Question

Blood osmolarity decreases with the secretion of
i. ADH
ii. aldosterone
iii. angiotensin II
iv. ANP

• A. i and ii only
• B. ii and iii only
• C. ii and iv only
• D. i only

Hint:

Key idea: ADH $\rightarrow$ Water $\uparrow$ $\rightarrow$ Osmolarity $\downarrow$

Answer 1

The Correct Option is D

Concept: Blood osmolarity depends on the concentration of solutes relative to water in plasma.
• ADH (Antidiuretic hormone): Increases water reabsorption $\rightarrow$ dilutes blood $\rightarrow$ decreases osmolarity.
• Aldosterone: Increases Na$^+$ reabsorption (water follows proportionally) $\rightarrow$ osmolarity not decreased significantly.
• Angiotensin II: Promotes vasoconstriction and Na$^+$ retention.
• ANP: Promotes loss of Na$^+$ and water but does not directly reduce osmolarity significantly like ADH.

Step 1: Identify effect of ADH.
ADH increases water reabsorption without solute, lowering osmolarity.

Step 2: Evaluate other hormones.
• Aldosterone: Increases Na$^+$ retention
• Angiotensin II: Increases Na$^+$ and water
• ANP: Reduces volume but not primarily osmolarity

Step 3: Conclusion.
Only ADH decreases blood osmolarity. Final Answer: Option (D)