Which of the following acts as a check on RAAS?

Options

A. ANF
B. Aldosterone
C. ACE
D. Renin

Answer

### Step-by-Step Solution:

1. **Understanding the RAS System**: The Renin-Angiotensin-Aldosterone System (RAAS) is a hormone system that regulates blood pressure and fluid balance. It involves three main components: renin, angiotensin, and aldosterone.

2. **Components of RAS**:
- **Renin**: An enzyme secreted by the juxtaglomerular (JG) cells of the kidney in response to low blood pressure or low sodium levels.
- **Angiotensin**: A protein produced by the liver that is converted into angiotensin I and then into angiotensin II by the action of angiotensin-converting enzyme (ACE).
- **Aldosterone**: A hormone produced by the adrenal cortex that promotes sodium and water reabsorption in the kidneys, increasing blood volume and blood pressure.

3. **Activation of RAS**: The RAS is activated when there is a decrease in blood volume, blood pressure, or glomerular filtration rate (GFR). This leads to increased blood pressure and restoration of blood volume.

4. **Identifying the Check on RAS**: The question asks which factor acts as a check on the RAAS. Among the options provided:
- **Atrial Natriuretic Factor (ANF)**: This is secreted by the heart's atria when blood pressure is high. ANF promotes vasodilation and increases sodium excretion, which lowers blood pressure.
- **Aldosterone, ACE, and Renin** are all components of the RAAS and do not act as checks on it.

5. **Conclusion**: The factor that acts as a check on the RAAS is **Atrial Natriuretic Factor (ANF)**. Therefore, the correct answer is the first option.