Nephron Function, Part 1

welcome this video is about nephron physiology and urine formation it's going to be a fun one it will probably take two videos but we'll see maybe I'll get it done in 20 minutes or less so nephron physiology and urine formation ready here we go okay so the first thing we'll talk about um are is is Bowman's capsule and what you're looking at here this is a nephron it's made up of Bowman's capsule the proximal convoluted tubule the loop of Henley the distal convoluted tubule and the collecting duct and any fluid that is able sorry we got a little blurry here any fluid that is able to make it out the bottom of the collecting ducts will go into What's called the renal pelvis and then it will go down a ureter and to the bladder so anything that makes it out of this area here will end up as urine all right so first of all Bowman's capsule we'll do that with a yellow highlighter it was named after one of the early anatomists that described the structure and Bowman's capsule is where filtration occurs so we can put that over here this is the site of filtration so it's filtering blood all the time and brace yourself because these are some giant numbers look at this about 125 mils per minute is filtered by all the nephrons in your kidney every minute and that comes too if you look at the course of 24 hours about 200 liters a day now of course these numbers can vary a little bit but for for the maximal health of your kidneys there are a variety of ways that the kidneys can make sure that it stays at 125 mils per minute if it drops below that too much that's bad for our health and if it goes too high above that that's bad too so we want to hit that sweet spot of about 125 mils per minute of course most of that doesn't actually end up being urinated maybe a mil a minute if if that so most of this is going to end up going right back to the blood so this is where students often like kind of blows their mind a little bit imagine if there's a bunch of blood right here and a lot of the water and the salts and the glucose in the blood enter these tubes imagine it's like a water slide and you enter the water slide and then the fluids move through but as they're moving through the fluids are actually able to go out of the tube and back into the blood we call that reabsorption so as you can see if you only make about one mil of urine a minute not 125 then most of it is being reabsorbed back into the blood and that's really going to be the story so it's a very expensive process to filter but it's important because it makes sure that any impurities in the blood are removed from the body okay so what are some of these things that are going to be able to go from the blood into Bowman's capsule and start going through the Nephron well water but not all of it because if you've imagined that there are these capillaries here so we'll put an afferent arterial coming in and then what's called a glomerular capillary bed and then an efferent arterial going out if all of the water that was in this blood vessel here were able to go into the tubule well what would happen right you would end up with no water in the exiting blood vessel and then blood blood cells couldn't move the blood would not be blood anymore it would just be blood cells so that would be really dangerous and fatal so instead some of the water comes out depending on how high the pressure is so it kind of squirts it out but some of it stays too and we'll talk more about that too okay so water can come out and nitrogenous waste can come out nitrogenous wastes are going to include primarily these three things creatinine and creatinine is evidently so bad for our body to have in high amounts that 100 of it that gets filtered will end up coming out in the urine there will not be any of it that is reabsorbed in a healthy kidney and it is a byproduct of making ATP in a hurry so if you imagine like a football player and they're coming off the line or they're starting up at a Sprint then that power they need for the first 10 seconds the waste product from producing that quick ATP power is called creatinine and then it goes out of the muscle cells and to the kidneys and then it's filtered and it comes out in our urine another nitrogenous waste just meaning it has a nitrogen in it is urea and this is actually how urine gets its name because there's so much urea in it and a slightly more I mean I guess I would just call it a slightly more uh concentrated version called uric acid and these are can actually crystallize out in if they're too high in the body and that can cause gout like in the big toe for example okay what else can get filtered well electrolytes can I'll name a few just to get your jog your memory about electrolytes sodium potassium calcium magnesium all of these are electrons electrolytes that are freely filtered and depending on how much salt we need in our body maybe how much we need to raise our blood pressure most of this sodium can either leave or some of it can be reabsorbed actually lots of it will be reabsorbed into the body we're not as good at reabsorbing potassium in fact we reabsorb very little of it but we can get rid of extra which is called secretion and we'll talk about that later too and though that's important when we talk about what kind of diuretic is prescribed you might have heard of what's called a potassium sparing diuretic and we will talk about that too later okay so these are all electrolytes I hope it doesn't seem like I'm going too slow in this video but there is a lot to cover on this and it really um I think is worth the time to take a long time to go through how the nephron works so that you can really appreciate it glucose of course can be filtered but in a healthy person the glucose shouldn't end up in the urine same with amino acids and then acids and bases is called bicarbonate and then something that makes the urine yellow if you've ever wondered why it's because of a broken down product from that's left over from the pigment and red blood cells and it is called Euro Chrome it's a basically a form of bilirubin or a color for it I guess and this is what gives urine it's yellow color okay oops I'm going to go ahead and put bilirubin here because I know you've all heard of that but it's and bilirubin is yellow I think eurochrome is the specific name for the pigment that's in it okay so um not everything should get to come out of the blood and go into Bowman's capsule though so let's also have a list of things that can be filtered so things that were filtered and then things that can't be filtered so to do that let's put filter with the big big cross thread so no filtering allowed for these things these are things that if they're in the blood and they're passing into this glomerular capillary bed even if the pressure is high in there these things can't get out into the water tube things like red blood cells and white blood cells do you know why they can't get filtered it's really just because they're too big and it's the same with big plasma proteins like fibrinogen these things are all just too big same with hormones or a lot of hormones I should say like insulin so those things that are too big can't fit through the little gaps in the red blood cell or in the capillary cell wall and can't get into Bowman's capsule okay so now I also want to take a moment to Define some blood vessels for you so we'll just keep using our black pen this blood vessel right here is called the afferent arterial and arterial is just a very tiny blood vessel and whenever you see afferent it means going towards something so like in the nervous system we learned about afferent neurons are sensory neurons they're going to the brain well in this case the blood vessel is going to Bowman's capsule and then in Bowman's capsule it becomes a very tiny capillary bed called the glomerulus usually I write glomerular capillary bed when I'm a little tight on Space right here and that's where that's where the filtering actually occurs and then this exiting blood vessel is called the efferent arterial it's really important for healthy kidneys to always filter 125 mils per minute so if there's not enough filtering happening then the afferent arterial can dilate and let more Blood come into Bowman's capsule and more fluid can be filtered if too much is being filtered then the after arterial can actually constrict down and protect the delicate glomerulus from the high blood pressure all right so trying to move along so that I don't lose you to La La Land let's go to the next part and that's the proximal convoluted tubule I'm going to make it Orange okay well right about it up here proximal I'm using Orange convoluted tubule or the PCT okay so what happens in the PCT well first of all we have to try and figure out its name too the word proximal means that there's probably a distal right sure enough yeah there is a distal convoluted tubule so what does the proximal mean and what does the distal mean well the proximal means that this convoluted tubule is closest to Bowman's capsule the distal convoluted tubule see is a couple sections later so it's farther from the from Bowman's capsule convoluted means twisty and tubule because it is clearly a tube so what happens in the proximal convoluted tubule well as it turns out tons happens here about 80 percent of what was filtered here will actually be reabsorbed [Music] so all almost all of the water almost all of the salts when we say reabsorbed we mean it goes from the tubule to the peritubular capillaries I'll just put caps so about a hundred mililiters that got filtered here is reabsorbed by the end of the proximal convoluted tubule and or if you want to look at how much for a day about 160 liters a day but you could tell this is not going to be enough to keep you from becoming dehydrated like if your nephron just ended right here you would still have 40 liters of urine in a day and that is impossible right some rare disease states that can happen like diabetes insipidus but more likely what we're looking at here is there must be a lot more reabsorption of water that happens later on especially in the collecting duct so we'll talk about that as we as we move along the tubule so about 40 so I'm going to put this symbol here it means therefore about 40 liters a day passes this part everything else already got reabsorbed so what does get reabsorbed what what do we really care about here well all of the glucose will get reabsorbed but you do have a transport maximum like how many molecules of glucose can be returned to the blood as they pass through and if there's so much blood sugar then it surpasses the transport maximum then you can lose glucose in the urine and so that's why diabetics can end up with glucose in their urine okay it's time for me to draw on here some paratubular capillaries so remember we have to get to the affirm arterial to deliver blood to Bowman's capsule and this will constrict or dilate to control how much is going to get filtered and then whatever isn't filtered here continues out of the efferent arterial and then the efferent arterial actually branches to become another capillary bed called the peritubular capillary bed and I'm just going to draw cartoon style like this so that you get the idea that it is surrounding all of the parts of the tubule and that's how it's able to reabsorb back into the blood oops I just messed up on my 3D sorry that's funny we will continue with the peritubular capillaries so something that got filtered right here interestingly enough so it's coming in the blood let's say um an atom of sodium or sodium electrolytes it's coming in here it's coming in here pressure's high in here so it pushes out of the blood vessel into the tube it's going along here going along here and then Boop just goes straight back to the blood again that it just came from that's what reabsorption is okay so what else gets reabsorbed well all of the amino acids in a healthy person should be if someone has protein showing up in their urine that's a sign that the glomerular capillaries are damaged and large molecules like proteins that normally shouldn't be able to come out could come out and then go through the tube then um adjusted I'm gonna put this for acidity adjusted levels of hydrogen and bicarbonate the purpose of that is if the blood is too acidic right here then it can secrete hydrogen into the proximal convoluted tubule and if the blood is too basic here it can actually reabsorb hydrogen ions back into the blood so they're reabsorbed and secreted as needed and also any creatinine that might not have been filtered here can be secreted from the peritubular capillaries into the tubule because remember I said that our body gets rid of all the creatinine as it passes through the kidneys okay so we're obviously going to need a part two with this and I'll pick up with the loop of henle in that

Channel: Science with Susanna

Views: 50,271

Keywords: nephron

Id: 9z37hTsiVbY

Length: 19min 13sec (1153 seconds)

Published: Thu Dec 17 2015