Lecture 8 - Structure & Function of the Urinary (Renal) System

so let's take a quick look at the kidneys and have a look at their location and their structure and then also have a look at the urinary system as a whole so when we talk about the urinary system or renal system we talk about the two kidneys that we have so remember the kidneys are this bean shaped organ around about the size of the hand to about the second knuckle they're connected to two ureters which you can see here are two tubes that travel down to the one bladder which is a storage unit for a urine and then one urethra which transports that urine from the bladder out to the external environment so again two kidneys two ureters one bladder one urethra okay now when we have a look at the location of the kidneys you can see that they actually sit relatively high up in the body now they don't sit towards the front they sit towards the back so they actually sit behind the peritoneum remember the peritoneal cavity is the cavity that holds the majority of the grt the gastrointestinal organs okay so in that you could say that the kidneys sit retroperitoneal behind the peritoneal cavity okay and actually sit at the back of the abdominal wall okay now sitting towards the back of the abdominal wall the top of the kidneys are actually resting upon the diaphragm as well and if you have a look at the kidneys and haven't necessarily drawn them as well as i probably should have but you should see that the right kidney sits a little bit lower than the left kidney and the reason why the kidney on the right sits a little bit lower than the kidney on the left is because remember that you have that large liver on the right hand side that pushes that kidney down so the right kidney sits a little bit lower than the left now in this image you can see that i've drawn the skeletal system from a posterior view and you can see the pelvis here and you can see the vertebrae coming up and you can see two ribs so looking at this a couple of reasons why i've drawn it like this is because you can see that the kidneys aren't very well protected by the rib cage okay your lungs are your heart is by the sternum and rib cage but the kidneys aren't in actual fat you can see that this is the last rib the 12th rib that you can see here 12th rib and part of the 11th rib protecting the kidney now it doesn't actually protect it very well in actual fact this can be more dangerous than helpful a lot of patients may come in from car accidents and the way that the car crash and the way that their body twisted that rib can snap and actually sever the kidney now because of this fact the kidneys among other reasons are surrounded and i haven't drawn it here by a lot of fat and now this fat that surrounding the kidneys is called peri renal fat and this perirenal fat isn't like the type of fat that you put around your belly and around your thighs and around your bum this is functional well that fat that you put here is called functional fat but the fat that you have around the kidneys is called structural fat there is a difference functional fat we use for energy structural fat we often use for protection and anchorage for example and that's exactly why this what this perirenal fat does it protects the kidneys because the ribs don't do a very good job of that and therefore it's very open to being hit by at the flank and it's there to anchor the kidneys as well so keep the kidneys where they are so they don't start floating around there's been a number of reported cases in which patients have come in and they've had scans done and their kidneys are floating around now why the kidneys floating around well they found that a number of these patients were either malnourished or they were marathon runners for example now think about that when you're a marathon learner think about how much energy you use and if you're not eating appropriately well what could happen is that you move through your glucose glycogen stores and you start to move on to your fat stores and you go to your protein stores and you get muscle wastage but if you've used up all your fat stools which is very hard to do your body starts to move from that functional fat to that structural fat and some of these patients have had the structural fat around their kidneys started to get broken down to use for energy now without this fat that's anchoring the kidneys these kidneys can be start floating around okay so we have the kidneys sit behind the 12th rib sit at the level of the 12th rib you can see here and goes down to around about the third lumbar vertebrae so one two three four five so one two third lumbar vertebrae l3 so between the twelfth rib and the third lumbar vertebrae is where these kidneys sit and again attached to the ureters bladder and urethra now let's have a closer look at the kidneys so let's draw up the kidneys and let's section in and see what we can find so if you were to draw the kidneys up you can see that the kidneys are made up of two predominant layers an outer layer which i've drawn here which we call the renal cortex and an inner layer here which we call the renal medulla you can also see that there's like an entry and exit point here which we call the hylum now this hilum is where we have you can see here the ureter coming away also have veins coming away and then fatics as well and it's also where we have the artery renal artery coming in you have the abdominal aorta the descending abdominal aorta with a renal artery branch that comes out okay and i'm not going to draw that yet but i'll draw it shortly when we have a look at the medulla you're going to see a couple of things first thing you'll see is that there are a number of pyramids that are located here in the medulla now we call these renal pyramids unsurprisingly and you have between eight to twelve of these renal pyramids so you have the renal cortex then you have these renal pyramids and they've got these striations these lines through them and you can see between them you have these renal columns and in actual fact these renal columns are extensions of the cortex but come down and these renal pyramids what you'll find are connected and i'll draw it in a different color it's like little cups i like to think of it as your hand place like this as though you were asking for somebody to pull some water into your hands and you were to hold it like that so you could hold the water that's what these are like and these are called a calyx or calices to be plural i'll write that down calyx and calyx does actually mean cup now these smaller calices are called minor chalices but what you'll find is that these minor calluses all connect up with each other and one of these minor calluses form when they connect up with each other well they form a major calyx a major cup now that this major calyx forms a funnel right here which is called the renal pelvis now what's the whole point of having these little cups here and this big cup here this renal pelvis here so minor calcius major calyx and then renal pelvis well that's because when our kidneys filter the blood to create urine what happens is that the majority of it happens here in the cortex and the urine or the filtrate that's been made drip down these renal pyramids drip drip drip drip drip into the minor calcius which then all pull into the major calyx and goes to the renal pelvis and then where do you think this goes from the renal pelvis well this is the ureter remember you have two kidneys so we're just highlighting one particular kidney here okay now i just said that we take the blood in and we filter it from here so that means that there must be an artery coming in which we do have remember you have the descending abdominal aorta with a renal branch that comes in now this renal branch will split here and segment and go towards the back and towards the front and continue to branch and branch a branch of branch if we were to look at these branches okay what you'll find is as it branches and this image is going to start to become a little bit messy i'm sorry so as it branches you'll see that it starts to branch between the lobes here between the pyramids these renal pyramids and these are these loba segments of the arterial of the artery that's come through so you have loba arteries that branch through okay now these lower arteries like i said will go between these renal pyramids and what do they do they turn the corner like this and they go around the renal pyramids now when you take that corner it's called an arcuate okay a turn an arcuate so these are accurate arteries now these arcuate arteries have other branches that come off them in the cortex now these other branches that come off are called globular arteries okay lobular artery so we have so remember we have segmental arteries we have lobar arteries or interloba arteries because they're between the lobes interlobal then we have arcuate arteries and then we have interlobular arteries coming up through and that's not the end yet unfortunately because these interlobular arteries have more branches coming off them like this and this is where it gets to become very important because these branches are no longer arteries they are arterioles remember arterioles are small arteries and that these and these are the only ones i'm going to label for you these smaller arterioles are called afferent arterioles okay why is this important well as this remember this blood comes in branches branches branches into these afro arterioles and this is where we filter the blood in the cortex and what we have in the cortex are the functional unit of the kidneys so the structural portion of the kidneys that does all the filtering and what this thing is called is it's called a nephron okay and you have now what does a nephron look like i'm going to wipe this off here and show you a nephron looks like this has a little pac-man head to it and then starts to look a little bit like a snake that's what a nephron looks like now this nephron so let's write that down n-e-p-h-r-o-n this nephron this little cup here is actually here at all these arterioles so that means if i were to draw it like this we've got a nephron here and if i'm here here if i'm here so you've got nephrons everywhere now the thing is that you actually have per kidney around about 1 to 1.2 nephrons so for both kidneys you have 2.4 ish nephrons which means you have a great capacity to filter okay so you can see if i want to draw the afferent arterial that's coming in comes in like that like you can see here and then it forms this capillary bed in that little capsule like that and then pops out the other side so and here you have the afrin arterial like i stated and on the other side you actually have what we call an efferent arterial which i'm going to talk in more detail in the next video an effort arterial and it's here at this little capillary bed is where all the substances from the blood that are small enough and are of appropriate charge can get filtered through okay so this is important so that means the blood comes in it gets filtered gets pushed through into this tube which we call a nephron okay and we'll follow through the tube and go down this big tube here now this big tube here moves down into the renal pyramids so if i were to draw a bigger nephron so there's the capsule there's the afrolateral oh so there's the capsule there's a proximal tubule it goes down like this and then moves down into the renal pyramid now as it moves down into the renal pyramid this is where the fluid starts to move down so the urine that you've just formed moves down the renal pyramid and like i said drips into the minor calyx then drips into the major calyx and then goes out into our p okay so this nephron is the site of filtration the blood gets filtered and travels through this tube and comes out as penny okay in the next video i'm going to focus on the nephron and talk about exactly what happens but what you need to know from this video is couple of things two kidneys two ureters one bladder one urethra the kidneys sit behind the peritoneal cavity which we call retroperitoneal at the level of the twelfth rib to the third lumbar vertebrae okay it's surrounded by this structural fat called peri renal fat it's there for protection and anchorage and that the kidneys if you segment it if you cut it you can see that it's made up of two major components the cortex which is the outer component and the medulla which is the inner component the filtration happens in the cortex and that the urine that's being filtered drips down into the renal pyramids and into these cup-like structures which we call the minor calyx and then the major calyx and then out via the ureter the way it gets filtered is that blood comes in through the renal artery and this artery branches and branches and branches and branches branches into these segmental arteries into interloba arteries into accurate arteries into interlobular arteries and then into afrin arterioles and it's the afferent arterioles that enter into the nephron as capillaries and this is where the blood gets filtered the nephron will take all that filtrate the blood that's been filtered and drip it down the renal pyramids for us to pin out okay so hopefully that all made sense hi everybody dr mike here in this video we're going to take a look at the genitou urinary system also known as the renal system so firstly the renal system comprises of two kidneys which we've got here two ureters which we've got here one bladder and one urethra now the kidneys don't just filter our blood to produce urine they play a vast array of roles within the body but before we get to those roles it's important to talk about firstly where the kidneys are located so if you were to slice into my stomach god forbid and have a look inside you would have to pull out all of my abdominal organs my intestines my stomach my liver you'd have to pull it all out and then by the time it's all out you'd find the back of my abdominal wall which we call the parietal peritoneum you would then have to go through that parietal peritoneum to find my kidneys what that's telling you is my kidneys are located way at the back of my body behind that peritoneal cavity and therefore the kidneys are termed as being retro peritoneal retro peritoneal now when we look at the size of the kidneys you can go through if we're working with centimeters for example 12 6 and three they're 12 centimeters by six centimeters by three centimeters so 12 centimeters tall or long six centimeters wide and three centimeters thick they weigh around about 150 grams and interesting what you're going to find is that the kidney on the right so again this is the right kidney compared to the kidney on the left actually sits lower and the reason why is because our liver that big organ is sitting above it on the right it's pushing it down so the right kidney is actually lower now where do they sit alright so the kidneys actually sit at around about when we look at the top of the kidney around about t11 t12 so you're going to find that the top or the kidney on the left compared to the kidney on the right we'll be sitting at around about t12 so the thoracic when we look at the thoracic vertebrae 12 this is around about the 11th thoracic vertebrae and when we look at the bottom of it it's a roundabout l2 l3 so from around about t11 to l3 are where the kidneys sit now you know that the 11th and 12th thoracic vertebrae actually have ribs coming around them they call their floating ribs so two ribs now what that means is there's going to be two ribs that wrap themselves around the kidneys it doesn't offer much protection but it can be dangerous and often in car accidents these kidneys can break or shear so basically cut the kidneys and damage them significantly so that's an important clinical point and again the kidneys towards the back retroperitoneal what are the functions of the kidneys what roles do they play in the body so i like to think about this i use this particular mnemonic to help remind me on the functions of the kidneys all right i say very clever pigeons migrate east and then i add another e for good measure very clever pigeons migrate east now let's get rid of the rest of the word and keep that first letter and let's have a look at some of the functions of the kidneys so first v up here is going to be volume the kidneys are really really important in maintaining blood volume fluid volume fluid balance within the body and we know that if we have too much fluid we can pan out not enough we can tell the kidneys hold on to that fluid really important and we also know that there's a direct correlation between volume and blood pressure and therefore the kidneys are really really important in maintaining our blood pressure what's the c the c is concentration so it maintains the concentration of things within our blood most importantly the concentration of ions remember ions are charged atoms or elements and examples of ions include things like sodium potassium chloride magnesium hydrogen bicarbonate calcium there's so many important ions and again the kidneys can regulate the concentration of these ions in our blood too many p out not enough hold on to it what's the p stand for in this case the p stands for ph so the kidneys help regulate long term acid-base balance long-term acid base balance how does it do this well it does this through the regulation of concentration of hydrogen and bicarbonate because we know all acid is is the concentration of hydrogen ions and to make something less acidic we need to give a base which binds or mops up those hydrogen ions so the kidneys can maintain ph by controlling how many hydrogen ions or how many bicarbonate ions we actually have in the system what's the m the m is metabolic important metabolic processes are controlled by the liver the kidneys sorry so these metabolic processes include gluconeogenesis gluco means glucose neo means new genesis means the beginning of read it backwards the beginning of new glucose if our body has run out of sugar for energy we can use fats via the kidneys and some proteins to produce glucose as energy brilliant it also plays a role in glycogenesis so this is the storing of glucose's glycogen and glycogenolysis glycogenolysis this is now breaking apart the stored glycogen to turn into sugar to use for energy and last but not least here for metabolic is vitamin d synthesis importantly the kidneys are the last step in activating a vitamin d precursor what does vitamin d do it helps control our blood calcium levels now the last two e's let's just move them down down a little bit so we have some space the last two e's are going to be excretory and endocrine the excretory functions the kidneys play a really important role in getting rid of waste drugs and toxins so wastes include metabolic wastes so things that we produce as a by-product but we need to get rid of because if they stay in our blood they can be dangerous for us so these wastes can include urea so when we break proteins down and we split apart those amino acids we produce ammonia and we know ammonia is not great to stay within our body so we turn it into urea and we need to get rid of this urea and also creatinine which is a byproduct of muscle metabolism creatinine not creatine but creatinine what about drugs the types of drugs that the kidneys get rid of are water-soluble they need to be water-soluble because this is urine we're talking about if they're fat soluble the body continues to reabsorb them through the digestive system until it's broken down or it's passed through our digestive tract and also toxins whatever those particular toxins may be kidneys play an important role in getting rid of them what about the endocrine function of the kidneys so endocrine means hormones so what are some important hormones that the kidneys produce well that includes renin renin is important when it comes to the renin angiotensin aldosterone system what is this system basically this is a system that maintains fluid volume and blood pressure and how does it do it ultimately helps hold on to water in the body and helps reabsorb sodium and chloride because wherever salt goes water follows remember when you eat some chips for example some salty chips you get thirsty so wherever salt goes water follows so what the kidneys can do specifically after renin's released is it helps tell the kidneys to hold on to salt in the blood and water will be pulled back in maintaining blood volume maintaining blood pressure and another endocrine function is that of e p o which is erythropoietin erythro erythromeans red so an erythrocyte is a red blood cell erythropoietin poisous to create erythropoietin is the production of red blood cells so the kidneys play a really important role in controlling how many red blood cells you are producing in the body why because the kidneys are very metabolically hungry they only weigh 150 grams but they take around about 20 percent of our cardiac output that means of the five liters of blood pumped out of our heart every single minute 20 percent of that goes to the kidneys that's how important they are so they need oxygen they need nutrients and they need to be able to filter all this blood and when they filter the blood they do all of these particular roles so this is a quick run through of the kidneys hi everyone dr mike here in this video we're going to take a look at the filtration membrane in the kidneys so remember your kidneys two of them are made up of things called nephrons and they're the subunits of the kidneys that do all the filtering now they do it at an area called the glomerulus remember you're going to have an afrin arterial coming in and then what looks like a ball of yarn but i've simplified it here turn the glomerulus this is where things get pushed out into the nephron remember this is called the glomerular capsule which wraps around the glomerulus and that's called the efferent arteriole anything that didn't get pushed out continues through now when we talk about filtration i told you 120 milliliters per minute gets pushed through from the blood into the capsule and only one percent of this continues all the way through to be paid out the rest gets thrown back into the body question is of all that stuff that gets pushed out what gets pushed out and why and it's all because of three filtration membranes all right so the three filtration membranes number one is the filtration membrane that comprises the blood vessel itself remember all hollow organs and structures and external structures are lined by epithelia right so what we've got inside of a blood vessel is epithelia but we call it endothelial now i've got endothelial there but it's endothelia and when we look at the glomerulus the endothelial at the glomerulus have holes in it this is called fenestrated endothelial so fenestrated just means holes so number one we have fenestrated endothelia at the glomerulus now the width of these fenestrated endothelia so what size things can get through it only lets through things that are between 70 to 100 nanometers that's its diameter so anything smaller than that it lets through now let's put that into perspective okay when you've got one meter one meter you divide that by a thousand and you've got a millimeter you divide so you've got one meter and then you divide it by a thousand and you get one millimeter you divide that by a thousand and you get one micro meter you divide that by 1000 and you get one nano meter all right so 70 to 100 nanometers very small what can it let through well let's think about it let's think about red blood cells going past how big's a red blood cell they're pretty small they're 10 micrometers that's here though 10 micrometers means it's way too big to get through this is 100 nanometers and a red blood cell is 10 micrometers okay so it's way too big to get through what about a white blood cell that's coming through well white blood cells are bigger than red blood cells white blood cells around about 100 micrometers so it's definitely not getting through but everything else that's small enough will so that means proteins are going to get through ions are going to get through glucose is going to get through fluid is going to get through so this first membrane is simply going to be the fenestrated endothelia it's a membrane for cells it's not letting cells through okay now the next one remember all epithelia sit on top of connective tissue that's just what it is all throughout the body all endothelial sit on connective tissue the connective tissue here called the basement membrane is filled with collagen and one thing you should know about collagen it's negatively charged now this is important because proteins which are going to be floating through also are negatively charged now what do we know about like charges they repel each other so the basement membrane being negatively charged because of collagen repels proteins this is the protein membrane doesn't let proteins through now the third membrane these little things that look like they've got extensions they're called podocytes i've written that up here and their diameter they can let some things through what's their diameter that they're letting through it's between it's around about between 10 to 40 nanometers which is even smaller than that of the fenestrated endothelial which means that's even too small for most proteins so it's another again it's going to stop any cells that may have gotten through it should be stopping most proteins that have made it through as well so again that's the potasites these are the three membrane layers it's the fenestrated endothelial it's the basement membrane that's negatively charged and it's the potasites as well they're the three which means here there should be should there be cells no should there be proteins no what happens if we have let's just say something called glomerulonephritis where your antibodies are attacking this basement membrane and that's destroyed what do you think might be getting through proteins because that is the layer that predominantly stops proteins therefore if you're peeing out a lot of proteins they may have a look and go maybe this individual is in the acute stage of glomerulonephritis so that's a quick run through of glomerular filtration membranes everybody dr mike here in this video we're going to take a look at kidney filtration also known as glomerular filtration so i've drawn up a strange looking diagram on the board let me briefly explain it we've got the heart and we know that coming out of the left side of the heart specifically the left ventricle we've got the aorta and the aorta is going to have multiple branches now once we're in the abdomen one of its branches is that of the renal artery going to the kidneys so what i've isolated here is one of the very small branches of the renal artery that we call an afferent arteriole now the afferent arteriole what do you know about that the afferent arteriole is a very small artery that's going to the nephron remember each kidney has one milli nephrons and this is the filtration unit of the kidneys this is what deals with the components of the blood there's an afferent arteriole on one end then we've got a glomerulus here this is where the things get exchanged glomerulus is latin for ball of yarn and then on the other end we have the efferent arterial and what you can see is the efferent arteriole then wraps itself around the tubules of the nephron and these are called peritubular capillaries peri tubular capillaries and what's happening is here at the glomerulus afrin arterial glomerulus things are being pushed out of the blood into this capsule called the renal capsule all right what's been pushed out is everything's small enough so no cells no proteins but everything else basically has been pushed into this renal capsule and moving through the tubules of the nephron no oxygen is being or no gas exchange is happening at this area however once the efferent arterial snakes itself around the tubules and now is the peritubular capillaries this is where gas exchange can happen to the cells of the tubules it's also the place where things get thrown back into the blood alright now take her message is this whatever remains in the capsule and the tubules turn into urine okay so let's now have a quick look coming from the heart every minute you know that the cardiac output so the amount of blood our heart pumps out per minute the cardiac output is 5 liters now of that 5 liters 20 percent is going to the kidneys so 20 percent is going to the kidneys and that's one liter now of that one liter which is a thousand mils what you're going to find is that around about 400 mils of that 1000 mils are things that are too big to be pushed across that glomerulus so these are going to be cells proteins for example okay now the rest the 600 ml is going to be plasma so this is stuff that can be pushed through right now of this 600 mils every minute remember every minute of the 600 mls getting to the glomerulus the question is how much of this 600 mls is being pushed through into the capsule and the answer is 20 percent so what's 20 percent of 600 it's 120 mils so 120 mls per minute so every minute 120 milliliters of fluid within the blood is being filtered into this renal capsule now that's a minute let's think about how much is being filtered so this is the filtration process right there's little holes here that filter what we need to get through if it's too big it doesn't or if it has a particular charge it won't let's calculate how much is getting filtered per day right so if that's per minute if we've got 60 minutes in an hour times 24 hours in a day that gives us 1440 minutes if we multiply 1440 minutes by 120 then that will give us around about 172 800 milliliters so every day we filter into our nephrons 172 800 mils that is 100 let's just round it up to 173 liters per day we filter now think about that that means 173 liters is going into this capsule and moving through these tubules now think about that if it remains in the tubules do we pee out 173 liters of urine every day no of course we don't we pay out 10 of this we pay out 1.7 give or take a little bit 1.7 liters per day which means 90 percent actually 99 we only pay out one percent of that not 10 percent 1 that means of that 99 of everything that gets filtered gets thrown back into the blood and you can see of this efferent arterial the peritubular capillaries that wrap all the way around it this is where it gets thrown back so some stuff that's here is going to get thrown back into the capillaries here some is going to get thrown back here some is going to get thrown back here some is going to get thrown back here some is going to get thrown back and now that's 99 percent gets reabsorbed back into the blood and what happens with this it goes back to the heart perfect this is renal or glomerular filtration hi everybody dr mark here in this video we're going to take a look at the components of a nephron so first thing we need to look at is the blood supply going to this nephron that needs to be filtered now ultimately this blood is coming from the renal artery but what we need to know is that in the cortex of the kidney we've got this blood vessel coming through and this blood vessel is called the afferent arteriole so that's the first thing you need to be aware of afferent arterial and this afrin arterial becomes what looks like this ball of yarn and this ball of yarn actually has a name called the glomerulus which means ball of yarn the glomerulus now on the other end of this twisting and turning looking bit of blood vessel we've got another blood vessel that comes out and this blood vessel that comes out is called the efferent arteriole so we have the afferent arterial coming in and we've got the efferent arterial going out now one thing to remember here is that they're not capillaries they are arterioles which means they have huge amounts of smooth muscle around them that's going to be important for future concepts now at the glomerulus this is where the blood gets filtered out into the nephron itself so we need to talk about the very first part of the nephron which is a capsule that looks a little bit like pac-man here and this capsule is called the glomerular capsule also known as the bowman's capsule glomerular capsule so that means all this stuff gets filtered the blood gets filtered into the glomerular capsule and now we're starting to talk about the tubules of the nephron so the very first tubule is called the proximal convoluted tubule so this tubule here is the proximal convoluted tubule proximal convoluted tubule proximal because it's cl it's the tubule closest to the glomerulin the glomerular capsule convoluted because it wraps and snakes its way around this is a simplistic version but it really is quite um distinct in the way that it's wrapped itself around and a tubule because it's a very small tube now the next part of the nephron is a part that starts to move its way down and then it starts to take a bend and come back up and as it comes back up it thickens the width of that tubule so what we have is the entire thing is called the loop of henle or the nephron loop loop of henle or nephron loop but the nephron loop is made up of different components for example you've got the descending limb d sending limb of the loop of henle you've got the ascending limb of the loop of henle and specifically two different parts you've got the thin ascending limb and the thick ascending limb now descending limb then ascending limb thick ascending limb all right now we start to move on to the distal convoluted tubule again distal because it's far away convoluted because it's wrapping itself around it snakes its way around and tubule because it is a small tube it's the distal convoluted tubule and this distal convoluted tubule comes together to this tube called the collecting duct this collecting duct actually collects all the filtrate that is moving its way through these tubules again this is called the collecting duct what ultimately happens is the collecting duct will drain itself into the pelvis ultimately of the kidney and then that will go into the ureter bladder and urethra for exit last thing i want to talk about is the capillaries that wrap itself around the tubules these capillaries come from the efferent arteriole and like i said they begin to wrap themselves around the nephron because they wrap themselves around the nephron they're called peri tubular capillaries and peritubular capillaries will reabsorb some contents from the tubules and they'll throw contents back into the tubules but that's for another discussion so what we've got here is a quick run through of all the different components of a nephron hi everybody dr mark here in this video we're going to take a look at tubular reabsorption and secretion now what is this referring to it's referring to something called the nephron this is the filtration subunit within all of our kidneys and remember the blood is going to come in through something called the afrin arteriole turn into what looks like a ball of yarn it's a capillary bed called the glomerulus and this is where we filter the blood into these tubes which are called a nephron now each kidney has a million nephrons which means we have 2 milli nephrons in total and we only effectively need 1 million to do this process properly now when the blood comes in and through how much of the blood is filtered well it's around about 120 milliliters per minute which ends up being around about 180 liters per day so 180 liters per day get filtered into this tube now if it remains in this tube all the way through and comes out this particular end here this then turns into p now what do we pee out per day it's not 180 liters it's only one percent of this so that ends up being 1.8 liters per day so what that means is throughout this process going from the glomerulus to the capsule so that's called the glomerular capsule through what we call the proximal convoluted tubule the descending limb of the loop of henle the ascending limb of the loop of henle the distal convoluted tubule and the collecting duct 99 of the stuff that gets filtered needs to be thrown back into the bloodstream so remember there's all these capillaries that wrap around these tubules and these capillaries are called peritubular capillaries they're going to reabsorb 99 of all the stuff that's been filtered called filtrate and we need this to happen so that we pee out around about 1.8 liters and so that our body maintains the appropriate concentration of stuff ions amino acids glucose urea all those types of things all right so let's take a look at this process first thing is at this part here that we call the proximal convoluted tubule what you're going to find is that around about 65 percent of everything gets reabsorbed here so here we're talking about reabsorption so when i use the term reabsorption it's not absorption absorption happens in the gut where we absorb things into the body this is effectively when you think about stuff being in this tubule you need to think of it as though it's outside the body so when it goes from this tubule back into the capillaries back into the bloodstream of the body that's called reabsorption so 65 of all the stuff that gets filtered gets reabsorbed here at the proximal convoluted tubule this loop of henle right here what you'll find is around about 15 percent of everything gets reabsorbed and like i said this is called the loop of henle this is called the distal convoluted tubule and another 15 of everything gets reabsorbed here and then this is called the collecting duct and around about 5 of everything gets reabsorbed at the collecting duct so when we draw this up i'm going to talk about reabsorption in these particular areas when we draw this up what we want to look at is this what's getting reabsorbed here here here here and here back into the body that's really important because if we were to alter this reabsorption by 10 percent let's just say we didn't reabsorb everything we needed so here instead of reabsorbing 65 we absorbed let's just say 62 and here we reabsorbed only 13 percent and here we reabsorbed only 13 and here we reabsorbed only 4 percent if we did that what you'd find is we wouldn't pay out 1.8 liters per day would pay out 18 liters per day and that's not possible if we did that we would die very quickly all right so what's getting reabsorbed back into the body at the proximal convoluted tubule all right sodium ions potassium ions chloride ions calcium ions magnesium ions we are now going to just term these the ions there's obviously more but these are the ions i want you to remember these ions are being reabsorbed at the proximal convoluted tubule now as we move through if i use the term ions again these are the ones i'm talking about now in addition to this bicarbonate has been reabsorbed you're probably thinking but that's an ion true but i'm not including it in this group for a particular reason bicarbonate water amino acids urea and glucose these are the main things being reabsorbed back into the body now an important point here is this this is the only place where glucose gets reabsorbed back into the body of all the glucose so most simple sugar that gets filtered here 100 percent needs to be thrown back into the body at the proximal convoluted tubule if too much glucose gets filtered we won't have enough time to throw it all back and it will come out in the urine and this is something that often happens with diabetics because glucose has what we call a strong osmolarity has a strong pulling force it's going to pull water with it and then you end up peeing out more fluid and this is one reason why diabetics urinate a lot all right that's important proximal condylar tubule here at what we call the thin descending limb of the loop of family you can see there's a thin descending limb and the thick ascending limb here at the thin descending limb water is the only thing that's reabsorbed this is really important because the longer this tube is the longer this thin loop of henle is the more water that gets thrown in the thrown back into the body that's important in times of dehydration it's important for animals for example that don't get enough water in so if you find desert dwelling animals that don't ingest enough water you'll find if you look in their kidneys that their loop of henle is very long because it helps concentrate the urine think about it whatever stays in here becomes urine if we throw more water out this or the stuff in this tube becomes more concentrated so the thin descending limb is important for concentrating urine if we look at the thick ascending limb what we're reabsorbing is ions so that's these ones here and bicarbonate if we look at the distal convoluted tubule what we're reabsorbing is ions bicarbonate and water and if we look at the collecting duct we have sodium chloride bicarbonate water and urea so these are the major ions nutrients and substances that have been reabsorbed back into the body in these particular areas that's very important and that's the process of reabsorption now if we look at the process of secretion this is where we take things that are in the blood and throw it back into these tubules so let's have a look here at the proximal convoluted tubule what we're throwing back is we're throwing back urea we're throwing back uric acid we're throwing back creatinine we're throwing back hydrogen ions we're throwing back drugs we're throwing back ammonia these are all the things that we want to pee out or secrete so in the blue we've got reabsorption in the red we've got secretion now nothing has been secreted here nothing actually one thing has been secreted here i should say and that's urea urea is being secreted here nothing is being secreted here here and here what we've got is hydrogen ions are the predominant thing being secreted here but we've also got some drugs and we've also got ammonia so if we have a look at this process we filter most things into these tubules we reabsorb nearly a hundred percent of it back into the body but we secrete very specific products back into the tubules so that overall we only pee out one percent of everything that we've filtered and this is the process of reabsorption and secretion at the tubules you

Channel: Dr Matt & Dr Mike

Views: 7,076

Rating: 4.9470201 out of 5

Keywords: glomerular, filtration, renal, kidney, nephron, anatomy, physiology, nursing, medicine, nclex, secretion, reabsorption, urine, ureter, bladder, urethra, cortex, afferent, efferent, renin

Id: qwizcF3y67c

Length: 55min 24sec (3324 seconds)

Published: Tue Aug 25 2020