JG cells, under low glomerular blood flow release

Options

A. Angiotensin I
B. Angiotensin II
C. Aldosterone
D. Renin

Answer

**Step-by-Step Solution:**

1. **Identify the Cells**: The question refers to JG cells, which are known as juxtaglomerular cells. These cells are specialized smooth muscle cells located in the afferent arterioles of the kidney.

2. **Understand the Function of JG Cells**: Juxtaglomerular cells play a crucial role in regulating blood pressure and glomerular filtration rate. They respond to changes in blood flow and pressure.

3. **Recognize the Trigger**: When the kidney experiences low blood volume, this results in low glomerular blood flow. This condition is detected by the juxtaglomerular cells.

4. **Response to Low Blood Flow**: In response to low glomerular blood flow, the juxtaglomerular cells are stimulated to release a specific substance.

5. **Identify the Substance Released**: The substance released by the JG cells under conditions of low glomerular blood flow is renin. Renin is an enzyme that initiates the renin-angiotensin-aldosterone system (RAAS), which helps to increase blood pressure.

6. **Final Answer**: Therefore, the correct answer to the question is that JG cells under low glomerular blood flow release renin.

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