 Okay, everybody, Dr. O here, and this is where we're going to talk about the ureter real quickly, but we're going to focus on the bladder. So here we see the kidneys and then remember the kidneys where urine is made, urine is going to be propelled or carried to the bladder by your ureters. Ureters are both about 12 inches long. They're lined with smooth muscle, so smooth muscle contractions propel or carry urine into the bladder. So that's really the only thing I know about the ureters. One last thing though, and the reason I wanted to talk about in the same video was the bladder, is when the ureters get to the bladder, they turn medially and they come in at an oblique angle. This is very important because it forms like these little one-way slits or valves. This is going to keep urine, hopefully, from propelling back up into the ureters and into the kidneys. So urine should be sterile, but urine should never travel backwards. If these valves don't work properly and urine can get back into the ureters and to the bladder, that can be, sorry, into the kidneys, that can be a very serious issue. The thing about the ureters is how they come in and they form these little one-way slits in the bladder. Looking at the bladder in general, just a real big picture, I think of it the same way I do the stomach. It's kind of an odd, but most hollow organs have two layers of smooth muscle. The stomach and bladder are the two that have three. So the three layers of smooth muscle found in your bladder is called the detrusor muscle, which you see there. So it has three layers of smooth muscle like the stomach. When the bladder is empty or nearly empty, it's going to have folds in it called rugae, just like the stomach does as well. The bladder is retroperitoneal, meaning it's behind the peritoneum, but you notice this peritoneum on the top. So the dome of the bladder is covered with peritoneum, but the actual organ itself would be retroperitoneal. Location of the bladder, it sits in front of or anterior to the uterus in females, which is why if you're pregnant, as your uterus gets larger, the ability of your bladder to get to fill or get larger before it fills is going to be lessened, which is why, you know, I know when my wife was pregnant with Oliver. She had to urinate quite often. There was a baby standing on your bladder, so it couldn't fully expand. What else about the bladder here? So we have, I talked about the detrusor muscle, and that's very important because the job of the bladder is to squeeze and squeeze urine from the bladder through the urethra to the toilet. But you'll see here, you have the two ureters coming in at the top, and then you have the urethra at the bottom. They form this funnel shape called the trigone. That's to make sure. So you see the little teeny slit-like ureter openings, and then this trigone funnel are designed to make sure that urine keeps flowing in the right direction. So that's a really key point there. And then you can also see the smooth muscles involved. So the muscles that hold urine in the bladder until it is time to micturate are the internal urethral sphincter, which is smooth muscle, and external urethral sphincter, which is skeletal muscle, meaning you can voluntarily control it. We'll come back to that in just a moment. What else? The lining of the bladder is covered with transitional epithelium. That's going to be the textbook example of transitional epithelium everywhere because an empty bladder, the cells are going to look maybe more cuboid, and they're going to stretch out when the bladder fills and look more squamous. That's why you have transitional epithelium. Well, I think that's plenty there. Let's just talk about micturation for a second then. So if this bladder is starting to fill, once there's maybe a really, really full bladder can probably hold a liter of urine, but that's going to be very uncomfortable for most people. By 500, 600 milliliters, you're definitely going to want to urinate. But let's say this bladder has 150 milliliters of urine in it. You now have the urge to urinate, but it can be overridden. That's why I think of urination and defecation kind of like examples of positive feedback because I could urinate, I should urinate, I absolutely have to urinate, I wet my pants or whatever. So there is the urge to urinate pretty early, but you can overrule that if you want. But then as the bladder gets fuller and fuller, this urge to urinate is going to be increased. And you might reach a point, and you've probably all been there, where the bladder is now so full of urine that this internal sphincter pops open. So the only thing to keep you from urinating is actually holding urine in, which means that only your voluntary skeletal muscle externally retrosphincter is working. So you've probably been there where you've been holding urine in. But the actual mixturition reflex, it's a parasympathetic reflex, and it involves the relaxation of both of these sphincters. So with defecation, you can pretty much just increase abdominal pressure and defecate. Urination, you need to relax these sphincters. So that can be a little difficult. There's a term maybe you've heard called stage fright where if someone's watching you urinate, like if you have to do a drug test or a test for the DOT or something, it's difficult to urinate when someone's watching you. Or like, I've been to sporting events where people are lined up in troughs and urinating. It is kind of difficult to urinate if you can't relax. So maybe you'll run water or things like that. But the point is you have to consciously relax these sphincters, and that's what will allow for mixturition or urination to occur. All right, that's the ureters, that's the bladder, and that's the mixturition reflex or how we urinate. I hope this helps. Have a wonderful day. Be blessed.