In the context of physiological feedback loops, is blood clotting an example of positive feedback?

• A. No; blood clotting is negative feedback because it counteracts the initial stimulus by decreasing platelet activation as clotting begins.
• B. No; blood clotting is a homeostatic set-point mechanism that maintains constant blood viscosity without amplification of the response.
• C. Yes; platelet activation releases chemicals that recruit and activate more platelets, amplifying clot formation until the break in the vessel is sealed.
• D. Yes; blood clotting is positive feedback because it lowers body temperature to slow bleeding and restore homeostasis.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the difference between positive and negative feedback loops. Negative feedback loops work to counteract a change and restore the system to its set point, while positive feedback loops amplify the initial stimulus, driving the process forward until a specific outcome is achieved.
2. Step 2: Analyze the process of blood clotting. When a blood vessel is damaged, platelets become activated and release chemicals that attract more platelets to the site, which in turn release more chemicals, creating a cycle of amplification.
3. Step 3: Recognize that this amplification continues until the break in the blood vessel is sealed by the clot, effectively stopping the bleeding.
4. Step 4: Conclude that because the response (platelet activation and recruitment) amplifies itself rather than counteracting the initial stimulus, blood clotting is an example of a positive feedback loop.
5. Step 5: Note that positive feedback loops in physiology are typically self-limiting by the nature of the process ending once the desired effect (sealing the vessel) is achieved.