Explain the counter-current mechanism.
The flow of the glomerular filtrate in the two limbs of Henle’s loop and the vasa recta is in a counter-current pattern.
NaCl is transported by the ascending limb of Henle’s loop which is exchanged with the descending limb of the vasa recta.
NaCl is returned to the interstitium by the descending portion of the vasa recta.
Similarly, minute quantities of urea enter the thin segment of Henle’s loop which is transported back to the interstitium by the collecting tubule.
The counter-current pattern and the proximity between the Henle’s loop and the vasa recta help to maintain the osmolarity in the inner medullary interstitium, i.e. 300 mOsmoiL−1 in the cortex and 1200 mOsmoiL−1 in the medulla.
This process is called the counter-current mechanism.
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