Positive feedback
In this the initial disturbance in the system sets off a train of events that increases the disturbance even further.
Thus positive feedback does not favour stability and often displaces a steady state away from its steady state operating point. Positive feedback is therefore also known as ‘vicious cycle.’
A mild degree of positive feedback can be overcome by negative feedback control mechanisms of the body and thus vicious cycle fails to develop.
Examples:
Example of a positive feedback is the release of oxytocin hormone on stretching of cervix of uterus at the time of labour. Th is positive feedback occurs as follows:
Release of hormone oxytocin Causes contraction of uterine muscle Pushes the baby downwards This causes stretching of cervix of uterus due to baby’s head being pushed down Stretching of cervix acts as a stimulus for release of more oxytocin This positive feedback leads to a vicious cycle which causes greater and greater oxytocin secretion leading to greater and greater contraction of uterine muscle, ultimately leading to delivery of the baby.
Another example is the blood clotting mechanism which is a very useful positive feedback. When a blood vessel is ruptured, multiple enzymes called clotting factors are activated. Some of these enzymes act on other yet inactivated enzymes of the immediately adjacent blood, activating them and causing still more clot. Th is process continues until the hole in the vessel is plugged by the clot and bleeding no longer occurs.
In this the initial disturbance in the system sets off a train of events that increases the disturbance even further.
Thus positive feedback does not favour stability and often displaces a steady state away from its steady state operating point. Positive feedback is therefore also known as ‘vicious cycle.’
A mild degree of positive feedback can be overcome by negative feedback control mechanisms of the body and thus vicious cycle fails to develop.
Examples:
Example of a positive feedback is the release of oxytocin hormone on stretching of cervix of uterus at the time of labour. Th is positive feedback occurs as follows:
Release of hormone oxytocin Causes contraction of uterine muscle Pushes the baby downwards This causes stretching of cervix of uterus due to baby’s head being pushed down Stretching of cervix acts as a stimulus for release of more oxytocin This positive feedback leads to a vicious cycle which causes greater and greater oxytocin secretion leading to greater and greater contraction of uterine muscle, ultimately leading to delivery of the baby.
Another example is the blood clotting mechanism which is a very useful positive feedback. When a blood vessel is ruptured, multiple enzymes called clotting factors are activated. Some of these enzymes act on other yet inactivated enzymes of the immediately adjacent blood, activating them and causing still more clot. Th is process continues until the hole in the vessel is plugged by the clot and bleeding no longer occurs.
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