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

To solve the question regarding the RAAS (Renin-Angiotensin-Aldosterone System) mechanism and how angiotensin II increases blood volume and blood pressure, we can break down the process step by step.

### 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 activated in response to low blood pressure or low sodium levels.

2. **Role of Angiotensin II**: Angiotensin II is a potent vasoconstrictor that plays a crucial role in increasing blood pressure. It is formed from angiotensin I through the action of the angiotensin-converting enzyme (ACE).

3. **Stimulating Aldosterone Release**: One of the primary actions of angiotensin II is to stimulate the adrenal cortex (specifically the zona glomerulosa) to release the hormone aldosterone. Aldosterone promotes sodium reabsorption in the kidneys.

4. **Sodium and Water Retention**: When aldosterone is released, it signals the renal tubules (nephrons) to reabsorb more sodium (Na+) and water (H2O). This retention of sodium and water increases blood volume.

5. **Increased Blood Volume and Pressure**: As blood volume increases due to the reabsorption of sodium and water, blood pressure also rises. This is because more fluid in the bloodstream leads to increased pressure against the vessel walls.

6. **Incorrect Options**:
- Option C states that angiotensin II causes relaxation of the glomerular blood vessels, which would lead to decreased blood pressure. This is incorrect because angiotensin II actually causes vasoconstriction, which increases blood pressure.
- Therefore, the correct answer is that angiotensin II increases blood volume and blood pressure primarily by stimulating the adrenal cortex to release aldosterone (Option A) and by signaling the renal tubule to reabsorb more NaCl and water (Option B). Thus, the correct answer is both A and B.

### Final Answer:
Angiotensin II increases blood volume and blood pressure by activating the adrenal cortex to release aldosterone and signaling the renal tubule of the nephron to reabsorb more NaCl and water (both A and B).

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