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[A] : The hormone aldosterone is secrete...

[A] : The hormone aldosterone is secreted by adrenal cortex after the low `Na^+` content in blood and the resultant low BP causes the kidney to release renin.
[R]: Renin in blood leads to the formation of angiotensin II which causes adrenel cortex to release aldosterone that causes kidney to retain `Na^+` and, therefore, water is reabsorbed and BP rises.

A

If both A and R are true and R is the correct explanation of A

B

If both A and R are true but R is not the correct explanation of A

C

If A is true and R is false

D

If both A and R are false

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The correct Answer is:
### Step-by-Step Solution: 1. **Understanding the Assertion (A)**: - The assertion states that the hormone aldosterone is secreted by the adrenal cortex in response to low sodium (`Na^+`) levels in the blood and low blood pressure (BP). - This indicates that aldosterone plays a crucial role in regulating sodium and blood pressure. 2. **Understanding the Reason (R)**: - The reason explains that low sodium levels and low BP trigger the kidneys to release renin. - Renin then leads to the formation of angiotensin II, which stimulates the adrenal cortex to release aldosterone. 3. **Mechanism of Action**: - The process described is part of the Renin-Angiotensin-Aldosterone System (RAAS). - When blood pressure drops or sodium levels are low, the juxtaglomerular apparatus in the kidneys detects these changes and releases renin. 4. **Formation of Angiotensin II**: - Renin converts angiotensinogen (produced by the liver) into angiotensin I, which is then converted into angiotensin II by the enzyme ACE (Angiotensin-Converting Enzyme). - Angiotensin II is a potent vasoconstrictor and also stimulates the adrenal cortex to release aldosterone. 5. **Role of Aldosterone**: - Aldosterone acts on the kidneys, promoting the reabsorption of sodium (`Na^+`) and water. - This reabsorption increases blood volume, thereby raising blood pressure. 6. **Conclusion**: - Both the assertion (A) and the reason (R) are true. - The reason (R) correctly explains the assertion (A), as the sequence of events leading to the release of aldosterone is accurately described. ### Final Answer: Both A and R are true, and R is the correct explanation of A. ---
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