In RAAS mechanism of kidney regulation , angiotensin II increases the blood volume and blood pressure by :

Options

A. Activating adrenal cortex to release aldosterone hormone.
B. Signalling renal tubule of nephron to reabsorb more NaCI and water.
C. Causing relaxation of glomerular blood vessels of arterioles .
D. Both (A) and (B)

Answer

### Step-by-Step Solution:

1. **Understanding the RAAS Mechanism**: The Renin-Angiotensin-Aldosterone System (RAAS) is a critical regulatory system in the kidneys that helps control blood pressure and fluid balance.

2. **Role of Renin**: When there is a decrease in blood pressure or blood flow to the kidneys, the juxtaglomerular cells in the kidneys release an enzyme called renin.

3. **Conversion of Angiotensinogen**: Renin converts angiotensinogen (a protein produced by the liver) into angiotensin I.

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

5. **Effects of Angiotensin II**:
- **Vasoconstriction**: Angiotensin II is a potent vasoconstrictor, which means it narrows blood vessels, increasing blood pressure.
- **Stimulation of Aldosterone Release**: Angiotensin II stimulates the adrenal cortex to release aldosterone, a hormone that promotes sodium and water reabsorption in the kidneys.

6. **Reabsorption of Sodium and Water**: Aldosterone acts on the renal tubules (specifically the distal convoluted tubule and collecting duct) to increase the reabsorption of sodium ions and water. This leads to an increase in blood volume, which contributes to higher blood pressure.

7. **Conclusion**: Therefore, angiotensin II increases blood volume and blood pressure by:
- Activating the adrenal cortex to release aldosterone (Option A).
- Signaling the renal tubules to reabsorb more sodium and water (Option B).
- The option stating relaxation of glomerular blood vessels is incorrect.

8. **Final Answer**: The correct answer is both A and B.