Which is an example of positive feedback in biology?

• A. Oxytocin-driven uterine contractions during childbirth.
• B. Regulation of blood glucose to stay at a set value.
• C. Negative feedback to reduce heat loss.
• D. Water reabsorption in kidneys to maintain osmolarity.

Answer: (A)

Positive feedback occurs when a stimulus triggers responses that amplify that same stimulus, creating a self-reinforcing loop that continues until a final event ends the process. In childbirth, oxytocin promotes uterine contractions; those contractions push the baby downward, which stimulates even more oxytocin release and even stronger contractions, driving labor to completion. This amplification is the hallmark of positive feedback, unlike the stabilizing responses seen in negative feedback.

The other scenarios illustrate negative feedback, which aims to restore a set point rather than amplify a change. Keeping blood glucose within a narrow range involves insulin and glucagon acting to counter deviations; reducing heat loss is a response to maintain body temperature and oppose the initial drop; and water reabsorption in the kidneys adjusts to maintain osmolarity, countering disturbances rather than amplifying them.