okay let's look at glomerular filtration one of the most important parts of what's going on in the kidneys and of course the functional unit of the kidney is the nephron and remember there are probably about a million nephrons and each kidney so we are actually in the you know functional unit area part of that functional unit is this renal corpuscle which was made up of the glomerulus this capillary here and the Bowman's capsule and then of course we can see the afferent and efferent arteriole here where you know we're sending blood in and blood out of here and we are filtrating the contents of the blood into this capsule to form a product called filtrate then we're gonna send it to the proximal convoluted tubules so hopefully that makes sense so far but what we really want to understand on this is what's going on in here and also this is really important the three main processes of what the kidney is doing is filtration which is going to basically be happening here and all these renal corpuscles at the glomerulus reabsorption because most of what we filter out has to be reabsorbed back into the blood or we'd be dead just a couple of hours if we didn't reabsorb most of it and secretion which is a very minor but important function is going on before we finish making turning the filtrate into urine okay so let's continue and talk about this couple things that you know it helps to know going into this is first of all what we already mentioned the nephron being that series of of cells that make up the Bowman's capsule make up the glomerulus so that's their neural corpuscle of course we've got the proximal convoluted tubule the loop of Henle the distal convoluted tubule and the collecting ducts and then we have the peritubular capillaries that are you know kind of surrounding those tubes so we can reabsorb the filtration so if you're not familiar with that go back over the lab material look back over that okay now the next thing we need to talk about though the difference in hydrostatic pressure and osmotic pressure hydro means water and of course osmosis has to deal with water movement but so hydrostatic pressure and osmotic pressure both have to deal with the pressure of water but it's two different types of pressure and the best way I can describe it is a hydrostatic pressure would be like kind of like the pressure of water in a water hose how fast is the fluid moving through here in how forcefully is it leaving here okay whereas osmotic pressure what's the pressure of how water moves in a in a either isotonic hypotonic or hypertonic solution if you remember water always goes from a high concentration to a low concentration and that's our definition of osmosis it is the diffusion of water so whatever our concentration is of the water in other words do we have a hypertonic solution especially when we're preparing especially when we're comparing the solution of the filtrate to the solution of the blood then those are going to be pressures that are going to be involved in understanding our glomerulus and understanding the the higher pressure that we have to exert in this area and for those reasons which we'll get into so again even looking at this picture we again see our renal corpuscle that glomerulus with the Bowman's capsule you see the proximal convoluted tubules we see the afferent arteriole descending blood in here we see the efferent arteriole notice how the afferent arteriole the diameter of its bigger the efferent arteriole the diameter is smaller and then of course what we're doing we're filtering the you know part of the plasma and part of the contents of the plasma and it's becoming something called filtrate and then it's running and that's our first step filtration it's running through the proximal convoluted tubule with these cells that have what we call brush borders on them because it got micro villi on them and then what we're going to do is we're going to reabsorb the majority of what we filtered out back into the peritubular capillaries which is what the effort arteriole becomes so remember what we filter out we're going to reabsorb most of it back into the blood stream keep in mind though even when we're filtering it back in a blood stream there's still interstitial between the cells of the tubules and the cells of the capillaries here so here we actually can see and let me make this a little bit more clear we can see the different parts of the nephron of course this is a blown-up version of what we have here and here we say our proximal convoluted tubules our loop of Henle our descending loop our ascending loop here we see that the ascending loop end becomes the distal convoluted tubules one actually so here's the ascending loop at this point here well we're gonna form a structure called the juxtaglomerular apparatus at that point then it will extend on past that and become the distal convoluted tubules right over here to the collecting duct again notice how the efferent arteriole is wrapping back around and paralleling the it's becoming the peritubular capillaries and kind of parallel in the tube for this all-important reabsorption and also for something called the the counter-current multiplier and exchange system which will mention later all right so but let's keep it rather basic right now and talk about what's going on so again here are the parts we talked about the afferent arteriole the glomerulus being the capillary the capsular space being the space between the capillary and the capsule and of course that the glomerulus and the glomerular capsule together make up the renal corpuscle again we see the efferent arteriole notice the diameter again if this is bigger the diameter of this is smaller notice we actually have our proximal convoluted tubule coming out and that continues on as the rest of the tubules here again we have our peritubular capillary where the efferent arteriole is is you know too much paralleling with the tubules so can reabsorb the majority of what we filtered out okay here's that first step again where we're literally are filtering whatever is flowing through here is leaking out and becoming this material called filtration or cutsie become filtrate and that process is called filtration now we'll talk about what how what is able to get out here and how does it leave the capillary and become the filtrate we'll be talking about that in the near future but right now we're just saying the process of it leaving at the inside the capsule and becoming filtrate is filtration again remember this is happening in million a million of these in each kidney okay so filtration was happening here but notice when the filtrate goes into the tubules now we need to reclaim the majority of what we filtered out because it was mostly size and charge independent as why it filtered out it didn't mean that everything that filtered out was step we wanted to get rid of now the waste products were getting rid of most of it did happen to be the correct size and the correct charge but we also filtered out a majority a big but a big amount of things that we can't afford to lose or will die so notice the arrows are showing that what was filtered out is now being reabsorbed back into the blood stream going from the what's called the lumen of the tube you'll through the cells in cellular transport into the interstitial and then from the interstitial back into the blood stream so this again is this important process called reabsorption okay notice our third steps called secretion and in and what we're doing now is we're having very minut adjustments of product that was still in the blood stream didn't get filtered out initially that still we don't want to keep in the blood but that we want to get rid of so we have basically one more chance to get rid of products even though again this is a very very small amount compared to what was filtered out and compared to what was reabsorbed but it is our last chance to make some adjustments to what we want to get rid of you know we haven't really talked about the adjustments and the water content but as far as the as far as that what's in the filtrate that's becoming urine here's our last chance to basically fine-tune that okay the pressure of the blood coming in and the fact that this afferent arteriole is normally a larger diameter and this efferent arterioles number normally a smaller diameter the pressure of that coming in is going to push blood through the capillary well in the meantime we literally have three things that we need to be able to cross it's called a filtration membrane that we need to be able to cross to get out of the lumen of the capillary and into the Bowman's capsule space here so what we have to do is we have to wipe that basically if you'll notice here is the inside of that capillary so here's plasma and here's a red blood cell but the contents of the blood that we're filtering out have to go through three parts of the membrane okay the filtration membrane the three layers asked to go through is first of all fenestrated glomerular endothelium now remember the actual simple squamous epithelial cells that line a capillary are called the endothelium and fenestrated means that it has little bitty holes in it little bitty holes that if you're bigger than those little bitty holes you should not be able to leave this so a red blood cell or proteins should never be able to leave the blood because first thing they shouldn't be able to go through that fenestrated glomerular endothelium the little holes in the squamous cells that that line the lumen okay now the next thing is the basement membrane remember epithelial cells are always connected to other tissues or to other allele cells by by basement membrane so we have to have a pore basement membrane so you got to go through the little epithelial cells you got to be able to go through that basement membrane and finally there's something called filtration slits which are formed as this is by the pedestals of the podocytes now the podocytes are the cells that make up the outside of the capillary so these are very specialized capillaries they're not just simple squamous epithelial cells like most capillaries these are specialized capillaries they've got that the endothelium which is more like a normal capillary except it does have the fenestrations or the holes in them then it is connected to this outer layer of cells called a photo site and this outer layer of cells has what they call fringe like extensions and the fringe like extensions are almost like little fingers that that are outside and where they overlap with other fringe like extensions we literally have little space between it so we call those filtration slits so you've got to go through the holes you've got to go through the basement membrane and you got to go through where the overlapping pedestals of the cells called photo sites enter if we actually use the term interdigitate like putting your fingers together from one hand into another and then seeing the space between the fingers the space between the fingers would be the filtration slits so again you've got to be pretty small to be able to cross all three of those things and so we know that we should never find big items in your urine or something as damaged this area to allow large things out okay okay so we see these large things being kept in but we see the small things passing through those three the the three things we just talked about the glomerular endothelium with the ministrations the little holes within the endothelium the basement membrane and then finally the filtration slits which are which are basically found where pedestals interdigitate from the podocytes of the cells now I know that's a lot but the main thing you need to know is it gets the fenestrations the basement membrane excuse me yet through the fenestrations of the endothelium through the bet port porous basement membrane and through the filtration slits of the outer cells which would be the pota sites okay what are we actually filtrating what is it that is able to go through that filtration membrane and become our filter right here in the in the space the glomerular space okay so obviously water is part of it because blood is mostly water and and this is plasma you know was mostly water so that water is carrying all the other stuff out where ions are small enough to go through this so sodium potassium and chloride which we can afford to lose some of this we can't afford to lose all of it now here's what we're really looking to get rid of in the water is the nitrogenous waste these are the wastes that the cells produce that the blood picked up but if we keep these wastes in our body then they will start damaging us and in breaking down our tissues and we all know that if somebody has kidney failure if they don't get