Talk:Thin ascending limb of loop of Henle

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[edit] Sodium transport

I always thought that sodium was actively transported out of the ascending loop. Because the concentration outside would have to be high so the water potential is low enough for sufficient reapsorbtion from the descending loop.

Am I misinformed? or should it be changed. Thanks Robbos Jan 8, 2007 (UTC)

Yes, you are right and it should be changed. A couple of points:

1) At every point along the ascending limb, the osmolality of the (medullary) interstitium is higher than that of the tubular fluid. So, nowhere along the length of the ascending limb is there a concentration gradient that would favor the passive diffusion of sodium from the lumen into the interstitium. (In the case of the descending loop, the lumenal fluid is isosmotic w.r.t to the interstitium — that is, it increases it descends —  due to the water permeability of the tubular epithelium). Anyway, the article is incorrect about sodium.

2) You are right that sodium is transported out of the ascending loop. My renal phys book describes the sodium transport mechanisms for the thick segment, but says of the thin segment only that its mechanisms are still poorly understood. However, this is a 1994 book — Vander (Lange series) 5th edition. Maybe it's better understood now, I don't know.

Mark Lundquist (talk) 03:09, 14 March 2008 (UTC)