The function of angiotensin II is

Options

A. to enhance the water and sodium reabsorption from renal tubule
B. stimulation of adrenal medulla to secrete aldosterone
C. to decrease the heartbeat and dilate arterioles
D. all of the above

Answer

### Step-by-Step Solution:

1. **Understanding Angiotensin II**:
- Angiotensin II is an active form of angiotensin that plays a crucial role in regulating blood pressure and fluid balance in the body.

2. **Formation of Angiotensin II**:
- Angiotensin II is formed from angiotensin I, which is derived from angiotensinogen (an inactive precursor).
- The conversion from angiotensinogen to angiotensin I is stimulated by the enzyme renin, which is secreted by the juxtaglomerular apparatus in the kidneys.

3. **Functions of Angiotensin II**:
- **Enhancement of Sodium and Water Reabsorption**: Angiotensin II promotes the reabsorption of sodium ions in the renal tubules, which in turn leads to increased water reabsorption. This helps to increase blood volume and blood pressure.
- **Stimulation of Aldosterone Secretion**: Angiotensin II stimulates the adrenal cortex (not the adrenal medulla) to secrete aldosterone, a hormone that further enhances sodium reabsorption.
- **Vasoconstriction**: Angiotensin II causes constriction of blood vessels, which increases peripheral resistance and contributes to raising blood pressure.

4. **Analyzing the Options**:
- **Option A**: "Enhance the water and sodium reabsorption from the renal tubule" - This is correct.
- **Option B**: "Stimulation of adrenal medulla to secrete aldosterone" - This is incorrect; aldosterone is secreted from the adrenal cortex.
- **Option C**: "Decrease the heartbeat and dilate the arterioles" - This is incorrect; angiotensin II actually causes vasoconstriction.
- **Option D**: "All of the above" - This is incorrect because not all statements are true.

5. **Conclusion**:
- The correct answer is **Option A**: "Enhance the water and sodium reabsorption from the renal tubule."