Question

descrbe two physiological properties of tge LOH ascending limb?

Answer 1

Ascending limb of loop of Henle contains two segments: thin segment and thick segment.

Thin segment has less expression of Na K ATPase channels and is impermeable to water. Therefore absorption of salts occur with passive diffusion.

A) Thick segment is impermeable to water and also expresses a channel called Na K 2Cl cotransporter. This channel removes one Na, one K and 2 Cl ions from the tubule into interstitium. This makes the fluid in the lumen diluted. The hypertonic urine which has come from the descending limb of loop of Henle becomes hypotonic in this limb. Thus thick ascending limb of loop of Henle is also called as Diluting segment. This channel is blocked by loop diuretics.

Thick segment also has Na-H antiporter which mediates the reabsorption of Na transcellularly and secretion of H.

Also there occurs a paracellular passive reabsorption of Na, K, Ca and Mg. The increased salt reabsorption by the thick ascending limbo increases the magnitude of positive charge in the lumen which plays a major role in driving passive paracellular reabsorption of cations.

Na reabsorbed from this segment is the main driving force behind the counter current miltiplier system which concentrates Na and urea in medullary interstitium.