Good morning, everyone, how are you? Feeling excited to talk about my favorite part of the GI tract? All right. Make sure I know how to work these slides. Okay. So, you know, if we take a bird's eye view of the GI tract, that portion that we just covered is like taking your outside nutrients, what you're seeing in your environment, and turning it into something that you can actually make calories and nutrients out of. That is the job of your small intestines and some of the extra organs around it. And then your colon's job is to take what's left over, compact it into waste, and get it out. So it's very simple. It's very complex at once and very simple. There's turning it into something that you can actually break down, utilizing it, and then getting rid of it. So that's where we have our small intestines here, this kind of loopy space, and then our large intestines or colon, which is kind of circling and encasing this. And they don't really hold their space the way we see in these lovely schematics. They kind of float around in there a little bit. And so we'll get into that. So first off, the small intestine. Interestingly, no matter how tall you are, short you are, surgeries you've had, we all have about the same amount of intestines in there. So you can imagine people may have difficulties with digestion just based on anatomy. Women, for example, issues with constipation. More stuff, less space. So with the small intestines, it's 20 to 25 feet. And that's where the stomach, which we just learned a whole lot about, dumps what it's made of, what we put in our mouth, into our intestines. And its major function there is for the digestion of the food and absorption of the nutrients. And that means like our vitamins and our calories. All those things are happening in this like very, very intricate network of 20 to 25 feet. So the small intestine is actually comprised of three different parts. There's the duodenum, which is the first part. The jejunum, which is the second part, and the ileum. There's really no distinction in terms of the transition from the latter two. But the first part we're actually able to see when we do upper endoscopy. So when we're looking down there with that scope, we can pass through that stomach kind of like duck that she said, that little channel, and see a good portion of the first part of the small intestines. And a lot of diseases live there. So we take biopsies a lot of times and things like that. Okay, so here we are, the duodenum. This is the big part. So there's your pylorus, which we just talked about from the stomach. And it's got a, it's like a muscle contraction that opens and allows things to dump in that we pretty much have almost liquefied to that point to start making, you know, calories and absorbing our nutrients. And then passing through that place, we've got our bulb. Interestingly, when we talk a little bit more about GI pathologies and things like that, we find that when we're working up bleeding, for example, things like that, that's a very high prevalence place that we're looking because it's a vulnerable location. Sitting actually, and we'll go into that later, in this little hub space in between is where the pancreas and the gallbladder coming off of the liver, they duck, they kind of come together in a network called the major papilla, and they dump some of those secreting like enzymes and acid and things like that that we need to help make the most of our calories. And then dropping down, we have our descending portion, then our horizontal ascending portion, and then we go into our jejunum, and then furthermore into our ileum. As you can see, the first section is the shortest segment, and it's about 12 inches long. And as you can see here, there's a lot happening in that first little part of the small intestine. So we take a good look at that. Okay, so kind of circling back from that last picture, with the duodenum, we have the gallbladder here, which is your little green sac, and it just kind of helps make bile and things like that to help us break down our food, and it kind of churns. And so sometimes, you know, we'll have people come in with these like random attacks of pain and things like that associated with eating. That's because of gallbladder disease. That can be because some of that sludge and the acid there turns into stones, may get out and get trapped in these areas, and we'll go into that later. But when things are working nicely, they all culminate together and then dump into the small intestines to mix in with that food that we made and start helping us break down those things that we need for calories. This organ here is the pancreas, which works in that same network, and it has a lot of function for not only blood sugar control, but digestion. And that's where we see a lot of things, and we start thinking about diarrhea workups, and we'll go into that. And then there's, of course, just the remainder of the duodenum before we go on. All right. So, as I said before, your bile ducts here and your pancreas empty into the duodenum, and we're actually able to see sometimes a little, little spot when we're passing the scope through where it's dumping into that space, and we can see things kind of passing. All right, Vance and Dawson, we're getting that for you. The functions, however, are to break down food. So, enzymes in the small intestines, enzymes from the pancreas, bile from the liver and gallbladder all start mixing together and helping to turn that sandwich that you had into something that you can actually utilize. And then, of course, we start working on absorption, and that's where the actual lining itself becomes more important. So, iron is only absorbed in the duodenum. So, you think about people who have surgeries, for example, for weight loss or other things where portions start to be removed, they tend to have issues with vitamin deficiencies like iron. So, it's important that they're followed to have those things kind of checked. Other than that, we also start seeing the beginning of absorption of other nutrients. So, the next portion is the jejunum. That's the mid-portion of the small intestines, about 8 to 10 feet. There's really no clear demarcation between that portion, the last portion, the ileum, but it's all kind of working in that big overall network of nutrition with absorption and utilization of those calories that we're taking in. So, the most interesting part about the small intestines, and so we're seeing a histologic picture here, but it looks very, very different from how we saw the esophagus look endoscopically, how the stomach looks endoscopically, and then our small bowel actually looks completely different as well. So, we're able to identify where we are as we're passing through some of these landmarks based on that. And the jejunum is interesting here because of the fact that it's got these villi. And so, they have this kind of like finger-like projection, as you can see here, which is obviously a bit longer than what we just saw on that stomach pathology, right? And so, that helps to maximize those nutrients that we're taking in with this network. So, we've got columnar epithelium here on the outside, and we have mucous cells kind of intermixed in between, then a complex network of capillaries and nerves, along with the lymphatic kind of system, helping to not only help with our immune system, but also help with our nutrition and absorption. And then we, of course, are now starting to turn that sandwich into specifically what it is. Is it fat? Is it protein? Is it minerals? Like, what is it that we're trying to pull out of that? So, here's where I was explaining where it looks endoscopically different. So, you can see how this looks quite a bit more furry, if you will, than those other places that we saw. And that allows for the surface area to increase in order for us to maximize that nutrition. And so, you can see here that if it's stretched out, the small intestines could be the surface of a tennis court. Imagine that inside your body. That's insane. I think so, at least. That's kind of what got me interested, obviously, in GI. So, one of the main things to know here is that you can have disorders, for example. Like, if you have an autoimmune condition or an autoallergic condition, like celiac disease, for example, where eating something that your body does not tolerate can erode this lining. And when you have erosion of the lining, then you start to have issues with absorption and digestion. And we'll see things like deficiencies in vitamins and diarrhea or pain or things like that. And so, it's important that we understand what each portion of the GI tract does to help figure out lesions when people present just with symptoms. So, that's why we ask those types of questions. Like, as you said, with the swallowing, there's different parts. We want to know, like, what type of foods? Where do they have the pain? What does the diarrhea look like? You know, is it watery diarrhea? Is there something else in the diarrhea? So, that's why we study those things to help people figure out what's going on. So, finally, the last portion of the small intestines is the ilium. It's about 8 to 15 feet, and it connects to the colon at the IC valve. So, interestingly, when we're doing just basic endoscopy, we can see a portion of the duodenum, and we can also see on a colonoscopy coming from the bottom, the first part of the ilium. But it's very difficult for us to just easily get to that kind of middle, no-man's area in between. And that's where we use some of our other technologies, like capsule endoscopy, to visualize that. We sometimes use imaging modalities to give us an idea of what's going there. But it's technically very difficult to get into that space and see truly, inch for inch, what that small intestines lining looks like. It connects to the colon, as you can see here, with the IC valve, which is a very interesting piece, because it kind of creates almost like a break, if you will. For, like, you know, we're making all these things. Things are moving through really fast. The peristalsis, then it hits this point where it's like, okay, we're transitioning into another job of sucking out some of this extra stuff to solidify it into waste so that we can excrete it. The functions of the ileum are for continued absorption of nutrients, and most specifically for some of the other ones, like bile salts and vitamin B12. So when people have, like, their gallbladder removed or they've had some type of resection in that area, we may see that they're more inclined to have diarrhea because they've lost some of that actual surface area they need to control it. So the large intestines. We've kind of, you know, moved through this place, the, like, no-man's gray area in terms of being able to see it endoscopically, but we know that things, major things, important things that help us maintain our weight and our energy are happening into the, like, okay, we're wrapping it up. On our donut, we're done. We're about to get rid of it. So the large intestines, it's also called the colon, and so that's why we have colonoscopies, allows us to see that kind of final four to five feet in length. And its function more or less is just to absorb water and electrolytes out and compact it so that we can eliminate it as solid waste. Because if we didn't do that, then we would just, you know, be spilling out the bile and everything else. We make several liters of bile every day, whether we eat or drink. So we need some type of mechanism to help control that. So the colon itself has a couple of parts here. So starting from the bottom, working our way back up to the ileum, we have the anus, which is on the outside, our rectum, which is the most distal portion. Then we have this very twisty, turny space called the sigmoid colon for obvious reasons. The descending colon, and then passing here, if it gives you like a landmark idea of where you are, this is the splenic flexure. So those kind of organs up top when people complain of belly pain. We've got our spleen on the left and our liver on the right. So we have a splenic flexure or turn here to the transverse colon. And then we have our hepatic flexure going up to the ascending colon. And this is here, this little tail thing is our appendix hanging out right there. And we're able to actually see its opening called the appendicillorifice when we do colonoscopies. And that's one of the landmarks that we use to kind of ensure that we have made it to the end. A lot of us, especially those who focus on IBD, for example, like to go beyond the colon, like I said, into the distal portion of the ileum, because that's where we see a lot of disease there. We want to ensure that that's healthy. So motility, which we've already talked about quite a bit. It's a whole big network of things that, you know, are happening. There's muscles that are smooth that we don't really control, but our brain does the signaling for us and just kind of moves whatever you ate for breakfast. It's already on its way downstream doing its thing. So it occurs throughout the entire GI tract in varying times in certain forms and fashions. So it's important, of course, here, again, for mixing and propelling things. And it's also coordinated contraction of smooth muscle. So here we can see that we've got kind of our outside lining, and we can see that the muscles are going to start to move. And so peristalsis is like almost like a wave-like contraction. Some of it's forward. Some of it's a little bit backwards, that kind of churning that we need to kind of keep breaking things down and moving them through and giving our bodies time to do what it needs to. But gravity does help. So here's peristalsis. And so as you can see, we're starting on the right side. That's your ascending colon. And secum here. And then it moves forward and sometimes a little bit backwards to kind of give us more time to do what we need to do. And as we keep going, it kind of hits a transverse colon. It's still kind of, you know, moving back and forth, kind of like a two-step forward, one-step back kind of thing. And then we have mass peristalsis when we get over to the left side of the colon, which gravity actually helps quite a bit to help move things through. So you can imagine that if you've had, for example, abdominal surgeries for women, for example, like C-sections where they literally cut you open. They take your intestines out to take out your baby. Then they stuff them back in. Your furniture's been moved around a little bit. There might be some scar tissue. It's already a twisty space. Getting things through may be a little bit more difficult than for a 6'2 man who, you know, goes three times a day. All right. And so here at the very, very tailed end is our rectum and anus. So the anus is kind of our most external portion and then the rectum. The anus itself has an external and internal sphincter and a dentate line. And so when we're doing the colonoscopies, we can actually see right at that edge. Generally, we know that anything distal to that dentate line is going to be exquisitely sensitive, so we try to avoid doing maneuvers in that space. And the rest of the tissue is similar. And I generally tell people, you know, you kind of treat your bottom like you treat your nose. So if you're, like, rubbing your nose raw, it's probably going to feel the same. Or if you've eaten something spicy, you might feel it kind of the same coming out. That's because it's somewhat similar. So the rectum, it retains the stool. It's almost like a little bit of a reservoir, if you will, until you're ready to go and sit on the commode and evacuate. That's where you kind of get that control back from that smooth muscle. And then your anus has the two sphincters. Some of them have, like you said, again, voluntary versus involuntary control for that actual evacuation. So defecation, which I talk about in my office so much. Everybody poops. No one wants to talk about it until they get in the room with me. So main things to know is that there's an angle here. It's the anal-rectal angle. This plays a big part into how effectively we're able to evacuate that solid stool. Another thing to consider is that depending on what you ate, your hydration level, if you have motility disorders, what is actually being delivered to that reservoir may be easier or harder to pass. And so you have more or less control over that. So at rest, you can see here the difference in the angle when you're just kind of sitting normally versus when you're kind of bearing down or straining how it opens up in the scent of the pelvic floor. The pelvic floor is really important because it has a network of basically like just underlayers of tissue and things, muscles, ligaments, et cetera, that have to work in coordination in order to have effective evacuation. And so a lot of times, as you can see, there's a little sling called the puborectalis muscle here that kind of helps to relax and open with that. Sometimes when you have a large baby, for example, and there's a big tear or an episiotomy, there can be injuries to those nerves or to the muscles or the ligaments or just generalized pelvic floor weakness for anyone as we age, where control over that becomes much more difficult. As you can imagine, we lose control of the organs in the pelvis as a result of that, leading to things like urinary incontinence, constipation, incomplete evacuation, all those things. And so to come up with a great device, if you don't have one at home, is getting your knees up above 90 degrees with things like a squatty potty. Right? Watch the YouTube. It's not an endorsement, but it's a great video for the commercial to kind of help show the mechanics of exactly like really truly like this is what is happening. This is actually what we do. And so that's pretty much it about the colon and the small intestines. If you guys have any questions, I'm happy to answer them. Thank you. Questions for Dr. Callaway? Yeah. I have a combination question. Sure. I'm curious what are the most common motility disorders that you see on a pediatric side versus the most common ones on the adult side? Yeah. Does this work? We are probably pretty similar in what we see. So esophagus, you've got to think about something called achalasia. That's sort of a classic motility issue. And then colonic motility is, I mean, so small bowel, it's so long and so complicated and really I think there's no great way to really make or understand even yet the small bowel motility. I mean, you may know better. They actually have a capsule now I think you can swallow that gives you a little bit. And that, by the way, if anyone's ever had surgery, the surgeons sort of stand over the bed and they're listening for bowel sounds, but there's not much that we know what to do to make the small bowel start moving again. We just sort of wait. So that's, you know, if anyone's ever had that experience, it can be frustrating where everyone's like, have you passed gas? That's really a sense that things are moving again. And then the colon, you're going to... Yeah, I think adult issues with colonic causes of constipation tend to be multifaceted. It certainly depends on surgical history, obviously genetics to some degree. So there are people who just have by nature very slow motility or slow transit constipation, which we do work up. Pelvic floor tends to have an overlap quite a bit for women. And then a lot of times it's just a matter of diet and the sheer mechanics of going with constipation. Like adults, we eat a lot of processed foods and not a lot of water, all those lovely coffees and things like that. So it's more, you know, kind of figuring out and teasing out those little intricate pieces about each person uniquely that may be it. But the biggest thing is usually a combination of some type of pelvic floor dysfunction. Most of the time adults have had some type of surgery, so adhesions or scar tissue in the belly. And then occasionally there is some underlying, like, motility disorder where things just tend to move slow in general. And then gastroparesis, I guess, from the upper side is what we see quite a bit for adults, usually secondary to diabetes because those nerves, enteric nerves, are coated just like the tingling in the hands and feet with the blood sugars can coat the nerves as well in the stomach. So then things don't...it's like almost having earmuffs on the signaling. They hear it, but they're not really doing what they're supposed to. And we talk a lot about poop in pediatric GI, too. Yes. I'm actually from Massachusetts, so I can agree on the donut side there. Okay, good. But my question is with the rise of the steep rise in colon cancer, especially in young patients, do you find that that has something to do with the shift in the way food is processed? Like you were saying, more processed foods and things like that. I know that's probably a deeper conversation, but does that play a role in the rise in young patients with colorectal cancer? There's definitely research there. We're not entirely sure, but as you all know or may not be aware, that they recently decreased the screening age for average risk colon cancer screening to 45 because we are indeed seeing higher risk lesions in younger people. And a colonoscopy in and of itself is actually a quite benign procedure in the grand scheme of things. But there is a lot of thought about is it genetic predisposition versus dietary versus some of the things that we're potentially heating our food up in. There's so many things that it's really hard to say if it's just one in particular. What I'll add to the genetic pieces, I think you're just at the tip now of understanding genetics of colon cancer, and so we're starting to look more and more earlier and earlier. I think there's going to be a whole evolution of understanding how that plays into it. But, yeah, no, it's a big deal. All right. Great. We've got one more. Just in terms of if you have two people sitting next to each other eating the same thing, someone gets more indigestion or it just doesn't suit well, and so terms like an ironed stomach or something like that, what's really kind of happening in terms of that? Okay. So this is a conversation I have a lot in the office. And, indeed, I say, I mean, these are my words I'll say to my patients, but I say people are wired differently. And so, you know, it could be that. I say sort of half the people are very sensitive and they have irritable bowel, which I always say you're not irritable. It's an old-fashioned term for your GI tract is sensitive. And then you have the ironed stomachs, right? It's probably a little bit of wiring, a little bit of that motility discussion, a little bit of inflammation, and EOE is part of our understanding more about inflammation, I think, and also a lot about the microbiome. So a lot about what bugs live inside you and what are they doing in terms of fermenting the non-digestible foods that we eat. So I'm happy to talk about that one over a snack, which will all be non-digestible. And each microbiome is unique to each person. So, you know, like what is a happy place for me may be different for someone else. Okay? Awesome. Thank you so much. Thank you.

gastrointestinal tract

small intestines

large intestines

digestion

absorption

colon