Positive feedback can be identified
as a mutualistic interaction, in other words the output affects the input and/or
the input affects the output, it is a cycle, and is commonly referred to as a
loop. Positive feedback loops are very rare, yet necessary for life. This
mechanism does not directly contribute to the maintenance of homeostasis, it actually
pushes the system further away from its equilibrium due to its reinforcing nature.
I used the term ‘reinforcing’, because instead of opposing the unfavorable changes
occurring in the homeostatic environment like negative feedback, it enhances
them; the initiating stimulus will cause more of that same stimulus. Constant
activity of this mechanism could have detrimental effects. Typically, there is
some sort of definitive endpoint, often described as an explosive event.
example of positive feedback is the secretion of oxytocin during childbirth,
this hormone is produced by the hypothalamus and is responsible for coordinated
contractions of smooth muscle in the uterus. Oxytocin is also responsible for
milk letdown during lactation, and it has some involvement in bonding behavior.
As mentioned previously, the releasing of this hormone promotes uterine
contractions, and being that it is regulated by the positive feedback
mechanism, these contractions in turn promote more oxytocin to be released,
thus causing stronger uterine contractions. The oxytocin continues to increase
and the contractions continue to get more fierce, that is until the ‘explosive
event’ occurs, which in this case will be the actual delivery of the child.
Once the child has been expelled from the womb, oxytocin secretion ceases, stopping
the uterine contractions.
Though rare, and potentially very dangerous, positive
feedback is a much appreciated aspect of life. In its absence there would be no
blood clotting, action potentials, or inducing of childbirth.