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  • The counter-current mechanism operates inOption: 1 Ascending and descending limb of loop of Henle only<div class='qna-option'

The counter-current mechanism operates in

Option: 1

Ascending and descending limb of loop of Henle only


Option: 2

Ascending limb of the loop of Henle only


Option: 3

Descending limb of the loop of Henle only


Option: 4

Loop of Henle and vasa recta


Answers (1)

best_answer

 

 

Mechanism of Concentration of Urine -

  • Mammals have the ability to produce concentrated urine. 
  • The Henle’s loop and vasa recta play a significant role in this. 
  • The flow of filtrate in the two limbs of Henle’s loop is in opposite directions and thus forms a counter current. 
  • The flow of blood through the two limbs of vasa recta is also in a countercurrent pattern.
  • The proximity between the Henle’s loop and vasa recta, as well as the countercurrent in them,  help in maintaining an increasing osmolarity towards the inner medullary interstitium, i.e., from 300 mOsmolL–1 in the cortex to about 1200 mOsmolL–1 in the inner medulla.
  • This gradient is mainly caused by NaCl and urea. 
  • NaCl is transported by the ascending limb of Henle’s loop which is exchanged with the descending limb of vasa recta.
  • NaCl is returned to the interstitium by the ascending portion of vasa recta.
  • Similarly, small amounts of urea enter the thin segment of the ascending limb of Henle’s loop which is transported back to the interstitium by the collecting tubule.
  • The above-described transport of substances facilitated by the special arrangement of Henle’s loop and vasa recta is called the countercurrent mechanism.
  • This mechanism helps to maintain a concentration gradient in the medullary interstitium. 
  • Presence of such interstitial gradient helps in easy passage of water from the collecting tubule thereby concentrating the filtrate (urine). 
  • The overall function of the countercurrent mechanism is to concentrate the sodium chloride in the interstitial fluid and thereby cause water to diffuse out of the collecting ducts and concentrate the urine. 
  • Human kidneys can produce urine nearly four times concentrated than the initial filtrate formed.


 

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The counter-current mechanism operates in loop of Henle and Vasa recta. Hence the correct option is d

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