Renal Physiology Step 2: Tubular Reabsorption - Video Tutorials & Practice Problems
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1
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Introduction to Tubular Reabsorption
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All right. So let's get into tubular reabsorption. Now, a quick note before we begin, this topic is going to involve quite a bit of memory and transport. So things like primary transport, secondary active transport, passive transport if you don't remember those super, well, I do recommend you go back and refresh your memory before diving in here, we are gonna be talking about them, but we're not gonna have time to like redefine them and go over them in detail. So keep that in mind as we go forward. Now, as weve mentioned previously, tubular reabsorption is the process of moving water and other solus out of the filtrate and putting them back into the blood stream and filtrate is formed at a very high rate. And as I've said, about 99% of filtrate gets reabsorbed back into the blood. And can we just like geek out over our kidney for a second because your kidneys filter your entire plasma volume every 24 minutes, which like is insane by itself. But then without reabsorption, that means that you would lose all of the plasma in your body through urine in under 30 minutes like in spain kidneys are incredible. Like I cannot get over that fact, like kidneys are amazing you guys. So as you can imagine, reabsorption is going to prevent the body from losing very useful substances that end up in the filtrate. So, water obviously, um electrolytes like sodium, potassium, calcium nutrients like glucose. We don't wanna lose all of that in here. We wanna keep all that good stuff in our body and that is the whole purpose of reabsorption. Now, there are two routes that substances can take when they are being reabsorbed. So first is our trans cellular route and this is when substances pass through tubule, L and I'll show you this in our image in one second. And then we also have our paracellular route, which is when substances pass between hal self. So if you look down at our image here just to kind of orient you to what you're looking at, we're basically looking at like a cross section of the proximal tubule. And we're kind of zooming in on the wall of that proximal tubule. So that is what you're seeing here in this like tannish yellow color. We have this interstitial space in between the um tubule and the capillary. And then over on the right of the image is of course, our capillary. And so formally, this inside of the tubule is kind of empty space where filtrate would be flowing, it's called the tubule lumen. And then on the actual cell uh that make up the walls of this tubule. We have our um apical membrane, which is the side closest to our lumen and our basolateral membrane, which is the side closest to the interstitial fluid. And I always remember that because it just goes in order of like A and then B so if we're going from the inside out, it's just alphabetical order epical and then be the lateral. Now what we are looking at here, we can tell that it's definitely the proximal tubule because we have all these micro vli, remember the proximal tubule is where about 65% of reabsorption will be happening. And so it needs to have those prominent micro vli in it to increase surface area. So that is what we are looking at here. So as you can see in this little purple box, we have our trans cellular root and we're gonna have our water and other clues passing right through the middle or anywhere within that cell. And then here in blue, we have our paracellular root where we're gonna have water and other clues weaving in between the tight junction between these cells and it is quite a tight junction. Um But there is usually enough space that these cells are leaky enough that water and very small solute and just kind of squeak through and get into that interstitial fluid. All right. So that is our little introduction to tubular reabsorption. And I will see you guys in the next one. Bye bye.
2
example
Renal Physiology Step 2: Tubular Reabsorption Example 1
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OK. So what is the route taken by substances being reabsorbed via the trans cellular route? Which means we're going through the cell. Now, our answer choices here are just like a mishmash of anatomy in all different order. So to help us solve this, I'm just gonna draw it out and then we can just label what we're seeing in the order that we're seeing them. So bear with me might not be pretty, but we will get there in the end. I'm just gonna draw a little, you know, lumen here. So this will be the cavity of our proximal tubule. We're gonna draw some tubules cell. These are the micro vli which I'm sure you knew. But just in case you were like, what the heck is that? So those are the tubule cells. I'm gonna label those as TC. We're gonna label our apical and basolateral membrane. The number in alphabetical order from the inside out though the apical membrane is closest to the lumen and then the basolateral membrane is over here, closest to the interstitial fluid, which I'm just gonna label as if and then we'll have our capillary over here, which I will label with ac we'll just draw that in red there. And our trans cellular root is going to again take us straight through one of those tubule cells. So in order we are looking at the lumen, the apical membrane, the tubule cell, the basolateral membrane, the interstitial fluid and then the capillary, which means our answer is going to be c So there you have it.
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Problem
Problem
Which of the following is NOT a purpose of tubular reabsorption?
A
To avoid losing important nutrients in urine such as glucose & amino acids.
B
To ensure urea is taken back up by the blood.
C
To maintain fluid balance in the body.
D
To avoid losing too much sodium.
4
concept
Map of the Lesson on Tubular Reabsorption
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OK. So reabsorption actually looks slightly different in each part of the Nephron. There are different like membrane transport processes, different substances are going to be absorbed in different sections. So I just have a quick little map of how we structured the next few videos just to kind of preface what you're gonna be seeing um pretty soon. So we're going to begin by talking about reabsorption in the proximal tubule. And we're gonna have a separate video talking about reabsorption of sodium and other nutrients like glucose. And then we'll have a video talking about the reabsorption of water in the proximal tubule. And then we'll move on to reabsorption in the Nephron loop. So we'll be talking about how reabsorption looks in the descending limb versus the ascending limb. And then we will finish by talking about re um reabsorption in the distal tubule as well as the collecting duct. Those two structures have pretty similar reabsorption and those structures are unique because reabsorption is partly regulated by hormones in those structures. Then we'll talk about that when we get there. All right. So that is our little map of the lesson. And I'll see you guys in the next one to start diving into this.
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concept
1a) Reabsorption of Sodium & Nutrients in the Proximal Tubule
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All righty. Let's begin talking about the reabsorption of sodium as well as other nutrients in the proximal tubule. And if you're wondering why sodium gets its name in the title versus like potassium or calcium is just because sodium is one of the most abundant substances that gets reabsorbed from the filtrate. So that's why it gets its name in the title there. And when I say nutrients, I'm gonna be focusing a lot on glucose in this video just because glucose is one of the other most abundant substances that gets reabsorbed by the kidneys. So sodium and glucose are kind of the stars of this video. Now, reabsorption in the proximal tubule can either be active, which just means that it uses a TP or it can be passive, which just means that it doesn't use a TP. Now, sodium reabsorption specifically is driven mainly by active transport and that is going to be primarily through the trans cellular route or going right through those tubule cells. Um despite this, you know, mainly driving sodium through active transport, sodium and other nutrients can also travel via secondary active transport as well as passive transport. So we're gonna go through some specific examples of all of those. Now focusing in on primary active transport, we are gonna have our old friend the sodium potassium pump and gosh, I have missed her. I'm so happy to see her. And this sodium potassium pump is going to be um fairly abundant in the basolateral membrane. So you guys remember that the basolateral membrane is the one closest to the interstitial base. We go a apical b basolateral kind of in order there. So we're gonna have a whole bunch of sodium potassium pumps on that basolateral membrane that are gonna be actively transporting sodium ions into our interstitial base. You guys remember that our sodium potassium pumps, we think they were a little pumpkin, right. We pump k in and we toss all that sodium out. So we're gonna get um three sodium getting chucked out of that cell as we're bringing into potassium. And so that is kind of the main way that sodium is going to be leaving our proximal tubule cell. And so if you look down at our image here just to kind of orient you to what we're looking at, we have our filtrate over here, all these little purple dots that you see represent sodium ions. So these are those prominent micro villa. You can see how that's really gonna be increasing the surface area of this proximal tubule. We have our tubal cell here, our interstitial space and then of course, our capillary And so you can see along this basolateral membrane here, we have this little sodium potassium pump right there. And so that is going to be a form of active transport. Ok. So it's pumping all of our little purple sodium ions out into our interstitial space where they can then be reabsorbed by that capillary. Now, you may be wondering, well, how did the sodium get into that tubule cell in the first place? And what a fantastic question you are on the ball today and that is going to be via secondary active transport. So what's happening here is that basically because this sodium potassium pump is working so hard to get sodium out of these tubule cells. The sodium over here in the filtrate now has a pretty um steep concentration gradient pulling it to these tubule cells. Remember sodium are introvert, they wanna get out of this crowded filtrate and into this nice quiet tubule cell with no other sodium. And so these pumps establish this concentration gradient and then sodium ions from the filtrate are gonna get pulled in to our tubule cell via co transporters that also carry some kind of specific nutrient. So things like glucose or amino acid and those are usually moving against their concentration gradient. But the energy that is created by that sodium concentration gradient is enough to pull both of them in. So if you look down at our image, you can see we have this um kind of blue oval right here on the apical membrane now. And that is a sodium glucose co transporter. What's it's gonna be doing is basically pulling in one of our little green glucose and one of our little sodium and they get pulled in simultaneously using the energy from that sodium's concentration gradient. And so that um cot transporter is gonna pull them both in and put them into that tubule cell. So that is our secondary active transport. I'm gonna label that now. All right. And then finally, we also have passive transport happening. So this is when solutes travel from the tubule cell into the capillary passively, they either be a simple diffusion and that will typically just be lipid valuable substances like some vitamins will travel that way as well as facilitated diffusion. And that will be um things like glucose as well as other nutrients as well as other ions even. So, if we're thinking of facilitated diffusion, we're usually just thinking of like some kind of um nutrient specific channel that's gonna be along that basolateral membrane. So here we're looking at just a little glucose channel there on that bao lateral membrane that will allow the glucose um to leave the cell. So that is our passive transport. The just to kind of summarize whats happening here really briefly, we have some glucose and some sodium hanging out in our filtrate. Those are going to simultaneously get pulled into our tubule cell via secondary active transport through this sodium glucose co transporter. And that's gonna be using the energy of the concentration gradient of the sodium. So now they are both in our tubule cell, but they're gonna take different routes to get out of it. So our sodium is going to get kind of sucked out of the cell um via primary active transport with this sodium potassium pump. And that will dump it into our, our interstitial space where it can then enter our capillary. And then our glucose will just travel through this tubule cell and then exit passively via this glucose channel, enter our interstitial space and then enter our capillary from there. All right. So that is our little summary of reabsorption of sodium and other nutrients in our proximal tubule. And I'll see you guys in our next one. Bye bye.
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example
Renal Physiology Step 2: Tubular Reabsorption Example 2
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All right. So which of the following substances primarily utilizes secondary active transport at the apical membrane and facilitated diffusion at the basolateral membrane. So, based on what we just talked about out of all the substances listed here, both sodium ions and glucose are going to be entering the tubule cell using secondary active transport. So those are typically going to be using those like cot transporters like the sodium glucose co transporters. Um just as kind of a quick aside, both water molecules and urea tend to move for a more passive transport. Um mean. So both sodium and glucose will enter our tubule cell using secondary active transport. However, only one of them uses facilitated diffusion at that basolateral membrane. Remember, the basolateral membrane is going to have quite a few sodium potassium pumps. So that is a form of primary active transport and that will be the main form of transport that sodium are going to take during the process of reabsorption. Whereas that glucose will be traveling through more passive means through like glucose channel. The answer here is going to be d glucose primarily utilizes secondary active transport at the apical membrane and then facilitated diffusion at the basolateral membrane and there you have it.
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Problem
Problem
Which of the following solutes are primarily reabsorbed by primary active transport?
A
Potassium ions.
B
Sodium ions.
C
Urea.
D
Glucose.
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concept
1b) Passive Reabsorption of Water & Solutes in the Proximal Tubule
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OK. So let's get into the passive reabsorption of water in our proximal tubule. And we're also going to be talking a bit about solute here as well because what happens in the proximal tubule is that water and solute reabsorption follows kind of a cyclical pattern. So first, like we just talked about, we're gonna see all this movement of sodium and other Stute. You can see here in our capillary. Um we have all of this sodium and glucose and all of these so have left the tubule cell and they're now hanging out in the interstitial space. They're going to hang out in that capillary and the movement of all of those solus is going to establish a strong osmotic gradient. Remember, water wants to move toward high concentrations of solute, but now all of our little water molecules over here are being drawn toward those high solu concentrations in the interfacial space and the capillary. And so this osmotic gradient causes water molecules to be reabsorbed via aquaporin. You can see we have our little aquaporin here on our apical membrane of our tubule cell as well as our basolateral membrane. And those water molecules will just travel right through those aquaporin following that osmotic gradient to get them closer to those high um solute concentration. And this is sometimes known as obligatory water reabsorption. And it's called that because the water is basically obliged to follow that osmotic gradient. But now we have a whole bunch of water hanging out in our capillary. And that is going to create a steep concentration gradient for other solutes in the filtrate because now the filtrate is becoming more and more concentrated and those solutes want to escape the high concentrations and they wanna go toward low concentration. So these solutes essentially follow the water. And so all of these solutes over here in the filtrate are going to be drawn away from these high concentrations to low concentrations. And so you can see how it basically um the reabsorption of sos and water essentially creates a cyclical pattern that drives really um fast and very efficient reabsorption in the proximal tubule. And that is how we get the whole much of that filtrate reabsorption happening in that very tiny section of our Nephron. All right. So I'll see you guys in our next video. Bye bye.
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example
Renal Physiology Step 2: Tubular Reabsorption Example 3
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What is the primary driving force that causes water to follow, felt out of the tubule and into the capillary. So remember when sodium and all those other sos are leaving the filtrate and entering the capillary that is going to create a strong osmotic radiant, which is going to draw the water toward those high concentrations of. So the right answer here is going to be a let's do. Keep in mind that the presence of aquaporin is what allows the water to follow all of that salt. But the aquaporin themselves are not um driving the water movement at all. So aquaporin don't like pull water into them or anything like that. The water is following its osmotic gradient and the aquaporin are just acting as a channel that water can move through and movement through. Aquaporin is considered passive. It is not considered a form of active transport. So the primary driving force of water movement in the proximal tubule is going to be its osmotic gradient. So there you go
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Problem
Problem
In the proximal tubule, _________ ions are pumped out of the tubule via ____________ transport. This creates an ____________ gradient, causing water to be reabsorbed through _______________.
A
Potassium; active; osmotic; gaps between cells.
B
Sodium; passive; osmotic; aquaporins.
C
Potassium; active; ionic; gaps between cells.
D
Sodium; active; osmotic; aquaporins.
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concept
2) Reabsorption in the Nephron Loop
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All right, let's get into reabsorption in our Nephron loop. Now, so for the most part reabsorption in the Nephron loop is gonna be employing the same mechanisms that we saw in the proximal tubule. However, permeability of our descending and ascending limbs actually differ. So they are basically permeable to different substances. Now, one thing to note is that about 65% of the filtrate gets reabsorbed in our proximal tubule. And that includes about 65% of water and 65% of ion as well as over 99% of organic solute. I'm gonna write that like that. So that includes things like glucose and amino acid. So for all intents and purposes, organic solutes are basically out of the filtrate by this point. And once filtrate reaches our Nephron loop, it is mostly water and ions with sodium. Of course, being the most abundant of those ions. Of course, there's also some lace products in here as well like urea which don't get reabsorbed. So mostly water and ions. So we're gonna go through our descending and ascending limbs separately talking about what water and ion reabsorption looks like in each one. So starting with our descending limb. So our descending limb contains abundant aquaporin. And so um in this limb, water is going to get reabsorbed via osmosis. The exact same way that we saw in the proximal tubule. However, our descending limb is impermeable to ions. There are no cot transporters, there is no sodium potassium pumps, there is none of that. So there is no ion reabsorption happening in a descending limb at all. So if you look at our image here, we have the capillary over on the left, we have the lumen of the tubule here on the right. And our little tubule cells and they do look quite different than what we just saw previously. The tubule cells in the descending limb are quite skinny and small. So that's why they look so different. And you can see we've got aquaporin all along that basolateral membrane and a ton of water movement happening. And about 20% of water is gonna get reabsorbed in our descending limb. And again, no ion reabsorption at all happening here. Now, moving over to our ascending limb here, aquaporin are gonna be very scarce. And so basically osmosis does not occur and we really don't have any water movement happening here. However, there is plenty of ion movement happening. So we're gonna have some secondary active transport happening along our ethical membrane and some primary active transport happening along our basolateral membrane. And so if you look at our image, we have the lumen of the tubule. And you can see it's all full of ions. We've got our purple sodium or pink potassium, our little orange chloride there. I mean, we've got cot transporters all along that apical membrane and we've got our sodium potassium pumps along that basolateral membrane there. So, we've got all kinds of active transports of ions happening and about 25% of ions are gonna get reabsorbed in the ascending limb of the Nephron loop. All right. So that is our reabsorption in, in the Nephron loop. And I'll see you guys in the next video. Bye bye.
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example
Renal Physiology Step 2: Tubular Reabsorption Example 4
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OK. So this is a true false. If it's false, we're gonna be correcting the statement. The descending limb of the Nephron loop is very permeable to water but impermeable to ion. And that is true, right? Our descending limb is abundant in aquaporin which allows for a huge amount of water reabsorption. About 20 to 25% of the water in our filtrate will get reabsorbed in that descending limb. However, there is a notable absence of transporters and pumps that makes it fairly impermeable to ions. So our answer here is that this is true.
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Problem
Problem
Predict what would happen if the tubule wall of the descending limb suddenly lost all its aquaporins.
A
More reabsorption would occur in the nephron loop.
B
Urine would be higher in volume & more dilute.
C
Urine would be lower in volume and more concentrated.
D
Urine would have the same volume but be more concentrated.
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concept
3) Reabsorption in the Distal Tubule and Collecting Duct
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OK. So let's dive into the reabsorption in the distal tubule and the collecting duct, which in my opinion is the coolest type of reabsorption. So one thing to note is that reabsorption in the proximal tubule and the Nephron loop tends to occur at a pretty constant rate. So it just kind of is what it is. But the distal tubule and the collecting duct kind of shake things up a little bit. The reabsorption in these locations actually varies depending on your body's need. So, there are actually four main hormones that can influence the rate at which certain substances are going to be reabsorbed within our distal tubule and our collecting duct. So I always think of these as kind of like our little urine customization um sections of our Nephron where like, you know, maybe your body needs a little bit more water to be retained. They can handle that. Maybe you have to get rid of some salt, maybe you have to reabsorb some calcium, you know, who knows? Your distal tubule knows which is like, oh cool, right. So we're gonna go over these four hormones and we'll talk a little bit about what they each do. So first up, we have our old friend aldosterone, remember him from the ren and angiotensin aldosterone sys uh mechanism. So this is our salt retaining hormone. Remember, and it's going to increase the rate of sodium reabsorption. So it's making sure that sodium is leaving the filtrate and getting put back into the blood. And this can actually create an osmotic gradient that will also increase water reabsorption via osmosis. Remember that from that um renin angiotensin aldosterone mechanism. So the aldosterone itself specializes in alt retention and alt reabsorption, but it can have the indirect effect of more water reabsorption as well. So if you look at our image here, number one, I'm gonna label this as aldosterone plora. And you can see we've got sodium channel over here on the apical membrane. We've got sodium potassium pumps here on the uh basolateral membrane and a whole bunch of sodium reabsorption is going on in that image there. All right. Next up, we have our atrial natriuretic peptide or A NP. And this is basically the opposite of aldosterone. So it's going to actually reduce the rate of sodium reabsorption, which just means that sodium is going to be staying in the filtrate and it will end up in the urine. So if you look down at our image, use the number two, we have our atrial natriuretic peptide there. And we've got all these little sodium um ions just hanging out and they're not really doing anything. They're not getting reabsorbed, they're just kind of sitting in that fil tree and they're gonna end up in the urine. And I always remember that this one deals with salt because I look at that N A in natriuretic and I think N A means sodium. So that's how I remember that one next up. So moving on from sodium, we have an anti diuretic hormone or a DH and an anti diuretic hormone is pretty intuitive based on its name. So it's going to reduce the volume of urine by increasing the rate of water reabsorption. Of course, a diuretic would put more water into the urine and it would increase urine volume. And so our anti diuretic is doing the opposite. It's helping us reabsorb water and then it's reducing the urine volume um through that reabsorption if it's all ending up back in our blood. So, looking at our image on number three, we have our anti diuretic hormone and you can see we've got little aquaporin here and they are helping water get reabsorbed and put back into the blood. And then finally, we have our parathyroid hor um hormone or PTH and this will be stimulating calcium reabsorption specifically in the distal tubule. If you look down at um our last image, we have our parathyroid hormone. You can see we have all of our little little triangular calcium ions there and they are getting reabsorbed and put back into the blood. All right. So those are kind of the four main hormones that work in our distal tubule and our collecting duct and that is how they kind of customize our urine breath, which is so neat, huh? All right. So I'll see you guys in our next video. Bye bye.
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example
Renal Physiology Step 2: Tubular Reabsorption Example 5
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Ok. So which hormone causes aquaporin to be inserted in the wall of the collecting duct. If we're gonna be inserting aquaporin into the wall of the collecting duct, what that is going to do is increase water reabsorption. And out of all the hormones listed here, the one that deals with water reabsorption is our anti diuretic hormone. So that is our answer. Remember how that name is. Nice and intuitive. It's basically the opposite of a diuretic. Though a diuretic would increase the amount of water that ends up in the urine. This is doing the opposite. So it's increasing the amount of water that is being reabsorbed. Remember our aldosterone and our atrial naic peptide both work with odium and our parathyroid hormone focuses on calcium. So this one would be our anti diuretic hormone.
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Problem
Problem
Dr. Miller is a pediatric nutritionist working with a patient who has a low dietary calcium intake. Concerned about the possibility of hypocalcemia, she orders bloodwork. What hormone would you expect to be elevated in this patient’s bloodwork?
A
Aldosterone.
B
Atrial Natriuretic Peptide.
C
Antidiuretic Hormone.
D
Parathyroid Hormone.
17
concept
Transport Maximum (TM) & Renal Threshold
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In this video, we're gonna be talking about transport maximum and renal threshold. And these are both constructs that give us information about our kidneys ability to reabsorb certain substances. And they can also be useful indicators of health. So transport maximum is the maximum amount of a substance that can be reabsorbed within a certain unit of time. And it's measured in milligram per minute. Now, transport maximum is generally reflective of the number of transport proteins that are in the renal tubule that can actually carry or ferry that substance um across that tubule cell and into that interstitial space to get reabsorbed. And generally speaking, what we see is that for substances that we really want to reabsorb like water, glucose, sodium, we have plenty of transport protein because we don't wanna hit transport maximum. For those, we want to be able to reabsorb as much of that as we can. Whereas for substances that um you know, we don't really care about reabsorbing like urea, for example, we're gonna have very few if any transport proteins. Now what can happen is that when all transport proteins are saturated, any excess of that substance is going to get excreted into the urine. So if you look at our little cartoon here, we have this lovely little river bank going on and this um little tan sandy area is our filtrate and we have our little green glu coat. And you can see that the glucose are trying to leave the filtrate and cross through this channel protein. This little bridge here, they're trying to get into that interstitial space to get reabsorbed. Now, what has happened here is that this little bridge, this um channel protein is at capacity, it is fully saturated. And now these glucose are basically stuck in the filtrate. They have no way to get reabsorbed and they are going to end up in urine. And that's why a really common example of transport maximum is going to involve um glucose levels and diabetes because what's gonna happen is in some diabetic, they're gonna have, you know, a lot of glucose in their blood, which means they have a lot of glucose in their filtrate. And what happens is that, you know, they, they basically hit transport maximum for glucose. All of those channel proteins get totally saturated and maxed out and they have an abundance of glucose in the filtrate that cannot get reabsorbed. And so they'll have high glucose levels in their urine. So that can be indicative of hyperglycemia. Um So that is transport maximum. Now, renal threshold is the blood concentration or the plasma concentration at which a given substance will begin to appear in the urine and this is measured in milligrams per deciliter. So to continue with our glucose example, in a typical healthy adult, um the renal threshold for glucose is about 100 and 80 mg per deciliter. Now imagine for example, in my body, right now, my glucose, my blood glucose level was about 100 and 60 mg per deciliter. So at that point, I have not hit renal threshold yet, which means that all of this glucose can get reabsorbed and that that's all gonna go right back into my bloodstream. I can use it for energy. That's great. Now, let's imagine my current glucose level was 220 mg per deciliter. At that point I have hit renal threshold, which means we are going to start to see glucose in my urine. So my blood glucose level has hit renal threshold and we're gonna start to see the excess um glucose entering my urine. Now, I know at first glance, these can seem like very similar constructs, but they are measuring very different things. So keep in mind that transport maximum is looking at the maximum amount of a given substance that can be reabsorbed within a certain unit of time at a certain rate. Basically, whereas renal threshold is examining the blood concentration at which that given substance is going to start appearing in urine. So they are related concepts, but they are measuring um and looking at very distinct things. All right, so I will see you guys in our next video. Bye bye.
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example
Renal Physiology Step 2: Tubular Reabsorption Example 6
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All right. So in which of the following conditions, would you expect to see high levels of glucose in the urine? So, if we are seeing glucose in the urine, that means we have reached our renal threshold for glucose, which as a reminder, renal threshold is the blood concentration or the asthma concentration at which that substance would appear in the urine. So, if we're seeing glucose in the urine, that means we have an excess of glucose in our blood, which is what is making us hit that renal threshold. So based on these answer choices, that would be hyperglycemia or an excess of glucose, obviously, hypoglycemia would have our glucose levels below renal threshold. So we would not be seeing it in the blood at all. Hypercalcemia is too much calcium. So we'd be seeing more calcium in the urine and then lupus is an autoimmune disease. This is unrelated to seeing glucose in the urine. All right. So our answer here is the hyperglycemia.
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Problem
Problem
Ryan just ate a very protein-rich meal. Because of this, the amino acid levels in his blood currently exceed the transport maximum and the renal threshold for amino acids (65 mg/dL). What will happen to the excess amino acids?
A
They will be reabsorbed.
B
They will bond to sodium ions.
C
They will end up in the urine.
D
They will build up in the nephron.
20
concept
Review of Tubular Reabsorption
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OK. So we have learned a lot in this section. There's a lot of information in here. We're just gonna do a quick review to help us kind of step back and process the most important takeaways. We're gonna go over each section of the renal tubule and talk about what type of reabsorption that section specializes in. So as a quick summary reabsorption helps our body to reclaim important substances from the filtrate. So starting with our proximal tubule, we're gonna be reabsorbing a little over 99% of glucose and other organic oue. So things like amino acids and vitamins. So that gets reabsorbed almost in its entirety right off the bat. This um area will also be reabsorbing about 65% of the water from the filtrate and about 65% of the ions. So things like sodium, potassium, chloride and calcium. So there's a lot going on in that proximal tubule very quickly. Keep in mind that this tubule has those micro vli to really help increase surface area to make all that reabsorption possible. So then moving on to the descending limb of our Nephron loop, we're gonna be reabsorbing about 20% of the remaining water. Remember, the descending limb is impermeable to ions, but it is highly permeable to water. And then in our ascending limb, we see kind of the opposite pattern where here we're um reabsorbing about 25% of the remaining sodium and chloride. And then finally, in our distal tubule and our collecting duct honestly, by this point, we are reabsorbing most of the remaining water and solute. Keep in mind that 1% or even less than 1% of the filtrate actually goes on to become urine. But by this point, most of it has been reabsorbed. Ok. So that is kind of our quick little review there. I hope that that was helpful and I will see you guys in our next video. Bye bye.
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example
Renal Physiology Step 2: Tubular Reabsorption Example 7
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OK. So how much of the water filtered through the glomerulus is normally reabsorbed in the proximal tubule? Remember that the proximal tubule is doing the bulk of reabsorption in general and reabsorption of all materials. Ions, water solus is quite high. Um So we're looking more at like the right side of the screen over here at, at B and D. Now it's not gonna be as high as ad um The only thing that gets reabsorbed at a rate of about 99% in the proximal tubule is going to be glucose and other organic values. So our answer here is d about 65% of the water from the filtrate will get reabsorbed in the proximal tubule.
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Problem
Problem
In which section of the nephron is the process of reabsorption influenced by hormones?
A
Proximal Tubule.
B
Descending limb of nephron loop.
C
Ascending limb of nephron loop.
D
Distal tubule & collecting duct.
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