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Homeostasis or homoeostasis is the property of an open system to regulate its internal environment so as to maintain a stable condition, by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. The term was coined in 1932 by Walter Cannon from two Greek words (to remain the same).
1 Overview
The term is most often used in the sense of biological homeostasis.
Multicellular organisms require a homeostatic internal environment, in order to live; many environmentalists believe this principle also applies to the external environment.
Many ecological, biological, and social systems are homeostatic. They oppose change to maintain equilibrium. If the system does not succeed in reestablishing its balance, it may ultimately lead the system to stop functioning.
Complex systems, such as a human body, must have homeostasis to maintain stability and to survive. These systems do not only have to endure to survive; they must adapt themselves and evolve to modifications of the environment.
1.1 Properties of homeostasis
Homeostatic systems show several properties:
- They are ultrastable ;
- Their whole organisation, internal, structural, and functional, contributes to the maintenance of equilibrium
- They are unpredictable (the resulting effect of a precise action often has the opposite effect to what was expected).
1.2 Mechanisms of homeostasis: feedback
Main article: FeedbackIn cybernetics and control theory, feedback is a process whereby some proportion or in general, function, of the output signal of a system is passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic behaviour of th
When a change of variable occurs, there are two main types of feedback to which the system reacts:
- Negative feedbackNegative feedback is a type of feedback, during which a system responds so as to reverse the direction of change. Since this process tends to keep things constant, it is stabilizing and attempts to maintain homeostasis. When a change of variable occurs wi is a reaction in which the system responds in such a way as to reverse the direction of change. Since this tends to keep things constant, it allows the maintenance of homeostasis. For instance, when the concentration of carbon dioxideCarbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. One of the best known of chemical compounds, it is frequently called by its formula: :CO (pronunciation: "see oh two") Carbon dioxide results from the combustion of organic in the human body increases, the lungThe lung is an organ belonging to the respiratory system and interfacing to the circulatory system of air-breathing vertebrates. Its function is to exchange oxygen from air with carbon dioxide from blood. The process in which this happens is called " extes are signalled to increase their activity and expel more carbon dioxide.
- In positive feedbackPositive feedback is a type of feedback. Open systems (ecological, biological, social) contain many types of regulatory systems, among which are systems that involve positive feedback and its relative negative feedback. When a change of variable occurs in, the response is to amplify the change in the variable. This has a de-stabilizing effect, so does not result in homeostasis. Positive feedback is less common in naturally occurring systems than negative feedback, but it has its applications. For example, in nerveA nerve is an enclosed, cable-like bundle of nerve fibers or axons, which includes the glia that ensheath the axons in myelin. Neurons are sometimes called nerve cells though this term is technically imprecise since many neurons do not form nerves. Nervess, a threshold electric potentialThe threshold potential is the membrane potential to which a membrane must be depolarized to initiate an action potential. triggers the generation of a much larger action potentialelectrophysiological recording of an action potential showing the various phases which occur as the wave passes a point on a cell membrane. As the traveling signals of nerves and as the localized changes that contract muscle cells, action potentials are a. (See also leverage points.)
