It is my pleasure to start us off by talking about the esophagus and the stomach. And as we would say, this is the upper part of the GI tract. This is a disclaimer that I will show. And I will move into talking about the gastrointestinal tract. And you'll see that referred to in a lot of different ways. If you're British, you might talk about it as the alimentary tract. You'll see it as the digestive tract. It is T-R-A-C-T. Sometimes I see T-R-A-C-K, and it makes me cringe. It is really, it's an extraordinary organ. It's a continuous tube. It begins in your mouth, and it ends at your anus. And I'm from Massachusetts, where we are the home of Dunkin' Donuts. So the way I talk to my patients is I explain, everybody's a donut. We all have a skin on the outside, and then we all have a hole that goes from our mouth to our bum. And that's the part of the GI tract is what you get to look at with endoscopy. It's about 30 feet in the average adult, so it's quite a long hole. And it really has three functions, digestion of food into nutrients, absorption of nutrients into the bloodstream, and then elimination gets important. So this is the basic layout of the gastrointestinal tract. And sort of tucked up here, heading into the chest, is the esophagus. You can see the esophagus runs behind the liver into the stomach. The stomach empties into the small intestine. I always say those are the wiggly things. These are sort of in front of what then becomes, down here, the large intestine. The large intestine is actually running what we say retroperitoneal. OK. So that's your whole head of your donut. OK. It is truly a complex and wondrous system. I think for many of us, it's not that we went into medical school, at least I didn't go into medical school thinking of it as my driver with going to medical school. But somewhere in medical school, for many of us, we encounter it. And it's very complex. It's perfectly designed. And most of what it's about is getting every calorie out of every meal that you're eating. So whatever you ate for breakfast, its job is to absorb that and get energy from it. Of course, we'll be sitting for a lot of this morning. But that's what your body really relies on, is your GI tract doing its job. The esophagus and the stomach, which I'm focusing on, is really the entry point. It's designed to get the food into the system and start the process of digestion. There's actually no absorption that happens in the esophagus or the stomach. So this is the journey through digestion. And actually, I think in many US classrooms, this is now taught in second grade. But I'll just remind us all that it starts in the mouth. The posterior mouth is called the pharynx. Somehow it's transmitted to the esophagus and not into your lungs. It gets into the stomach. It goes into the small intestine and then into the large intestine. And really, the liver and the gallbladder are contributing their pieces to the digestive process in the small intestine. So digestion really begins in the mouth. I told you no absorption is happening. But you do start digestion the second you put anything in your mouth. And that really starts with chewing mechanically to break down your food. The presence of food, which stimulates saliva production, which is the beginning of some enzymatic action. And then your tongue. And I'm a gastroenterologist. I don't really focus on the tongue. But anyone out there who's thought about speech and language pathology knows the tongue is pretty impressive, too. And it's really important for arranging food bolus for swallowing. Saliva has a lot of different functions. And basically, a lot of it's about moistening the food. There's a lot of parts of the mouth where the salivary glands are located. And there's amylase in saliva, which initiates carbohydrate digestion. And also has some antibacterial effects. So much of your GI tract is about really respecting that you're constantly introducing the world into your system, into that hole of your donut. And it is important that your body is constantly vigilant for any bad actors that might be coming in as part of your eating. So as the food moves into the esophagus, that's where things can get a little bit hung up. And that's because it's really the narrowest part of the GI tract, with the exception of the appendix, which is much further down off the beginnings of the large intestine. So the esophagus is actually quite narrow. That's particularly at the top, in an area we call the upper esophageal sphincter. And then it also is quite narrow, again, as it passes through the diaphragm into the stomach. And this is just showing the upper right here is going to be upper UES. And then the LES, the lower esophageal sphincter, is going to be down here. The esophagus in the chest is sort of traversing a number of things. It's got to stay around and sort of keep away, if you will, from the aorta, which is also in there. And when we do endoscopy, we're very aware of the heart beating. I mean, you literally can see the heart beating that's in the chest right here. And after a while, you stop thinking about it. But when you're training people, they are very aware that you can literally see the heart beating. The esophagus is vertically oriented, obviously. The goal is to get stuff into the stomach. It's slightly to the left of median. It then passes across the right side of the aortic arch, descends into the posterior mediastinum along the right side of the aorta. And then at the diaphragm, it's actually passing a little bit in front and to the left of the aorta. I will tell you, I am not a cardiologist. My husband's actually a cardiologist. But as the body's developing, there's a lot going on here. And when things don't go well, you can have sort of your aortic arch doing weird things and stuff like that. The goal is to have it exactly the way it's designed, to show up in the abdomen in the right place. All right. So I just wanted to talk a little bit about terms of swallowing, because I think you guys are going to be asking and thinking a lot about swallowing. And you'll see a lot of terminology around what's going on there. So first off, when we talk about feeding, that's actually the placement of food into the mouth. And then the manipulation of that food in the oral cavity prior to actually swallowing. And so that might be the chewing part. That's definitely a lot around the tongue, actually getting all the food that you've just chewed up into small pieces into the right place. And it's basically quite a complex process. So unfortunately, well, in pediatrics, we don't see that really developing until 6 to 12 months of life. And then it is, as you become elderly, it can be one of the functions that starts to go. Swallowing is placement of the food in the mouth. And then it's this oral and pharyngeal stages of the swallow. So it enters into the esophagus through what we call the crico-pharyngeal juncture, which is really right here at the top of your throat. And then deglutition is the process of swallowing. So these are three different ways to think about swallowing. And honestly, not all difficulties with swallowing are the same. So it's really, where is that difficulty happening? And a lot of when we try to understand what people are describing around eating or what they're feeling in terms of where it's getting stuck, we're trying to pick out what's happening. In terms of phases of swallowing, that amazing function of actually getting stuff to the back of your mouth and swallowing it takes about one second. It's very quick. The pharyngeal phase, which basically a lot of that is about elevation or retraction of the vellum. So you don't have stuff go up your nose, and you also don't have stuff go into your lungs. So all of that gets very important. That's also about one second. And then once it's in the esophagus, it really takes about 8 to 20 seconds to make its way from the crico-esophageal juncture into the gastroesophageal juncture. So a lot happening, but most of the process of actually the swallowing is in the esophageal phase. All right, so moving into digestion. Digestion is where we've broken down the food into smaller components, and it's really important that that happens early on, right? So if you don't do it early on, it's sort of leaving a lot of solid food that needs to be sort of... There's no chewing that happens beyond the mouth. But that's important because that allows the body to absorb nutrients and minerals in food, and that's obviously how we grow, if you need to grow. And most of us don't want to grow anymore, but you need to grow. And then you need to have a good metabolism and your body maintenance, and also important for us as beings for reproduction. All right, so mechanical pieces, like I said, all are mostly happening in the mouth. It's mostly around mastication, but there is movement through your GI tract. It's actually important that stuff is being moved through the GI tract, and that is also a mechanical process. So most of that process is propelling stuff forward. That is called peristalsis. And really, peristalsis starts in the esophagus, so you need to have movement. It's really a mechanical movement of stuff through the esophagus. And then there's a process called segmentation, where the body can be good at mixing stuff, and I'll show us a picture of this to distinguish peristalsis from segmentation. And then there's lots of enzymes and chemicals that your body is secreting to help with digestion, again, starting with saliva. You have a very strong hydrochloric acid that lives in your stomach, unless you are taking medication to keep that from being there. And not all acid is bad. That gastric acid does a lot of great things for us, much of which we have really started to appreciate now that we've spent 30 or 40 years suppressing people's acid in America. We really sort of focus now on all the good things gastric acid does. Pancreatic enzymes are very important also for digestion, and then bile is important as well. If you think about it as a process, so much is around the motility. If you have any issues at all with stuff getting stuck, again, you've got a 30-foot process you have to get through. If it gets stuck early on, it's going to be a problem. And a lot of that really has to do with muscular movements of the GI tract. So we don't think of our gastrointestinal tract as a muscular organ, but it very much is one. And again, it's really all around this peristalsis and segmentation. And then you move into secretion, which is the acid and enzymes. And then much further down in the small intestine is going to be absorption. Sorry, forgot about my slide. So thinking about that motility as the key component of digestion, really the two goals are the propulsion and mixing. This is looking good. OK. So this is, I think, a nice diagram that really shows the difference. So peristalsis is the movements, the muscular movements that the intestine is doing to push basically the bolus forward. In segmentation, it's sort of mixing it up a bit. So it starts seeing a red-blue, and then you're seeing as it's mixing them together, they're starting to get more purpley. Does that make sense to everyone? OK. All right. I actually had to study up on this myself. So all right. So back to the GI tract, I'm going to focus on the esophagus as the most important organ, at least for our purposes. So the esophagus is a hollow muscular tube. It connects the mouth to the stomach. It's transporting all that saliva that you've made in your mouth and the food. And of course, when we stick an endoscope in, we're used to seeing it nice and expanded, and we can sort of talk about its diameter. But it's really quite collapsed at rest. So if you don't have anything in it, it is not expanded. It's sort of a collapsed organ. It's flat in the upper 2 thirds, and then it's rounded in the lower third of the esophagus. And it's remarkably thin-walled. So the esophagus is about 2 to 4 millimeters thick. And you are going to see, I think, some amazing videos and pictures of what, thankfully, I don't do too much of, but my colleagues, some of them over here, really do a lot of extraordinary work in the esophagus. That's all happening within a 2 to 4 millimeter thickness area. So it's really quite dramatic stuff that you can do within those 2 to 4 millimeters. There's four distinct layers to the esophagus, which I'll go through. And then importantly, the esophagus is a piece of the GI tract. It is the piece of the GI tract that does not have what's called a serosa, which is an outer lining, basically. So there's really not much barrier between the esophagus and the rest of the mediastinum, which, as I explained, includes the aortic arch and the heart. So it's not exactly encapsulated. It does grow with you. So newborns have an esophagus that's at about 8 to 10 centimeters. By the time you're five years of age, you have become much taller. We say you double your birth length in the first year of life. You never grow like that ever again. But certainly by five years of age, you're about three times your birth length. And now your esophagus is about 16 centimeters. At 15 years of age, it's pretty close to your adult size. And in adults, it's somewhere between 18 and 26, even 30 centimeters. Depends how tall you are. It's one of those organs that has to go with you. The diameter really depends on whether there's something in it or not. But it is different. So it gets wider as you get growth. So it's only 5 millimeters at birth, 15 millimeters at five years of age. And then for most adults, we consider the diameter naturally to be about 20 millimeters. It can stretch. So you put food in it, and it's a stretchy organ. And it'll get big and handle a bigger bolus. All right. Am I moving too quickly, too slowly? How are you guys doing? Everybody okay? All right. I'm watching everyone writing. Don't write. I think you're all... Don't they get the slides? They get the slides. Okay. So what you want to see is adults have a very important function going on. I mean, write if you like writing while you're listening, but don't write if... I promise this isn't on the quiz, right? I don't know. So what you want to see here is the esophagus in an adult is much longer than the esophagus in a newborn. But it also... What adults have going for them is gravity. So most of us do not try to eat lying down. We are eating standing up. And what you want to notice is in the adult who's just eaten, food is actually somewhat in the esophagus, somewhat in the stomach. And there is actually natural reflux that happens. It's not a one-way valve at the bottom, and I'll talk about that. Newborns have a much shorter esophagus. Any bit of food will immediately be in their mouth. And you can see this is actually why infants all spit up a lot, and luckily grownups do not, because we have gravity working for us. And longer esophagi. Okay. Getting into the wall layers of the esophagus. So I'm going to start in the middle. This is it kind of collapsed. This is a nice endoscopic picture. What I can tell you quickly is this looks nice. There's a little bit of saliva in it. And then what you're seeing is a nice vascular pattern. I always say when you can see a vascular pattern, it means there isn't a rash going on inside. So what you're seeing here are the layers. So we know about the mucosa. It's the innermost layer. Then there's a very thin layer of muscles called the muscularis mucosa. Then there's some cells below that called the submucosa. And then there's two layers of muscles. There's a circular muscle and a longitudinal muscle. So this is it in cross-section. This is a biopsy showing histologically what you're seeing. So this is the mucosa. And what you want to notice is it's stratified and squamous. And you're going to say, well, how would I know that? And the answer is, I'm going to show you columnar in a second. But a lot of the esophagus is the stratified squamous epithelium. And then as you're getting into these different layers, you're seeing the submucosa down here. All right. So the upper third of the esophagus is skeletal muscle, which is up here, versus the lower two thirds, which is smooth muscle. And we do think of skeletal muscle as voluntary muscle. Like you have a little bit technically more control over that. By the time you're into smooth muscle, it's involuntary, really just doing its own thing. And then this is the concept of how those two muscular layers are really working to help swallow. So you have the inner muscular circular muscle, which is contracting the esophagus and moving food boluses down it. And that's quite different from the outer longitudinal muscle, which essentially shortens the esophagus and helps it sort of move things along like that. And it all relies on what we call the enteric nervous system. So certainly a lot of swallowing disorders that have to do with the fact that the neurons are what we call the myenteric plexus has been affected in some way, sometimes by autoimmune reasons, sometimes from radiation, sometimes different things, caustic injuries. But really the enteric nervous, and sometimes we don't know what affected it. So the enteric nervous system is an object of fascination for our motility experts, none of which I think are here today. All right. So getting into the gastroesophageal junction. So this is the esophagus. And it is where it hits the stomach. And what you want to notice is that's all where the diaphragm is coming in. So we do think of the lower esophageal sphincter as a special muscle. But a lot of it has to do with the diaphragmatic ligaments on the outside of the esophagus, which you can't see from inside it. What you can see inside is what we call the squamo-columnar junction. And that lets you know you are about to enter the stomach. So that whole area where the diaphragm is coming in and creating what we call the angle of hiss, or sometimes we call it the crural diaphragm. So it's really those crural ligaments are what's holding the lower esophageal sphincter together at the bottom. That is a really critical area. And it's also what keeps you from refluxing too much. So if that's not working well, or frankly, if these are not quite beautifully aligned with each other, you might have more reflux going on, or what we call a hiatal hernia. So I think you'll see pictures of that later. The lower esophageal sphincter is a really important piece of our function. And you notice it if it is not functioning well. It is working all the time for you. It relaxes when you swallow. And most of you are sitting here having had some coffee, or water, or you're eating. And it's actually still working for you. It's basically relaxing in a transient way. And then it contracts pretty quickly back to allow backflow. So you don't want to be refluxing too much. But it is, again, it's not a one-way valve. And there's a little bit going on back and forth. And if you don't have that, if for surgical, let's say surgically, you've had that wrapped in some way, we call it, so that it isn't relaxing when you swallow. It's actually a little uncomfortable. Sometimes you need to burp, and you can't get the air up. And again, these are all things we just take for granted. But it's a remarkably important part of you that makes you comfortable all the time. And those transient lower esophageal relaxations, again, are something our motility experts have become really fascinated by, and have all kinds of ways of looking at it. So this is something called impedance monitoring and pH monitoring, trying to look at pressures. But it's very important that the lower esophageal sphincter is able to transiently relax. So this is a swallow happening in impedance. And then this is what it looks like endoscopically. So you are seeing the esophagus, that smooth, shiny pink, hitting a darker pink of the stomach. And very importantly, here's that squamous epithelium hitting columnar epithelium. Let me see if my pointer still will work. Yes. This is the columnar epithelium here. And it looks completely different from this type of skin cell. So with my final minutes, the stomach is this J-shaped reservoir. Some of us think of it as a kidney bean, or you can think of it different shapes if you like. But it's a J-shaped reservoir of the digestive tract. The food is being mixed in there with acid and enzymes that break down the food. And then small amounts of partially digested food over time are being released into the small intestine in a sort of paste way to now continue their 30-foot journey. And we can break the stomach up into various parts. So you have, again, the lower esophageal sphincter, which you can look back on. And then you can go down to the bottom of the esophagus and see the pylorus, which is the drain of the stomach. So this is the area called the antrum that corresponds to here. And now you're heading towards the drain of the stomach called the pylorus. Here this is looking back up at the scope coming through the lower esophageal sphincter and what we call retroflexion. And it is looking up at an area called the fundus or the cardia. And that is indeed partly because the heart is sitting right here. And then you have the greater curvature of the stomach. And you have the lesser curvature of the stomach. And this very big J-shaped body of organ is called the body of the stomach. So you're really seeing the body of the stomach. A lot of these pictures are essentially showing body. Body has got this very distinctive rugae or gastric folds. If you put enough air in endoscopically, you can absolutely flatten these. But these get really important for, again, all the secretion and digestion that's going on. It's a very distinctive look. Looks very different from the esophagus. So even the fellows know when they've made it into the stomach because it's kind of obvious. It's almost July, so sorry. All right, so the stomach layers are basically the same as the esophagus with that exception of the serosa. There's really a serosal surface to the stomach. So something that's really encapsulating it. And if you look with what's called endoscopic ultrasound, you can see all these different layers. You can do that in the esophagus too. And again, seeing the mucosa, the muscularis mucosa, the submucosa, the muscularis propria, and then the serosa at the bottom. And stomach mucosa in those rugae is, as I said, very, very different from the stratified squamous epithelium of the esophagus. So you're seeing columnar epithelium. These are really glands. They really do a lot of secretion. And they also are encapsulated in these muscular layers. And the stomach actually has a third layer. So it has the longitudinal layer, a circular layer. And then it also has an oblique layer. And it's really a very muscular organ. And it's really capable of some pretty intense contractions, most of which, unfortunately, you feel when you vomit. So it's really capable of expelling if it needs to. That's very much a muscular organ. And then I think the stomach is mostly famous for all the stomach acid that it does. And there's a lot of different cells involved in a feedback loop, which both can stimulate acid secretion from the parietal stele and also can downregulate acid secretion, depending on whether you need to be digesting or not. And really, what's extraordinary about, I think, in particular, the parietal cells and what we call the proton pump, which is in those, is it's basically the only organ in the entire body that secretes hydrochloric acid with a very strong acid to it. So the pH of stomach acid, unimpeded, is about 1 to 2. So it's quite a strong acid. I think that brings me to the end. So. OK. Thank you. That was short.

esophagus

stomach

digestion

absorption

elimination

structure