Which of the following illustrates a positive feedback mechanism?

• A. Secretion of parathyroid hormone in response to low blood calcium
• B. Regulation of blood glucose levels by insulin
• C. The release of oxytocin during childbirth, which intensifies uterine contractions
• D. Thermoregulation by sweating to cool the body

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of feedback mechanisms. Feedback mechanisms are processes that help maintain homeostasis in the body. They can be classified as positive or negative feedback. Negative feedback works to counteract changes and restore balance, while positive feedback amplifies changes and drives processes forward.
2. Step 2: Analyze the examples provided in the problem. For each example, determine whether it represents positive or negative feedback. Positive feedback mechanisms amplify a response, while negative feedback mechanisms work to stabilize and reverse a change.
3. Step 3: Examine the example of oxytocin release during childbirth. Oxytocin stimulates uterine contractions, and these contractions, in turn, signal the release of more oxytocin. This creates a loop that intensifies the contractions until childbirth is complete. This is a classic example of positive feedback.
4. Step 4: Compare the other examples to the definition of negative feedback. For instance, secretion of parathyroid hormone in response to low blood calcium works to restore calcium levels, which is a stabilizing process and thus negative feedback. Similarly, regulation of blood glucose by insulin and thermoregulation by sweating are processes that aim to restore balance, making them negative feedback mechanisms.
5. Step 5: Conclude that the release of oxytocin during childbirth is the correct example of a positive feedback mechanism, as it amplifies the response rather than stabilizing it.