- [Lecturer] Today's video is on the urinary system. And with that, urination really does begin with the kidney. So we're gonna start by drawing both of our kidneys out and we're gonna draw both out, but we're gonna draw some different structures on each one just so we have enough room to identify everything that we need to with the kidneys. All right. So just you know the right kidney is going to be a little bit lower than the left one when we're looking at this anterior view of the kidneys. Just because the liver kind of displaces that right kidney down a little bit. So they're shaped just like a kidney bean, and we're gonna draw all the different structures out first. This is going to be essentially a frontal cross-section. So we're gonna cut it in the frontal planes. We can look at the inside here but it still has an anterior view of that. So let's draw out a few different structures here. Again, the right and left are gonna look a little bit different just because of the number of structures that we have to fit in here. And as always, hang in there with me. I was trying to make these as detail-oriented as we really need them to be but not too much more detail-oriented 'cause I don't want it to get too crazy. And then these ones are gonna look a little wild just to start off with, but hang in there with me and I'll explain them in a moment. All right. So remember when we were talking about the circulatory system, we were talking about a renal artery and vein. So this is going to be our inferior vena cava here that's gonna be passing by these kidneys. And now these kidneys, I squish them together a little bit just for the purposes of our drawing. They're actually spread a little bit further apart. So this is our inferior vena cava right here. And since we already know the name of that, I'm just gonna write the abbreviation right here, IVC. And then we are gonna have our renal veins going off to the side here. And that's going to bring blood from the kidney into the inferior vena cava. Now, we're also going to have the aorta right here. And then the only bummer is that the renal arteries are going to be a little bit overlapping the veins right here. So what we're gonna do is we're just gonna draw the renal artery peaking out here just a little bit so we can have a glimpse of it. And again, we're gonna draw in a similar color. So we'll use this bright pink we have here and that's gonna be bringing blood to the kidneys. All right. So now we're getting into the structure of the kidneys themselves. All right. So, with this frontal plane cross-section we're going to break the kidney down into a few different parts, but to start off with, there is an outer layer on the very outside of the kidney and that is going to be called our renal capsule. So I'm just going to draw it on this one just to simplify things. So, remember when we were talking about the meninges around the brain and we described one of the, almost like a hotdog casing, it's gonna be very snug and tight. That's gonna be the same way that this renal capsule is around the kidney. And of course, both of these structures, or all structures here will be on both aspects of this, of each kidney but we're just going to draw on one 'cause it makes it easier. All right. So then we're going to have two different parts of the kidney which is analogous to the two different parts of the adrenal gland which actually sits right on top of the kidneys. And we're just leaving those out for simplicity at this point, but we have the cortex, which is the outside. So that's from here to here. Actually not, let's just go for it. We'll color it in. I was gonna attempt to do arrows but I feel like coloring it in makes it a little bit easier to memorize. And that's what I want. I want you to have an easier time memorizing things. So we're just gonna go for it. This yellow pen is running out of juice though. Maybe we should use a different color. I think we're gonna make it. So like I said, that is going to be our renal cortex. All right. So then on the inside, we're going to have a renal medulla. So, see where all these pyramids are, they sit within the renal medulla, but I'm just not drawing them on this side so we can distinctly be able to separate the renal medulla from the renal cortex. And how I remember which one is in which spot the cortex or the medulla is when I hear the word medulla, I think middle. So that's how I always remember that the renal medulla is in the center or in the middle. All right. So within the renal medulla, we're gonna have these things called renal pyramids. So, renal pyramids are going to be these pyramid structures. It's gonna be anywhere between six to eight. So I just drew six to keep it simple. And that's kind of how we cut up or we distinguish the kidney in it's different sections is by pyramids So, then what I want us to draw next is something called the renal papilla, which is essentially the very end part of each renal pyramid before it makes its way to something called the minor calyx which is these little noodle-looking things coming off of the pyramids right there. So, let's first name our renal papilla, which is the opening of something called collecting ducts. But we don't need to know that, it's just the very end of the pyramid. So let's make that this nice turquoise color. All right. So those are our renal papillas. All right. So let's label our minor calyx first. That's gonna be what attaches to all of the different renal papillas. And then what brings those together is our major calyx. And then that is finally going to bring us to our renal pelvis. So, this renal pelvis is then going to actually turn into our ureter, which is going to be this brown part there. Now, with everything bunched together in this area, it's going to be known as one single area called a renal hilum. And the renal hilum will consist of, it's basically the point of entry and exit of the renal arteries, veins, lymphatic vessels, nerves, and this and large portion of the ureter. So, because it is like this whole section right here, it's kind of difficult for me to actually give that a true little coloring it in as we need to. So what I'm gonna do is I'm gonna have to kind of draw a highlighted circle around it. So it's going to be, well, it's kind of like an oval. It's my attempt. So imagine if we have like a big orange circle right there, so everything in that area, it's not a true structure and not its own thing poking out of there but it is going to be our renal hilum which is going to incorporate a few different things. Renal hilum. And I'll write down what it is. I will put this there. So, it is the renal vein, renal artery, lymphatic vessels, nerves, and the ureter. That's everything that is considered part of the renal hilum in this area. Now a couple of other things I want to draw another structure here and it is the functional unit of the kidney. And that is the nephron. So the nephron is this functional unit of the kidney and it filters plasma. Now, I'm just going to draw it out. You'll go into more detail about the function of the nephron and all the specifics of it when you go into physiology but I'm just going to draw out the structure so you see kind of what it looks like here. Getting like, "Is this is a simplified version of it?" But this is what an nephron looks like. It's the functional unit of the kidney. And there are a bunch of them within the kidney. So this is like a microscopic view of them. And I always like to inform you of what the functional unit is. So, that's what that is. I know one other side note is that I want to talk about the area in the body that the kidney is sitting in. So one last thing I'm going to do on this paper here. So let me just separate. This is our nephron and then I'm going to show you a midsagittal cut of a side view of a person. Here we're gonna have their butt, actually, accidentally have a really pointy butt. But anyway, here is where their iliac crest is is about right here. And then here is their diaphragm. And then let me just give him a face. He has no neck. Oh, well, anyway. Here's our little dude looking all funky like I always make him. And my point in showing you this is that we are going to separate this abdominal cavity into two main spaces. Now this is an extremely simplified version of what we're gonna discuss later, or actually what you, we may or may not discuss it a little more later but if you take further anatomy classes, they'll definitely discuss it. But overall, most of our abdominal organs sit within something called our peritoneal cavity And that encompasses most of those structures that we reviewed when we talked about the digestive system. However, a few of those structures actually sit in something that's for the most part, more posterior. And again, this is a huge simplification of what these spaces are like. It's actually a lot more complex. But this other space is called retroperitoneal space. And that's where the kidneys are and a few other structures. There's actually an acronym for it if you ever do need to learn all of those structures for another anatomy class. I'm not gonna make you learn it in our course, just because I don't think it's necessary, but our kidneys are living in the retroperitoneal space. So they're just one of the many structures there. So that wraps it up for the kidney. So, remember we talked about the medulla and the cortex and then all of these structures within the medulla as they make their way over to the renal pelvis, all of the structures involved in the renal hilum and then how things exit the kidney going in through the ureter. Now, just like we have been talking about with the other systems, at this point we're going to follow the ureter all the way down. And our next view is going to be essentially the extension of the ureter and how urine continues to pass through. Now, just as a reminder, we went from our renal pyramids to our renal papillas, to the minor calyx, to the major calyx, and then into the renal pelvis. So that flow of that fluid that's coming out of the kidney, down into the ureter. So now that we have that pathway down in our minds let's follow it as it makes its way down the ureter. We also have our renal columns, which are in between each pyramid and really just connect the pyramids. So, let's add in renal columns. That's just one last thing I forgot to add in. So in following the pathway of urine down our ureter the next place that's gonna go after going through the ureter is to the bladder. So let's review the bladder on this page. So this is going to be an anterior view. So we're going to have our bladder which the purpose is storage. Of course, that's where we store urine. So, let's draw our bladder which is kind of like a spherical structure. I wish it was the one more symmetrical, but we do what we can. So there's our bladder. Now, we had ureters and how the ureters work is that they are going to be coming one from each kidney and they're going to actually travel behind the bladder and enter kind of the inferior bladder. So I'm gonna mark a little spot where they're going to enter and we're gonna draw them coming from above, one from each kidney. And then I'm going to draw it as a dotted line so we know that it's not traveling in front but it's actually behind the bladder. And then there is going to be a little triangular area right here. All right. So something to note is that let's see, let's draw in our ureter and I'm gonna kind of, I'm gonna color it in, but just note that the black lines means that it's traveling behind the bladder, the dotted lines. Ureter. So what I wanted to point out to you is that the ureter and the bladder are both transitional epithelium. And that's important because they are both meant to stretch. So, that's why I wanted to point that out in terms of tissue composition. All right. So, our urine is traveling through ureters one from each kidney going behind the bladder inserting into the bladder. Now, there is a little area right here. Oops. You know what? I don't wanna forget to label the bladder, or identify the bladder just in case you're looking back at your notes and you're like, "Wait, is this huge circular the structure of the bladder? I'm not sure." So before I forget, I wanna label that. So, we have this triangular structure there and that is actually called our trigone and that where it kind of, two of the points of this triangle are where the ureters enter the bladder from behind. But the trigone may have a little bit more function in terms of urination than we're aware of. There's still ongoing research, but it does have a lot of important stretch receptors which is very important for the bladder. So, now that we covered the bladder itself, the trigone, one other thing is that the bladder itself is composed of a muscle all around it. So it's like this wall of muscle that encompasses the bladder and that is called our detrusor muscle. Let me draw that in blue here. All right. So what happens during urination is, actually, you know what? I'm gonna write this out for us. Urination. The clinical name for urination is micturition. So, in case you ever have a patient in the future where they talk about frequent micturition is how they talk about urinary frequency. So for urination, first, you're going to have stretch receptors that stretch. Then your detrusor muscle is going to contract. And then what's going to happen is we have a few other important muscles that I want to point out. So we're going to have a, let's see what color I wanna be good. We're going to have two different sphincters. So, I'm gonna draw them both out for us. So, our first sphincter is going to be right here. And remember, we oftentimes have a sphincter muscle when we're talking about transitioning from one organ or one area to another. So what this maroon thing right there is, it's called our internal urethral sphincter. And it is smooth muscle. So remember, smooth muscle is involuntary. So the next step and our urination is we have stretch receptors that sense that the bladder is being stretched. Then our detrusor muscle contracts to get the urine out. But we have a little sphincter muscle right here. So that internal urethral sphincter that's right there has to relax for urine to be able to come out. Because if not, we won't be able to get urine out through that sphincter. Now, after we have that internal urethral sphincter that is actually going to be the transition point for the beginning of our urethra. So oftentimes people will get the ureter this brown thing, confused with the urethra. So let's make sure we don't get confused with that. I'm gonna draw it in right here. Urethra. And then we have the external urethral sphincter as well. It's gonna be this right here. Now, what's important to note is that this external urethral sphincter is skeletal muscle. That means it's voluntary. So, after our internal urethral sphincter relaxes to let urine down into the urethra, we have to actively be able to relax our external urethral sphincter to allow things to go out. So that's why we can hold our pee in if we feel like we have to pee. So oftentimes, we'll hold our pee in we'll contract that external urethral sphincter and maintain that contraction until we go find a toilet, at which point we will actively relax the external urethral sphincter and allow for urination to take place. So those are the different steps that go on during urination. Now, the bladder is so interesting and I deal with the bladder a lot as a pelvic physical therapist. And I believe I may have told you all this before but there's something really cool that's very important with the bladder itself, and this is just an extra information not that it's part of our general anatomy course but I wanted to explain to you that there is something called a somatic visceral reflex. And again, I believe I told you about this but there was a study where they took a bunch of rats that were perfectly healthy and they wrapped a tight cord around each of the rats tails. And now the rat's tails is analogous to the human coccyx. Remember that's like our tailbone. So what happened with these perfectly healthy rats is after a period of time of having their tail squished by that cord, they develop bladder pathology or bladder disorders that were not there to start with. And they've seen the same thing happen in humans, where if they have very tight pelvic floor muscles pulling on tailbone and other structures, it can actually lead to irritation of bladder tissue without there being an origin of any bladder pathology present to start with. So it's very interesting in terms of, oftentimes people will have a ton of workup done with physicians, and it turns out that it's actually muscles that's causing the issue. The same thing goes with burning with urination. I've seen so many patients who report burning with urination and they get a bunch of tests done and they think they have a UTI or a bladder infection and they take a bunch of antibiotics, but then it turns out that it wasn't their bladder infection at all. It was their pelvic floor muscles deferring pain when they pee because of what happens with all of these sphincter muscles and how the pelvic floor muscles have to relax to allow for urination to take place. And with that, they experience this burning sensation. And after we treated their pelvic floor muscles the burning sensation was gone. So anyway, that's just my little spiel about this. So this is what we have covered with the bladder so far. Now, let's follow this urethra down and kind of look at how it looks like in both males and females. So let's start with our next view. We're going to do like a midsagittal cut All right. So let's draw some people out and some pelvises. So our midsagittal cut. In this section, we're going to be kind of following the kidney down and we're going to be talking a little bit more about the urethra as well. So I'm not gonna give it a title. It's kind of just an extension of what we did before. So, let's draw a female. We're gonna start here. Here's one of her kidneys. And so, here's her abdomen. We're working down to her pelvis. So down here, this is her butt and we're gonna have her sacrum coming down like this and her coccyx at the end there. And then let's just draw the different structures. Finish off the front of her as well. So back here, we're going to have our rectum then on women we're going to have a uterus or people with a uterus, this is how it's gonna sit. And then here is vaginal canal and then we're gonna have a bladder. That's gonna kind of look like that with a urethra coming through. And then let's also draw out for just to know, here is our pubic synthesis in the front. So let's do the same thing for a male. It's gonna be pretty similar overall. Oops. I forgot to have something connecting our kidney down to our bladder over there. Let's do the same for a male. We'll give him a kidney too. And then it's gonna be pretty similar down here in the pelvis region, but it's going to be a little bit different only in that the structures will be different in that there is going to be no uterus. So we'll give him a butt too. And then he has super thick thighs, that is on accident. He will also have a sacrum and coccyx, he will also have a rectum, no uterus, but then he's going to have a bladder. He's gonna have another structure here called the prostate, and then also penis. So, let's label some of those guys in. Oops. I forgot to give him a connection here too. All right. You got her nice kidneys over here. And then remember we're gonna have our ureter going all the way down to the bladder. Let's label our rectum as well and we can label our sacrum and coccyx. Here we're gonna label in our uterus, which is just in the female. And then the vagina will also just be in the female as well. Now, what makes the males different is a male has a prostate. And that prostate sits directly inferior to the bladder. Now, we're also going to have something go through the, it's gonna go from the bladder through the prostate and out through the penis. So, I'm gonna draw a little bit of a zoomed in version of that as well, to make it a little bit clear but from the bladder, we're then going to have the urethra that exits on the way out. So let's do our urethra in this nice turquoise color. Urethra. And we're actually gonna have this urethra for the male go through the prostate and then through the penis. Oops. And I forgot to label the penis. Let's make the penis yellow. We can still see that urethra well. So when we're comparing the female urethra to the male urethra, they're a little bit different. So, for the urethra itself, the female one is only about four centimeters long and the male one is about 20 centimeters long because it has to pass through the prostate and all the way down the penis. So remember we talked about the internal and external urethral sphincters. I'm not gonna draw those in just because they're pretty small and we covered those last time in our last page of notes. But I want to kind of take a zoom in and break down the different parts of the male urethra. So, let me zoom in on that structure. So, we're going to start with a bladder here. And we're gonna have a urethra that's gonna pass through here and then go down through the penis. So, let's draw our prostate and then the penis around it. Let's color those in just so we can see them a little bit better. Here's our bladder. It is really time for me to get a new yellow and a new green marker here. Did me well this semester but I'm running low. So there's our bladder again. We have our prostate here and then penis as well. We'll go over the different parts of the penis in the reproductive system lecture. All right. Remember, we talked about, let's see, I'm gonna draw a little line to separate things out. Just so we know. All right. So for the urethra, for the male one, we're gonna have a couple of different parts. So we're gonna have the prostatic urethra, then the membranous, and then the penile or spongy urethra. So I actually started this penis a little bit too early. I'm gonna give it a little bit of space here before it starts. Let's talk about those three different parts of the urethra. Let's give it the first part, which is going to be as it goes through the prostate that's going to be our prostatic urethra. Remember, this is only in males and then we're going to have a short membranous urethra. And then lastly, we'll have the penile or spongy urethra which is gonna be the urethra as it travels through the penis. Now, one other thing that I want to label is your urethral orifice, which is essentially right where the urine exits the urethra. Do this right here. Urethral orifice. So I'm gonna make a note back up here with the urethra. So for males, it's about 20 centimeters, and females, it's about four centimeters. Now you have a urethra orifice for females as well and that's right where urine exits. Now, the urethra itself is going to transition. Remember how we talked about the ureter and bladder are composed of transitional epithelium because it has to stretch. It makes the transition out of that for the urethra. So just so you know, keep that in mind. I won't test you on it but it will turn into stratified squamous epithelium. But I really just want you to know that the bladder especially is made of that transitional epithelium because it's designed to stretch so it can hold more urine. So just as a review, we talked about, let's see, where did we start? We started at the beginning with kidneys. So we talked about the little nephrons which is the functional unit of the kidney which takes place in these renal pyramids. Then we have the fluid go out through the renal papillas, minor calyx, major calyx, renal pelvis out through the ureter. And that's all taking place in this retroperitoneal space. And then as we follow the ureter down, it goes one from both sides it's going to go into our bladder from behind. Then we're gonna have our detrusor muscle contract once it receives information from the stretch receptors that there is increased urine in the bladder. And then both our internal and external muscles, sphincter muscles will relax to allow for urine to flow through out through the urethra. But taking a little closer look at the urethra itself as it comes out from the female, it's pretty short just about four centimeters. And then it ends with the urethral orifice. And the male is basically the same, but it goes from the bladder out through the prostatic urethra, and then membranous urethra, and then the penile urethra to end with the urethral orifice as well. So that covers the urinary system and all of the structures involved.