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Current time:0:00Total duration:7:18

Glomerular filtration in the nephron

Video transcript

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 kind of 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 way there's a branch going this 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 a ferrant 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 and then we branch off again and this gives us the same arteriole you know this is the same vessel we just started off with so we're going this way and spinning around coming out as one single vessel but we call this part of it the efferent arteriole efferent meaning that we have left 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 it's really interesting it's the main site for filtration where we take blood that came in from the renal artery and we pull a shout 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 going to turn into a capillary and then it's going to 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 going to draw it like that and it kind of keeps going this way this is going to continue on to 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 dr. 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 glomerulus the inside right here is just open space so they call it Bowman's space as well so it's just space that's going to collect our filtrate so this point you should be asking yourself why is it that we're going to 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 sort of half of it like that right there and it's kind of going this away okay so that's our vessel that's right here this vessels got a lot of good stuff like our red blood cells our white blood cells platelets some really really big proteins so I'm going to just draw something really big right here there's that's a giant protein and it's not going to leak out into our Bowman's capsule so this stuff kind of moves along that way then again we've got other things like ion so I'm a right sodium right there we've also got smaller protein subunits like amino acids I'll just write a a and we've also got glucose in here these are things that can leak out so how is it they get from the arterial into Bowman's space so our vessels are 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 kind of 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 going on I'm not going to go into that kind of 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 right that in parentheses 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 holy 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 kind of 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 and the two Bo so this is sort of another membrane that's right here I'll just kind of draw it shaded in like this and it's not a complete barrier it's semipermeable 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 context 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 for 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 sites right podo meeting foot photo sites and so there are some Poteau sites in addition to these tubular cells there are some that are just to Buell cells to Buell cells and another term for that is just an epithelial cell this is an epithelial cell okay 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