The increase in osmolarity from outer to inner medullary interstitium is maintained due to :
\((i)\) Close proximity between Henle's loop and vasa recta
\((ii)\) Counter current mechanism
\((iii)\) Selective secretion of \(HCO _{3}^{-}\) and hydrogen ions in PCT
\((iv)\) Higher blood pressure in glomerular capillaries

A \((i)\) and \((ii)\)
B Only \((ii)\)
C \((iii)\) and \((iv)\)
D \((i), (ii)\) and \((iii)\)

Verified Solution

Answer & Solution

Correct Answer

(A) \((i)\) and \((ii)\)

Step-by-step Solution

Detailed explanation

The correct answer is option (1) as both the statements (i) and (ii) are correct because counter current mechanism is based on special arrangement of Henle's loop and vasa recta and this mechanism maintain a concentration gradient in the medullary interstitium. Statement (iii) is incorrect as PCT helps in selective secretion of \(H ^{+}\), ammonia and \(K ^{+}\) ions and reabsorption of \(HCO _{3}^{-\text {from it. }}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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