Counter-Current Multiplier

This is in relation to the Loop Of Henle, in the Kidney. The book describes this as a counter-current multiplier - what exactly do they mean?

Reply 1

Mustard-man

All I can recall is the longer the nephron, the greater the multiplier effect. This causes the area around the distal convoluted tubule to have an ever high solute concentration, therefore allowing more water to enter the capillaries by osmosis because there is a greater gradient

Reply 2

rahmed

The ascending loop of henle is more permeable to sodium and chloride ions, these passivly pass out of the ascending loop in the medulla. They are then actively pumped out as well.

This means that there is a high solute concentration in the medulla.

The descending loop of henle is more permeable to water, so water passes out of the descending loop and into the surrounding capillaries.

At any point in the loop, the soulte concentration is always higher in the descending loop of Henle due to the amount of water that has passed out.

This is what they mean by the counter-current multiplier.

Hope you understood that :smile:

Reply 3

Revenged

WokSz

This is in relation to the Loop Of Henle, in the Kidney. The book describes this as a counter-current multiplier - what exactly do they mean?

More ions pumped out the loop, more water is reabsorped into the blood at the collecting duct.

Reply 4

crazy_hamster

The counter-current multiplier is needed in the nephron to allow the concentration of urine. Concentration of urine happens because of the gradient of concentrations between the medullary interstitial fluid and that of the tubule.

The descending limb of Henle (permeable to water) travels cortex to medulla and the ascending limb of Henle (permeable to solutes) travels medulla to cortex. As the descending limb is permeable to water this moves out of the limb and into the medullery region by osmosis creating a hypertonic solution in the tubule. In the ascending limb cotransporters work to reabsorb solutes (particularly Na+ and Cl-) out of the tubule leaving behind a hypotonic solution in the tubule.

Simply the countercurrent multiplier is a mechanism of the Loop of Henle to concentrate the urine and conserve water. (however ADH does play a role also in water reabsorption; the more ADH there is secreted, the more water reabsorption there is in the collecting ducts and the more concentrated the urine is).

Thats what I thought the countercurrent multiplier was. . . . if anyone could tell me what I have worng. . .I am learning this for my exam so any pointers would be useful! :smile:

Reply 5

WokSz

Let me get this straight:

Na+ and Cl- is pumped out by the ascending limb into the surrounding tissue fluid, causing its water potential to decrease. This means that water in the descending limb moves out, into the tissues, down its gradient.

Na+ and Cl- also goes into the descending limb, causing it to get more concentrated. When the urine then flows up the ascending limb, the process starts again. However, the higher the urine goes in the ascending limb, the less concentrated it becomes. However, the concentration inside the tubule is always higher than the surrounding tissue.

Is this correct?

Also, is the Distal Convoluted Tubule, where the ion concetration in the blood is controlled, by the exchange of Na+ coming in, and K+ going out?

Thanks for everything :smile:

Counter-Current Multiplier

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