A fall in GFR can activate the juxta glomerular cells to release_____

Answer

To solve the question "A fall in GFR can activate the juxtaglomerular cells to release_____," we can follow these steps:

### Step-by-Step Solution:

1. **Understand GFR**:
- GFR stands for Glomerular Filtration Rate. It is the rate at which blood is filtered through the glomeruli of the kidneys. A normal GFR is approximately 180 liters per day.

2. **Identify the Role of Juxtaglomerular Cells**:
- Juxtaglomerular cells, also known as JG cells, are specialized cells located in the walls of the afferent arterioles near the glomerulus. They play a crucial role in regulating blood pressure and GFR.

3. **Recognize the Trigger for Renin Release**:
- A decrease in GFR indicates that the kidneys are not filtering blood effectively, which can occur due to low blood pressure or low blood volume. This fall in GFR activates the juxtaglomerular cells.

4. **Determine What is Released**:
- In response to a decrease in GFR, the juxtaglomerular cells release the enzyme **renin**.

5. **Understand the Renin-Angiotensin Mechanism**:
- Renin initiates a cascade of reactions leading to the formation of angiotensin I, which is then converted to angiotensin II. Angiotensin II causes vasoconstriction, which helps to increase blood pressure and subsequently increases GFR.

6. **Conclude the Answer**:
- Therefore, the answer to the question is **Renin**.

### Final Answer:
A fall in GFR can activate the juxtaglomerular cells to release **Renin**.

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