(Homoeostasis is an acceptable, though unusual alternative spelling) (from Greek, homo: same, stasis: stopped, stationary) Homeostasis means, literally, the same state. It describes the observation that living systems tend to maintain constancy. The concept of homeostasis originates with the French physiologist Claude Bernard (1813–1878) but in fact the word homeostasis was coined and first used in 1932 by the American physiologist Walter B.Cannon (1871–1945). It is well established that physiological mechanism, operating at many levels—the individual CELL, systems and whole organisms—tend to maintain a constant state. ENERGY BALANCE, WATER BALANCE, BODY WEIGHT, TEMPERATURE REGULATION are among the basic physiological processes thought to be governed by homeostasis. Brains contain many mechanisms for the detection of change in various physiological measures—for example, the concentration of GLUCOSE in the blood stream, levels of HORMONES, body water content (see OSMOREGULATION)—and there are many effector systems that serve to change physiological processes and behaviour in order to correct imbalances. Homeostasis is without doubt an important principle, but caveats to it need to be expressed. First, it was once assumed that physiological processes worked by SET POINT mechanisms, with precisely defined levels determined in advance. If a measure deviated above or below this point, corrective processes would take effect to return the system to stability. This would be a very rigid system. A mechanism with upper and lower limits—that is to say an acceptable range of levels rather than a set point value—is more plausible (see Herman & Polivy, 1984 for a description of a boundary model for the regulation of body weight).
Second, authors now lay emphasis also on the concept of ALLOSTASIS, which stresses ADAPTATION and flexibility in response to challenge. The role of LEARNING in adapting to changing conditions is emphasized. Clearly, adaptation is of enormous value for either an individual animal or a species to survive. Third, related to this last point, homeostasis is held to be one of the fundamental principles of physiology. Another is NATURAL SELECTION, the engine of EVOLUTION. Natural selection also emphasizes adaptation and FITNESS. It is curious that biology should have two fundamental principles apparently at variance with each other.
Herman C.P. & Polivy J. (1984) A boundary model for the regulation of eating. In Eating and its Disorders,, ed. A.J.Stunkard & E. Stellar, pp. 141–156, Raven Press: New York.
This is the complete article, containing 390 words
(approx. 1 page at 300 words per page).
