In this video, we're just gonna do a quick introduction to the Nephron. Now everyone get comfortable because we're gonna be spending the bulk of the chapter talking about the anatomy and physiology of these little guys. So nephrons are microscopic structures that are basically the functional units of the kidney. And when I say functional unit of the kidney, what I mean by that is that these are the structures that are actually going to be filtering blood and producing urine and each kidney will usually contain about 1 to 2 million nephrons. So they are very, very abundant. If you look over at our image here, this is a Nephron and you know what I'll say it, they're kind of weird looking, huh? So if you're looking at that and you're like, what the heck is that thing? Fear not friend. By the end of this chapter, you will understand every single microscopic inch of these little guys, I promise. Now, nephrons are located in the renal cortex and renal medulla. You can see we have this lighter colored region right there that is our renal cortex and then they can dip a bit deeper into the kidney into this darker colored region that is the renal medulla. And this makes sense, right? Remember how in our last video, we talked about how the cortex and the medulla are the urine forming structures of our kidney. So it makes sense that the functional units of our kidney would be located within those regions. Now, nephrons have two main components. They have a renal corpuscle and a renal tubule. And I will see you guys in our next video to start diving into those in a bit more detail. See you there.
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example
The Nephron Example 1
Video duration:
50s
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OK. This one asks us which of the following statements is all. So let's run through them. So, a reads, nephrons are the functional units of the kidney. That is true. So A is out B reads that nephrons are located in the renal pelvis and that is all right. So the renal pelvis is just the structure where urine basically drains into and kind of pools and collects until it goes down into that ureter. Remember, the urine forming structures of the kidney are the renal cortex and renal medulla and those regions are where our nephrons will be found. Keep in mind that nephrons do indeed filter blood and produce urine. That is their main function. And between both kidneys, we do indeed have 3 to 4 million nephrons. Each kidney individually has about 1 to 2 million nephrons. Though our answer here is the
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example
The Renal Corpuscle
Video duration:
4m
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OK. So let's dive into that renal corpuscle. Now, the renal corpuscle filters blood. OK. So that is its main purpose. Now, we're gonna talk about the physiology of how this filtration works in some upcoming videos. So for now, we're just gonna stick to kind of the anatomy of what makes up this actual structure and the main filtration features of it. So each renal core puss has two hearts. So first up, we have a glomerulus. So a glomerulus is a group of fenestrated capillaries, which are also sometimes called glomerular capillaries. Now, fenestrations are literally just pores within the membrane or within the plasma membrane of those capillaries. And so the fenestrations or those pores make the capillaries highly permeable. Another way to think about these capillaries is that they're very leaky. So they're leaky and permeable and certain fluids can basically pass through them, which is an important part of this filtration unit. So if you look down at our image here, you can see we have our glomerulus labeled. So we basically have a blood supply coming in to our renal core puss and it just turns into this big messy looking ball of capillaries and that is the glomerulus. And honestly, I think it kind of looks how it sounds just like the word glomerulus just sounds like a big messy ball or something to me. So that's how it looks, looks kind of weird, but that's OK. Still a great part of our body. And then next up, we have our glomerular capsule. So our glomerular capsule is a sheath of tissue that surrounds our glomeruli. And the glomerular capsule consists of an outer parietal layer which basically just forms the outer portion of the capsule. It kind of gives it like its shape and like struct and like structural integrity, gives it the actual capsule shape. And then it has an inner visceral layer. And that inner visceral layer is composed of pod toys which are modified epithelial cells. And these potes actually surround the glomerulus and they literally wrap around the capillaries themselves. So if you look at our image here, we have our glomerular capsule and you may also hear this called Bowman's capsule, it means the exact same thing. So we have our um glomerular capsule here and you can see how we have this outer layer of kind of giving it its shape. So that is that outer parietal layer there. And then we have these potto sites which you can see are these little epithelial cells that are literally like wrapped around the capillaries and you can see them better on our little zoomed in image. So this right here would be a poochy. Now, each pottery has something called foot processes or pedestals and those foot processes weave together to form a filtration lit. So the foot process, you literally look kind of like this and then they weave together and you can see how there's tiny gaps between my, my fingers there and those gaps would be our filtration lit. So on our image here, you can see how there are these little gaps where you can see capillary in between those foot processes. Um and those are the filtration slit. And again, that that's acting as a really important part of this major filtration unit happening. So the whole point of this is to get some fluid to come out of the blood, right. And so the fluid that actually makes it through those um penetrated capillaries and pod aytes is called filtrate. So, filtrate is a plasma derived fluid and it it's, it's gonna contain water, electrolytes, nutrients and all types of other small molecules. And the filtrate will be collecting in a in, in um the capsular space, which is a hollow region basically between the parietal and visceral layers. So if you look at our image here, we have these kind of just empty hollow part. So that is the cap space and that is where filtrate it's gonna be building up until it eventually comes out of the um renal core pus and enters the renal tubule. Now, I know that this is a lot of information. It's kind of some odd looking anatomy to get used to. So take your time with it. I do recommend the most important terms to know here. Um We should know glomerulus, you know, know what a glomerular capsule is. Understand that the glomerulus is permeable or leaky. Understand that pot toys are gonna act as one of the major filtration units here. Um And then understand that the fluid that comes out of it, it's gonna be called filtrate. Those are kind of the most important takeaways from this lesson. All right, so I will see you guys in our next video. Bye bye.
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example
The Nephron Example 2
Video duration:
47s
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OK. So this one asks us true or false. If false, we're gonna be choosing an answer that would correct the statement. The statement being the fluid that passes through the first grated capillaries is urine and that is false. This fluid is not yet considered urine. This is something that we call filtrate though our answer is going to be b here, this fluid is called filtrate, which is easy to remember because it's basically just filtered blood, filtered filtrate, right? Um This is no longer considered blood, it does not have any blood cells in it or platelets or things like that. Um This fluid is made mainly of water, electrolytes, um nutrients and other small molecules. So our answer here is B this is false. The fluid that passes through those leaky capillaries is called filtrate.
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Problem
Problem
Which component of the renal corpuscle forms filtration slits?
A
Glomerulus.
B
Glomerular capsule.
C
Glomerular capillaries.
D
Podocytes.
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concept
The Renal Tubule
Video duration:
4m
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All right, let's dive into that renal tubule. So you can see in this image on kind of the upper corner of your screen, we've kind of faded out that renal corpuscle. We already know all about that. We've also faded out this limb over here on the right. We're going to learn about that very soon. And what we are focusing on here is this winding tube that makes up the majority of our Nephron and that is our renal tubule. What we are seeing here is basically a very zoomed in image um looking at the renal tubule that is all color coded and we're going to go through what each of those color coded segments are in this video. So the renal tubule is a winding tube that basically modifies filtrate and it does that by either conserving or eliminating certain substances. And we're going to talk about the physiology of this tube, a ton in upcoming videos. So for now, we're just going to be talking about the anatomy of it. So our renal tubule has three main regions and they each have a unique structure and function. So first up is our proximal tubule and proximal, just refers to this being the initial or the first segment of our renal tubule. You can see that segment over here in the purple. I'm gonna label that as one for us. And the proximal tubule is located in the renal vtec. Now, the proximal tubule is a bit unique because it contains prominent micro vili and those micro vili are really important because they basically increase the surface area of the proximal tubule, which allows for a very high volume of filtrate to get modified very quickly. And that is important because about 65% of filtrate modification happens in this little tiny part of our tubule, this little purple part. So it has to be very efficient at what it's doing. Those micro vli really help with that. So that is our proximal tubule. Next up, we have our Nephron loop and the Nephron loop is this entire U shaped loop um in our our renal tubules. And so our Nephron loop is located in the renal cortex. It's always going to start in the renal cortex, but it can dip down into the renal mela as well. And the Nephron loop is divided into two limbs and each limb does have a distinct function. So first we have our descending limb which you can see here in green. I'm gonna label that as two A for us. And this is the part of the limb that is basically traveling toward the renal medulla. And then we have our ascending limb, which you can see here in orange. I'm gonna label that as two B and this is the part of the Nephron loop that is traveling toward the renal cortex. And we'll talk about the unique um function of those in upcoming videos as well. And then finally, we have our distal tubule. So this is the final segment of our renal tubule and you can see it here in blue, we're gonna label that as three for us. And this is also located in the renal cortex. So typically, our distal tubule and our proximal tubule are gonna be about level with each other like approximately. Now, one last um um structure of note in our renal tubule are the macula denso cells. So the macula denso cells are a group of densely packed cells. So denso literally just means dense here. Um and they are basically gonna be located at the transition point between the ascending limb and the distal tubule. So, what we are looking at in this image is basically this location over here. So, right where that blue distal tubule is meeting that orange, ascending limb of the Nephron loop. And you can see we have our kind of uh slightly prominent densely packed um macula denso cells here that we've done in green. So those are the macula denza and what these cells do is they're gonna, they're gonna be monitoring the sodium chloride content of the filtrate and that is going to actually play a role in regulating filtration rate as well as blood pressure. And we're gonna have a whole video talking about how that happens as well. All right. So that is our renal tubule and I will see you guys in our next video. Bye bye.
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example
The Nephron Example 3
Video duration:
35s
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OK. So this one asks us nephrons modify a high volume of filtrate very quickly, which portion of the renal tubule contains prominent micro bila to aid in this process. And that is going to be our proximal tubules. It looks like our answer is going to be a remember, 65% of filtrate modification happens right in that initial segment happens very quickly. And so we have to have all those micro vili right front loaded in that first part of our tubule to increase the surface area to allow um for more filtration to happen. So our answer is a the proximal tubule.
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Problem
Problem
Macula densa cells monitor the ________ concentration of the filtrate.
A
H2O
B
Na+
C
NaCl
D
Ca2+
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concept
The Collecting Duct
Video duration:
3m
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In this video, we're gonna be talking about the collecting duct though the collecting duct is a tubule that further modifies the filtrate. So if you look at the image here on the top, right, basically, at this point, the filtrate has gone through the entire renal tubule and it is exiting from the end of that distal tubule and it is exiting into this long straight duct right there and that is our collecting duct. So this is considered the final portion of the Nephron. Now, whats interesting is that each collecting duct actually collects filtrate from multiple Nephron. So if you look at our image here in the center, you can see that there is that collecting duct in the middle with that blue highlight behind it. And we have two nephrons here, one on the left and one on the right. And both of their distal tubules are emptying into that one collecting duct in the center. So each collecting duct is attached to multiple nephrons. Now, each collecting duct consists of two structures. Each one has a cortical collecting duct, which is simply the portion of the duct located in the renal vortex. And then they each have a medullary collecting duct, which is simply the portion of the duct located in the renal medulla. So those are nice and easy to remember. So if we're looking at our image here, this portion of our collecting duct in this lightly colored region would be considered our cortical collecting duct. And then this portion of our collecting duct located in that renal pyramid would be considered our medullary collecting duct. Now, as these collecting ducts are coming down the renal pyramid and approaching the renal pelvis, they actually fuse into something called a papillary duct. Ok. So this right here is our papillary duct and it's called the papillary duct because it's located at the pilla or the tip of that renal pyramid. And this is kind of hard to picture from our little cartoon here. And most textbook images don't really show this either, but it's kind of imagine each renal pyramid has 100 of collecting duct. And about, you know, as they're coming down toward the tip of that renal pyramid, about 5 to 10 of them will fuse into one of these papillary ducts. And when filtrate reaches the end of that papillary duct, it is finally officially considered urine. So we did it guys, we finally made urine. So just to kind of put all of this anatomy together for you a little bit. What's happening here is we have our Nephron located in the renal cortex, filtrate is moving through the renal tubule getting modified the entire time. It's moving through the collecting duct. It's still getting modified that entire time. The collecting duct is going down the renal pyramid toward the tip toward the papilla. And that filter is finally gonna be coming out of that papillary duct at that point, it is considered urine. So the urine is coming out of the tip. The papilla of that pyramid, it is emptying into a minor hali which will then empty um empty into a major Cali which will then empty into the renal pelvis, which we know is continuous with the ureter. And so urine will travel down the ureter and then enter the urinary bladder just to kind of put all that together for you. All right. So that is our collecting duct and I will see you guys in our next one. Bye bye.
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example
The Nephron Example 4
Video duration:
56s
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OK. So this one asks us at which location would filtrate officially be considered urine. Let's run through these options. So, a reads at the end of the proximal tubule and remember that's the very first part of the renal tubule. So at that point, we are definitely still filtrate. So A is out, B reads the ascending limb of the Nephron loop. At that point, we're still in our renal tubule. This is still definitely filtrate. So B is out C is the beginning of the collecting duct. Remember, the collecting duct continues to modify filtrate. This is not the final product yet when it hits that collecting duct. So C is out and we are left with D which is the correct answer when it reaches the papillary duct. The is a long journey to get there. But by the time filtrate has gone through the entire renal tubule and the entire collecting duct and it's coming out the papilla, the very tip of that pyramid in that papillary duct, it is officially urine at that point. So our answer here is deep
11
concept
Types of Nephrons
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2m
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So up until this point, we've been talking about nephrons pretty generally, but there are actually two types of nephrons. So we're gonna go over these in this video. So first up, we have cortical nephrons. Now, cortical nephrons as their name implies are located in the renal cortex. Though the majority of the nephron will be in that cortex, but the tip of their nephron loops can dip into the renal medulla. And in terms of distinguishing features aside from just their location, um these tend to have shorter Nephron loops. So if you look at our image here, you can see how the majority of this Nephron is located there in the renal cortex and it has this little tiny Nephron loop that's just barely dipping into our renal medulla. And cortical nephrons are quite prevalent. They make up about 80% of all nephrons and in terms of their function, they are doing what all nephrons do. They filter blood, they modify filtrate. And these also specialize in helping regulate blood pressure and in terms of their blood supply, these are fed by peritubular capillaries which we will talk about in an upcoming video for you. So those are our cortical nephrons and then we have our juxtamedullary nephrons. Now, this name is also very intuitive. These are located at the boundary of the renal cortex and the renal medulla. So juxtamedullary, meaning like next to the medulla. And these um or for these, their nephron loop is going to go deep into the renal medulla. And because of that, these need to have long nephron loops, you can see that they look quite distinctive. So they're located right much closer to the boundary of that cortex in the medulla. And they have these nice long nephron loops that are going deep into that Mandula, deep into that renal pyramid there. So they look very distinctive when you see them um side by side. And these make up approximately 20% of all Nephron. Now, once again, in terms of their function, they're doing what all nephrons do, they're filtering blood, they're modifying filtrate. But ju Miri nephrons also specialize in creating concentrated urine, which we will talk about in a future video. And in terms of their blood supply, these are also supplied by peritubular capillaries as well as a specialized structure called the vasa recta. So we will see that again in an upcoming video. OK. So those are our two types of nephrons. Again, luckily, they were named very intuitively based on their location. So they're pretty easy to remember. All right, I'll see you guys in our next one. Bye bye.
12
example
The Nephron Example 5
Video duration:
1m
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OK. So this one asks us which of the following statements is correct. Now, I'm not gonna read all of these verbatim because they can be a little bit long. But just looking at these answers, I can tell that our correct answer is going to be D which says that cortical nephrons have shorter Nephron lo and are located mainly in the renal cortex. Whereas ju medullary nephrons have those longer loops and can extend deeper into the renal medullas. So our answer is D now just to take a quick look to make sure that we all understand why A through C are incorrect. A reads that cortical nephrons have longer loops and that Juul nephrons have shorter loop. It should be the reverse, right? So A is incorrect. B read that Juul nephrons are more abundant. The cortical nephrons, the opposite is true, right? About 80% of nephrons are cortical nephrons or it's about 20% are jury. So that's why B is incorrect. And then for C, we do have the correct um locations there, but we have incorrect Nephron loop lengths on both of these. So that is why C is incorrect. And our answer here is D.
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Problem
Problem
Which of the following statements best describes the role of the juxtamedullary nephrons?
A
Juxtamedullary nephrons filter large volumes of blood to increase urine volume.
B
Juxtamedullary nephrons play a role in forming concentrated urine.
C
Juxtamedullary nephrons play a key role in regulating blood pressure.
D
Juxtamedullary nephrons control K+ and Ca2+ levels.