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Negative feedback

occurs when some function of the output of a system, process, mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by other disturbances

Negative feedback is a basic concept of cybernetics; it is the basis of regulation and control. It is important in engineering and physiology. In biology and physiology negative feedback is known as homeostasis.[1]

Negative feedback occurs when the output of a system acts to oppose changes to the input of a system. This has the result that the changes are made less, and the system kept within limits. The classic example is a central heating system which cuts off when a (suitably placed) temperature sensor hits a pre-set mark. The negative feedback part is the thermostat.

HomeostasisEdit

Virtually all aspect of living systems involve homeostasis, and disease follows when any of these systems fail. Examples: blood pressure, glucose level, liver functions, cell division, and so on.

Homeostasis [2] was defined by Claude Bernard and later by Walter Bradford Cannon in 1926,[3] 1929[4] and 1932[5] is the property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition. The concept came from that of milieu interieur which was created by Claude Bernard and published in 1865.

If the overall feedback of the system is negative, then the system will tend to be stable.

ReferencesEdit

  1. Raven P.H. & Johnson G.B. 1999. Biology. 5th ed, Boston: Hill. p1058
  2. from Greek: ὅμοιος, hómoios, "similar" ὅμοιος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus and στάσις, stásis, "standing still"; στάσις, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
  3. Cannon W.B. 1929. Physiological regulation of normal states: some tentative postulates concerning biological homeostatics. in: A. Pettit (ed) A Charles Richet: ses anims, ses collegues, ses élvès, p91. Paris: editions Medicales.
  4. Cannon W.B. 1929. Organization For physiological homeostasis. Physiol Rev. 9: 399-431.
  5. Cannon W.B. 1932. The wisdom of the body. W.W. Norton, New York.