The increase in osmolarity from outer to… - NEET UG 2020 Zoology PYQ

NEET UG 2020 — Zoology Excretory Products and their Elimination

2020mcqhard

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 ${\mathrm{HCO}}_{3}$ $-$ and hydrogen ions in $\mathrm{PCT}$

(iv) Higher blood pressure in glomerular capillaries

Official previous-year question

Held on 30 Apr 2020 · Verified 9 Jul 2026.

Options

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

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Solution

In the outer part of the medulla, the osmotic concentration of interstitial fluid is $300\mathrm{mosmol}/\mathrm{litre}$ . It gradually increases and reaches a value of $1200\mathrm{mosmol}/\mathrm{litre}$ in the inner part of the medulla. This gradient is maintained for the concentration of urine as it passes through the collecting tubule. The vasa recta contribute to the maintenance of the hyperosmotic condition of ECF in the medulla by a mechanism known as counter-current exchange. The counter-current mechanism works by exchange of water and electrolytes between Loop of Henle and vasa recta.

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