Health and medicine
- Meet the kidneys!
- Kidney function and anatomy
- Glomerular filtration in the nephron
- Changing glomerular filtration rate
- Countercurrent multiplication in the kidney
- The kidney and nephron
- Secondary active transport in the nephron
- Introductory urinary system quiz
- Intermediate urinary system quiz
- Advanced urinary system quiz
Glomerular filtration in the nephron
Created by Raja Narayan.
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- This may be silly, but I was a bit confused about the filtration in the glomerulus. Just to make sure my understanding is correct, so the blood comes in from the renal artery, then into the afferent arteriole, being filtrated in the glomerulus, while the filtrated blood being carried into the efferent arteriole (and then the renal vein), the waste products and extra ions are being caught by the bowman's capsule and transported to the rest of our nephron. Is it correct?(10 votes)
- Yes. The filtered blood goes to the renal vein and back to the inferior vena cave. The filtrate in Bowman capsule goes to the rest of the nephron. Much of the rest of the nephron works to reabsorb the water glucose, amino acids, salts and water from the filtrate so that it is more concentrated urine. The water, glucose, amino acids, salts and water that are reabsorbed from the filtrate are put into the peritubular capillaries that are closely associated with the nephron, so that they are also returned to the renal vein and the inferior vena cava. The remaining filtrate moves out of the kidney and into the urinary bladder.(15 votes)
- I heard the color of urine changes when we are dehydrated, does this relate to the kidney in any way(3 votes)
- It does! When we are dehydrated, the kidney makes an effort to reabsorb more water and so the urine ends up more concentrated giving it a darker color(10 votes)
- so active transport requires energy and passive transport does not?(2 votes)
- Yes, in a nutshell.
Active transport is like running uphill to get to a destination (requires energy) and Passive transport is like taking a slide to your destination (it just happens without energy).(11 votes)
- At1:50, Raja mentioned that the fluids get taken out of the blood, are turned to filtrate, and the rest of the blood (ie platelets, red blood cells and white blood cells) flows on. If we drain all the fluid out, wouldn't our blood become super dehydrated and dry?(2 votes)
- Yes, so almost immediately, in the proximal convoluted tubule, the water is moved from the filtrate back to the blood into the peritubular capillaries. Also reclaimed by the blood are the glucose, amino acids and some salts that got filtered out of the blood by the glomerulus. So, the point is, the glomerulus acts like a sieve, and then the rest of the tubule works to manage the filtrate or urine so it is concentrated with wastes.(5 votes)
- what is a eukaryotic cells(1 vote)
- Eukaryotic cells are cells in animals and plants. They have organelles, such as a nucleus and mitochondria for example. Prokaryotic cells are cells of bacteria and archea that have enzymes, ribosomes and areas of function, but no organelles. Eu means good or true, karyo means center, so eukaryotes were named for their true center or nucleus. (Greek roots)(6 votes)
- is glomerular filtration passive transport?(2 votes)
- Blood pressure is not the factor leading to filteration, but rather the presence of the blood at the semipermeable membrane and this is proved by the fact that normally hypotensive still produce urine.(2 votes)
- Raja, thank you for the info. Could you answer my questions about glomerular filtration rate? I think I am confused about the terminology. Glomerular filtration refers to the volume of blood that is filtered into the Bowman's Capsule, right? And GFR refers to the speed at which the blood moves through the kidney, correct? Also, the only way the GFR (speed) can be manipulated is by dilating/constricting the arterioles. Where do I go wrong here? Dilating the afferent will speed up GFR and increase the volume sent into the Bowman's Capsule. Constricting the afferent will do the opposite. Dilating the efferent will speed up GFR and DECREASE the glomerular filtration. Constricting the efferent will decrease the GFR and INCREASE the glomerular filtration. Thank you for your help.(2 votes)
- Why is there no mention of Glomerular capillaries? Why are these referred to as arterioles? Shouldn't it be described as afferent arteriole leading to glomerular capillary leading to efferent arteriole?(2 votes)
- Explain the term glomerular filtration rate, what is it and how can you measure it?(1 vote)
- Why is this video in the cell transport across a cell membrane list?(2 votes)
Voiceover: All right, so I think we have a pretty decent appreciation of renal anatomy; we know how the kidney is structured, now we just need to take a look at some of the finer details. We started talking about the nephron, which I kinda drew right here, and we said, "This is the functional unit of filtration "and collection in the kidney." So let's start off with the very beginning of the nephron. The first part of the nephron is called the "glomerulus"; it receives branches that come off the renal artery, you see a branch going that a way; there's a branch going this a way, and just like any artery, it branches off into arterioles, and it's an arteriole that comes up first to meet the glomerulus. So if we look down here, we're going to have something that came off of the renal artery, that's an arteriole, so I'll write, "arteriole," right here, and we actually further specify this: we call this the "afferent arteriole," "afferent" meaning, "going towards." And so, this is the afferent arteriole, or the arteriole that's going towards the glomerulus. The glomerulus then, is this really loopy structure; there's a lot of spinning that goes on here, then we branch off again, and this gives us the same arteriole, this is the same vessel we just started off with, so we're going this way, and spinning around and coming out, as one single vessel, but we call this part of it, the "efferent" arteriole: "efferent," meaning that we have left the glomerulus. And that of course leaves this ball-like structure over here, that's going to be known as the glomerulus. Now the thing about the glomerulus that's really interesting: it's the main site for filtration, where we take blood that came in from the renal artery, and we push out a whole bunch of fluid, that we're then going to take out some ions, and some water, and some waste, and we'll get rid of the waste or the extra ions. The glomerulus is where we take blood and turn it into filtrate, and let the rest of the blood flow on. So this efferent arteriole is gonna turn into a capillary, and then it's gonna go into venules, and then collect back, and come out as the renal vein; we'll talk about that in a later video, when I talk about other parts of the nephron. The glomerulus though, just leaks out fluid, and it needs to be caught somewhere. That fluid that leaks out is caught in a capsule, that's kind of hugging the glomerulus right here. So I'm gonna draw it, like that, and it kinda keeps going this way, and this is gonna continue on, into the rest of our nephron, but this thing right here, it's a capsule, and actually it has a name; it's named after a British scientist, "Doctor Bowman," so we call this, "Bowman's Capsule." This is Bowman's Capsule, and this is where we're going to collect the filtrate, or the fluid that comes out of the glomerululs. The inside right here is just open space, so they call it, "Bowman's Space" as well, so it's just space that's gonna collect our filtrate. So at this point, you should be asking yourself, "Why is it that we're gonna have fluid leak out here? "I mean, there's all this wrapping that goes around, "so we've got high pressure, but how is this different "from other arterioles in our body? "Why is it that we have so much leakage, "purposefully happening here, "but it doesn't happen everywhere else in our body?" So let me answer your question, and why don't we just blow up that part, right here, and open this window so we can take a better look. So the point where the arteriole meets Bowman's Capsule, there's a lot going on. Recall, that when we have a vessel, I'll draw half of it, like that, right there, and it's kind of going this a way, okay, so that's our vessel that's right here. This vessel's got a lot of good stuff, like our red blood cells, our white blood cells, platelets, some really really big proteins, so I'm just gonna draw something really big, right here; that's a giant protein, and it's not gonna leak out into our Bowmans' Capsule. So, this stuff kinda moves along that way, then again, we've got other things like ions, so I'm gonna write, "Sodium" right there. We've also got smaller protein sub-units, like amino acids; I'll just write, "AA," and we've also got glucose in here. These are things that can leak out, so how is it they get from the arteriole, into Bowman's Space? So our vessels, our arterioles, just like anything else in our body; they're made up of cells. And the cells that line our vessels over here, I'll just draw a whole bunch of these guys, kinda hanging out, so these guys are called, "endothelial cells"; each of these is an endothelial cell. So an endothelial cell is a lot like most of our eukaryotic cells: They've got a nucleus, and they've got all their organelles, and stuff like that goin' on; I'm not gonna go into that kinda detail for right now, but just recall that they're eukaryotic cells. Now something that's special about these vessels, is that they're fenestrated. Write that in parenthesis, "fenestrated," and if you don't know what this term means, all it means is that these vessels have a lot of holes; they're very "holey," and so, because of that, the holes allow small things like sodium, and amino acids, and glucose to leak through, so it's got some holes in them, you know, the way that they're sort of connected. So there are holes where these guys can kinda slip through. And actually some of these holes can allow bigger proteins to come through, but these proteins still don't, because there's another added layer, that sits in between these endothelial cells in the in the tuble, so this is sort of another membrane that's right here. I'll just kinda draw it shaded in, like this, and it's not a complete barrier; it's semi-permeable, meaning some things can leak through, but this is another membrane, that we call, the "Basement Membrane"; this is a basement membrane, and you may have heard about this in other contexts. So the basement membrane right here, helps to make sure that small things pass through: things like sodium can get through these fenestrations, and leak out; our amino acids can do the same; and our glucose can, at times, as well; but these bigger proteins bounce back; they bounce back, because either they can't make it through the fenestrations, or the basement membrane prevents them from leaking into Bowman's Space. And then finally, we've got the tubular cells, tubular cells that make up the interaction point on the end of the Bowman's Capsule. So they sort of look like this; they're pretty long cells, and the funny thing about them is that some of these guys actually hug the vessel; they hug the endothelial cells, like that. And so, they're sort of like these legs; this is sort of a leg-like projection, and so, if you remember a doctor you might see, if you've got problems with your feet is a "podiatrist," and so this type of cell, we call these "podocytes" right, "podo" meaning "foot." Podocytes, and so there are some podocytes, in addition to these tubular cells, there are some that are just tubule cells. And another term for that, is just an "epithelial cell"; this is an epithelial cell, okay? And so, we go from the endothelial cell, to the epithelial cell, and I think I should also mention that these podocytes are a certain class of epithelial cell, as well, and so, these guys hug around the arteriole; that sort of helps for this connection to stay close.