 Okay now that we have discussed the blood flow we're going to move on into the nephron. The nephron is the functional unit of the kidney so it is in charge of performing the functions of the kidney which is filtering the blood so that you can reabsorb the things that you want to save while secreting into it the things that you wanted to get rid of so that you can eventually excrete the waste. Okay filtering means that just as before when the blood goes into a capillary there's going to be hydrostatic pressure that's forcing the fluid out through the sieve into its surrounding tissues. Whenever the blood is forced out of the glomerulus okay all those fluids, solutes, things that can fit through those filtration barriers they're going to be caught by the first part of your nephron which is called the Bowman's capsule. So you can see those two are closely associated together. Glomerulus is going to send the fluid out and it's going to be captured by the Bowman's capsule. Now there are some Starling forces that are at play here. We're not going to get into that right now we're just going to go over the anatomy but there will be another video that goes through Starling forces so please see that one in relation to this process of filtration it is very very similar. Okay so Bowman's capsule is the first structure that is going to catch the filtrate once it is made. I do want to make a special note that the Bowman's capsule is referring to the capsule that surrounds the glomerulus. Oftentimes you'll see a term called renal corpuscle. A renal corpuscle is referring to the glomerulus and the Bowman's capsule together. Okay so if you can imagine putting your hand as a C okay that is the Bowman's capsule. Make your other fist or your other hand into a fist and call that the glomerulus. Okay so you can see Bowman's capsule is the C glomerulus is your hand in a fist and when I put those two things together I make what's known as the renal corpuscle. Okay so that's to kind of clarify that term. Once the filtrate has been made and caught by the Bowman's capsule it is then going to be transferred down the proximal convoluted tubule also abbreviated as PCT the proximal convoluted tubule. Once it moves into this area the main function of this area is reabsorption so we're going to be reabsorbing about 99% of the filtrate that we just made. So 99% of things like water, glucose, amino acids, different ions those things were going to be reabsorbing and when I say reabsorbing I mean saving them from possible elimination. Your body accidentally filtered these out because they were the right size to fit through the sieve but you didn't want to get rid of them. You wanted to save them so we call that reabsorption and that's the main function of this area is reabsorbing things like water, glucose, ions, etc. So we're saving them we bring them back into the blood and they're being reabsorbed into those closely associated paratubular capillaries right there in the cortex. Okay from there the filtrate is going to travel down the descending limb of the loop of Henlea so descends down. This limb is very thin and so here we have reabsorption of water remember reabsorption is saving the good stuff so we're saving the water from the filtrate. Once that water moves out of the descending limb it is going to be absorbed into the vasorecta which is the capillary bed in the medulla. Okay in our nephron the filtrate continues to move and moves up the ascending limb for the loop of Henlea because it moves up the ascending limb you're going to transport out various ions like sodium potassium chloride and as you pull these solutes out of your ascending limb they are going to be put into your vasorecta as well. So your vasorecta is helping to reabsorb these components of the filtrate save them if you will back into your blood. Okay now we move into the distal convoluted tubule once again we have more reabsorption that happens here we also have secretion a lot of secretion that happens here so creation is getting adding things to the filtrate that you wanted to get rid of but you haven't been able to so far because it was too big to filter so a good example of these are things like toxins or drugs or even something that's beneficial like antibiotics your body doesn't make antibiotics therefore you will get rid of antibiotics they're not things that are naturally made therefore they're going to be removed from your body so those antibiotics are secreted from the peritibular capillaries into the distal convoluted tubule they were too big to be filtered at the glomerulus they need to be removed so we're going to secrete them at this later part. Okay this is why when you are sick and you take antibiotics you don't just take one antibiotic and be finished one penicillin pill done it doesn't work that way what you have to do is take a course of antibiotics and that is because you're secreting them in the nephron you're getting rid of them and they're showing up in the urine. Okay after that we move into the collecting duct with the collecting duct this is kind of a unique structure we do have some reabsorption and secretion that happens here as well the main function in this area though is when we talk about anti diuretic hormone the hormone that's released when you're dehydrated this hormone is going to act on the collecting duct and it's going to make the apical or side of the cells that's the top facing the filtrate it's going to make that apical surface permeable to water so that water is going to be able to penetrate through the cells of the collecting duct and you can reabsorb that water when your anti diuretic hormone is is high so that means that when you're dehydrated you're going to be able to reabsorb most of that water back. Okay so so far we've talked about the nephron with the reabsorption secretion all of this so that we can create our end product which is going to be urine. Okay one analogy I'll use this terminology does get a little bit confusing especially when you start talking about directions of movements think about it like spring cleaning you're going to your closet and you're going to say you know what all of this has to go you go in and you reach in and you grab an armful of clothes and throw them on the bed okay that is filtration you have just a bulk movement of materials from one area to the another so we're filtering out all those clothes all right that's what happens in the glomerulus to the Bowman's capsule. Once we pulled all the clothes out now we can start looking at them more closely and saying oh I didn't mean to get rid of that and oh I still wear this and you start pulling some of those clothes out of the pile to put them back in your closet right so you're reabsorbing them you're saving them from possible elimination okay as you're putting those back in you notice that maybe there's a sweater that's crumpled up in the corner something that you don't really wear and you want to get rid of so you're going to reach in and you're going to grab that and throw it on to the pile that's secretion you're taking something that you missed with filtration but adding it to the pile for elimination okay after you finish the whole process reabsorbing everything that you wanted to keep then you're left with a pile of clothes that you don't want and those is what becomes your elimination products that's what will become in your body urine so the stuff that you wanted to get rid of the stuff that you've added to it to get rid of that's going to be the urine product.