Which of These is an Example of a Positive-Feedback Mechanism

Question

Which of these is an example of a positive-feedback mechanism?
A) An increase in blood pressure activates mechanisms that decrease blood pressure.
B) Increased amounts of a hormone in the blood cause a decrease in the secretion of that hormone.
C) Increased carbon dioxide in the blood increases breathing rate, which decreases carbon dioxide in the blood.
D) Increased amounts of fluid in the blood result in increased quantities of urine, which decreases fluid content of the blood.
E) Increased stretch of the uterus causes it to contract, which further increases stretch.

Accepted Answer

A positive-feedback mechanism is one in which the initial stimulus leads to a response that amplifies or increases the stimulus, leading to a further response. The example in choice E, increased stretch of the uterus leading to further contractions and stretch, is an example of positive feedback. The other choices describe negative-feedback mechanisms, where the initial stimulus leads to a response that counteracts or opposes the stimulus, leading to a decrease in the response.