okay so it's all about the nephron so even though this thing is ridiculously small I mean you have over a million of them per kidney and complicated as we've already seen kind of going through the anatomy this is where it's at so we call this the functional unit of the kidney because the kidneys job is to clean the blood and make urine and that's what this guy is doing so he's crazy complicated but I promise you it'll make sense once we get into it and we'll see how important it is that he is so crazy complicated so the nephron consists of the renal corpuscle and that's up in the cortex part which is the lighter edge of the kidney and then the renal tubular to the medulla so the renal corpuscle remember is a tiny structure but it's crucial because it's that meeting of two organ systems so we have the cardiovascular system and we have the urinary system coming together to make up the renal corpuscle so we have that globular Asst which is the capillary bed which is pictured here and Bowman's capsule or the kalam Mueller capsule which is the urinary system so the whole point of this is this this combination is to make sure that we get the blood clean and collect the filtrate so we call it filtrate until it's X pretty much exiting your body and then we can call it urine okay so how does it filter blood so you have the renal artery and then it's gonna split into an afferent arteriole just like other arteries become arterioles and then capillaries right we're doing the same thing except for we're doing the renal artery because we're talking about the kidney the a ferrant arteriole remember a ferrant means you're bringing blood in so if you look at this picture the arrow is bringing the blood in we're bringing it into the globular as' which is that little curled around capillary bed in there remember capillary beds are holy they have the fenestrations which means things can leave the capillary so the only time we can clean the blood is in that capillary bed is is from that globular 'us otherwise the arterioles are bringing the blood in and out there's no exiting there's no holes in those arterioles so then the filtrate collects in Bowman's capsule and we're gonna see how it's gonna go on down the road and then the blood once it's clean leaves the Bowman's capsule leaves the corpuscle out the efferent arteriole because remember efferent means exit so if we look at the anatomy of Bowman's capsule or the globular capsule we have a layer if you look at the top of this picture how it has that kind of like brownish stuff and then the bottom has like you could actually see the red blood cells so that's just kind of showing you that parietal layer versus the visceral layer so remember the parietal layer is gonna be actually lining Bowman's capsule because parietals like actually lining the cavity right and then the visceral layer is that brownish layer that's laying on top of the capillary bed because visceral means organs so that's the layer that's actually touching the organ in this case the globulars in this case the capillary bed so it's just made of simple squamous epithelium which remember looks like little fried eggs so the visceral layer is actually touching the capillary whereas the parietal layer is kind of lining Bowman's capsule and so that space in between is where the skanks gonna collect so our whole goal is to clean the blood that's in that globulars and so we need to send the filtrate into that space and Bowman's capsule and then we're gonna send it down the road so in this picture they're just showing the proximal convoluted tubule like cut but you can see those little Swain --mess cells like real well on that picture there so the space between just gives us somewhere for that filtrate to go and so the visceral layer which is that weird kind of brownish tannish looking stuff that covers the capillaries our cells that are called podocytes and so the reason i have an octopus like you know the clipart there is because it kind of the cells themselves I have a picture of them have like little extensions coming off of them like an octopus leg but Poteau means foot so it's like this literally means foot cells what kind of looks like these little feet and it creates um another layer of pores so you already have the capillary bed remember that's holy that's got the fenestration okay but by having this other layer on top it gives you another holey layer so it's basically like if you go fishing and you have your fish net and you have one net and you pour your fish in the bucket water through and it catches the fish right this would be like having two Nets so oftentimes like you would use two Nets if like you had really really tiny fish right just to make sure you don't you know lose any of your fish so it's the same thing here we have two layers instead of one most capillary beds have just the one layer because most capillary beds we want things to leave really really easily well with this capillary bed we want things to leave but not everything so we want to make sure that just the waste leaves the blood none of the good stuff so this just kind of gives us like a double layer of webbing a double layer of Nets just to make sure that yeah we're cleaning the blood but want to make sure that like a lot of stuffs not just escaping into the blood because remember our end game here is to make urine and that's gonna leave your body so we want to make sure we're not losing good stuff from the blood into the urine okay so here's our picture of a nephron I recommend that you get out a piece of paper and you draw this because I'm gonna have a drawing coming up and so I recommend just kind of copying it okay of course you can print it but I think it is better if you draw it like I just think you kind of spend the time to maybe understand it a little better but you'll have to do anything that dime pay taxes okay so the first thing that we want to understand about the nephron is the basic anatomy so you have the afferent arteriole going in so that's what that little arrow is the efferent arteriole going out and while it's coiled around inside Bowman's capsule recall to glom mueller's so remember that's all blood so the blood is going in and out to get cleaned then we have the globular capsule or Bowman's capsule which is the yellow cup like structure that's going to collect the filtrate so once the filtrate drains off of Bowman's capsule or globular capsule its gonna go into that first gnarly twisty tube which remember is the proximal convoluted tubule proximal because it's closest to Bowman's capsule convoluted because convoluted means all twisty and weird right like if something's convoluted it's confusing then we have the nephron loop or loop of Henle if you prefer and it's going down and up because this is a fluid so it's like a river it's only flowing in one direction so the filtrate is gonna go down and it's gonna go up and then it goes into the distal convoluted tubule which isn't just convoluted but it's still twists a little bit right and then into the collecting duct so that's the first thing is to kind of just know that Anatomy okay the other thing I would want you to add to your drawing is the descending limb so what I would do and I have a picture coming up of this is I would take a dash line and just like kind of separate this at the loop of Henle so I would draw a line just straight down this picture separating the descending and ascending limb because the descending and ascending limb act very different and so this is very complicated we're gonna take our time with it okay but for now the descending limb is permeable to water so everything on the left side of this drawing Bowman's capsule the proximal convoluted tubule and the descending limb if you have water inside that yellow tube it's free to leave so that's what permeable means right like the permeable cell membrane means things can get through it so water is free to leave that side of the nephron now the right side of the nephron once the filtrate starts Det starts heading up in the a sending limb is not permeable to water so this is a key point and it's one of the beginning points okay so the left side of the drawing water has a free pass water can leave as much as it wants to the right side of the drawing water is trapped in that yellow tube the collecting duct if you remember that when we just kind of went through the anatomy the collecting duct if you look especially at the above picture see how that collecting duct is heading to the papillae to the tip of the pyramid so once it gets into the collecting duct it's pretty much destined to become urine so at that point we could probably start using the term urine so this is gonna then send it into the minor calyx which remember is the first cup like structure and then major calyx and then outside you know down the renal pelvis ureter bladder urethra the world so this water thing is our first big key point so at this point like I said I recommend you draw it use a full piece of paper because we're gonna add a lot to this drawing okay you don't need anything fancy something basic like this okay you could then label all the anatomy and again add the water thing that's where we're at right now isn't this fantastic aren't you so sad you're not in class drawing this so you can see this is my drawing it's not fancy okay it doesn't need to be fancy we just need to understand very basic things right now okay so what I've drawn in my drawing you have the a ferret arterial Christy my little arrow in you have the little twisty kalam you Luis and then you have the efferent out I labeled Bowman's capsule I labeled the proximal convoluted tubule the distal convoluted tubule and the collecting duct I didn't label the descending and a sending limb because I figured at this point we kind of get that I did add this fr-s thing which is what we're doing next okay but the water thing is the most crucial so permeable to waters to see what I mean by kind of draw the dashed line like halfway down the left side is permeable to water so anywhere along that path Bowman's capsule proximal convoluted tubule and the descending limb of the nephron loop if I'm water I can leave if I want to by the time we start heading back up by the time we're in the a sending limb and the distal convoluted tubules if your water you're trapped like a wrap so this is the key point one side waters free to leave one side it's not so why is this thing so twisty and weird so if you're sitting there wondering what is the point of this why can't it just be a straight shot why can't we just suck all that skank out of the blood and get it to the bladder and call it a day okay well that's because of timing remember as I kind of said when I was doing the anatomy okay the blood doesn't want to be cleaned okay the Bloods got other things to do right it's amazing to me just like when I order something from Amazon and it gets to my house so quickly it's amazing to me how efficient your cardiovascular system is the fact that you ship out all the good stuff and pick up all the waste and you're back to the heart and under a minute is crazy then you add the fact that we're also doing this so the blood is spending milliseconds getting cleaned so I have to grab if I'm the urinary system I'm trying to clean the blood right if I'm the urinary system I have to grab that waste as quickly as I can well if you go in and grab things really quickly you're probably gonna make mistakes right and so is the kidney okay so that is why the nephron tube is designed the nephron loop is designed the way that it is it's based on the ultimate idea of take C's backsies if you do something you grab something you didn't mean to grab you can change your mind okay so I think of it a lot like having your garage sale when I have a garage sale because I'm an only child and I don't like to share my toys it's really really hard for me to get rid of things but I'll get into these moods at least like once a year where I'm like forget it I don't want any stuff because I just get like tired of stuff so I'll go in especially into my closet and I just start grabbing things and I end up with this pile of clothes that's like embarrassing because it's sad how many clothes I have and I'll stare at that pile and I go oh my god that feels so good to get rid of all those things and so I'll bag it up and I'll set it in the hallway and then that night when I'm laying there in bed I'm like well maybe I should keep that pair of pants because I might lose 5 pounds which who are we kidding or that sweater was expensive maybe I should keep it or oh that one sweater is kind of ugly but maybe I'll need it for an ugly sweater party or oh maybe I'll go on a job interview and I need a suit so then you sit there and you like shop at your own garage sale right so I don't know if any of you do this but so bad at this so even though I take out half my closet I end up putting half of it back because I was in the mood to clean and then it was like then I sat there and started thinking about regret right that is the design in the nephron loop that at Bowman's capsule you're gonna clean so much stuff and there's gonna be stuff that ends up in the filtrate that you have no intention of getting rid of but because it was such a cleaning frenzy just like when I'm cleaning out my closet and I'm just grabbing stuff sometimes I'll grab one of my favorite shirts I never have any intention of taking that to the Salvation Army I didn't mean to grab it I was just like over-ambitious so because the blood is flying in and out of Bowman's capsule and there's only so much time to clean the blood isn't it better to over clean than to under clean even if I'm gonna grab some of the good stuff on accident isn't it better to grab more waste because I have such a limited time to clean the blood and the design of this system is if you accidentally grab something good who the hell cares because we're gonna be able to dump it back into the blood anyway okay so we're starting with the proximal convoluted tubule the loop of Henle and the distal convoluted tubule so the proximal convoluted tubule is right after Bowman's capsule so that's the first place the waste goes after we've sucked it out of the blood so we're gonna see the job here's reabsorption and secretion which will mean more here in a second okay so reabsorption is bringing things back into the blood so your reabsorbing it back into the blood so if you picture the blood going into that little globulars capillary bed and we're pulling off the waste and sending it into Bowman's capsule and then immediately it goes into the proximal convoluted tubule so this is the new like the stuff from the clean it's like the new filtrate the stuff that we just pulled out of the bloodstream well the problem is yeah there's waste in there that's the whole point of this right is to clean the blood there's lots of waste in proximal convoluted tubule but the problem is there's a lot of good stuff too so this is day one of cleaning your closet you pull you have that giant pile that's got a lot of good stuff in it but you just wanted to clean your closet cuz you were in the mood so immediately I'm gonna look at that pile and go oh I had no intention of getting that shirt that's my favorite shirt we're gonna do the same thing here immediately in proximal convoluted tubule we're gonna reabsorb a lot of stuff back into the blood we never had intention of pulling it out of the blood we accidentally pulled it out of the blood because the blood is in and out of there so fast that we grabbed a bunch of the skank but we grabbed the good stuff too so this is where almost all of your glucose reabsorption is we have no intention of getting rid of our glucose we do not want a piece sugar peeing sugar is like throwing money out your car window you need that glucose to make ATP so making energy is crucial right you need that sugar desperately plus you don't want sugar in the urine especially if you're a female because that can lead to yeast infections good times okay so we don't want a pee blood or pee oxide we do not want to pee sugar okay we want that sugar in the blood where it's supposed to be but we accidentally grabbed it because sugar is small and we were so desperate to clean the blood so quickly we grabbed it on accident so we're gonna put that right back into the blood amino acids which I have no idea why abbreviated AAA so amino acids the building blocks of proteins you don't want to pee those proteins expensive right you go to the store to buy a steak that's gonna cost you like six bucks whereas you go to buy ramen noodles that cost you like 10 cents so carbs are cheap but protein you earned that right and we desperately need protein think of all of the things in your body that are protein based your muscles your antibodies your cells your hair your nails your skin your hormones your proteins are everything right so it's like we do not want to pee the building blocks of proteins that we spent a lot of time digesting and we spent a lot of money on so we want to put that right back in the blood and a lot of ions like calcium or sodium like ions that we have a purpose for why would we want to pee them we didn't mean to grab them anyway it's just that we were so desperate to clean the blood that we grab grab grab grab grab but that's okay because the proximal convoluted tubule is all about making sure we just have time to change our mind the loop of Henle looks like a little hairpin like a little Bob pin and then the distal convoluted tubule is eventually gonna empty into the collecting duct so once we hit the collecting duct that's like the sewer line that's leaving your house it's destined to to leave your house right so once we hit the collecting duct we're pretty much heading out the body it's now urine it's heading towards the bladder so if there's something good in the collecting duct we're gonna lose it so we have the proximal convoluted tubule the descending the ACE ending and the distal convoluted tubule to change our mind so this guy we're gonna see the distal convoluted tubule behaves very very differently for water balance so we're gonna see the hormones come back in ath now the Steyr on don't worry about them right this second okay but we are gonna see these guys come in with water balance but one of the biggest things that happens in the distal convoluted tubule is secretion so secretion if you secrete something like you secrete tears right you're like secreting it like you're like juicing it okay so secreting is getting rid of something so reabsorption you're bringing things back into the blood secretion you're dumping it into the urine so the distal convoluted tubule is the last place we can dump stuff and get it to exit our body it's kind of like the night before the trash man picks up your trash or hell even sometimes that morning like I hear the trash guy in my neighborhood and I'm like oh I forgot to set out the trash so I'm that crazy lady that's running down their driveway with the trash can because it's like my last opportunity to get rid of something so the distal convoluted tubule is the last opportunity we have to get rid of waste so we can secrete things into the distal convoluted tubule to get rid of it so again we're gonna tie all this together okay so right now I want you to know that reabsorption is going back into the blood and secretion is going into the urinary because this is like a tug-of-war it's a tug-of-war between cardio and urinary right urinary wants to clean the blood cardio wants to keep things in the blood and deliver them around your body so reabsorption almost all of your reabsorption happens in the proximal convoluted tubule almost all of my shopping at my garage sale occurs that day like like practically before I even set it out on the tables I changed my mind like right away the proximal convoluted tubule is where we have that's why it's so twisted it's where we have plenty of time to say ooh there's something in there that's good I don't want to pee that I want to keep it so we reabsorb it back into the blood so this is just kind of introducing us to these terms how does all the secretion and reabsorption take place so secretion remember is putting it into the urinary reabsorption bringing it back into the blood as always it has to be capillaries remember when we did the blood the arteries the veins the venules the arterioles they didn't have fenestrations they didn't have holes right nothing leaves a vein nothing leaves an artery the only time things can go back and forth in the blood is at the capillary bed that's why we drew the capillary exchange and all that stuff before with cardio so there are capillaries that are surrounding this nephron loop and I never add them to any of my drawings because then it's they're so crazy cuz they just like lay on top of it like a vine around a tree like sometimes a vine gets so thick around a tree can you see the tree well these peritubular capillaries that you can hardly see the nephron so peri means around like a perimeter fence tubular just comes from this fact that this is the tube right the nephron loop is it too so again think of the job of capillaries the job of the capillaries is to let stuff go or bring stuff back so things are going back and forth from these capillary beds so how does blood get to or from these capillaries well it's going to depend on diffusion like everything else in this class moving things from high concentration to low concentration and blood pressure as we had before so this picture here is showing that capillary so see the a ferrant arteriole bringing the blood in to Bowman's and then the efferent bringing it out and then it becomes the peritubular capillary that wraps around especially the twisty part of the nephron so those capillaries are there to say hey I'll take whatever you want so if there is something good in that proximal convoluted tubule that wraps around and gets all gnarly and twisty if there's something good in there I have plenty of time to reabsorb it back into the blood I have plenty of time to suck it back into that peritubular capillary the peritubular capillaries wholly because it's a capillary which means if there's sugar in there I have time to take it back and put it into the blood if there's amino acids in there I have time to take it back and put it into the blood the path of blood flow then goes descending aorta then the renal artery comes off of that remember we had that with the first lab practical a ferrant arterial which is just the little arterial delivering blood into the kidney the ghulami ler s which is a capillary bed the efferent arteriole brings the blood out and then the blood wraps around the nephron loop or renal tubular nephron however you want it to become the peritubular capillaries then eventually the renal vein and the inferior vena cava so Bloods going round and round and round like it always does so overall the nephron is very very twisted okay so for our drawings I want you to draw it like I had it drawn like kind of straight but if you look this guy kind of is twisted on itself this has an important function that will care about later but right now every drawing of the nephron is like the one I did where it's a little more straightforward instead of this kind of twisty thing but they always follow the same path proximal or Bowman's capsule proximal convoluted tubule descending a sending distal convoluted tubule collecting duct they always follow that same order so on my drawing I had added FRS so there are three crucial steps to making urine filtration reabsorption secretion filtration reabsorption secretion filtration reabsorption secretion F RS so this is like BCS on the heart this is like scr on the eye like it's not a word even though it kind of spells first FRS even though that's not how you spell first but you've got to know this FRS you've got to know this in order so this is how we make urine filtration reabsorption secretion so if you look at this diagram here I like it because they tried to keep it simple now we're gonna spend a lot of time on this and we're gonna repeat ourselves and I'm gonna repeat myself a zillion freaking times because I know this is hard so you're gonna have moments that you're gonna go I have no idea what's going on it's going to come together just got to have patience okay so the AVA if you look at this picture you can see the a Ferren arteriole bringing the blood into the globulars and the efferent arterial the blood leaving so that's the cardio right so the blood is running in and out of Bowman's capsule to get cleaned so that's happening really really fast right so Bowman's capsule is shown there and letter A is filtration if you look at the little key there the little arrow so filtration like making coffee you put a coffee filter to get your flavorful coffee goodness right we're filtering the blood we're cleaning the blood so filtration is happening at Bowman's capsule and so that's our first step we are sending the dirty stuff the skanky stuff from the blood to the urine so that's filtration going from the blood to the urine we're filtering out the gross stuff then in the proximal convoluted tubule which is that first stretch here we have letter B so if you look at letter B it's showing how things are going from the urinary back to the blood because the peritubular capillary is what they're showing in this picture so filtration was going from the blood to the urine reabsorption is going from the urinary system to the blood so reabsorbing as I said previously reabsorbing is reabsorbing things back into the bloodstream you never had any intention of getting rid of that stuff it's just you accidentally grabbed it because you were cleaning the blood so quickly so this is me shopping at my own garage sale saying oh yeah I'm putting that back in my closet and then let her see secretion if you look at this picture secretion is going from the blood back into the urine secretion is me being sitting there at my garage sale going oh I kind of like this I'm getting rid of stuff and I'm making some money so that day I go back into my closet and grab more stuff secretion is a last-ditch effort when there's something skanky in that blood you can still dump it directly into the urn so I know it's exhausting it's takes these back sees it's changing your mind three times but that's what chicks do right if you're a woman you totally relate to this so filtration we're taking it out of the blood reabsorption we're putting it back in the blood and secretion we're taking it back out of the blood but it's so crucial to make sure we're pulling all of the toxins out of our blood so we don't die but also making sure we're not peeing sugar and peeing amino acids and getting rid of good stuff so it is crazy but making urine is complicated SRS starting with the F so glom Euler filtration so filtration occurs at Bowman's capsule so what causes filtration to happen blood pressure just like before we've already done this with capillary exchange remember when we drew capillary exchange and I said on the arterial side of the capillary bed that blood is pounding into that capillary bed and that blood is desperate to leave so the artery the artery blood has a lot of pressure in it the blood the water everything in there is really crowded so remember as soon as it got to the capillary bed and there were those holes all of a sudden the water inside your blood can escape so that's the same thing that's happening now a good strong blood pressure sends blood in the afferent arteriole it sends it into the globular as' which has holes in it which is going to force stuff out into Bowman's capsule just like before the cells and the larger proteins don't filter so just like before with coffee I said you use a coffee filter to let the coffee flavor goodness get through but you don't want your coffee grounds to get through because no one wants chunky funky coffee right so our capillary bed is designed with fenestrations but we don't want those fenestrations so big that they let the blood out if the blood leads the blood is not blood right so the cells and those large proteins like the albumins and fibrin engines those guys stay behind so things filter according to size these are really tiny little holes just like making coffee you get filter according to size so we call this filtrate because there's still good stuff in it so the stuff the filtrate that gets into Bowman's capsule and the proximal convoluted tubule we don't call urine yet because we're about to take these backsies we're about to pull back a lot of that good stuff back into the blood so it's not technically urine yet so that was filtration we filter we pull off all of this gank and unfortunately some good stuff too so that's our F now we have our our reabsorption so during reabsorption like shopping at my own garage sale I never meant to get rid of any of that stuff I accidentally pulled out some good stuff when I was in my cleaning frenzy so we're in a cleaning frenzy at Bowman's capsule we accidentally grabbed a lot of really really good stuff well now we want to reabsorb it back into the blood and so this is moving things like sugar and putting it back into those peritubular capillaries putting it back into the bloodstream we do most of this at the proximal convoluted tubule in the descending limb and then we have the s tubular secretion this is additional stuff that you want to get rid of this is that last ditch like I said I'm chasing my trash man down the street this is the last ditch effort that there's something skanky in that blood that you can dump into the urine so secretion is more for things that you're always getting rid of you're always secreting K and H so potassium and hydrogen ions these are things were always secreting so this is like things that are in your trash every week every week there are wine bottles in my trash yeah there are and cat litter like always so I don't have to go out and say excuse me trash man sir there's wine bottles and cat litter in there like I'm sure by now he knows that my trash is gonna be heavy with cat litter and wine bottles okay so these are things I'm always getting rid of okay so these are waste products that your body always has in the blood so you're always dumping it into the urine so secretion is just something that's kind of almost standard it's like you're always secreting these things so potassium you're always secreting potassium because if you remember we talked about heart contraction especially too much potassium can weaken your heart and affect heart rhythm so you want to get rid of excess potassium well most foods that we eat have potassium in them so getting rid of potassium every day is important because your the next meal you consume you're probably gonna get plenty of potassium hydrogen ions hydrogen ions are produced from breaking they're it's like an organic acid so from breaking down proteins well you're always breaking down proteins or you're dead so excess hydrogen ions can acidify your blood and kill you so you're always wanting to get rid of those so these are just two things like cat litter and wine bottles these are two things I'm always getting rid of potassium and hydrogen so we're always dumping these into the filtrate we're always getting rid of these into the urine so fr-s filtration reabsorption and secretion