Negative feedback
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.
Homeostasis
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.
Negative Feedback Media
A simple negative feedback system descriptive, for example, of some electronic amplifiers. The feedback is negative if the loop gain AB is negative.
Blood glucose levels are maintained at a constant level in the body by a negative feedback mechanism. When the blood glucose level is too high, the pancreas secretes insulin and when the level is too low, the pancreas then secretes glucagon. The flat line shown represents the homeostatic set point. The sinusoidal line represents the blood glucose level.
An example of a negative feedback loop is the process of increasing and decreasing glucose levels in out bloodstream
Basic error-controlled regulator loop
A regulator R adjusts the input to a system T so the monitored essential variables E are held to set-point values S that result in the desired system output despite disturbances D.
Negative feedback amplifier with external disturbance. The feedback is negative if βA >0.
A feedback voltage amplifier using an op amp with finite gain but infinite input impedances and zero output impedance.
The ballcock or float valve uses negative feedback to control the water level in a cistern.
Control of endocrine hormones by negative feedback.
References
- ↑ Raven P.H. & Johnson G.B. 1999. Biology. 5th ed, Boston: Hill. p1058
- ↑ 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
- ↑ 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.
- ↑ Cannon W.B. 1929. Organization For physiological homeostasis. Physiol Rev. 9: 399-431.
- ↑ Cannon W.B. 1932. The wisdom of the body. W.W. Norton, New York.