In which the following condition can activate the JG cells to release renin `:-`

Options

A. More `Na^(+)` inblood plasma
B. More blood volume
C. High glomerular blood pressure
D. Fall in GFR

Answer

### Step-by-Step Solution:

1. **Understanding Juxtaglomerular (JG) Cells**:
- The juxtaglomerular cells are specialized cells located in the juxtaglomerular apparatus, which is formed by the distal convoluted tubule (DCT) and the afferent arteriole of the glomerulus.

2. **Function of JG Cells**:
- The primary function of JG cells is to release renin, an enzyme that plays a crucial role in regulating blood pressure and fluid balance.

3. **Conditions for Renin Release**:
- JG cells are activated to release renin primarily in response to a decrease in the glomerular filtration rate (GFR). This can occur due to low blood pressure or low blood volume.

4. **Mechanism of Activation**:
- When there is a fall in GFR, the macula densa cells (part of the DCT) sense the decrease in sodium chloride concentration. This triggers the JG cells to release renin.

5. **Renin-Angiotensin System**:
- The released renin activates the renin-angiotensin system, which leads to vasoconstriction and an increase in blood pressure.

6. **Conclusion**:
- Therefore, the correct condition that activates JG cells to release renin is a fall in the glomerular filtration rate.

### Final Answer:
The condition that activates the JG cells to release renin is a **fall in the glomerular filtration rate**.

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