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Positive Feedback

Human Biology (Year 12) - Homeostatic Control

Ben Whitten

What is positive feedback?

Positive feedback differs from negative feedback, as the response to a stimulus reinforces and intensifies the stimulus; it plays no role in homeostasis. The intensified stimulus results in an even greater response, and so forth. This could not result in homeostasis, but a few situations do exist where  some processes must be executed rapidly.

An example of positive feedback occurs during childbirth, a process which must be completed as efficiently and rapidly as possible in order to avoid stress and injury to both the mother and the baby. The baby on the cervix triggers the release of oxytocin, which intensifies contractions and pushes the baby further, and so forth. Once the baby is delivered, the cervix is no longer stretches; it never ceases impulses to the brain and the positive feedback cycle stops.

Positive feedback can also be harmful, for example during fever. A small rise in body temperature can be beneficial in fighting off infections, however, if body temperature rises above 42 degrees Celcius, a dangerous positive feedback loop can occur. The raised body temperature causes a higher metabolic rate which produces more heat, raising the temperature further, and the cycle repeats. Unless medical treatment is provided, death will result when the body reaches approximately 45 degrees Celcius.

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