It's really thrilling to be here to talk about the GI tract, and it does sound like we have people at multiple different levels. Can I see a show of hands how many of you do know a lot of GI? I'm going to let you qualify a lot. Please let me know, because I can tailor this. Okay, I've got a corner over there, a lot of GI, some tentative hands. Who knows no GI? Okay, that's important. So I'm a believer in, we bring everybody up to speed. So I'll try to tailor this accordingly. But mostly, you know, sometimes it feels like you're going back to literally grade school. I think my kids have done a digestion module, well, they're both now in college. But in second grade, I began to realize they were talking about digestion in the, you know, Massachusetts school system. So we'll just go through things. There's a little bit of disclaimers, which we just talked about. And I'll take us to talking about the GI tract, which is also known as the alimentary tract, if you are from the UK, and the digestive tract, T-R-A-C-T. I've seen some very embarrassing slides where people spell it T-R-A-C-K. Do not do that. So it is really a continuous tube, and it starts in your mouth and ends at your anus. And I am from Boston or Massachusetts, where people like their donuts. That's where Dunkin' Donuts is from. So I tell my patients, we are all donuts. I literally do this, and I explain, we have a skin on our outside, and we have a lining that goes from our mouth to our bum. And this is really the whole of your donut is your GI tract, so T-R-A-C-T. So it measures about 30 feet in the average adult. And of course, it has three functions, which is digestion, absorption of nutrients into the bloodstream, and then elimination of solid wastes. And this is just a picture, obviously, over the next day or the next hours, we're going to go through the whole thing. But we're going to focus on the top part of it, which is really the esophagus and stomach. So I think it's really a complex and wondrous system. Somewhere I got interested in it. Of course, it's something everybody should be thinking about, because it's what keeps us alive. So I'm married to a cardiologist, and of course, the heart is super important. But I will tell you, the stomach is how you survive. And it's really not your stomach, but your GI tract. And it's all beautifully designed, unfortunately, to acquire every calorie out of every meal. So something we're focused on in developed countries these days is, what do we do about that? This esophagus and the stomach, the top part, is really all about getting food into the system and starting that process of digestion. And this is what the kids learned in second grade. But basically, the journey of digestion starts in your mouth to your esophagus, to your stomach, to your small intestine, and then your large intestine. And there's a couple of entry points right in the small intestine, I don't know if it's going to work, yes it is, where the liver and gallbladder and pancreas actually dump some juices into here to help with digestion. But it's basically a tube. So in terms of it beginning in the mouth, chewing is really a key piece of digestion. That's what mechanically breaks down your food. And then the presence of food, again, you're beautifully designed, stimulates saliva production. And you have a tongue that helps to arrange the food bolus for swallowing. The saliva is important. It moistens stuff. It's got some glands to it. We know it has amylase in it that's starting to digest some carbohydrates. And there is some antibacterial effect to saliva. Once food moves into the esophagus, it's starting to potentially not fit. So your esophagus is actually your narrowest part of the GI tract, excepting the appendix. And that's particularly at the top. So the very first act of swallowing actually protects you from anything too big that wouldn't move past the upper part, the upper esophageal sphincter. And then right where it hits the stomach, at the diaphragm, is your lower esophageal sphincter. And your esophagus is really oriented vertically. It's slightly to the left of the median of your chest. And it's basically kind of moving around the aortic arch. And so you can see the layout here. But it's descending basically in the posterior medial stynum alongside the right of the aorta. But right at the diaphragm, it's going to pass in front and a little bit to the left of the aorta. So there are these different terms we use in terms of swallowing. And this will get important for EOE, because swallowing is what people are having difficulty doing. So feeding is actually placing the food in the mouth, manipulating it back, and somehow swallowing it. Swallowing is actually getting it to the oral and pharyngeal stages of the swallow through to where the food enters the esophagus, really right here at the upper esophageal sphincter or the cricopharyngeal juncture. And then there's this concept of deglutition, which some people will use, which is basically all about the process of swallowing. So feeding is your hand. Swallowing is what you do sort of without thinking about it. And what's amazing about swallowing is it is an extraordinarily complex act that is happening super quickly. So the oral phase involves closing your mouth, which I tell my kids to do, and then using your anterior to posterior tongue movement to move something back. And then in this pharyngeal phase, which only takes one second, there's all this stuff going on very quickly. So nobody's still eating, but I will probably have some breakfast after this talk. And I will tell you that what you want to keep in mind is all this stuff happening. So you've got elevation and retraction of various pieces of your mouth to keep stuff from entering the nasal cavity. You want to get your pharynx working. You need to close the larynx to keep stuff from going into the airway. And then also, you want to relax this upper esophageal sphincter or the cricopharyngeal sphincter in order to allow stuff to enter the esophagus. So all of that happens super quickly without thinking about it, really, from birth. And then the esophageal phase takes about 8 to 20 seconds. And basically, once the food's in the esophagus, it's passing through. Digestion itself is all about getting stuff as small as possible. And it is necessary for growth, metabolism, and body maintenance, and reproduction, everything we have to do as humans. In terms of digestion, you need to do it mechanically. And we'll talk about those pieces beyond mastication, peristalsis, and segmentation. And then there's all these chemical parts to digestion that we won't be able to go into as much in this lecture. Maybe talk about it a little bit later. Really, digestion in terms of the upper esophagus is all about motility of the esophagus. So you have this muscular movements of the GI tract and these two concepts of peristalsis and segmentation. And then you're starting to have secretion, although that isn't going to happen in the esophagus itself. Absorption happens much later on in the small bowel. In terms of the motility of the GI tract, peristalsis is about trying to move something forward with contractions, while segmentation is mixing the food with simultaneous contractions. So I'll show some pictures of that. So this is peristalsis. So you basically need to move stuff forward. And ideally, to that long continuous tube that's about 30 feet in us, stuff starts in the esophagus moving forward and keeps going forward the whole way. It never goes backwards, OK? So when it goes backwards, we all feel it. Segmentation, intriguingly, is actually mixing as you go. And it's really that concept of as the peristalsis is happening, you actually have mixing happening. So I'm going to focus on the esophagus and stomach, and we'll start with the esophagus. So the esophagus is a hollow muscular tube. Again, it's connecting the mouth to the stomach. And I think what I want you to know about it is it is collapsed at rest. So when we go in and work with the pig stomachs, you will see it quite collapsed if we pull back the curtain or the towel, which you should do. You should see what it looks like at rest, because we all think of it endoscopically. But the truth is, that's with a fair amount of air pushed into it. But what's really important is that it is collapsed at rest. It's flat in the upper 2 thirds, and it's rounded in the lower third of the esophagus. And it's incredibly thin-walled. So I think most gastroenterologists even don't like to think about just how thin it is. So it's only 2 millimeters thick. And again, on the one hand, you want to cover up your pig stomach. And on the other hand, you want to take a look at just how extraordinarily thin this organ is. But in those 2 millimeters, you have four distinct layers. You have the mucosa, the submucosa, the muscular layer, and the outer fibrous layer, which we'll show. The esophagus is different from every other part of your GI tract in that there's no distinct cirrhosis. So it's all about mucosa for the esophagus. In terms of length, I'm in pediatric GI. I deal with very short esophagi. And then once you're an adult, so all of us in the room have an esophagus that's somewhere between 18 and, I would say, 30 centimeters in adults. Babies are born with a short esophagus, and they literally grow. And as they grow, their esophagus gets longer. So it's about 8 to 10 centimeters at birth. And by 5 years of age, it's about 16 centimeters. And then by the time you're a 15-year-old, you're pretty close to adulthood. That does have an impact for us in pediatrics because the body is basically designed to get longer. So the ligaments at the bottom of the diaphragm, which hold the lower esophageal sphincter together, are a little bit looser to allow for that growth. But bottom line is your esophagus fits your body. It's not squished in there at birth and getting longer. And then similarly, diameter really is, again, it's a flat organ. But diameter, it's getting bigger as you're getting older. So we want to think of it in adults as 20 millimeters in adults at rest. And it has an ability to stretch up to about 30 millimeters. And that gets important when we start talking about dilation. What are we trying to dilate to? So more to come there. But this all leads to this concept of esophageal capacitance, which is how much can your esophagus handle? And this is a grown up person. They sit up, they stand up. They especially do this when they're eating or after they eat. So hopefully everybody did have some coffee and breakfast. What you are all doing right now is refluxing, unless you've had antireflux surgery. And I won't ask for a show of hands on that one. But unless you've had something cut you off, you are actually designed to allow something to come up after you eat. And again, you are sitting up and you're standing up, but you guys are sitting up. And that's allowing gravity to help stuff not go up too far. But it probably comes up about 5 to 10 centimeters after eating due to transient relaxations of the lower esophageal sphincter right here at the diaphragm, which I'll talk about more. What's going on with babies? They have an extremely short esophagus, 8 to 10 centimeters. They are lying down unless we hold them up. They have a small stomach. And you can just see that they are perfectly designed to reflux everything up. So that is why there are more and more pediatric gastroenterologists every day, because all babies spit up. I mean, it's part of what you do as a human being. And it must be for good evolutionary reasons. There's just no way anybody would have designed the system this way if it didn't do something good for you to do this. So we are always trying to figure this out with families. But you can see as the baby grows, gets a longer esophagus, starts to sit up, they get to become this adult. Everybody following me? Yes. So, whoops, that one went backwards. So getting to those esophageal wall layers, what you're seeing here are in those two millimeters. So this is the flat esophagus here. Did I do that right? OK. Here's the flat esophagus here. And these are the different layers. And what you're seeing is a submucosa here. And then you're seeing a couple of layers of muscle. And this is a normal-looking esophagus. So for any of you who have not seen this before, this looks like a healthy esophagus with some spit in it. And here I would describe this as a normal vascular pattern. And honestly, when I'm explaining this to families, I say, look, you have that hole on the inside of your donut. I get a chance to look in it. Again, it should be flat, but we've put air in it. And you are seeing vessels, which is good if you had a rash. And I usually point to the back of my hand, like EOE. All of a sudden, it's a rash. It's a little bit swollen. You are not going to see those vessels. So when I can see vessels, I'm happy, because I know it's only two millimeters thick. It's not swollen. More on that. This is esophageal mucosa. It is very specific in the GI tract. It's stratified squamous epithelium, which means it's kind of flat-looking cells. And that's very different from the stomach, which I'll show you that in a second. The upper third of the esophagus is skeletal muscle, which we think of as voluntary muscle. I mean, you don't really have any control over your esophagus swallowing. But technically, that muscle there is skeletal muscle at the top third of the esophagus. And the lower two thirds of the esophagus are smooth muscle or involuntary muscle. And again, those muscular layers are all about moving stuff along. So the inner circular layer is what's moving the food, peristalsing the food down to the stomach, while the outer longitudinal muscle is really all about the segmentation piece, the mixing. And the whole thing relies on a nervous system that's really extraordinary that's sort of between these layers. The nervous system is its own thing. So not controlled by the brain, or you can actually think of it as your very first brain, because later on, we grew this thing at the top of our head. But when we were worms, and worms can do this, they can peristal stuff. So this is all about all these neurons, again, designed to get stuff into you and then get the nutrients out. I'm making my colleagues laugh, at least, but you guys are. All right, so gastroesophageal junction is, this is where all the reflux action is happening. So you have your esophagus coming into your stomach. And it does that, when you can see, and I'll show you, this is the squamo-columnar junction, which is where the squamous cell mucosa hits the columnar mucosa. So that's a particular area we call the Z line. And that gets important for us endoscopically. Outside, the whole thing's being held together by your diaphragm. And it's really the ligaments of the diaphragm that are keeping it either closed or letting it relax. And of course, you're into the stomach. So this is all about what we call the antireflux barrier. So here's your lower esophageal sphincter. People think of it as its own muscle. It's not really. It's really where the crural or the diaphragmatic ligaments are coming in. And this is the angle of HISS. And again, relaxation of that, which you need to be able to do. Theoretically, again, you can do a surgery to keep that from happening. But unless you've done that surgery, you're physiologically designed to reflux for a certain amount of the day. About 10% of the day is pretty normal, especially after eating. So the lower esophageal sphincter is designed to let food into the stomach. So it's going to relax with swallowing. But then it also should ideally keep too much acid and food from coming back up into the esophagus at least all day long. OK. So this is the concept of transient lower esophageal sphincter relaxations. And over here, you're seeing what's called manometry, basically a picture of a swallow. My motility colleagues could do a better job of explaining all this to you. But suffice it to say, you can follow pH of the stomach. That's up here. And then you can actually see contractions and pressures building in the esophagus as food moves its way down. And the stomach, there is no pressure or contraction because it's a big open reservoir down there. And that is if you have too much transient lower esophageal sphincter relaxation and you're spending too much time with stuff in your stomach, you will actually feel it and will complain of reflux. Here's a picture of the Z line. So this is where the esophagus hits the stomach. You can see how different those tissues look. And under the microscope, you can really see that difference, the esophagus and the stomach. All right. So the last few minutes are about the stomach. So the stomach is a J-shaped reservoir. And it is where all that food that you manage to get into your stomach is starting its process of really being broken down chemically. So it's being mixed with a very strong hydrochloric acid and also other digestive enzymes that start to break down the food. So the stomach is designed not to dump it all instantly into the small intestine. If you have dumping, it's literally a syndrome. It's called dumping syndrome. So we don't want our stomachs to dump. We want them to slowly release small amounts of partially digested food and keep sending it through this tube of the digestive tract. The stomach has a lot of fancy parts to it. That's partly because it's a very, very big organ. So when you're in there and you're trying to describe where you are in the stomach, you want to be able to give it a name. So up by the esophagus, we talk of this in terms of the cardia. That's because you do, we're not seeing it, but there's a very large organ that sits right about here. That's your heart, like, sitting right there. And then the body of the stomach, this part here is called the fundus. We call this the body. We call this big piece is the greater curvature versus the lesser curvature, which is here. And then the drain of the stomach is called the pylorus. And right before the pylorus is an area called the antrum. All of these parts have their own histology. So when I take biopsies from the stomach, I put them all in the same vial because my pathologist can see, based on what cells they're seeing, where they are in the stomach. So the stomach does have a lot of pieces to it and function to it. And luckily, it kind of declares itself, not so much looking through the endoscope. It really, somebody takes a picture and says, I was looking at the stomach. I can tell it's the stomach, but I don't know where, but the pathologist can tell where, based on, again, what's supposed to be happening at that point. So this is what being inside the stomach looks like. And as you can see, it has a very different look. These folds here are called rugae. R-U-G-A-E, or one is a rugus, rugae. I don't know what the single, a rugus. Anyway, they all come in multiples because the whole stomach has got a lot of them. We can put a lot of air in during endoscopy and flatten the whole thing out. We can also take a lot of air out, and the whole thing gets sort of much more, a lot more folds. And really, what you're doing here is seeing the greater curvature, you're seeing the lesser curvature, and we're heading towards the pylorus there. This is a picture of us retroflexed. So we are looking, we've put the scope up. You guys will all get a chance to do this inside the pig stomach. And again, you will see just how thin some of these organs are and watch the scope flop around in there. So I guess my, we need to keep the pig stomachs moist. That'll become more clear as you go through it, but definitely take a chance to see what's going on by pulling back the towel. So this is the scope coming through the lower esophageal sphincter into the stomach, looking back up at itself and looking at the bottom of the lower esophageal sphincter. Okay, here's more rugae, or gastric folds. This is a little bit more decompressed. And those get really, oops, I'm not going backwards. Those get important for digestion. That's really the beginnings of starting to have lots of redundancy in the surface area of the GI tract. And then what you're also seeing in this particular cross-section are all the muscular layers, again, those same muscular layers. This is that concept of here's your lining. It has a surface epithelium, and then it also, underneath is all these different, very strong muscles, really, all designed to, like, continue to try to chime and segment and really get things to break apart mechanically. And these are different cells. So when I said the pathologist can tell me where they are, you have parietal cells in particular areas of the stomach, chief cells, different areas have more or less glands. So all of that gets important from taking biopsies from the stomach in terms of do we see what we want to see, see bad things, see good things. But more what I like is they can tell me where they were. This is EUS, endoscopic ultrasound. I can't remember if we talked more about it, but it's a great modality. And what's nice about it is using an ultrasound, you can actually pick apart these various layers of the stomach wall. You can also do it in the esophagus. You can do it anywhere. And then, let's see, this is the columnar epithelium. Again, you're seeing a completely different look to the histology, which you guys will be talking more about, many more glands going on in the stomach than the esophagus. Here's your muscular layers. And, of course, a lot of the stomach is about hydrochloric acid, which is incredibly strong and really designed for breaking stuff down chemically. So, again, we're just incredibly designed to get everything we possibly can out of what we're eating. Okay, I will stop there and ask if there's any questions.

gastrointestinal tract

functions

digestion

absorption

elimination

reflux