A fall in glomerular filtration rate (GFR) activates

Options

A. Adrenal cortex to release aldosterone
B. Adrenal medulla to release adrenaline
C. Juxta-glomerular cells to release renin
D. Posterior pituitary to release vasopressin

Answer

To solve the question regarding the activation that occurs due to a fall in glomerular filtration rate (GFR), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Glomerular Filtration Rate (GFR)**:
- GFR is a measure of how well the kidneys are filtering blood. A decrease in GFR indicates that the kidneys are not functioning optimally.

2. **Identify the Response to Low GFR**:
- When GFR falls, the body initiates several compensatory mechanisms to restore normal kidney function and maintain homeostasis.

3. **Activation of the Renin-Angiotensin-Aldosterone System (RAAS)**:
- One of the primary responses to a decrease in GFR is the activation of the Renin-Angiotensin-Aldosterone System (RAAS).
- Renin is released from the juxtaglomerular cells in response to low blood pressure or low sodium concentration.

4. **Effects of RAAS Activation**:
- The activation of RAAS leads to the conversion of angiotensinogen (produced by the liver) into angiotensin I, which is then converted to angiotensin II by the enzyme ACE (Angiotensin-Converting Enzyme).
- Angiotensin II causes vasoconstriction, increasing blood pressure, and stimulates the release of aldosterone from the adrenal glands, which promotes sodium and water reabsorption in the kidneys.

5. **Conclusion**:
- Therefore, a fall in GFR activates the Renin-Angiotensin-Aldosterone System (RAAS) to help restore GFR and maintain blood pressure.

### Final Answer:
A fall in glomerular filtration rate (GFR) activates the Renin-Angiotensin-Aldosterone System (RAAS).