homeostasis


homeostasis
homeostatic /hoh'mee euh stat"ik/, adj.homeostatically, adv.
/hoh'mee euh stay"sis/, n.
1. the tendency of a system, esp. the physiological system of higher animals, to maintain internal stability, owing to the coordinated response of its parts to any situation or stimulus tending to disturb its normal condition or function.
2. Psychol. a state of psychological equilibrium obtained when tension or a drive has been reduced or eliminated.
[1925-30; HOMEO- + STASIS]

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Any self-regulating process by which a biological or mechanical system maintains stability while adjusting to changing conditions.

Systems in dynamic equilibrium reach a balance in which internal change continuously compensates for external change in a feedback control process to keep conditions relatively uniform. An example is temperature regulation
mechanically in a room by a thermostat or biologically in the body by a complex system controlled by the hypothalamus, which adjusts breathing and metabolic rates, blood-vessel dilation, and blood-sugar level in response to changes caused by factors including ambient temperature, hormones, and disease.

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      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.

      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 mechanical circuits or by nervous and hormonal systems, are examples of homeostatic regulation.

      The stability in the self-regulating devices commonly used in engineering and industry is achieved primarily through the use of such regulators as gyroscopes, mechanical governors, and inducers. Biological systems, of greater complexity, have regulators only very roughly comparable to such mechanical devices. The two types of systems are alike, however, in their goals—to sustain activity within prescribed ranges, whether to control the thickness of rolled steel or the pressure within the circulatory system.

      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.

      The control of body temperature in humans is a good example of homeostasis in a biological system. In humans, normal body temperature fluctuates around the value of 98.6° F, but various factors can affect this value, including exposure, hormones, metabolic rate, and disease, leading to excessively high or low temperatures. The body's temperature regulation is thought to be controlled by a region in the brain called the hypothalamus. feedback about body temperature is carried through the bloodstream to the brain and results in compensatory adjustments in the breathing rate, the level of blood sugar, and the metabolic rate. Heat loss in humans is aided by reduction of activity, by perspiration, and by heat-exchange mechanisms that permit larger amounts of blood to circulate near the skin surface. Heat loss is reduced by insulation, decreased circulation to the skin, and cultural modification such as the use of clothing, shelter, and external heat sources. The range between high and low body temperature levels constitutes the homeostatic plateau—the “normal” range that sustains life. As either of the two extremes is approached, corrective action (through negative feedback) returns the system to the normal range.

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Universalium. 2010.

Look at other dictionaries:

  • Homeostasis — (from Greek: ὅμος, hómos , equal ; and ιστημι, istēmi , to stand lit. to stand equally ; coined by Walter Bradford Cannon) is the property of either an open system or a closed system, especially a living organism, that regulates its internal… …   Wikipedia

  • Homeostasis — (Del griego homo (ὅμος) que significa similar y estasis (στάσις) posición , estabilidad ) es la característica de un sistema abierto o de un sistema cerrado o una conjugación entre ambos, especialmente en un organismo vivo, mediante la cual se… …   Wikipedia Español

  • homeostasis — o homeóstasis (plural homeostasis) sustantivo femenino 1. (no contable) Área: biología Conjunto de mecanismos que aseguran el control automático de las constantes biológicas de los seres vivos, manteniéndolas fijas dentro de unos límites muy… …   Diccionario Salamanca de la Lengua Española

  • homeóstasis — (plural homeostasis) sustantivo femenino 1. (no contable) Área: biología Conjunto de mecanismos que aseguran el control automático de las constantes biológicas de los seres vivos, manteniéndolas fijas dentro de límites muy estrechos: La… …   Diccionario Salamanca de la Lengua Española

  • homeostasis — n. The ability and tendency of certain systems to maintain a relatively constant internal state in spite of changes in external conditions; this ability is achieved by the presence of feedback mechanisms which can adjust the state of the system… …   The Collaborative International Dictionary of English

  • homeostasis — homeostasis. См. гомеостаз. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • homeostasis — index balance (equality) Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

  • homeostasis — 1926, coined in Mod.L. from HOMEO (Cf. homeo ) + Gk. stasis standing still (see STET (Cf. stet)). Related: Homeostatic …   Etymology dictionary

  • homeostasis — (De homeo y el gr. στάσις, posición, estabilidad). 1. f. Biol. Conjunto de fenómenos de autorregulación, que conducen al mantenimiento de la constancia en la composición y propiedades del medio interno de un organismo. 2. Autorregulación de la… …   Diccionario de la lengua española

  • homeostasis — (also homoeostasis) ► NOUN (pl. homeostases) ▪ the maintenance of a stable equilibrium, especially through physiological processes. DERIVATIVES homeostatic adjective. ORIGIN from Greek homoios like + stasis stoppage, standing …   English terms dictionary

  • homeostasis — ☆ homeostasis [hō΄mē ō stā′sis ] n. [ModL: see HOMEO & STASIS] 1. Physiol. the tendency to maintain, or the maintenance of, normal, internal stability in an organism by coordinated responses of the organ systems that automatically compensate for… …   English World dictionary


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