Couter check on RAAS is

Options

A. IGF
B. ANF
C. JGA
D. GIP

Answer

### Step-by-Step Solution:

1. **Understanding RAAS**: The Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system that regulates blood pressure and fluid balance. It is initiated when there is a decrease in glomerular blood flow, blood pressure, or glomerular filtration rate (GFR).

2. **Role of Juxtaglomerular Cells**: When GFR decreases, the juxtaglomerular (JG) cells in the kidneys detect this change and respond by releasing the enzyme renin.

3. **Conversion of Angiotensinogen**: Renin acts on a plasma protein called angiotensinogen, converting it into angiotensin I.

4. **Formation of Angiotensin II**: Angiotensin I is then converted to angiotensin II by the action of the angiotensin-converting enzyme (ACE), primarily in the lungs.

5. **Effects of Angiotensin II**: Angiotensin II is a potent vasoconstrictor, which means it narrows blood vessels, increasing blood pressure and GFR. It also stimulates the adrenal cortex to release aldosterone.

6. **Role of Aldosterone**: Aldosterone promotes sodium and water reabsorption in the kidneys, further increasing blood volume and blood pressure.

7. **Counter Check Mechanism**: To counteract the effects of RAAS, the body has mechanisms to prevent excessive increases in blood pressure and fluid retention. One such mechanism involves the release of Atrial Natriuretic Factor (ANF) from the atria of the heart.

8. **Function of ANF**: ANF acts as a vasodilator, promoting the dilation of blood vessels, which decreases blood pressure. It also inhibits the actions of aldosterone and renin, thus decreasing GFR and promoting the excretion of sodium and water.

9. **Conclusion**: Therefore, the hormone that acts as a counter check on the RAAS mechanism is Atrial Natriuretic Factor (ANF).

### Final Answer:
The hormone that works as a counter check on the RAAS mechanism is **Atrial Natriuretic Factor (ANF)**.

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