Loops of Henle

[peacefulheart]

Long loops of Henle on juxtamedullary nephrons allow
for greater concentration of urine. For an individual with
highly concentrated urine, filtrate entering the loop of
Henle is likely to be:



A. more concentrated than filtrate exiting the loop
Henle.
B.less concentrated than filtrate exiting the loop of
Henle.
C.more voluminous than filtrate exiting the loop of
Henle.
D.less voluminous than filtrate exiting the loop of
Henle.

The answer is A. I choose A by sort of negative feedback mechanism but do not quite understand it.

thanks a lot.

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[MedPR]

Long loops of Henle on juxtamedullary nephrons allow
for greater concentration of urine. For an individual with
highly concentrated urine, filtrate entering the loop of
Henle is likely to be:



A. more concentrated than filtrate exiting the loop
Henle.
B.less concentrated than filtrate exiting the loop of
Henle.
C.more voluminous than filtrate exiting the loop of
Henle.
D.less voluminous than filtrate exiting the loop of
Henle.

The answer is A. I choose A by sort of negative feedback mechanism but do not quite understand it.

thanks a lot.

This question has been discussed quite a bit on SDN. First, it's tricky because it's a definitional question in disguise and second because C is also correct.

A is true because as filtrate descends the loop of henle it loses water (becomes more concentrated) then as it ascends it loses sodium (becomes less concentrated).

C is true because water does not enter the loop.

 

[peacefulheart]

This question has been discussed quite a bit on SDN. First, it's tricky because it's a definitional question in disguise and second because C is also correct.

A is true because as filtrate descends the loop of henle it loses water (becomes more concentrated) then as it ascends it loses sodium (becomes less concentrated).

C is true because water does not enter the loop.

1. Thanks for the explanation.

2. I understand A is right .

3. Not sure about C.

4. The explanation from EK book :"The loop of Henle concentrates the medulla via a net loss of solute to the medulla. This process is critical to the function of other parts of the nephron; a medulla with a high concentration of solute allows for the passive absorption of water from the filtrate in other areas of the nephron."


thanks a lot

 

[Hemorrage]

You should read up on how the loop does what it does- its called the countercurrent multiplier

 

[peacefulheart]

You should read up on how the loop does what it does- its called the countercurrent multiplier

what is countercurrent multiplier? Could you explain it ? thanks

 

[Hemorrage]

what is countercurrent multiplier? Could you explain it ? thanks

The basic idea is the following.

As the ultrafiltrate passes into the Descending loop, there is a large expression of aquaporins on the epithelial wall which absorbs much of the H2O in the ultrafiltrate. This in turn increases the osmolarity of the ultrafiltrate as it goes further down the DL. Once the filtrate heads up the ascending loop, water reabsorption is stopped and the high osmolarity filtrate gets its osmolarity lowered because there are alot of salt reabsorption mechanisms in the AL. This in turn creates high osmolar interstitial environment for the medullary collecting duct. This is important because as filtrate passes through the collecting duct it needs to be "concentrated" into urine.

You should look this up in vanders or guytons physiology it will make more sense in context

 

[MedPR]

1. Thanks for the explanation.

2. I understand A is right .

3. Not sure about C.

4. The explanation from EK book :"The loop of Henle concentrates the medulla via a net loss of solute to the medulla. This process is critical to the function of other parts of the nephron; a medulla with a high concentration of solute allows for the passive absorption of water from the filtrate in other areas of the nephron."


thanks a lot

C is right. At no point in the loop of henle is water added to the filtrate. However water is removed from the filtrate in the descending limb. Loss of water = loss of volume = less voluminous at the end than at the beginning

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