Expand RAAS.

Explanation

**Step-by-Step Solution:**

1. **Identify the Acronym**: The question asks to expand the acronym RAAS.

2. **Research the Full Form**: RAAS stands for Renin-Angiotensin-Aldosterone System.

3. **Explain the Components**:
- **Renin**: An enzyme secreted by the kidneys that plays a crucial role in blood pressure regulation.
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