Question 3e
Explain why negative feedback, and not positive feedback, is involved in homeostatic mechanisms. [5]
Answer:
1. Restores Balance
- Purpose: Counteracts changes to bring the body back to a stable state.
- Example: After drinking excess water, the blood’s water potential rises. Negative feedback reduces ADH release, increasing urine production to bring water levels back to normal.
2. Prevents Overreaction
- Purpose: Avoids extreme responses that could harm the body.
- Example: Once balance is achieved, the feedback mechanism stops; without this, urine production might continue excessively, risking dehydration.
3. Maintains Equilibrium
- Purpose: Keeps key variables, like blood water potential, within a narrow, safe range.
- Example: With high salt intake, the body releases more ADH, increasing water reabsorption to prevent further water loss and stabilize the internal environment.
4. Self-Regulating Mechanism
- Purpose: Operates automatically, without needing constant external control.
- Example: ADH release adjusts in response to blood osmolarity, either conserving water (in low water intake) or increasing excretion (after drinking large amounts of water).
5. Positive Feedback Would Destabilize the System
- Example: In urine regulation, positive feedback would worsen changes in water potential, risking dehydration (too much urine) or water overload (too little urine).
- Reason: Positive feedback amplifies changes, pushing the system further from its set point, which is unsuitable for homeostasis.