Question

Describe the function of the two counter-current mechanisms that operate in the human kidney.

Please cite references (400 words, references are not included in word count)

Answer 1

The vasa recta and the henle's loop forms the counter current mechanism .It play an important role in concentration of urine. The proximity between Vasa recta and the henle's loop as well as countercurrent mechanism between the two results in the maintenance of highest osmolarity towards the medullary interstitium from 300 mOsmol-1 to 1200 mOsmol-1 . The osmolarity gradient is maintained by NaCl and urea . The descending limb of loop of henle is permeable to water and impermeable to solutes whereas ascending limb of loop of henle is permeable to solutes . So as the filtrate passes through the descending limb of loop of henle the osmolarity increases as it passes through the ascending limb the osmolarity decreases .

Also , NaCl is transport by ascending limb of loop of henle which is returned back to the interstitium by the descending limb of the vasa recta . Similarly the small amount of urea enter the thin segment of ascending limb of henle's loop which is returned to the interstitium by the collecting duct. Mechanism is also known as counter current mechanism .

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