Feedback mechanisms

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The principles of feedback mechanisms

Negative feedback

This occurs when feedback causes the corrective measure to be turned off- in doing so its returned to its origianal level

For example, the regulation of body temperature

 

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If blood temperature rises then corrective measures are brought about. When the hypothalamus detects that the blood has cooled to its normal temperature then the corrective measures are turned off, and vica versa. 

Positive feedback

This is when the feedback causes the corrective measures to remain turned on. In doing so it causes the system to diviate even more from the original level. For example, during an action potential when an small influx of sodium ions increass the permeability of the membrane to sodium so more sodium ions diffuse through. 

Positive feedback often occurs more when there is a breakdown in control systems. In certain diseases, for example typoid fever, there is a breakdown in temperature regulation causing a rise in body temperature leading to hyperthermia. In the same way when the body gets too cold (hypothermia) the temperature control system tends to break down, leading to positive feedback resulting in the body temperature dropping even lower.

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