hi everyone and welcome to learn a little biology for free with miss a stroke if you aren't already a subscriber make sure to click below to subscribe to keep up stay on all the latest videos and if you do enjoy this video give it a thumbs up so in this session we're going to be going through the year 13 topic of filtering and reabsorption in the nephron if you want to make some notes as you go get some paper at the ready pause it as we go through so what we'll cover in this video is the structure of the nephron function of the renal capsule proximal convoluted tubule loop of Henle distal convoluted tubule and the collecting ducts we'll go through how ultra filtration occurs and where it happens and what selective reabsorption is and again where it happens so starting off then just with an overview of the kidney you don't actually need to know the structures in detail all you need to know is that the filtering and osmoregulation which we'll be in a later video occur in the nephrons the nephrons are found within the medulla which is just here so the nephron sin what they actually are is these long tubules which are surrounded by capillaries and you have about 1 million nephrons in each of your kidneys so the structure of the nephron just zooming in on one here you have as we said the capillaries surrounding them and leading into the nephron you have an afferent arteriole which then branches into lots and lots of small capillaries and that is what we call the glamorous so that there is lots of capillaries the dermal arrests now those lie inside of this capsule which is called the renal capsule sometimes called the Bowman's capsule or on this picture here the glomerular capsule but the 8th way spec calls it the renal capsule so that's what I'll be using after that it then leads into the proximal convoluted tubule which we can see winding around here into the loop of Henle then up to the distal convoluted you'll and the collecting duct so we'll go through what happens at each of these positions in the nephron to create urine so that's the overal function of the nephron is to create urine and that is because you're filtering the blood to remove waste so any excess water urea is going to be removed useful substances will be selectively reabsorbed back into the blood so the urine will only contain water excess water dissolved salts of mineral ions urea and any other small substances that can be filtered out so it could be hormones or excess Mitte means in a healthy person you should never find proteins blood cells or glucose and this is actually from GCSE as well the knowledge of knowing why you would never find a protein or blood cell in urine and why I'd never find glucose so just as a reminder the proteins and blood cells are both too big to be filtered out so they'll always remain in the blood glucose does get filtered out but all of the glucose is reabsorbed by active transport in the Selective reabsorption stage which occurs in the proximal convoluted tubule or PCT for sure so an overview first of all of all of this filtering and reabsorption step one is in the gloomy loris you have this ultra filtration of water and small molecules due to high pressure and that will force out the small molecules and water into the renal capsule then you'll have your filtrate which is called the lamellar as filtrates passing into the proximal convoluted tubule and at this stage 85% of that filtrate gets reabsorbed back into the blood the loop of Henle is the next stage and at this point the sodium ion gradient is maintained and that is to enable water to be reabsorbed by osmosis into the blood and then the final step we've got our distal convoluted tubule and collecting duct where further water is removed by osmosis or diffuses out bars maysa and is reabsorbed back into the blood and any of the remaining liquid in the collecting duct goes on to form urine so let's go through each of these stages then in detail starting with the ultra filtration so at this point we have blood entering through that reference arterial and the arterial splits into lots and lots of smaller pillories as we said at the start that's what the gloominess is because you've gone from a wider lumen or a larger space into lots of smaller narrower capillaries you end up creating this hydrostatic pressure so that high pressure forces out small molecules of water and it has to be small because it has to be small enough to be able to fit through the tiny gaps in the cells in the epithelium of the Penry's that forms the glamorous filtrate so we call it glamorous filtrate because it's formed from the motherís staying in the blood you'll have large proteins and blood cells because they're too big to fit out the gaps so they will then pass out of the efferent arteriole and continue to circulate around the blood in the body so just to show you where that is happening what zoomed in here we see our afferent arteriole splitting to make the gloom Alerus and then leaving we have the efferent arteriole so the ultra filtration will be occurring here and the glamorous filtrates will be going into this renal capsule so just here so that's the ultra filtration so that glamorous filtrate is now going to flow and pass into the proximal convoluted tubule and this is where selective reabsorption happens so 85% of that filtrate that's just been created gets reabsorbed back into the blood at this stage and the proximal convoluted tubule so we're going to go through how that happens before we do that I'm just going to point out some adaptation genes of the cells lining the proximal convoluted tubule and that's what we're looking at here so this bit is the lumen so that is the space in the middle that the filtrate passes through this bit proximal convoluted tubules cells so those are the epithelial cells we then got a slight gap which we call the interstitial space which is the gap between the proximal convoluted tubules and the capillaries that surround it and then here we have our capillary so the two key adaptations are the proximal convoluted tubules cells have all of these micro villi and that creates a really large surface area to maximize the reabsorption of glucose there's also lots of mitochondria within these cells and that's because energy is needed for active transport at this stage so those are our adaptations what we need to occur next then is how selective reabsorption happens so it's step one the concentration of sodium ions in the proximal convoluted tubule which I've just abbreviated to PCT and is low within that cell that is low because sodium ions are actively transported out of the PCT into the blood stream so that is why we have all of these mitochondria to provide energy for the active transport sodium ions out of the proximal convoluted tubule cells into the blood the impact that has it is the cell here has a very very low concentration of sodium ions compared to the glamorous filtrate which is going to be flowing through the lumen so that then means that the sodium ions can move into the proximal convoluted tubule by diffusion going down their concentration gradient now the protein that the sodium ions diffuse through is a co transporter protein and that particular protein both sodium ions and glucose attach to so when that's so my own attaches so does glucose and therefore that is how glucose gets from the glamorous filtrate into the proximal convoluted tubule so the final step is you'll now have a large concentration of glucose within your proximal convoluted tubule cell and because you've got a high concentration compared to the Bloods you have a concentration gradient so the glucose can diffuse from the PCT cell into the bloodstream and that is how all of the glucose is reabsorbed that was initially filtered out now one thing I just want to emphasize is reabsorbed if you just say absorb that is incorrect because absorb means it's the first time it was taken in this is reabsorption because it was already in the blood then it was filtered out but then we take it back into the blood so whenever you are talking about the kidneys you will only ever be using the term reabsorb so next then the filtrate would have passed through the PCT and now it's leading into the loop of Henle and at this stage the function of the loop of Henle is to maintain a sodium iron gradient so that's what we're going to have a look at but first of all just see the structure in more detail so the loop of Henle we described as being made up of two limbs so we have an ascending limb and a descending limb and this is named after the direction that the filtrate is moving in so this side here is the ascending limb because at that point the filtrate is moving up its ascending up through the loop of Henle and you can see on the diagram that it has really really thick walls and because of that it is impermeable to water so no water can actually move out of the loop of Henle in the ascending limb which is what these arrays are representing so demands are going to be actively transported out we'll come on to that the descending limb is where the filtrate is moving down the loop of Henle the walls are much thinner and therefore they are permeable to water and this is where the water is going to move out by osmosis to be reabsorbed into the blood so to go through the stages then of what's happening at the loop of Henle step one there are mitochondria within the walls of the ascending limb and that's to provide energy for the active transport of sodium ions so sodium ions are actively transported out of the filtrate into what we call the interstitial space which is the space between the nephron and the pillories in doing this there's an accumulation of sodium ions in this interstitial space in the medulla and it creates a really low water potential now the numbers that you can see here in the loop of Henle and in the interstitial space that is representing water concentration so we're having a low water concentration here we've got more sodium and moving in so we have a more concentrated solution or a lower water potential because there's a lower water potential that means the water in the descending limb of the loop of Henle will move out by osmosis into the interstitial space and then will be reabsorbed into the blood so that's how the water is reabsorbed into the blood fine things point on the loop of Henle is step four down here and it's at the very very base of the ascending limb because there's not a very dilute solution or very low concentration of sodium ions at the base some of the sodium ions will move out by diffusion so the next step in our nephron we've gone through the renal capsule proximal convoluted tubule the loop of Henle next is the distal convoluted tubule and the collecting ducts and at this point the filtrate which is going to be entering the distal convoluted tubule is at a very very low concentration or it's very very dilute because lots of sodium ions have already been actually transported out so the liquid that is entering the distal convoluted tubules very dilute so that daily liquid is going through the distal convoluted tubules and the collecting ducts but the section of the medulla within the kidney that those two parts of the nephron are in is actually very concentrated so the final step that happens is even more water is going to diffuse out from the distal convoluted tubule and the collecting ducts so all of the remaining liquid in the collecting duct is what will form the urine so that is the whole process of ultra filtration and reabsorption and how urine is created an example of an application question that comes up to do with the loop of Henle is the one we've got here so in the past students have been asked to suggest how the length of the loop of Henle will differ for a desert animal compared to a human and then you'd be asked to explain why so you said the loop of Henle the function is to maintain the sodium ion concentration gradients so that more water can be reabsorbed so if they're in the desert they're gonna need more water to be reabsorbed and therefore they'll have a longer loop of Henle so that more sodium ions can be actively transported out and therefore more Wars will be reabsorbed so if you've got this longer loop of Henle there's a larger surface area for sodium ions to be actively transported out so you'll then have even more sodium ions lowering the water potential more water will move out by osmosis and that gets reabsorbed into the blood and as a result they get more water going back into the blood and very very concentrated urine which were a desert animal that is essential for survival because their environments as fairness of water so whatever words they do get from their food or from their water it's essential that gets reabsorbed back into the blood rather than lost and wasted in the urine so just to summarize that the front is made up of the renal capsule the PCT loop of Henle DCT and collecting ducts and they're surrounded by capillaries the glomerular filtrate is created in the renal capsule glucose and water are reabsorbed back into the blood by the PCT the sodium ion gradient is maintained in the loop of Henle and that's to enable water reabsorption and then further reabsorption happens in the DCT and the collecting ducts so that is it for filtering reabsorption in the nephron make sure to watch the next video on osmoregulation so you can see the negative feedback and homeostasis of how the permeability of the distal convoluted tubule and the collecting duct changes and depending on how much water you have in your blood if you want to have a go at some practice questions attetion knowledge head over to miss Esther ich and if you aren't already subscribed make sure you click the button to subscribe and give it a thumbs up if you have found this video helpful you