasis, "standing still", yielding the idea of "staying the same".