Hey everyone, it's Sarah with registered nurstrn.com and in this video I'm going to be going over nefron physiology. This video is part of an inclelex review series over the renal system. So be sure to check out those other videos and at the end of this video you can access the quiz. So let's get started. So in the previous video we went over kidney and nephron anatomy. Now, we're going to take it a step further and we're going to dissect this nefron. And we're going to pay close attention to what is being filtered, what is being reabsorbed from that filtrate, and what is being secreted into that filtrate, which can leave the body as urine. And just to recap a little bit, we know that the whole role of our kidneys is to filter our blood. Our kidneys receive that fresh oxygenated blood from the heart via the renal artery. Then it branches off into like arterials which go to those nefrons. And remember each kidney has like millions of nephrons. And these nephrons, part of it sets in the cortex of the kidney and another little part of the nephron sets in the medulla of the kidney. And um it's filtered through there. And then the whole thing that what the nephron does is it filters, reabsorbs, secretes, and then excretes urine. And urine will flow out of the uh renal pyramid through the renal papila down through your minor and major klex. then down through the renal pelvis out through our ur the urittors stored in the bladder and then um it will be voided out through the urethra. Now let's take a closer look at the nefron. Okay, whenever I look at the nephron I like to divide it up into two sections based on its function. Okay, the first section is the renal corpusle which includes your glomeriius and bowman's capsule and they work together to filter the blood. So that's what the renal core pusles do. Then the second section are your renal tubules and what they do is they play a role in reabsorption taking the substances out of that filtrate and putting it back in the blood and secretion where the peritubal capillaries are secretreting substances into the filtrate to be excreted through the urine. So let's talk about the filtering part of the nephron. Okay, first part of the nephron is the glomeriius and the glomemerias is just this mesh of circular capillaries and it's receiving its blood flow through the apherant arterial and remember this came from the renal artery drained down from the heart that um is really nice and oxygenated. It's going to go to the nephron to be filtered out. So it hits the glomemeriius and due to that mesh of circular capillaries this secrete this causes a very high pressure which will cause ultrailtration and what will happen is that filtrate will start to leak from the glomerias and collect in this capsule. I like to think of it as if you have a strainer and you put maybe like pasta in your strainer and the water's dripping out of the pasta. In a sense, it's the same thing if you need a visual aid to help you. So, it's dripping down. So what exactly is coming out of the blood and collecting in this filtrate? The following water, some glucose, amino acids, ions which are like calcium, potassium, magnesium, phosphate, chloride, things like that, ura and creatinin. And I want to say one thing about creatinin. Creatin, as you're going to see whenever we go more in depth with the tubules, it's not really going to be reabsorbed or secreted. It's exclusively filtered from your bloodstream by the glomemerias and this lets us lets us know based on the rate of its excretion from the bloodstream how well the kidneys are working. So that is why we pay such close attention to creatinin because it tells us how well our kidneys are filtering the blood. Now some substances that are not normally um filtered by the glomemerias are blood cells and proteins. Then after the blood is done circulating through the glomemerias and has got filtered, it leaves the glomemerias through what's called the ephriant arterial. Ephri means away. And the ephri arterial goes and it turns into another important structure called the perittubular capillaries. And these capillaries have a very important role. They the capillaries go and they in a sense surround and go around your nephron because they're going to help play a role with reabsorption and secretion. And let me show you this. Right here we have these orange arrows and this in our diagram is representing the filtrate that is flowing through the nefron that's left Bowman's capsule. The black arrows represent substances from the filtrate that is leaving the tubules and going back into the bloodstream and it enters into the perittubular capillaries through there. And then you have secretion which is represented by these blue arrows and this represents substances leaving the perittubular capillaries and going into the filtrate to be excreted. So that's what the peritubular capillaries do. They play a role in allowing the reabsorption process and the secretion process with the nephron. And up here we refer to them as paratubular capillaries. And down here on the loop of henley um they are referred to as the vasta recta. Now the filtrate's going to leave the capsule and it's going to travel through these renal tubules. And depending on where the filtrate is in the certain part of the tubial depends on what's going to be reabsorbed and what's going to be secreted because different areas reabsorb um different amounts and um secrete different amounts. So um on this nefron pay attention to what parts lay in the renal cortex and which parts are in the renal medulla. This black dotted line will help you differentiate. These parts are up in the renal cortex and these parts which are the lube of henley and part of the collecting duct are in the renal medulla. Okay. So filtrates coming through here through what's called the first part of the renal tubule the proximal convoluted tubule. And here this is where most of our reabsorption is going to occur. So what is going to be reabsorbed? The biggest thing that's going to be reabsorbed is glucose and amino acid nearly 100%. Because these substances are very vital for our survival. We need them. Another thing that's really going to be absorbed is by carb. And we learned um in our acid base imbalance videos that we need some by carb. And if we don't reabsorb enough by carb, put it back in our bloodstream, we can enter into acidotic conditions. So that's why we really want some by carb. And then we're going to take in a lot of water and sodium and chloride salt about 60 to 70% from there because we need that as well to survive. And then other ions like potassium, magnesium, calcium, phosphate, things like that. And um about 50% of ura we're going to reabsorb. Now also in this proximal convoluted tubule we're going to experience some secretion from the bloodstream into the filtrate to get rid of it. What will be secreted is like uric acid and um other things like antibiotics or other drugs like diuretics things like that. Then the filtrate is going to flow down through what is called the loop of Henley. And as you notice, the loop of Henley is the only part of the nephron that is completely in the renal medulla. And let's talk about the renal medulla for a second because it's interesting. Inside the renal medulla, it has interstatial fluid. And that interstatial fluid is super super salty. It's considered hypertonic. So what happens that filtrate's flowing down through there and through the descending limb of the loop of Henley and it comes into contact with this highly salty environment. And we know that what's in the filtrate is water and all of our ions and things like that. Well, the unique thing about the descending limb of the loop of Henley is that it is only permeable to water. So it only allows water to flow through it. It does not allow ions like your sodium, your chloride, your potassium to go through. Will not let it go. So once that filtrate which has water hits this, all this water is going to come out of that descending limb because we learn through osmosis that water loves salt. So here comes that water sees that salt and it rushes out and allows us to reabsorb all that water. Which is why our loop of Henley main job is to really concentrate our urine and take the water that we need to maintain homeostasis and that renal medulla's interstatial fluid of the hypertonic fluid allows it to do this. So water has left the descending limb. Then your filtrate gets down here. And when it reaches this area, it's really concentrated because most of the water is left. All that we have is our sodium and our chloride, potassium, our ions. Now it's going to go up through the ascending limb. And this thick part of the sending limb, the sending limb is very unique because it only allows ions to leave. It's only permeable to ions. It is not permeable to water. So water will not leave this any lamp only ions. So once it gets there it act actively these ions specifically sodium and chlor chloride and a little bit of potassium leave it and enter in this interstitial fluid which allows that renal medulla to keep that hyper osmalerity environment. So this can keep continuing. Another thing I wanted to point out is that sometimes the loop of Henley secretes ura and whenever it does that it plays like a process in ura recycling which will help keep the osmolerity in the medulla increased because we want that osmalerity because it will help us save water. So it helps with water reabsorption and it helps maintain concentrated urine as it flows through the tubules. Then the filtrate will go through the distal convoluted tubule and this is where there's going to be some tweaking of that filtrate even more a little bit more reabsorption of this and secretion of that. So some things that are reabsorbed we have some sodium and water which will be under the influence of the hormone aldoststerone and remember aldoststerone conserves sodium which will cause water retention. Then um some reabsorption of calcium under the influence of the parathyroid hormone and a little bit of by carb. A lot of our by carb was reabsorbed in the proximal convoluted tubial but here it takes just a little bit more again just to maintain that pH in our blood. Some things secreted by the distal convoluted tubule are um potassium and hydrogen ions. Then the filtrate is going to go down through the last part of the nefron called the collecting tubule. And this is where there's going to be the final touches on that filtrate. What um needs to be reabsorbed gets reabsorbed back into the bloodstream. And what doesn't exits the body as urine. So um the clectin tubule what generally is reabsorbed is sodium water which is under the influence of the hormone um antidiuretic hormone which helps regulate the amounts of water in our body and some ura. So that happens then it leaves the collecting duct which connects straight to the renal pipela and remember the renal pipela was the end point of where the renal pyramid is and then it goes down into the minor klex the major klex down through the renal pelvis out through the urer stored in the bladder and then out of the urethra to be voided out. So after all this goes through the filtrate, what actually is in the urine? What makes up your urine? The end product is the ura which is a waste product that you don't want high amounts in your body. Water, excessive water that your body didn't need. It says we have enough, so let's get rid of this. Creatin, which is another waste product. And a bunch of ions that your body has enough of that um that your body said, I don't need this. Let's get rid of this. We have enough of sodium, chloride, potassium, magnesium, phosphate, and calcium. Okay, so that is the nefron physiology. Thank you so much for watching. Don't forget to take the free quiz and to subscribe to our channel for more videos.