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Question: Answered & Verified by Expert
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 HCO3- and hydrogen ions in PCT
(iv) Higher blood pressure in glomerular capillaries
BiologyExcretory Products and their EliminationNEETNEET 2020 (Phase 2)
Options:
  • A Only(ii)
  • B (iii) and (iv)
  • C (i), (ii) and (iii)
  • D (i) and (ii)
Solution:
1992 Upvotes Verified Answer
The correct answer is: (i) and (ii)
In the outer part of the medulla, the osmotic concentration of interstitial fluid is 300 mosmol/litre. It gradually increases and reaches a value of 1200 mosmol/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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