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Current time:0:00Total duration:10:53

Countercurrent multiplication in the kidney

Video transcript

so we've already talked about this part of the nephron right remember it's called the glomerulus the glomerulus and it's the structure that receives an arteriole that's called the half ferrant meaning going towards arteriole that's the arteriole that branches off of the renal artery and it gives off this vessel right there this is called the efferent arteriole efferent meaning going away from and these are all talking about the glomerulus so the afferent arteriole goes in becomes really really squiggly and then it comes off as a single vessel the efferent arteriole in this process a ton of fluid is filtered out of the blood and goes into this yellow capsule right here this is Bowman's capsule Bowman's capsule which is the first part of the nephron to actually collect fluid that's going to be filtered to become urine and in this sense the kidneys are pretty amazing do you know in Desert Rats these are animals that may never see free water in their entire life because they live in the desert their kidneys are so good at concentrating urine and absorbing water that sometimes their pee can actually be solid crystal that sounds pretty painful but it works for the desert rodents let's figure out how our nephrons work for us after the glomerulus the next part of the nephron is this guy right here which is pretty convoluted once you agree but it's close to the glomerulus so we name it according to those features its proximal to the glomerulus so we call this a proximal and because it's so windy we call it convoluted it's the proximal convoluted tubules small convoluted tubule kind of a mouthful but these words perfectly describe what it is the proximal convoluted tubule is very important for reabsorbing ions like sodium and chloride but also some of our other builders of macro molecules like amino acids and even glucose and remember when we're absorbing things like this and especially with sodium we're gonna take water with it as well so water is reabsorbed at the proximal convoluted tubule - in fact I've read somewhere that the proximal convoluted tubule reabsorbs about 65% of all of these important nutrients that's the most of anywhere else in the nephron that we're going to talk about so it's pretty important where does the nephron go next well it actually becomes this loop right here it descends deep into the kidney and then it ascends back up again this entire structure is affectionately called the loop of Henle the loop of Henle and it's got two limbs to it as I've shown here and they're going in opposite directions one is called the descending limb descending because it's diving deep into the kidney so this is the descending limb and the other part of it this guy right here is called the ascending limb ascending because it rises up ascending limb and the reason why this is significant is because remember the kidney is kind of broken up into two main overall parts right there's a part that we call the renal cortex that's above here and then there's a part we call the renal medulla which is down here and the thing to remember is that the renal medulla is very salty very salty because we have a lot of ion reabsorption happening here now I should further specify that the descending limb and the ascending limb of the loop of Henle reabsorb very separate things the descending limb reabsorbs water so we have mainly water come in here and in fact there are no ions that are reabsorbed at this point it is impermeable to ions on the other hand the ascending limb does the exact opposite here we reabsorb things like sodium chloride potassium and in fact this part is impermeable to water no water will be reabsorbed here in the ascending limb and because of this we have a very beautiful system that occurs as a result this is called counter-current multiplication counter current multiplication which is also I'll admit a mouthful but it completely makes sense I promise counter current multiplication we say counter current because the descending limb and the ascending limb go in opposite directions that's why it's counter current multiplication means that when we reabsorb ions in the ascending limb here and make the medulla salty by not reabsorbing water that drives water to be reabsorbed passively in the descending limb and we have a video that goes into detail about transport processes in the nephron but here just remember that water is reabsorbed passively so no energy is expended to reabsorb water and this is because we have used energy here in the ascending limb to reabsorb these ions so active transport is used here and by actively pumping ions into the medulla and no water in the ascending limb to make it salty we can multiply the amount of water that is reabsorbed passively because it's driven into this space around the tube you'll or the nephron the space around the tubules just called interstitial I'll write that off right here so this is the interstitial this is anything that is not the tube you'll or vessels and that's just space around here this is all just interstitial just hanging out right here and so all this ions that are reabsorbed into the medullary interstitial down here the interstitial of the medulla drive the passive reabsorption of water all right so I think we have a pretty good understanding of the loop of Henle and the counter current multiplication process that happens here the next part of the nephron is this guy that kind of loops back and just kisses the glomerulus right there and I'm sure you've astutely noted that just like the Box amol convoluted tubules to Buhl is also certainly very convoluted so it's a tube you'll that is convoluted let's say but it's not as close to the glomerulus as the proximal convoluted tubule is so instead we shall call this guy the distal convoluted tubules and this dude is responsible for the reabsorption of other ions like sodium and chloride and it helps to just pick up more of these important nutrients that we'd like to have in our bloodstream that we don't want to pee away the other thing I should mention now that I promise we go into more depth in in a separate video is this very scientific kiss that happens here when the distal convoluted tubules by the glomerulus again this produces something that's called and this is a mouthful the juxtaglomerular juxtaglomerular apparatus juxtaglomerular apparatus and all this is responsible for is to control blood pressure this is part of the kidney that's used to control blood pressure and we'll talk about this in detail in a separate video so now that the distal convoluted tubules come up here and kissed the glomerulus and kind of come out here it's time to collect whatever leftover fluid we have and we do so in this guy right here this is called the collecting tube you lure the collecting duct so it collects things that we have left over in the lumen or inside of this nephron and one thing to note is that there are many DC T's or distal convoluted tubules that feed into this single collecting duct so there's a DCT there's a DCT and there's another one down here right and we actually reabsorb a couple of things in the collecting tubules as well the main thing that we reabsorb into our interstitial is water and another thing we reabsorb that I'll show deep in the medulla right here is urea urea is one of the main waste components that we actually pee away but sometimes the kidneys like to hold on to urea to increase the odds mul arity in the medulla to help drive water reabsorption in the loop of Henle this goes into a process that's called urea recycling if you've heard of that term before but we're not going to go into detail for right now on that instead we'll just mention here that urea is reabsorbed to maintain osmolarity maintain the osmolarity our medulla that will help drive water reabsorption in the loop of Henle and finally I want to close the loop on what happens to this poor if errant arterial right here because we came off the afferent arteriole and this I promised you would turn into a capillary and then a venule and here's where I'm going to talk about that because we've reabsorbed all of these awesome things here in blue but we don't have a way to put them into the blood stream yet well the ferrant arterial gives us a way to do that and it does so by kind of coming off this way and just like all good arterioles it branches off into even smaller branches so much so that we branch off into smaller capillaries and these capillaries will dance across our nephron and collect all this good stuff that we've talked about here in blue that gets reabsorbed into our interstitial and I should mention that because these capillaries kind of hang out all over the place where our tubules are we say that they are Perry tubular Perry tubular meaning just around the tubules so sure enough their official name is Perry tubular capillary or we call them all peritubular capillaries and so after we've collected our nutrients in these peritubular capillaries we come back here where we then start doing the exact opposite because now we've lost our oxygen but we've reabsorbed these nutrients into our bloodstream and then this will kind of come back together and head off into I think you guessed it the renal vein and the renal vein will then take this back to the rest of the body and that leaves the rest of what we've collected here in our tubules in our lumen right here that goes away and this is going to become our urine our collecting tubules where we first have urine that's going to be sent off into our renal calyce's and then further on to be peed away