JG cells get activated when there is

Options

A. more GFR
B. normal GFR
C. fall in GFR
D. both (1) and (3)

Answer

**Step-by-Step Solution:**

1. **Understanding JG Cells**: JG cells, or juxtaglomerular cells, are specialized cells located in the kidney, specifically in the juxtaglomerular apparatus. They play a crucial role in regulating blood pressure and the glomerular filtration rate (GFR).

2. **Identifying the Trigger**: The activation of JG cells is primarily influenced by changes in the glomerular filtration rate (GFR). GFR is a measure of how well the kidneys are filtering blood.

3. **Condition for Activation**: JG cells are activated specifically when there is a **fall in GFR**. This decrease in GFR signals the JG cells to respond.

4. **Response Mechanism**: Upon activation due to the fall in GFR, JG cells release an enzyme called **renin**. Renin plays a critical role in the regulation of blood pressure.

5. **Renin-Angiotensin-Aldosterone System**: The release of renin triggers the renin-angiotensin-aldosterone system (RAAS), which leads to increased blood pressure. This system involves several steps:
- Renin converts angiotensinogen (produced by the liver) into angiotensin I.
- Angiotensin I is then converted to angiotensin II by the enzyme ACE (angiotensin-converting enzyme) mainly in the lungs.
- Angiotensin II causes blood vessels to constrict and stimulates the release of aldosterone from the adrenal glands, leading to increased sodium and water reabsorption in the kidneys, further increasing blood volume and blood pressure.

6. **Conclusion**: Therefore, the activation of JG cells occurs specifically when there is a **fall in GFR**, which leads to the release of renin and ultimately results in increased blood pressure.

**Final Answer**: JG cells get activated when there is a **fall in GFR**.

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