0x668143c4…385fsent to0x9e4e9d99…a81d·#12,979,185·view on Etherscan
"The purpose of the counter-current system in the loop of Henle is to reabsorb the O2 that is produced in the thin descending limb during the osmotic reabsorption of water there, that is how and where the kidney desalinates water and reabsorbs it into the renal vein. Without the loop, the O2 trapped in the nephron would just pass straight out into the urine, allowing only a one-time use of the osmosis cathode O2. If the body absorbs 22 mol O2 per day, and 1/5th of that passes into the kidney, there is only 4.4 mol O2 in the kidney, and if all of it were used for the desalination mechanism, without recirculation, it could only reabsorb 2*4.4 mol water, equal to 8.8/55.5 = 15 dL, far from the 10 L/d of water that is removed with the thin descending limb of the loop of Henle. The counter-current loop, and the vasa recta flowing in the opposite direction, allows the O2 to recirculate, and using 4.4 mol O2 as an example again, recirculating 63 times provides the osmotic cathode to reabsorb 10 liters of water per day, 63*8.8 mol / 55.5 mol/L = 10 L. "