Kidney Question

[Mountaineurons]

Could someone explain why the answer to this question is what it is?

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

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

Highlight for answer: A

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[syoung]

Well I chose A, and my reasoning goes like this: The a normal individual will have henle's loop filtering urine correct? and greater conc as well. Now the abnormal individual has HIGHER conc of urine, which means coming into the loop of henle, it's gotta be more concentrated as well!
Let's use numbers. A normal person has 100 units of solutes in his urine. His loop of henle would have taken 200 units of solutes out of his blood and reduced it to 100 units (100 going to urine). The greater conc of urine in Henle allows for more of it to filter out into the filtrate, otherwise it would backflow and you wouldn't be filtering.
Now this person has higher conc of urine. That means maybe he has 150 units of solutes in his urine. Then coming into his loop, he would have had maybe 300 units of solutes and the loop filters out 150 (150 going to urine). I hope I explained that well...

 

[MedPR]

Well I chose A, and my reasoning goes like this: The a normal individual will have henle's loop filtering urine correct? and greater conc as well. Now the abnormal individual has HIGHER conc of urine, which means coming into the loop of henle, it's gotta be more concentrated as well!
Let's use numbers. A normal person has 100 units of solutes in his urine. His loop of henle would have taken 200 units of solutes out of his blood and reduced it to 100 units (100 going to urine). The greater conc of urine in Henle allows for more of it to filter out into the filtrate, otherwise it would backflow and you wouldn't be filtering.
Now this person has higher conc of urine. That means maybe he has 150 units of solutes in his urine. Then coming into his loop, he would have had maybe 300 units of solutes and the loop filters out 150 (150 going to urine). I hope I explained that well...

Doesn't urine get concentrated in the loop of henle? So shouldn't filtrate entering be less concentrated than filtrate exiting?

 

[syoung]

Well the answer is A according to OP, so that's what I had picked before highlighting.
Oops, the descending loop reabsorbs water, resulting in less vol and more sol conc in the fluid, and the ascending reabsorbs solutes but not water, but overall yes there is more conc urine at the end of it all.
But I guess my point was that if the person has higher urine concentration compared to normal, then it must mean that his filtrate was higher in conc overall (entering and exiting)

 

[MedPR]

I'm not seeing why the filtrate would be more concentrated before than after. Isn't urine always more concentrated after the loop of henle? Even in a person with highly concentrated urine, the urine might be relatively more concentrated before, but would still be more concentrated after wouldn't it?

Either way, C seems like the best answer to me. The urine could be hyperconcentrated because of ADH and aldosterone, which both have no effect on the loops of henle. Unless this is a passage based question that explicitly states that the urine concentration in this particular case is not due to ADH or aldosterone, then C is the best answer because the only thing you know for sure is that a ton of water is dumped from the descending loop.

 

[chiddler]

I'm not seeing why the filtrate would be more concentrated before than after. Isn't urine always more concentrated after the loop of henle? Even in a person with highly concentrated urine, the urine might be relatively more concentrated before, but would still be more concentrated after wouldn't it?

Either way, C seems like the best answer to me. The urine could be hyperconcentrated because of ADH and aldosterone, which both have no effect on the loops of henle. Unless this is a passage based question that explicitly states that the urine concentration in this particular case is not due to ADH or aldosterone, then C is the best answer.

Is that true? I don't think so. Urine isn't always more concentrated after loop of henle. The descending concentrates it then the ascending dilutes it so it may be more or less concentrated.

 

[MedPR]

Well I chose A, and my reasoning goes like this: The a normal individual will have henle's loop filtering urine correct? and greater conc as well. Now the abnormal individual has HIGHER conc of urine, which means coming into the loop of henle, it's gotta be more concentrated as well!
Let's use numbers. A normal person has 100 units of solutes in his urine. His loop of henle would have taken 200 units of solutes out of his blood and reduced it to 100 units (100 going to urine). The greater conc of urine in Henle allows for more of it to filter out into the filtrate, otherwise it would backflow and you wouldn't be filtering.
Now this person has higher conc of urine. That means maybe he has 150 units of solutes in his urine. Then coming into his loop, he would have had maybe 300 units of solutes and the loop filters out 150 (150 going to urine). I hope I explained that well...

The problem with your explanation is that you are assuming that the filtrate is more concentrated. They only tell you that the urine is more concentrated, not the filtrate. You're assuming that the filtrate within or proximal to the proximal tubule is already more concentrated, which is not necessarily true.

 

[MedPR]

Is that true? I don't think so. Urine isn't always more concentrated after loop of henle. The descending concentrates it then the ascending dilutes it so it may be more or less concentrated.

Yea, I'm not sure either, but I don't understand the justification for answer A.

Saying that urine is more concentrated in an individual does not mean that pre-Henle filtrate is more concentrated in that individual than another individual with normal urine.

Edit: Based on this it looks like filtrate is more dilute in the distal tubule than the proximal tubule, which makes A true. However, it has nothing to do with how concentrated the person's urine is. With that said, why isn't C also true? The descending loop is very permeable to water, while the ascending loop is not permeable at all. In other words, the filtrate loses water in the descending loop and doesn't regain any of it in the ascending loop.

 

[pfaction]

I'll throw my input on this.

Filtrate entering the loop of henle goes to the descending loop. Water removed, so it's more concentrated here. From the ascending loop, it gets actively transported out. AT THE TOP OF THE LOOP IT'S HYPO compared to the descending. Only small amounts of salts and majorly urea is left at the top.

When hitting the collecting, aldo/ADH act assuming they're stimulated in the first place. (As a side note, I think the macula deals with osmolarity? -> Renin) So if it's concentrated urine A holds in place. I can also see why the answer is C; more solute = more water needed.... for filtration...but I'd go with A.

 

[SaintJude]

I'll throw my input on this.

Filtrate entering the loop of henle goes to the descending loop. Water removed, so it's more concentrated here. From the ascending loop, it gets actively transported out. AT THE TOP OF THE LOOP IT'S HYPO compared to the descending. Only small amounts of salts and majorly urea is left at the top.

Ah thanks pfaction, that makes a lot of sense.

P.s. what is the "filtrate"? I'm still confused by this terminology. Is that what goes INTO the loop of henle or what is eventually reabsorbed?

 

[MedPR]

I'll throw my input on this.

Filtrate entering the loop of henle goes to the descending loop. Water removed, so it's more concentrated here. From the ascending loop, it gets actively transported out. AT THE TOP OF THE LOOP IT'S HYPO compared to the descending. Only small amounts of salts and majorly urea is left at the top.

When hitting the collecting, aldo/ADH act assuming they're stimulated in the first place. (As a side note, I think the macula deals with osmolarity? -> Renin) So if it's concentrated urine A holds in place. I can also see why the answer is C; more solute = more water needed.... for filtration...but I'd go with A.

Macula? The only macula I've heard of is on the retina

 

[MedPR]

Ah thanks pfaction, that makes a lot of sense.

P.s. what is the "filtrate"? I'm still confused by this terminology. Is that what goes INTO the loop of henle or what is eventually reabsorbed?

The filtrate is what passes through bowman's capsule. It does eventually go into the loop of henle and the rest of the nephron.

 

[chiddler]

Macula? The only macula I've heard of is on the retina

macula is inner kidney. outer is cortex.

 

[chiddler]

can you explain a little bit more, please? i understand what pfaction wrote but do not understand how to conclude that A is the answer from that.

 

[pfaction]

Macula lutea: Eyes (cones, acuity)
Macula densa: kidneys, osmolarity->renin.

Original question: For an individual with highly concerntrated urine, filtrate entering the loop of Henle is likely to be

Filtrate: The fluid from the blood that is scooped into the Bowman's capsule. So right there, it has a large volume and a large amount of solute. (If we're arbitrarily quantifying: 100mL)
From here, it hits the PCT. PCT: LARGE AMOUNTS OF SOLUTE AND THUS WATER ARE REABSORBED. On that principle, this fluid is lower in volume than our filtrate AND in solute. (quant: 50)
From there, we hit the descending limb. Oh lawd, water flows right out. No explanation needed for this, if you don't understand you have to read the kidney again. (quant: 25mL)
Ascending limb time: Pump that salt right the hell out. (Pharmacy school knowledge) There's a Na/K/2CL transporter here. That, Mg, Ca, I think Zn get pumped out. So there's your problem right there. Salt is decreased, but not water. So we're still at let's say, 25mL...but leaving the loop of henle is small amounts of salt. AND UREA.

So let's compare so far. Filtrate was 100 and salty as ****. Now we're leaving the loop, and we're at let's say 25mL and consists of mainly urea.

We end at the DCT because the question dun want us to analyze the DCT.


A. more concetrated than filtrate exiting the loop of Henle
Yes, this is true. In the beginning it's more concentrated even if the urine wasn't super salty.

B. less concetrated than filtrate exiting the loop fo Henle
NO. I don't think this is ever the case, how could that occur? Descending is impermeable to ions, Ascending is impermeable to water. There's that small issue of the thin ascending but I don't know if that matters.

C. more voluminous than filtrate exiting the loop of Henle
Nope, PCT takes out a ****ton. PCT is before loop! So automatically there's less volume about to enter than in the filtrate.

D. less voluminous than filtrate exiting the loop of Henle
Can't be true.

 

[SaintJude]

Anyway, I think this question is just trying to make you understand a very common point about kidney homeostasis:
the filtrate entering the loop of Henle is eventually less concentrated by the time it reaches the distal convoluted tubule

How would you know definitively whether it's more or less "voluminous"? (if it actually means occupying more space")

Also, bless you MedPr for sticking around...you won't see me in this forum after May.12 baby--god-willing.

 

[MedPR]

macula is inner kidney. outer is cortex.

Don't you mean medulla?

 

[MedPR]

Also, I'm pretty sure the macula densa is in the distal tubule, while the JGA (which is responsible for secreting renin) is just before the glomerulus.. I guess the fact that the JGA is right by the distal tubule could mean there are macula densa cells there too. idk.

 

[chiddler]

Don't you mean medulla?

yes lol

 

[MedPR]

Anyway, I think this question is just trying to make you understand a very common point about kidney homeostasis:
the filtrate entering the loop of Henle is eventually less concentrated by the time it reaches the distal convoluted tubule

How would you know definitively whether it's more or less "voluminous"? (if it actually means occupying more space")

Also, bless you MedPr for sticking around...you won't see me in this forum after May.12 baby--god-willing.

Because you don't gain water anywhere in the kidney. The filtrate spits out water in the descending loop and doesn't ever get it back. Less water = less volume.

So I can see now why A is correct, but I'm not sure why it's a better answer than C. For all we know, this person's urine is hyperconcentrated because the ascending loop isn't doing its job (no active pumping). In that case, C is true and A is false.

At the same time, the urine could be hyperconcentrated because the descending loop has become impermeable to water, which makes C false and A true.

Or, the filtrate and the loop of henle could be normal, but there are abnormally high levels of ADH and aldosterone, which makes A and C equally true.

 

[pfaction]

Also, I'm pretty sure the macula densa is in the distal tubule, while the JGA (which is responsible for secreting renin) is just before the glomerulus.. I guess the fact that the JGA is right by the distal tubule could mean there are macula densa cells there too. idk.

Here's another pharmacy tidbit: The DCT and the Glomerulus are actually attached. I'll pull the picture from one of my textbooks. They're connected at the JGA exactly as you said and the same way you said.

So I can see now why A is correct, but I'm not sure why it's a better answer than C.

We should all feel ashamed that we missed the proximal convoluted tubule.

 

[MedPR]

Here's another pharmacy tidbit: The DCT and the Glomerulus are actually attached. I'll pull the picture from one of my textbooks. They're connected at the JGA exactly as you said and the same way you said.



We should all feel ashamed that we missed the proximal convoluted tubule.

What does the proximal tube have to do with it though?

 

[pfaction]

What does the proximal tube have to do with it though?

Bowman ------> ProxCT --------------------------------------------------------> Start of Henle.
Filtrate--------------^****ton of reabsorption of ions, thus water follows----> ^ automatically has less water and solute.

 

[syoung]

Macula lutea: Eyes (cones, acuity)
Macula densa: kidneys, osmolarity->renin.

Original question: For an individual with highly concerntrated urine, filtrate entering the loop of Henle is likely to be

Filtrate: The fluid from the blood that is scooped into the Bowman's capsule. So right there, it has a large volume and a large amount of solute. (If we're arbitrarily quantifying: 100mL)
From here, it hits the PCT. PCT: LARGE AMOUNTS OF SOLUTE AND THUS WATER ARE REABSORBED. On that principle, this fluid is lower in volume than our filtrate AND in solute. (quant: 50)
From there, we hit the descending limb. Oh lawd, water flows right out. No explanation needed for this, if you don't understand you have to read the kidney again. (quant: 25mL)
Ascending limb time: Pump that salt right the hell out. (Pharmacy school knowledge) There's a Na/K/2CL transporter here. That, Mg, Ca, I think Zn get pumped out. So there's your problem right there. Salt is decreased, but not water. So we're still at let's say, 25mL...but leaving the loop of henle is small amounts of salt. AND UREA.

So let's compare so far. Filtrate was 100 and salty as ****. Now we're leaving the loop, and we're at let's say 25mL and consists of mainly urea.

We end at the DCT because the question dun want us to analyze the DCT.


A. more concetrated than filtrate exiting the loop of Henle
Yes, this is true. In the beginning it's more concentrated even if the urine wasn't super salty.

B. less concetrated than filtrate exiting the loop fo Henle
NO. I don't think this is ever the case, how could that occur? Descending is impermeable to ions, Ascending is impermeable to water. There's that small issue of the thin ascending but I don't know if that matters.

C. more voluminous than filtrate exiting the loop of Henle
Nope, PCT takes out a ****ton. PCT is before loop! So automatically there's less volume about to enter than in the filtrate.

D. less voluminous than filtrate exiting the loop of Henle
Can't be true.

Was hoping to have done my explanation like him.. Shows to go that I still need to study. But intuitively I knew the answer!

Although, you explained the normal guy, which is normal conc urine, since the ? asked highly conc urine.
Isn't it just that since he has relatively more conc of urine compared to the other guy, his kidneys still do the same thing, ie more conc going into loop than filtrate coming out?

 

[Mountaineurons]

Hm - any chance someone wants to post a solidified, unconvoluted (no pun intended) answer (i know it's probably embedded somewhere in the multiple replies above) for why A is true and C is not?

 

[syoung]

Yea, I'm not sure either, but I don't understand the justification for answer A.

Saying that urine is more concentrated in an individual does not mean that pre-Henle filtrate is more concentrated in that individual than another individual with normal urine.

Edit: Based on this it looks like filtrate is more dilute in the distal tubule than the proximal tubule, which makes A true. However, it has nothing to do with how concentrated the person's urine is. With that said, why isn't C also true? The descending loop is very permeable to water, while the ascending loop is not permeable at all. In other words, the filtrate loses water in the descending loop and doesn't regain any of it in the ascending loop.

Mountain look at the picture. The numbers tell you the osmolarity or concentration of the filtrate as it passes through the kidney. Entering is about 300-400 and getting to 1200 at the bottom, and leaves at 200 to 100. So A is the correct answer.

 

[chiddler]

Hm - any chance someone wants to post a solidified, unconvoluted (no pun intended) answer (i know it's probably embedded somewhere in the multiple replies above) for why A is true and C is not?

If I understand correctly, C is impossible because the filtrate entering the loop can only lose water and therefore it must be lower in volume than the filtrate leaving the loop.

A is the only possible answer left.

Right?

 

[Buttafuoco]

I don't remember any source explaining the nephron function to me to the point where I felt like it really clicked. One point that Khan brought up on his kidney function video though is he claimed that the function of the loop on Henli was to increase the osmolarity of the medulla, which occurs by active transport of certain ions in the ascending limb. So if you really want to concentrate the urine, I would assume that you pump out a bunch of crap into the medulla in the ascending limb so that you can then draw more out later in the collecting duct via osmosis.

This isn't exactly a satisfying answer for me, but I'm thinking it might be what they're looking for. If you look at wiki's entry on the countercurrent multiplier system under Physiological Principles

http://en.wikipedia.org/wiki/Countercurrent_multiplication

The ascending limb is impermeable to water (because of a lack of aquaporin, a common transporter protein for water channels in all cells except the walls of the ascending limb of the loop of Henle), but here Na+, Cl-, and K+ are actively transported into the medullary space, making the filtrate hypotonic

 

[pfaction]

wtf did i say that no one understood i said the exact same thing as buttafuoco.

Chiddler's right, automatically C is out. The descending will pour out water, the ascending is impermeable to water. So the volume is less than the filtrate entering.

 

[chiddler]

wtf did i say that no one understood i said the exact same thing as buttafuoco.

Chiddler's right, automatically C is out. The descending will pour out water, the ascending is impermeable to water. So the volume is less than the filtrate entering.

lol

my understanding is based off what you wrote

thank you.

 

[Buttafuoco]

Sorry man, I've been braindead since Thursday- too lazy to read through everyone's posts.

I'm thinking foil C is probably messing with people's heads most? I was thinking about it like you have fluid exiting the PCT then entering the loop first losing water, then ions, so it should have less volume too when you compare it from just after it exits the PCT to just before it enters the DCT.

 

[MedPR]

wtf did i say that no one understood i said the exact same thing as buttafuoco.

Chiddler's right, automatically C is out. The descending will pour out water, the ascending is impermeable to water. So the volume is less than the filtrate entering.

Why is C out? You just wrote exactly what C says.. That the volume out is less than the volume in.

C. more voluminous than filtrate exiting the loop of Henle

More filtrate goes into the loop of henle than comes out. This is a fact.

 

[Mountaineurons]

Alas, while I get why A is right, I really don't understand this explanation for why C is out. If water pours out of the loop and doesn't come back in, then the volume at the end of the loop should be LESS than the volume you start with. Therefore C is right....(but not because it's not).

 

[pfaction]

Oh. Then I really dunno, I gave my PCT answer.

 

[Mountaineurons]

Why is C out? You just wrote exactly what C says.. That the volume out is less than the volume in.



More filtrate goes into the loop of henle than comes out. This is a fact.

Thank you MEDPR thank you! I feel like I'm on crazy pills.

 

[Buttafuoco]

Maybe it's related to the lower density of the final hypoosmotic pre-piss after the loop? It definitely seems like one of those questions designed to make you pick the very most correct answer, but it definitely doesn't seem satisfying to me.

 

[MedPR]

Oh. Then I really dunno, I gave my PCT answer.

PCT has nothing to do with the loop of henle. Whatever isn't reabsorbed in the PCT goes into the descending limb where water diffuses out of the filtrate. Once it reaches the bottom of the loop, the filtrate is isotonic to the medulla because the filtrate has lost a ton of water. As it ascends, solutes passively diffuse out of the filtrate in the thin ascending loop and are actively pumped out in the thick ascending loop.

All the water that you lose in the descending loop is lost for good. The only place water enters is at the glomerulus. Once there, the only way water goes is out -- either through the descending limb, distal tube, or collecting duct. Therefore, C is true unless there is pathology.

 

[pfaction]

It also helps that I interpreted filtrate as Bowman's filtrate.

I dunno anymore lol.

 

[MedPR]

Maybe it's related to the lower density of the final hypoosmotic pre-piss after the loop? It definitely seems like one of those questions designed to make you pick the very most correct answer, but it definitely doesn't seem satisfying to me.

Yea, for some reason A is better than C, but I don't see anything in the question stem that allows you to pick A over C.

 

[chiddler]

Why is C out? You just wrote exactly what C says.. That the volume out is less than the volume in.



More filtrate goes into the loop of henle than comes out. This is a fact.

isn't this is frustrating.

i'm not sure why i thought C is impossible now.

 

[Buttafuoco]

I could have sworn that it actually isn't called filtrate anymore after it hits the PCT, but what-hevz, this question is some some ticky-tacky jibber-jabber IMO.

 

[MedPR]

isn't this is frustrating.

i'm not sure why i thought C is impossible now.

Yea, luckily I didn't encounter any of this crap on my actual MCAT.

I could have sworn that it actually isn't called filtrate anymore after it hits the PCT, but what-hevz, this question is some some ticky-tacky jibber-jabber IMO.

I thought it was called filtrate until it exited the kidney.. I don't really know though. I don't pay as much attention to terminology as I probably should.

I guess A is a better answer because the function of the loop is to maintain an osmotic gradient within the medulla, and only answer A really talks about concentration..? Maybe the explanation says why A is better than C.

 

[Buttafuoco]

I hope it has a good explanation, because it almost seems like C is the better answer to me. If you're losing water then ions, it seems like you have to lose volume, but it almost seems like what if you lost more water in the descending loop than ions in the ascending loop?

 

[MedPR]

I hope it has a good explanation, because it almost seems like C is the better answer to me. If you're losing water then ions, it seems like you have to lose volume, but it almost seems like what if you lost more water in the descending loop than ions in the ascending loop?

Yea. The person's urine could be hyperconcentrated because their ascending loop is failing and no ions are leaving. If that's the case, then answer A would be false.

Who knows, though.

 

[SaCkO]

Macula lutea: Eyes (cones, acuity)
Macula densa: kidneys, osmolarity->renin.

Original question: For an individual with highly concerntrated urine, filtrate entering the loop of Henle is likely to be

Filtrate: The fluid from the blood that is scooped into the Bowman's capsule. So right there, it has a large volume and a large amount of solute. (If we're arbitrarily quantifying: 100mL)
From here, it hits the PCT. PCT: LARGE AMOUNTS OF SOLUTE AND THUS WATER ARE REABSORBED. On that principle, this fluid is lower in volume than our filtrate AND in solute. (quant: 50)
From there, we hit the descending limb. Oh lawd, water flows right out. No explanation needed for this, if you don't understand you have to read the kidney again. (quant: 25mL)
Ascending limb time: Pump that salt right the hell out. (Pharmacy school knowledge) There's a Na/K/2CL transporter here. That, Mg, Ca, I think Zn get pumped out. So there's your problem right there. Salt is decreased, but not water. So we're still at let's say, 25mL...but leaving the loop of henle is small amounts of salt. AND UREA.

So let's compare so far. Filtrate was 100 and salty as ****. Now we're leaving the loop, and we're at let's say 25mL and consists of mainly urea.

We end at the DCT because the question dun want us to analyze the DCT.


A. more concetrated than filtrate exiting the loop of Henle
Yes, this is true. In the beginning it's more concentrated even if the urine wasn't super salty.

B. less concetrated than filtrate exiting the loop fo Henle
NO. I don't think this is ever the case, how could that occur? Descending is impermeable to ions, Ascending is impermeable to water. There's that small issue of the thin ascending but I don't know if that matters.

C. more voluminous than filtrate exiting the loop of Henle
Nope, PCT takes out a ****ton. PCT is before loop! So automatically there's less volume about to enter than in the filtrate.

D. less voluminous than filtrate exiting the loop of Henle
Can't be true.

Pfaction your argument is not right, the PCT is before the loop of henle and the question is telling you to compare between liquid going in loop of henle and out of it, so PCT has nothing to do with question here. Using the word Volume in the answer choices makes choice C right too. The loop of henle is only permeable to water in descending limb where is leaves the loop like shown in the picture you posted. Since We are losing water we are losing volume, even if later on we changed the concentration of the filtrate in the acending limb but we dont change the volume since it is not permeable to water. BTW having concentrated urine has nothing to do with loop of henle and it is thrown in the question just to mix things up. The concentration of urine is dependent of the DCT and collecting duct which under influence of different hormones can regulate the concentration of urine. The loop of henle serves one purpose which is to Concentrate the kidney's medulla so that when the DCT and collecting duct want to concentrate the urine they would have an osmotic gradient for water to leave the filtrate to make a concentrated urine.
So the conclusion is That there are two right answers here A and C and this question is a pretty bad question. However, the good thing about questions like that before the exam is to make you go study the material and mechanism and physiology more to get a better understanding of it.

 

[Temperature101]

I came across this stupid question somewhere and I picked C as well--C seems more logical.

 

[Mountaineurons]

I came across this stupid question somewhere and I picked C as well--C seems more logical.

i'm glad this chain ended on a note of solidarity