Urine formation

so let's have a quick look at how the blood in our body moving through into the kidneys gets filtered and ultimately forms urine so we're going to have a look at urine formation so a couple of things you need to go through the previous videos and understand what a nephron is and understand how the blood supply gets to the nephron and how that blood supply starts to become filtered okay so just as a very quick recap we're going to go through some functional anatomy and we're going to name different aspects of this nephron so remember this is the functional unit of the kidney this is the filtration unit is the nephron and what you can see is a blood supply coming through now this blood supply is it here to give this nephron oxygen this blood supply is coming in because here is a capillary bed now remember this capillary bed is called the glomerulus remember glomerulus means ball of yarn so you've got a blood vessel coming in that branches into this gun Miralles capillary bed and this is where filtration happens and remember the tubules here of the nephron contain what's just been filtered from this blood and so this is called filtrate and if this filtrate remains in the nephron all the way through it comes out as urine okay so urine formation has to do with this filtration process here okay and what's happening to this filtrate all the way through the nephron that's what we're going to discuss today but before we begin let's label some things so that you know exactly where we are so first thing is that we have blood coming into or towards this nephron remember this is called the afferent arteriole and afferent arteriole comes down into a capillary bed which we call the glomerulus the glove mirrorless that continues down into not a vein remember but an artery another arterial which are called the efferent arterial and you can see that the efferent arteriole continues and it basically hugs all the tubules of the nephron and we call this peri tubular capillaries okay why does this capillary bed here hug the tubules of the nephron because remember what gets filtered into the nephron doesn't necessarily stay in the nephron 99% of this filtrate that gets into the nephron actually gets thrown back into the blood and it gets thrown back into this peritubular Network okay so that's labeling the blood supply let's label the nephron now I'm not going to write the labels down because I'll have to rub them out but what you can see is the first part here we call the glomerular capsule okay so that's the glomerular capsule looks like a little pac-man the first portion of the tube you'll closest to the capsule is called the proximal convoluted tubule proximal because it's closest to convoluted because usually you'll see it as these squiggly wavy lines but I've just drawn here straight for simplicity sake so proximal convoluted sugar you've got the loop of Henle also known as the nephron loop which is made up of the thin descending loop of Henle and the thick a sending loop of Henle then you have the distal convoluted tubule and then you have the collecting duct okay now when it comes to your information what you're going to find is couple things that urine formation is actually equal to a couple of things your information is equal to glove Marilyn filtration what that means is remember our ultimate goal is your information here so we're going to talk about how we can get from here to here firstly we need to start off with glomerular filtration let's write that as number one so you know from previous videos that as the blood comes through that there is a relatively high pressure here the glomerulus that now remember that at most capillary beds that pressures around about thirty twenty to thirty millimeters of mercury so what's that mean there's a hydrostatic pressure are pushed behind the blood pushing stuff out of the capillaries at the tissues of your body but once you get here to the kidneys this capillary bed is different and the push is greater it's fifty millimeters of mercury okay so you have this very strong push pushing substances within the blood plasma throat okay now remember proteins do not go through and cells do not go through why while cells are too big so white blood cells red blood cells and platelets they're all too big to move through this filtration membrane or I should say filtration membranes proteins well the proteins are actually small enough to get through but there is a negative charge at this filtration membrane and remember proteins are negatively charged and like charges repel each other so in a healthy filtration membrane proteins are repelled and stay in the blood okay first thing so filtration now off the blood that comes down through into here what you'll find is so think about cardiac output right so your heart will contract and relax contraction will exit as it does this it pushes out blood right so every time it contracts it pulls it pushes out around about 70 ml of blood from one ventricle so left ventricle squirt 70 mils of blood and it does that about 72 times a minute so if it squirts out 70 mils in one go times 72 in a minute that gives you around about five liters a minute so your heart pushes out from one ventricle five liters a minute that's the cardiac output and that five liters a minute goes to the whole body right so only a fraction of that's going to get to the kidneys 20% of that will get to a kidneys what's 20% of 5 blenders 1 litre so 1 litre of blood goes to the kidneys every minute now that 1 litre of blood is made up of all these different components is made up of cells it's about proteins it's made up of blood plasma and so forth what gets filtered only plasma right because the cells and proteins don't go through so of that one liter what you'll find is 60 percent of it is plasma so what's 60 percent of one liter six hundred mils so you have six hundred mils of blood plasma that's coming through that can be filled in it now of this how much of that six hundred mils actually goes through twenty percent okay so 20% of this six hundred mils gets filtered through how what's twenty percent of six hundred it's 120 mils so every minute every minute in here you have a hundred and twenty mils being filtered through so that means you create 120 mils of filtrate every minute in both both your kidneys together so not one nephron this is representing on both your kidneys okay so 120 mils a minute is what your kidney creates of filtrate now think about that 120 miles a minute now let's do some very quick math how many minutes are there in an hour 60 minutes so now okay how many hours are there in a day 24 so 60 times 24 is 1440 minutes okay 1440 minutes in a day but and you have 120 mils per minute being mowed so 120 times 1440 and this is something that I wrote down before here's 172 800 mils per day your kidneys create one hundred seventy two thousand eight hundred mils of filtrate per day that is nearly that's approximately 175 litres a day but you know that all this 100 that this is 175 litres you know PA you know P at 175 litres a day you actually pay out round about 1.7 liters per day it's something 1% so of everything that you filter through you only pay 1% so let's just say here 175 litres per day or by the time it gets to here it's only 1 point 7 litres a day so what does that mean that means of everything you've filtered 99% of it 99 percent of it goes back into your blood back into your body okay so that means that in order to create urine we need to add something else to this equation we said urine formation is equal to ik lamella filtration which is 120 mils per minute - tubular reabsorption right so this is that's the tubules and it's going back into the body so it's reabsorption not absorption because you've already absorbed this stuff before in the gr to your reabsorbing it back into the body okay so this is step two tubular reabsorption so let's just leave this a bit better here step one filtration and this is step two tubular reabsorption so tubular reabsorption you've got all these to do the proximal convoluted tubule you have the loop of Henle and the distal convoluted tubules are collecting that in actual fact that happens all throughout okay so if you'll have a look here you'd find that and the proximal convoluted tubule 65% of what's just being filtered goes back into the body and the proximal convoluted tubule 65% okay at the loop of Henle that you'll find is that 15% goes back into the body okay so what's that so far certainly only 80% okay here at the distal convoluted tubule you'll find that another 50% gets reabsorbed back into the body that's 95% and here at the collecting ducts four to five percent that equals 99 percent to 100 percent okay because remember 99 percent of what just got filtered goes back into the body 65 percent of it happens here at the proximal convoluted tubule 15 percent happens at loop of Henle 15 percent happens at the distal convoluted tubules and 45 percent happen at the collecting ducts now the great thing is your body can't alter this so it's not always going to be 65 percent 1515 and 4 or 5 percent if you want to reabsorb more this percentage can go up if you want to reabsorb less it can go down and vice versa with all these ok so for example if you want to reabsorb all why don't you can release 88 antidiuretic hormone which makes you reabsorb more water here at the collecting ducts if you want to reabsorb more sodium into your body you can release out dosterone and this can tell the process of the distal convoluted tubules to reabsorb more sodium okay so your information is equal to glomerular filtration - tubular reabsorption so let me just do some more room so does that make sense why it's - because we remember 120 mils per minute here but we need to - what's going back 99 percent so now we have 1 point 2 mils coming through run 120 mils take 1% of that is 1.2 mil because that 99% scrub back so now we only have by the time we reach here where they have one point two mils per minute which is one point seven liters a day ok coming through a one point two litres a day now that's not the end of it because your nephron can actually take some stuff from the bodies not just give substances to the blood it can receive substances the blood and this is called this is number three and this is called tubular secretion now why is it called secretion is because it's secreting substances from the blood into the tube you'll people get confused about reabsorption or secretion and so forth whatever is in the tube you need to remember is essentially being outside the body this is what's going to be pin out if it stays in the tube so if it goes fund the blood into into this tube you'll it's secretion and this is number three tubular secretion and again this can happen at different stages or different parts of the nephron okay but usually it's not a huge amount okay not a huge amount so what can we see we can see when it comes to urine formation it's made up of three different components glomerular filtration which is about 120 mils a minute chabela reabsorption throwing back 99% of all that stuff back into the body okay and tubular secretion throwing out some stuff this stuff is going to be for example urea for example this is urea can be thrown back into the tubules to be excreted or to be paid out so this is your information

Channel: Dr Matt & Dr Mike

Views: 224,539

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Id: n2yXVKa1b_Y

Length: 15min 32sec (932 seconds)

Published: Tue Oct 04 2016