hello and welcome to the lecture on chapter 12 the kidneys this is part one and I believe it's going to be a three-part lecture so as always we try to simplify as much as possible at the beginning of these lectures um so kidneys super simplified there are three main functions there's regulation that is helping the body maintain homeostasis waste removal there's a way out of the body taking things out of the blood and finally hormone production so let's take a look at each of those things with regulation uh one of the most important things that's being regulated is the amount of water that's in the body there's all we always have to have some uh water go out with the waste that's being released but in cases when the patient is a little dehydrated the kidneys do as much as they can to hold on to that water and vice versa if there's excess water on board the kidneys they release the the regular waste but they also try to unload some of that extra water uh the kidneys are also responsible for helping us manage our electrolytes and what I mean by electrolytes are these ions um sodium potassium calcium magnesium chloride Etc and uh kidneys help us manage our blood pH we've we mentioned when we were talking about the lungs and respiration we mentioned how the uh having an excess of carbon dioxide leads to an excess of hydrogen ions having too much acid on board well the kidneys can help with that um and so the the there there can be some renal compensation for things going wrong in the respiratory system and this is that mechanism is getting rid of the hydrogen ions um they're also bicarbonate ions and depending on what the blood pH is um the kidneys will either get rid of extra hydrogen ions or get rid of extra bicarbonate okay waste removal uh the important or the the famous ones uh that we hear about the most Ura uh this is going to we we'll go over a little bit where this came from um this is what gives urine its name um or this is this was named after urine I actually don't know which way the naming went um but it's basically getting rid of some nitrogen that was part of protein that was ingested uh other forms of nitrogen that also get eliminated ammonia and uric acid but the most famous one is Uria and it's the one we have the most of another waste product that you've heard about before and we keep track of not because it's so deadly but just because it helps us calculate something that's creatinine and we're going to talk about where creatinine comes from um and Drug metabolites um the kidneys are really good at getting rid of things sometimes better than we would like them to be um because they get rid of medications too uh but this is how you know many of our medications are processed and eliminated is through the kidneys and then finally the hormone production part there are three main hormones uh that are produced and released by the kidneys one of them renin um that's part of the renin Angiotensin aldosterone system and we'll talk some more about that and this one actually has an impact on the kidney itself the the renin um leads to ultimately leads to the release of an aldosterone and aldosterone has an impact on the kidneys both we'll get to that um these other two have impacts in other areas of the body so arthop potin is produced and released from the kidney uh this is the signal uh to the bone marrow that we need more red blood cells arthropo is also known as EPO why it's made in the kidneys nobody really understands but it's made in the kidneys and it's released from the kidneys uh but the target tissues are out in the bone marrow and then activated vitamin D yeah it's true that vitamin D can be made in the skin but it gets activated in the kidneys and this is important for calcium absorption from the digestive system and this will come up again we talk about things that go wrong so when kidneys aren't functioning and arthropoid isn't being made there are some consequences um or kidneys aren't fun functioning and the activated vitamin D isn't being made there are consequences for that as well then the other way of simplifying things is there are four main processes that the kidney does um through these structures called nephrons filtration this is when a liquid and solutes leave the blood and go into some tubes in the kidney uh most of the stuff that we just filtered most of that we're going to pull back um that's called reabsorption specific molecules are being pulled back from the filtrate it's like 99% of what just filtered gets pulled back and that sounds super inefficient um but if you've ever tried to get sand out of a bag or out of your pockets or anything yeah you could try to pick the sand out but it's just easier to pull your pocket inside side out dust it out and then put your change and your keys and your other things back in um and that's kind of the relationship here is yeah get everything out and then we'll pull back what we need um secretion this is the act of anything that didn't get out infiltration but we still want to get out of the blood um gets actively pumped over uh using secretion and then finally anything that's left out of the blood in this filtrate that's eventually going to be excreted from the body and that's going to be released as urine we will see these four steps I'm going to show them to you at least three more times today all right so the four kidney processes um as a way of understanding them I know I just gave you a pocket analogy but I I actually wrote in a closet analogy here um so we're uh pretend we're cleaning out a closet and the way that we typically clean out a closet is um in three steps we empty the closet we take stuff out of the closet um now we with the blood we can't empty the blood we can't dump everything out of the blood but we dump about 20% of the stuff out it's a b a fifth of the the plasma and the stuff that's in the plasma gets dumped out both good and bad things get dumped that step is what we call filtration then once we have that stuff out of the closet and on the floor we can we start picking some things through uh that's reabsorption we're going to pull back most of the stuff that we just took out of the closet um we're going to pull most of that back that's reabsorption and then we'll look in the closet again and there may be some more stuff that we can pick out that's the process C of secretion where we actively select things to pull out not just dump you know 20% of whatever's in the closet and then finally the stuff that's left out on the floor we take that out to the trash that's the process of excretion that that stuff that got left out of the closet is not going to find its way back in and we just need to get rid of it get it out of the house and that's urination okay a gross anatomy of the kidney and by gross I mean just big not disgusting um the outer layer of the kidneys referred to as the cortex uh then there's an inner part uh medulla these are general terms um cortex meaning shell and medulla meaning middle and then there's this inner funnel shaped thing um that's the renal pelvis that's going to be collecting all the stuff that's going to become urine and that funnels down into the urer and our textbook doesn't talk a lot more about other aspects of the urinary system it really does stay very focused on the kidney um kidneys contain nephrons yeah I'm going to mention it so there's these Transitions and I generally edit them out um but I didn't do that today so please don't be annoyed with me I'll get them on the next part um so kidneys contain these microsc microscopic structures called nephrons so here's the kidney on the left and we're going to zoom in on one little section and and blow it up um it has uh thousands and thousands of these uh structures called nephrons on this diagram this is not from our textbook but on this diagram I've U I'm indicating uh some of the capillaries that are present there are basically two capillary beds that the the blood goes through the the first one is the glomerulus which means ball of yarn in Latin because it looks like a ball of yarn um and the peritubular capillaries that are surrounding the this tubule this renal tubule now we're going to super super simplify that structure oops um and the glomerulus that I just showed as a ball of yarn this is being super simplified into this big ball here but you can picture bunch of little cap capillaries there's a blood supply that that brings blood to the glomerulus uh that's aparent arterial or afferent arterial afferent means on the way in and eer means on the way out so they're both arterials which is a little counterintuitive usually we think about the next collection is going to be a vein but because it's going to go through another capillary another set of capillaries um it's referred to as another arterial so there's the blood supply coming into the glomerulus and then there's the blood supply after the glomus going to this other peritubular capillary so this part the glomerulus that's going to allow us to dump stuff out of the blood and then remember we said 99% of that stuff we're going to pull back in where we pull it in is back into the peritubular capillary so that's why the two capillary beds um so let's take a look at those four processes again oh sorry let's look at the structures first um there's this glomular capsule you'll sometimes hear it referred to by the name of the the guy who's credited for describing it Bowman's capsule it means the same thing it's just this this kidney structure that surrounds the ball of capillaries and catches the stuff that we're filtering out and that funnels the stuff down into the renal tubule and the renal tubule as we will see is long and kind of convoluted um I'm just showing it as a straight line here but um this is made up of the proximal convoluted tubule the loop of Henley and the distal convoluted tubal now let's take a look at those four processes so filtration occurs from the glomerulus we're diffusing the the plasma largely water with stuff dissolved in it about 20% of the plasma and its stuff is coming out small stuff bigger stuff is not allowed out um blood cells are not supposed to get out proteins which are much larger than you know some of the smaller nutrients that we're going to talk about um proteins should not be getting out all right so that's filtration then reabsorption we said we're going to pull back like over 90% of what we just filtered out we're going to pull that back in and that's occurring from the tubal back into the bloodstream and then remember there was some more fine tuning going in the other direction so if there's more stuff we want to get rid of and there always is um we're going to actively pump that from the blood into uh the capsule into the capsule I'm sorry into the renal tubules that's called secretion and then once we put all three of these Pro you know the the end result of all three of these processes we filtered out some stuff um we pulled back most of the stuff but this was the only way we could get some of that trash out was to just dump it all um and so we pull back the stuff we want and then some stuff we do have the ability to secrete some more of that stuff and then everything that's left here in the tubul at the end that's what becomes urine and we excrete that we urinate that out all right this is a diagram from our textbook I know it's kind of busy um this tries to break down the total body fluids turns out the vast majority of the fluid in our body is actually tied up inside the cell so it's intracellular that's represented down here it's this big content um then the rest of our blood the extracellular blood some of that is it's out it's just right outside the cells um we call that interstitial fluid it's in the it's in the tissues but it's not inside the cells but it's kind of between the cells but it's not in the bloodstream either um so interstitial fluid and then the last category um you would have to cross into the blood vessel to get to and that's the plasma the plasma is the only fluid that the kidneys have access to and so yeah the kidneys work hard at regulating our fluids and our electrolytes but they but the kidneys really only have access to the plasma there's and we have to rely on you know mve movement of the fluids from inside the cell to outside the cell and so on but this is the part that the the kidneys can really act on all right so the nephrons we're going to look at them um and the the textbook diagrams were not great and I I just couldn't find a good diagram there is um on our additional resources uh there's a video from Crash Course uh it's the first one and so I took a bunch of screenshots uh so they're not perfect these little balls um in the animation they're they're just moving through so just I caught them they don't actually mean anything where the little where exactly the little balls are does means nothing okay what I want to show you is this is the big layout of a nefron um here's the ball of capillaries the glus that's where filtration is happening and Bowman's capsule uh is going to catch the stuff that that's coming out of the this capillary um and then it's going to flow down this whole long renal tubule so filtration happens in that this first part then we get to the proximal tubul so proximal and distal refer to how far away from the glus is it and I do recognize that it looks like this part is close closer to the glus than say this part but if you can like as the crow flies like it's a direct line here but the fluid think about the the the the the route you would have to take if you were part of this fluid um so that's what we mean by closer and further away um if you want to picture yourself like walking down this long hallway and there's no shortcut from this part of the hallway to this part of the hallway you just have to walk the whole hallway way all right so this first part is called proximal and then it's referred to as convoluted because it's really twisty so sometimes you'll hear it called the proximal tubule or the proximal convoluted tubal this is where we're going to pull back a huge amount of the water the electrolytes um the nutrients and we'll get into that in more detail later I just want to show you that there's a lot of reabsorption happening here there's a certain amount of secretion where we're pushing some things that are still in the bloodstream pushing them into the tubule then we get to the loop of Henley this this is It's a I don't know how to describe it other than it goes it's a straight and then a hair pin and then it comes it sorry straight down hair pin and then it comes back up and that is where we're going to reabsorb a lot of our water and where we're going to reabsorb um the sodium um pottassium and chloride we'll talk more about this later and then finally we get back to the this kind of circuitous route and that's another convoluted tubule but since we're further away from the glomerulus it's called the distal convoluted tubule and this this is where we do more fine tuning of the electrolytes you know how much sodium do we need how much potassium do we need um and yeah so we do some more fine tuning here and then finally the stuff that's um kind of dumping out of this tubule is going into what's known as a collecting duct and we're not quite done yet um we do some more fine-tuning of sodium levels and and water reabsorption here and yeah I know it's complicated um I tried to simplify it a little bit we'll get to why The Details Matter a little bit in part three of the lecture all right this is a diagram from our textbook um showing there's a couple of different kinds of nephron we're not going to get into that much detail but it's all the same steps that I just talked about um so here's the glomerulus um here's a proximal convoluted tubal then the loop of Henley and then we're back to a distal convoluted tubal same thing on this kind of nefron uh there's the glomerulus proximal Loop of penley distal and then into the collecting duct and the stuff that stays in here is the stuff that's destined to become urine I alluded to this but let's spell it out this is a nefron blood supply this diagram is from our textbook um let's take a look at here there's the glomular Caps capillaries there's an afer or AP ferent arterial it's usually it's actually pronounced afferent but that sounds so much like efferent that I mispronounce it so you can hear the difference aant coming in and eant going out um so afer bringing the blood in then uh we squeeze out a bunch of it a bunch of the plasma here in the capsule and then efferent uh the remaining blood goes to this peritubular capillary which wraps itself all around U the proximal and distal convoluted tubules and uh the loop of Henley and that's where that reabsorption and secretion that fine-tuning stuff is happening and then it gets recollected in a venule and goes out uh from from there and heads back towards the heart uh this is again a closeup of part of what we've been looking at this diagram is from our textbook um this is taking a closer look at the glomular capillaries so we have afferent arterial um and the fluid is is uh getting filtered out and so they're they're clearly the the cells of the endothelium here of the capillary but then there's also um some glomular cells and stuff that's in the blood needs to pass through both so there's there's a real fine mesh if you will that's not going to allow uh should not if it's working right it's not going to allow any of the cells through it's not even going to allow proteins through that's Bowman's capsule or GL glomular capsule means the same thing and so this is the stuff that's going to proceed down through the proximal tubule this diagram is also from our book and it it's basically trying to walk you through the pressures and all the different parts we're not going to go in so much detail but I did like a couple of things about this diagram one is here the pressure in the glomerular capillaries is pretty high um and remember what we said about that their hydrostatic pressures that are going to push out from the capillaries um that and the Bowman's cap capsule capillaries they're super super leaky um and so there's a lot lot of stuff that's going to come out about 20% as I've said um that suddenly becomes filtrate that's the term for it the stuff that we we took out um if you need that closet analogy it's the stuff that we took out from the closet and just put on the floor temporarily that's the filtrate uh so the glomular capillaries favor filtration that is pushing things out the peritubular capillaries this this is the part of the circulation that's now wrapping itself around the the renal tubule that favors pulling things back in reabsorption and so much of what got dumped on the on the floor is going to get pulled back in um in the peritubular capillaries it's the stuff that stays out in the filtrate that is the stuff that's destined to become urine so what stays out becomes urine and then this is the last diagram for this part of our lecture uh the summary of the renal processing it's those four steps again this is our textbooks diagram of it and it's kind of nice it's not as simplified as the one I showed you before but it's still kind of nice uh so we get the blood supply in there's the affrant arterial we get to U Bowman Bowman's capsule this is the glomerulus it's ball of capillaries remember there's that uh high pressure for capillaries pushing out so a lot of the the content 20% of the plasma is going to come out in this first step this is the filtering step then um we have the efferent arterial giving rise to a bunch of capillaries now here I like that it shows it they're they're buddies they're wrapped right against it the peritubular capillary is there to retrieve a bunch of stuff that was just dumped out earlier because it was the only way to get some of the other waste products out but there's a bunch of stuff that's in this filate that we want back um and that's the process here of reabsorption and then there are some waste products that uh weren't able to get them all out here during the filtration step or some of them we couldn't get out in the filtration step and we have to get them out in this other way but this costs energy you know it's easier less uh less energy intensive to just dump it out than to have to you know have transport proteins and have to pay for every single thing that we're going to take out so that's secreted and then finally the stuff that um is not reabsorbed that stays here in the filtrate that's the stuff that excreted in the urine yay so that's a wrap up of part one