So we're going to move on here, we're going to talk a little bit about the GI tract from top to bottom. So I'll do esophagus and stomach and then we'll move on to an organ I feel a little bit more comfortable with which is the small and large intestine. But basically here's like a Netter's picture, if you ever hear that word Netter's was this book or now it's probably all online that we all became accustomed to when we were in our training on how the GI tract looks. And so this is just sort of giving you a guideline of how things go, right? So as we look at this, right, the esophagus is a tube. I always say to my patients, I'm a plumber. I realized that I did not go into the smartest organ system in the body, right? Like I didn't become a brain surgeon and I certainly didn't become a nephrologist which is one of the most interesting organs. I became a plumber. And honestly, my entire field is based on plumbing. And I need to acknowledge that there's not a lot of knowledge in this organ system. In fact, I usually describe it to my patients as a temperamental teenager. The GI tract gets really affected by the things that go on around us, right? Sometimes when we're upset, we get hungry or we get nauseous, right? And it goes with the wind, right? You never know what to expect from the GI tract just like you never know what to expect with a 17-year-old. And I say that not having a 17-year-old but I have a 10-year-old who I think is gearing up to be quite an interesting 17-year-old. So as we look at the intestines, we've got the esophagus which is just a straight tube. This is why we're constantly telling patients that, you know, you need to stay upright because we want things to be able to get into the next organ which is the stomach which there's a connection in the end of the esophagus into the stomach called the GE junction. It's like a cap. When the cap opens this way, it's supposed to open downward to let food in. It's not supposed to open upward, right? When that opens upward, what happens? We reflux. But in general, like normal anatomy, it opens downward, it lets the food go into the stomach which is the next thing that you're seeing here. And then the stomach is a J-shaped organ that is usually higher up like right under the end of the ribcage and can extend over through here. That big red organ, the liver, is on the right side. And so interestingly, like when patients will say or when people will say like, oh, my stomach hurts down here, it's probably more of the intestine, right? The stomach is actually quite high up inside of the body. And the pancreas, which you can kind of see in this picture, gets hidden by the stomach and the liver on a frontal view anatomy and represents a really little like atrophic alien like structure that has very important meaning inside of the body. But it's connected through ducts that you'll hear about later on into the liver and then into the duodenum. From the stomach, you enter into the small intestine, which we'll talk about, and then the large intestine. And then the small intestine is not adhered to anything. So it free floats inside of our abdomen. And the large intestine is a box, as you can see there. And it goes, it starts on the right side, and it goes up, over, and down. And those are the different digestive organs. There's the rectum down there that you'll sometimes hear about. Typically in IBD, in Crohn's disease, we talk about Crohn's disease affecting the mouth to the anus. So the mouth can technically be considered an organ in and of itself as that's part of the digestive tract. So as we think about the way that we digest foods, we break down foods into smaller components. And then once we break it down, we allow the body to absorb those nutrients and minerals in different parts of the GI tract. And all of this is obviously necessary for growth and metabolism and maintenance of reproduction. The thing about it is the way that we digest that food is different in everybody. So there is something to say about chewing your food really well and really macerating it with the teeth before it gets down there. The stomach is going to be responsible for really being an acidic environment that breaks down that food and then lets it go smaller. But sometimes it'll leave the stomach still in somewhat of a solid form. And as we talk later about some of the different things, one of the very common things that any gastroenterologist is well aware of somebody eating the night before is corn. So corn will look exactly like it did when it was on the cob. And so there are different things that can leave the stomach still in full form. Otherwise there are, the stomach is responsible for making it very liquid. If you have ever seen a patient that has like an ileostomy, typically what will come out of there is almost like a liquid or almost like a mud consistency because that's the way it's broken down in the first part of digestion. But yet if you have a rectum, it then comes out as sort of a solid form. That's because, and we'll talk about this later, that the large intestine is largely responsible for pulling the water out and then giving it form again. Lots and lots of vitamins and nutrients are absorbed in the jejunum which we'll talk about. But as we focus here on the stomach, stomach is breakdown and then the esophagus is just a conduit to get from the mouth into that first organ inside of the body. Mechanical digestion, right, that's the chewing. Peristalsis is that way that the GI tract moves throughout the body and so it's sort of like a coming and going. And then segmentation is like there's different segments that are part of that digestive process. And then there's different components to what breaks that food down. Chemical components include saliva that we produce and that's a very, very important thing in the way that we digest. And when we don't produce enough saliva, sometimes the food can even get stuck with the pharyngeal swallow process. And then there's gastric acid which I spoke of just briefly, pancreatic enzymes which play a huge role in this, and then bile. And bile can sometimes be quite a bad guy in the field of GI disease, especially when you talk about patients who don't have a gallbladder. GI motility is an interesting topic. Sometimes motility can be too much. Sometimes motility can be not enough, right. Any of you guys in industry may have medications that are specifically revolved around the process of what is going on motility-wise. But the digestion is multifactorial. It's why there's not just one drug or one medication out there that can improve it or make it better. It's because there's muscular components to the digestive movement. And then there's this peristalsis and that's, like I said, this propulsion of food throughout the GI tract. And sometimes people have decreased gastric motility because that peristalsis just doesn't work regularly. And the contraction and the mixing of food is also a process that can be different based on somebody's overall motility. There's different GI factors that play a role in motility. Sometimes it can be surgical and whether or not your patient has had any of those, has had anything done to the GI tract. Sometimes it can be genetic, right, when we talk about different conditions. Sometimes it can be acidic, right. There's acidic processes that can play a role here. And sometimes it can just be idiopathic or they have decreased motility because of the fact that they were exposed to a virus or an infection. And then lastly, different processes that occur in females such as childbirth, things like that. So this is sort of giving you guys the idea of what peristalsis in comparison to then segmentation is, right. So you can see here peristalsis is just that process of the GI tract moving in a symmetrical manner. And then that segmentation is then the combination with the food into that overall process. And it's, they're one in the same, but they're two different processes based on the area of the GI tract that you're in, what you've eaten, like I said, your overall anatomy, but they play a part together in how this goes on. And so, wait, I went the wrong way. Oh no. So, okay. So as we talk about motility, when we talk about those muscular movements of the GI tract, we can also talk about the secretion. The secretion is then the added addition of enzymes and acid to mix with the food to help break it down. And this is where you're seeing the bile component, the pancreatic enzyme component, the gastric secretions and the gastric acids. And so, as we think about this, as it pertains to pathophysiology, right, if there's an overproduction of acids, sometimes we've got patients that can either get a reflux upwards, or they can get a peptic ulcer, or they can get ulcer-related disease like gastritis. When we think about the release of enzymes, sometimes patients can release not enough pancreatic enzymes and they can be deficient, and that can cause a malabsorptive process to occur where you're not absorbing enough vitamins and nutrients into the body. And this can happen because of, again, underlying disease states, diabetes, or they've had some sort of pancreatic issue in the past, or it can just happen. Sometimes we see it in conjunction with other disease states. And then, again, as we talk about the release of bile, bile is really interesting. Obviously, bile is an acid that is stored in the gallbladder, but that's not the entire bile process. Bile is actually reabsorbed in the terminal ileum, and so if you've had anything go wrong with the terminal ileum, then sometimes that reabsorptive process, even if you still have a gallbladder, can be abnormal. And if too much bile gets into your stool, again, you're going to deal with a malabsorptive or a secretory type of diarrheal process. The absorption of nutrients and water are really important. Water is largely going to be reabsorbed inside of the colon, and we'll talk about that a little bit later. But nutrients are absorbed in different parts of the body as are vitamins. Iron is absorbed in a different part of the GI tract than fat-soluble vitamins. And then, like I said, most nutrients you're going to have to reabsorb inside of the jejunum. So there are parts of the GI tract that are necessary to survival, and there are parts of the GI tract that are not. One of those organs that's not going to be necessary, which we'll touch on, is a colon. You can live without a colon, but you can't live without a jejunum. I mean, you can. You'll end up getting food through an IV, but there are certain parts of the GI tract that you need to digest appropriately and maintain adequate nutrition. So here's sort of our journey, right? Mouth, esophagus, stomach, small intestine, large intestine, really easy. And then liver, gallbladder come in on one side, and pancreas come in on the other, again, giving us those enzymes, those nutrients that we need to properly digest. And you can see that they're going to come in at the small intestine, and we'll talk about their interaction with the duodenum later. So we'll get into the different organs up top. So the mouth, obviously, it's how we break down food. We also stimulate saliva production. You can see chemotherapy, certain medications that can cause dry mouth can decrease the amount of saliva that we're producing. The tongue also plays a huge role here, because the tongue is going to help us move that food forward and initiate the swallow. So you need that also to help stop things from going down. When you are, when you're swallowing too, you wanna be in control of it, you wanna be awake because you also don't want that food to go down the wrong pipe, right? Right next to the entryway into the esophagus is also the entryway into the trachea. And so we have seen this happen to many patients in the past and children and adults where the food will go down the wrong organ system and can lead to lots of different terrible processes, asphyxiation, it can lead to death, unfortunately. And so when the natural process of food not going down the right tube happens, our inclination is to cough it back up, right? Or even if too large of a piece is ending up going down our esophagus, our inclination is for it to go back up. Saliva is produced in part by the parotid gland, the submandibular and the sublingual glands. So these are also important because different people can get cancers in these regions or autoimmune diseases and they may need to be removed. So again, another cause for potential decreases in saliva production. But again, it helps to assist with the swallowing, but it also starts that process of digesting. And amylase specifically will help with the carbohydrate digestion and will allow us to break those foods down. And it's one of the reasons why we talk about carbohydrates being digested so quickly. So if we ever go to an IHOP and eat some pancakes and we're super full, but then an hour later we're hungry again, it's because we break down carbohydrates really quickly inside of the body. Also saliva has an antibacterial effect, which is really, really important for us because a lot of the foods we eat may not be properly cleaned or may have different bacterial products that are a part of them. And we all know of different pathogens that we can get from food poisoning. So the esophagus is a muscular tube, it's hollow. It's about 18 to 26 centimeters in length. And I told you, it's nothing but a transportation device of food from the mouth into the stomach. It has multiple different layers, right? All parts of the GI tract have these different layers. The mucosa is the lumen, that's the part that you see. And then you have a muscularis mucosa, a submucosa. And then in the esophageal layers, you have a circular muscle and a longitudinal muscle. And so all of these layers are necessary. That being said, it's not a super thick organ. So you can look at it under the microscope here. And this is where it's helpful for us to have a basic understanding of pathology because of histology, because if there is pathology going there, you're gonna wanna be able to tell what makes it different. So this is what it should look like. So therefore, if there's things like too many eosinophils, or if there is too many lymphocytes, or if these glandular structures start to become abnormal, these are what we use to determine things like a cancer or an underlying autoimmune disease. So here you can see the layers and the way that food is processing downward. So you have the inner circular muscle, contracts the esophagus and helps move down in a bolus type of fashion. And then the outer longitudinal layer is gonna help shorten the esophagus over time. So the esophagus has different components. So the upper one third is skeletal or voluntary muscle. The lower two thirds are involuntary muscle. So you have no control over what happens in that part of it. And so you can kind of see here, you have control over those beginning parts. Once the muscle, once the food reaches a certain point, it's involuntary. This plays a role a lot in cancers because you'll see different types of cancers depending on the area of the esophagus that's involved. And then the G junction I talked to you about before, this is that area where the stomach and the esophagus interact. And you can see in the line here that you've got your esophagus. And then we call it the Z line. When we do EGDs, we're always looking to see if that Z line is regular or irregular. So an irregular Z line could be anything from just reflux related disease all the way up to Barrett's or even a cancer. So that Z line should be short. It's not supposed to be really long. And it should, when we call a Z line regular, that means that we can clearly see it's not a straight circle, but it doesn't have peaks and valleys or islands that we would call them that would make us wonder about something like Barrett's. The diaphragm also is going to sit right over here and it plays a really important role because as you see patients that will develop hernias, that's a herniation of the stomach beyond that diaphragm right there. And so you don't want the stomach to be able to get above the diaphragm. The diaphragm helps protect you. It's another thing that helps push on that GE junction to keep food from coming back up. And when you get a little bit of a herniation, which is sometimes due to weight, is sometimes just due to uncontrollable factors, the food can then move upwards. And the lower esophageal sphincter is again, gonna be part of the way that that food gets down and then prevents the backflow of stomach acid and food from coming back up into that esophagus. The diaphragm is gonna help play a role in protecting that and making that stronger. But as we age, sometimes the GE junction or that sphincter can loosen and it's easier for food to go up there. It's why when we were all in college, we were able to go to Denny's at two o'clock in the morning and get French fries with bacon and cheese and dip it in ranch. Not that I know of anybody who did that, but you can't do that anymore as you get older, right? That ability to contract is going to decrease over time. And these are some pictures. So as you talk about when we're doing an endoscopy and we're looking at that Z line, that's what we're looking at right there. And you can clearly see the beginnings of the stomach and the ending of the esophagus right around that area. So that's a perfect, so that's on, we're doing an endoscopy, we're gonna write Z line regular on our endoscopy report. If that's irregular, what we tend to try to do is grab biopsies right from that junction so you can get a little bit of both and we can see if there's any abnormalities there. And then you can see under the microscope here, the differences between the esophagus and then the beginnings of the stomach. And then the stomach is a J-shaped organ and it's where food mixes with acid and enzymes and the small amount of partially digested food that has been exposed to things like saliva and amylase enters into here and then it's digested further and then released into the small intestine. So there's different parts of the stomach here. We call the top part the cardia. Think about it as it's closest to the heart, so cardiac. And then the fundus, which is that little like out shooting of the J over there. Then you've got the main body and within the body you have the lesser curvature, which is the short part of the J and the greater curvature, which is the larger part of the J. The pylorus is right where the stomach is gonna meet the small intestine and then you have the antrum, which is the bottom part of the stomach. You can see that within the stomach, we have gastric folds, they're called rugae. And the gastric folds, as you blow up a stomach, which you'll see later today, are going to smooth out to some extent. And it's one of the ways that we're able to tell if something else is going on, we can see abnormalities within those gastric folds. The stomach has different layers, obviously, than the esophagus and you can see here that again, you're gonna have some of that same stuff, the mucosa and then the muscularis mucosa, the submucosa and the muscularis propria. And these are really important anytime you're doing things like an ultrasound because you can clearly delineate these different layers. And then within the gastric mucosa, you've got gastric pits and parietal cells and gastric glands, you've got enteroendocrine cells and chief cells. So all of these cells are responsible for the release of certain gastric acids and again, play a part, very important part in the digestive process. So as you see here, here's a picture of an endoscopic ultrasound. Part of the idea of ultrasound is being able to delineate these layers and get a better understanding of what's going wrong in different of these areas. When I'm looking at it from an intestine, not necessarily from an esophagus, we call it an Oreo cookie, but in the esophagus, you can see here, this is with an endoscopic probe. So there's got probe, obviously, that's going down into the esophagus and stomach and then they're able to get different layers exposed here. So you're seeing a little bit of the scope and a little bit of the layers, but if you focus on the layers, it's got sort of an Oreo cookie like component to it. The stomach mucosa is made up of columnar epithelium. That's why when we talk about cancers of the stomach, they're adenocarcinoma, that's what we see. Whereas when we talk about them in the esophagus, they can be adenocarcinoma or a squamous cell carcinoma. So there's those different, but it's got a very column like appearance and it's columnar and then there's three muscular layers. The stomach's one of our thickest organs. It's got a longitudinal layer, a circular layer and an oblique layer. And it needs to be really strong because it needs to hold a ton of food. It needs to be able to stretch and then come back together. And that becomes really, really important. And then here's sort of the acid physiology here, which I know is really intense. That's why I said you guys are gonna be ready for med school after this. But essentially, you've got different cells that are responsible for releasing acids. There's G cells that release gastrin, which can sometimes be overproduced and lead to abnormalities. There's ECL cells that release histamine, hence why antihistamines can sometimes be protective in and of the GI tract. But it's a secular process that's supposed to function to protect us, but sometimes can become abnormal. And so with that, we're going to take any questions that you guys might have on the stomach or the esophagus. Only the stomach and the esophagus. No, you guys can ask me anything. There was one phrase used in one of the diagrams in the mouth, the bolus, food bolus. Is bolus just like another general term for food that's massacred inside your mouth? Yeah, and a bolus is like, you can think about this in any way. Like if you give like a bolus of an IV fluid, you're trying to get, you're doing a lot in a time. So sometimes a food bolus is you are taking a big swallow. Like that would be like one way to think about a bolus of food, but it's any swallow process. So when we eat, right, we're not just eating and then it's constantly just flowing down. If that was the process, we wouldn't be allowing those patients to eat. But the bolus is that process of swallowing and then a bolus of food goes, and then you take another bite and another bolus comes down. Okay, thanks. Just a quick question. In the esophagus, the peristalsis, was it segregation? The one you refer to as motility? Is that, is segmentation then irregular when it happens in the esophagus? It can be. It doesn't have to be. It is a part of it. Like I said, when you have a bolus, the segmentation is the bolus of food that it's sort of coming down like in little bits. It's because like I said, it's not just a constant flow of things coming down. But yes, segmentation can be abnormal. And then that's where we start to see motility abnormalities there. But the understanding of segmentation is that it's the normal digestive process. But it can become abnormal, in which case you would have some sort of pathophysiology. So what you'll see is like, if you think about something like akalasia, that there's something wrong in that disease with the way that the esophagus is contracting and allowing food to go down properly. And so it's that segmentation isn't going in like a proper pattern. Peristalsis is making it pattern. The segmentation is the food going through each of those different points in time.

gastrointestinal tract

esophagus

small intestine

large intestine

digestion

peristalsis