So, let's welcome our first speaker, Dr. Neha Mathur, talking about the esophagus and stomach. Hi. Good morning, everyone. How are you all doing? Good. Okay. So, is this to go forward? Yeah. Go on. Excuse me. Hi. So, I'm Neha Mathur. I'm one of the GIA faculty, academic faculty at Houston Methodist, and have a special, you know, interest in eosinophilic disease as well, so I'm excited to be here. And I think this is my second time doing ARIA, so very grateful to be called back. So, we're going to talk today about gastrointestinal tract and health, and we're going to basically just kind of introduce the anatomy of the upper digestive tract, specifically the esophagus and stomach. Okay. That didn't work. Okay. There we go. So, just a disclaimer. This is all these slides are from ARIA ASGE course, so not me. What is the gastrointestinal tract? So, it's called the alimentary tract or the digestive tract, but it's basically plumbing, right? And so, it's a continuous tube that begins from your mouth all the way down to your anus. It's about 30 feet on average adult. I think that's like about 10 yards. So, it's pretty long and serves three functions, one, digestion of food into nutrients, two, absorption of nutrients into the bloodstream, and then three, elimination of solid waste. Oh, excuse me. Okay. So, this is kind of a schematic of our roadmap that we're working with. There's kind of two ways of looking at it. One is your digestive tract, what's coming from your mouth through your anus, and then you've got digestive organs that are helping to mix with that. So, when the food comes in, you're going from the esophagus into the stomach. I don't think I have a laser on this. And then into the small intestine, followed by the large intestine, also called your colon, and then you're interacting with digestive enzymes being made by the liver, the gallbladder, and the pancreas. So, it's a complex and actually kind of very interesting and wonderful system that the nature has designed, but its goal is to basically work with every calorie that you're giving it and absorb the nutrients out there. The esophagus and the stomach are designed to get food into your digestive tract and then start the digestion process. So, we kind of talked about this. The mouth, the food bowl comes in, goes into your esophagus, then goes to your stomach, and then next, the small intestine. At the small intestine site, we have the digestive enzymes mixing in from the pancreas, the liver, where the gallbladder stores our bile, and then squeezes out into the small intestine, interfaces with the meal that you have eaten, and breaks it down further for absorption, and then whatever's left, the last bits are taken care of by your large intestine. But really, the digestion starts in your mouth. So, what is the role? We're chewing our food, we're breaking it down, and then we're stimulating saliva production, and the tongue is an important organ as well. It's helping to push that food bowl's back in the back of our mouth to help us swallow. And this happens very, you know, subconsciously. You're eating, talking, doing a lot of things, but there's a very sophisticated process that's happening that's coordinated. Why do we need saliva? So, saliva helps to moisten food to assist in swallowing. It's produced by our salivary glands, and we got them in the parotids, on the schematic closer up on your, you know, buccal mucosa here, the cheeks, and then you've got sublingual glands, and then you've got some mandibular glands. And these digestive proteins basically are creating enzymes like amylase, and that helps to initiate the carbohydrate digestion. There's also an antibacterial effect, and there's some hormonal, you know, cascade that tells, hey, food is coming down. So, once we get past our mouth, it goes into the esophagus, which is, I think, the interest here today. So, the esophagus is the narrowest part of the GI tract, outside of the appendix, and we have kind of two gatekeepers, one up top, the upper esophageal sphincter, so it's like a valve that allows food to go into the esophagus, and then we have another valve at the very bottom of the esophagus called the lower esophageal sphincter. So, the esophagus is actually a chest organ. It's not in the abdomen, unlike the rest of the organs in the GI tract, and it's vertically oriented, and it's a little bit left of the median of the chest, and then passes on the left side of the aortic arch, the red arch going on this diagram, descends in the posterior media timing, a little bit in the back, and then comes back towards the diaphragm and passes in the front and towards the left of the aorta. It kind of has a meandering path. So, a couple of terms we should understand. When we talk about swallowing, we're talking about feeding, swallowing, and deglutitation. So, feeding, you know, you're placing the food in your mouth, you're manipulating it to break it down and to create a small bolus to hit in the back of your mouth and swallow it, and then swallowing, it's also a very coordinated mechanism where once the food is in your mouth, you have oral and pharyngeal stages of swallowing that help to bring the food into your esophagus, and it's a very well-coordinated path. And deglutitation is just the process of swallowing. So when we're looking at the oral phase and the pharyngeal phases of swallowing, they're very quick. And, you know, as you can tell, you guys ate a whole meal this breakfast, we weren't really thinking about the individual steps. So this is all very well-coordinated and almost subconscious. So what we do in the oral phase is we have to have a good seal because otherwise things will come out. You have to have an anterior to posterior tongue movement to move things in the back instead of spitting things out, so it takes a bit of coordination. Pharyngeal phase, again, very quick, about a second, and your elevation and retraction of the vellum to prevent material from entering into the nasal cavity, so you're protecting things from going up here. And then you're also going to close the flap—oops, excuse me—you're going to—apologize—close the flap, excuse me, and you're going to cover the trachea so we don't want aspiration into our airway. And then you're going to relax the cricopharyngeal sphincters, which are in the upper esophageal sphincter region, and help to get the bolus into the esophagus. Then the esophageal phase, where it carries the food bolus into the stomach, is a little bit longer, about 8 to 20 seconds. Once the bolus hits the esophagus, then there's other coordinated mechanisms within the esophagus to help it get down to the gastroesophageal junction and then into the stomach. So again, we've kind of talked about the key processes here. We want to break down the food into smaller components. As far as digestion, allow the body to absorb the nutrients and minerals in the food, and then we need all of this because we need the nutrients for growth, metabolism, body maintenance, and reproduction. So we're going to talk about mechanism of digestion a little bit more. Mechanical-wise, we're masticating. There's peristalsis, like physical movement through the luminal tract, and segmentation. Chemical parts are more your saliva, your gastric acid, your secretions, your pancreatic enzymes and bile that help to interface with your food and for absorption. So as far as the digestion process, we're going to talk about motility as well. Motility is very important because we have some gravitational benefits, but most of it needs to be coordinated and moved forward. So the muscular movement of the digestive tract carries the food forward, which includes peristalsis, where the food is propelled via contractions, and then segmentation, which is mainly mixing. The food interacts with some digestive enzymes and mixes, and then we have absorption. Secretions are important because the release of acid and enzymes are what mix with the food to help us absorb, and then the absorption process, where the nutrients and the water are absorbed by the GI tract into the bloodstream. So I think some of these we've talked about. The muscular movements are broken down into two parts, the propulsion, which is peristalsis, and then the mixing, which is segmentation. So peristalsis, looking at our left side of the screen, you have a food bolus, which is that white circular cartoon, and then with the contraction of the muscle, we are bringing it down and further down into the GI tract. And then segmentation, imagine the red and the blue being two different things that we're trying to mix, and as you kind of have this shaking and mixing, you will see that it becomes kind of a different color, which is a mixed component, so that's what we're trying to see here. So all of that is happening together. So again, going back to our GI tract, we have the digestive tract and the digestive organs that create the secretions. So we're going to talk about the esophagus. The esophagus is a hollow muscular tube connecting the mouth to the stomach, so it transports not just food but also saliva. Usually it's collapsed at rest, but it's more flat in the upper two-thirds of your esophagus and the lower one-third is more rounded. It's a very thinned wall, it's about two millimeters thick, has four distinct layers, the mucosa, the submucosa, the muscular isopropria, and the outer fibrosis layer called the adventia, and then there's really no distinct serosa. So it's very important we understand this because when we're doing procedures, we're examining this part of the organ, it's very easy to cause damage if we're not mindful of the thin layers and also to understand what we're biopsying, where we're looking at because all of that does matter to the disease process. As far as length, at birth, it's shorter, about 8 to 10 centimeters. As you're aging, about five years, you're at 16 centimeters on average, and then at 15, adolescent, you're about 19 centimeters, and adulthood, it matures about 18 to 26 centimeters. Diameter-wise, it varies when you're eating, fluid passing through or not. So again, at birth, it's a narrower caliber, it's about five millimeters, 15 millimeters at five years of age, about 20 millimeters in adult at rest, but it can stretch up to 30. So various diseases in the GI tract can affect this, and this is important for us as gastroenterologists because sometimes patients feel dysphagia or other symptoms, right? We'll talk about that, and sometimes that diameter has been narrowed. So sometimes those things are very important to understand how narrow things are. So this is kind of like a ballpark for you guys to know what is normal. So esophageal capacitance varies by age. So basically, it's showing that it's shorter as a child, infant, and you have smaller capacity, and then as you're growing into an adult, it expands. As far as the layers of the esophageal muscle, so on the innermost, like that star-like pattern, you have the epithelial or the mucosa, where the food and everything else is interacting with. And then you have a muscular mucosa, which is the outer layer of that, and then you have a separate layer called the submucosa. And then it goes into the muscular dyspropria, which is broken down into circular muscles, and then also longitudinal muscles, which are helping with contraction. So if you take a biopsy and you look under the microscope, a piece of tissue, you're going to see the cells of the esophagus look very different than the rest of the GI tract. It's one of the few places that you'll see stratified squamous epithelium, unlike the stomach and so forth, and we'll talk about that. So this is kind of a depiction of what it looks like, kind of these layers of sheets, in a way, in the top that you guys are seeing with squamous epithelium. So esophageal musculature is also a little bit controlled differently. We tend to divide the esophagus into thirds, and the upper third of the esophagus is more voluntary. You have skeletal muscles that are lining that, and then the lower two-thirds is smooth muscle, so it's involuntary. So you can swallow that. You know when you're swallowing a food item, and so you are controlling some of that up top. But once it hits the esophagus and gets two-thirds and below, this is on auto drive and your body is doing the involuntary movement. So we talked about the muscular layer, the circular and the longitudinal. So the inner circular muscle helps to contract the esophagus and move the food bolus down, whereas the outer muscle layer, the longitudinal, is shortening. So together, they help to move the food down. This is a broken down cartoon of the different layers we talked about. But to highlight that outside of movement, motility also has a great interaction with our nervous system. So there are about 100 million neurons lining our GI tract and it's a very sophisticated communication. So some of those nervous systems are embedded into these muscle layers. So it's very much a part of how patients' motility is, and sometimes the sensitivity, the sensation they're having, something burns, something hurts. So a lot of that is sensory here related to these neurons. Once we get past the stomach, we hit the junction where there's gastric and esophageal lining. So this is a specialized zone. We call that the gastroesophageal junction. So here, we have the interface between esophageal cells and gastric cells. We typically call this gastroesophageal junction or GE junction. Another term is squamo-columnar junction. Because of the biopsy on histology, you'll see squamous epithelium versus columnar on the stomach side. So you may have people talk about it that way. Or another short term that a lot of us use, especially in endoscopy, would be the Z-line. It's basically right where the diaphragm muscle hits the esophagus and the stomach zone, and it helps create that with the lower esophageal sphincter, that valve that helps to protect us. It allows us to get the food down so it opens up, but then immediately it does close up. So we don't want more reflux or regurgitation. So as you can tell, when patients are having some of these complaints, there may be issues with this zone or weakening of this zone. So this cartoon is showing us the esophagus in green, the lower esophageal sphincter is right at that zone, and that purple, that's your intra-abdominal esophagus coming out of the chest. There's a diaphragm muscles in the yellow and the stomach in the pink. So the lower esophageal sphincter, like we talked about, relaxes when you want to swallow. So we want that food bolus to go down. Then after that, we want to prevent the regurgitation or the backflow or the reflux. So it will close and contract to prevent that from happening. So if you look at some of these types of motility testing, when you see that somebody has swallowed a bolus, you have increased waveform, but then the lower esophageal sphincter, which is in the purple second color from the bottom, you can see that when you're actually swallowing, it's relaxing. So the pressure is going down and then it comes back up when it is contracting. So what does that look like? Not in a cartoon, in real life. So when we're doing endoscopy, this is what the gastroesophageal junction looks like. So you'll see two different color zones. So the lighter pink is your esophageal lining, and then the kind of salmon dark color, darker pink, is your stomach lining. So it should be nice and circular and kind of circumferential. But various diseases can affect this area. Inflammation can affect this area. So things can look erratic or abnormal. But this is what normal should look like. And you should have a pinch when we're going in there. So you'll learn about this during endoscopy today. So that's your diaphragm muscle coming through to give that lower esophageal sphincter that support. When we take biopsies of the zone, as expected, we should see two different cellular linings. So we're showing this gastric, which is the stomach columnar, and then the esophageal, which is the squamous. So you can see the sheets versus kind of more like longer tubular-like cells, and they look different. So that's how the pathologist helps us to differentiate. So moving on to the stomach. Stomach is basically a pouch or reservoir that's typically J-shaped. And its role is to mix the food that's coming in with acid and enzymes and help to break it down further. It's small amounts of partially digestive food that's released into the small intestine after the stomach handles it. So I kind of think about it like a blender. You put in a larger piece, and then it spits out smaller pieces into the rest of the digestive tract. So the stomach is subdivided into different anatomical zones, and that is important when we're doing endoscopy to understand and kind of more on the histology side as well, because certain cells are in different parts of the stomach. So in the top left, you'll see the cardia of the stomach, and then the kind of hump on the top is called the fundus. You'll have the body, which is the main sac of the stomach. And the body can be subdivided further into a greater curvature, which is the outer curve, which is the longer curve. And then the shorter curve towards the center is your lesser curvature. And at the tail end of the stomach, you'll have a zone called the antrum. And then at the very end of the stomach, you also have a valve called the pylorus. So the stomach has essentially the lower esophageal sphincter up top as a valve and the pylorus at the end. Another endoscopic kind of representation of the stomach looks like. You'll see these folds in the stomach and a big, you know, sac. And then this is the fundus. It's showing our camera, which is the upper endoscope in black tubing, kind of looking onto itself, and we'll learn about that maneuver later, you know, during this conference, and looking at different sites or zones in the stomach. So the stomach also has different muscular layers, but it has a very interesting kind of fold. We call them the rugae, and they're very important because they serve a purpose. I call it like the accordion effect. So the stomach can accommodate a lot of food. I mean, that's why we can feel full. We can keep eating, things like that. And it can hold the food for a while. So the rugae help to expand, and the stomach can accommodate more food. So it's kind of like that accordion that can expand more food coming through. So it's very interesting, whereas other tubular structures are very, you know, defined in their distension. So when you look on a biopsy specimen, you can see the different layers of the stomach. Similar to the esophagus, you have the epithelium, which is the mucosa where the food is interacting on the surface. And so you have the epithelium and the lamina propria, which is the top half we're looking at. That's called a mucosa. Then you have a muscular mucosa, similarly, and then the submucosa. And below that, we have our muscle layers. So in the stomach, going back here, we have slightly different. We have oblique layer, and then we have a circular layer and a longitudinal layer compared to the esophagus. So that's what we're seeing in our muscular propria. We have the oblique on the top, the circular in the middle, and then the longitudinal. And then you have a serosa instead of an adventitia. And there are different cells. So if we look at this surface epithelium, we have pits, and then we have different, you know, specialized cells lining those pits. So we have parietal cells, endocrine cells, chief cells. So they all make acid and different hormonal, like gastrin, signals that help to produce acid and have biofeedback to your brain saying, we have enough acid, please shut down the acid production. So it's a very sophisticated mechanism. We also do a specialized endoscopy that includes ultrasound to look at the layers of the stomach for various reasons. If there's lesions, concern for any growth or tumor, and we want to know which layer of the stomach because sometimes it's not on the superficial layer where we could target it as far as a biopsy or reach it. So it's important to understand the layers, which we just reviewed, the mucosa, the muscular mucosa, the submucosa, muscularis propria, and serosa. So if you look at the left side, that's our endoscopic ultrasound. And you have a transducer, which is the camera itself, and then you blow up a balloon and you have this ultrasound image that you will see. So you can see they're very, you know, small layers. So you'll see the mucosa is the first inner layer, submucosa, which is the SM, and then muscularis propria, MP, and then the serosa S up there. So it's kind of trying to show correlation of how we see it on endoscopic ultrasound. Again, we kind of talked about it earlier, the esophageal lining is squamous, but the stomach lining is different, columnar, because we're trying to produce secretions, enzymes, acid. And so we need all these specialized cellular lining to do that and for some absorption. I think we covered this, the musculars is three different layers, so longitudinal, outer, inner is circular, and most inner is oblique. So these are the specialized cells we were referring to. So you have your parietal cells that end up secreting hydrochloric acid, which is acid, and that goes to help break down the food. And then it also can negatively feed back to our G cells, which help to release gastrin that also work with the endocrine cells. And then that also has feedback to histamine production, and that can also trigger this acid production. So this is like a circular pattern where how much acid you have, do you have too much acid, and it can negatively loop back or positively loop forward. Okay, that was kind of a summary of the esophagus and the stomach. Any questions so far? Okay, thank you. Thank you. Oh, I'm sorry, excuse me, I have a question. I was trying to press the button, but it took a while to understand. No problem, go ahead. Sure, so the endoscopic ultrasound, what do you use it for? Good question, so it's used mostly by a lot of our interventional gastroenterologists. So they're doing assessment and evaluation of what is the problem, where is it located? So an upper endoscopy can show us a lot of findings, but it's very mucosal-based. So remember the layers, you're looking at it right at the surface. But if something is growing or penetrating into the different layers of the esophagus or the stomach, then you can't reach that or you can't tell that just by visual. You need something that can see through those layers so you can identify the penetration, the depth, invasion in the setting of like, say, cancer or tumors. And especially if you want to resect something, we wanna know how to do it, where all is it, where are the margins of these things so we can have a little bit more detail. So I usually use it as a tool for more details than an upper endoscopy can give us. So it's just an adjunct to our tools. Does that make sense? Yes, it does. Thank you. We have a couple of photos of it in the GI tools lecture that's coming up, so I can show you what all the samples are using. Yes, one more. Yes, so regarding the various junctions and valves that you had mentioned, whether it's the esophagus or in the stomach, are those valves or junction points triggered automatically to open and shut just via chewing or is it kind of like as the food hits a certain point within the body that signals these various like valves to start opening and closing? Right, so there's respiratory function with the lower esophagus sphincter where you have the diaphragm helping. And then there are more automatic like food boluses coming down. So it starts to respond to that and open up to relax. And then at nighttime it should be tight because hey, we're not eating, we're reclining, we're going to sleep. We don't want a reflux, so it's supposed to contract. So some of those are automatic and then they do respond and interact with the food coming down. That's a good question. Anybody else? Okay, thank you. Thank you.

gastrointestinal tract

esophagus

stomach

digestive organs

endoscopic procedures

digestive enzymes