M04.03.09 Negative Feedback Regulation

Negative feedback regulation is a crucial mechanism in maintaining homeostasis in the body. This process involves hormones that regulate various physiological functions by adjusting their levels in response to changes in the internal environment.

Example: Aldosterone Regulation

Mechanism of Action

• Aldosterone is a hormone produced by the adrenal glands that plays a vital role in regulating sodium and potassium levels as well as blood pressure.

Steps in Negative Feedback Regulation

1. Stimulus:
   • Decreased blood pressure (perfusion pressure to the kidney) triggers a response.
2. Renin Release:
   • Reduced blood pressure stimulates the kidneys to release renin. This is often due to reflex sympathetic stimulation.
3. Aldosterone Release:
   • Renin catalyzes the conversion of angiotensinogen (from the liver) into angiotensin I, which is then converted to angiotensin II in the lungs. Angiotensin II stimulates the adrenal cortex to release aldosterone.
4. Sodium Reabsorption:
   • Aldosterone promotes sodium reabsorption in the kidneys. This process increases extracellular fluid volume and, consequently, blood pressure.
5. Compensation:
   • The increase in sodium reabsorption helps to restore blood pressure to normal levels, completing the feedback loop.

Summary Table

Points to Remember

• Negative feedback mechanisms are essential for maintaining homeostasis.
• Aldosterone plays a critical role in regulating blood pressure through sodium reabsorption.
• The renin-angiotensin-aldosterone system (RAAS) is a key player in this regulatory process.

References

• Hall, J. E., & Guyton, A. C. (2021). Textbook of Medical Physiology (14th ed.). Elsevier.
• Johnson, R. J., & Feehally, J. (2011). Comprehensive Clinical Nephrology (4th ed.). Elsevier.
• Vascular Biology: The Role of Aldosterone in Blood Pressure Regulation. Journal of Clinical Hypertension, 2018. DOI: 10.1111/jch.13236.