It's my pleasure to give this presentation on the small intestine and large intestine, and I follow Dr. Lightdale, and she showed a slide on endoscopic ultrasound. You know the world's a small place, so she showed this slide on endoscopic ultrasound. What she failed to tell you was that her father was one of the founders of endoscopic ultrasound. I was in fellowship with one of my true heroes, academic heroes, so she failed to mention that. Charlie Lightdale is a great, great, great guy. Pass that on if you don't mind. I do endoscopic ultrasound a lot. So we're going to talk about the basic anatomy of the small and large intestine. Here's our disclosure slide, and you've seen this slide. And so the small intestine is about 20 feet long, so that's a deep pool times two, right? And it's wrapped on itself, if you will, as you can see, and it is not a static organ. It is constantly moving around, and I sometimes tell my patients it's kind of like spaghetti. Like when you get the spaghetti out, and you're careful to stick it together, so you put some olive oil on it, so it's kind of moving around, if you will, like a worm, in a very slick, smooth way, so the movement is key to the small intestine. And it serves a very important function, which is, of course, involving digestion and the absorption of nutrients. It's really quite remarkable what the small intestine does. As gastroenterologists, we're often focused more so on esophageal, gastric, and colonic disorders, admittedly, or pancreatic ovulary as well. There's some emerging problems with the small intestine that we're seeing a lot in our elderly population. We'll touch on that when we get to our pathophysiology section, but the small intestine, suffice to say, is a very interesting organ. So the small intestine is divided into three sections. The first section would be what's called the duodenum. Some people say duodenum. I think it's okay if you say either one. And section two would be what's called the jejunum, and the third section is what we call the ileum, and there are some differences in these sections. So in the stomach, food is processed. We heard all about it, that there's a word called triteration, and that's where food is broken down into very, very, very small particles, probably somewhere between one to three millimeters would be the size of the particles that are, under normal circumstances, the particles that are delivered through this structure that's called the pylorus, and the pylorus is the outlet, if you will, from the stomach, and then we then get into something that's called the duodenal bulb, and here we begin to see a change in the way the surface looks, and you can see these involuted areas, and in this second portion of the duodenum, or so-called descending duodenum, you can see this thing called the major papilla, and Dr. Martin's going to talk all about that. That's where the bile comes from, and the pancreatic juices, and then you can see there's this section that's called the horizontal section, or the so-called third portion of the duodenum, and then lastly, there's this thing called the ligamentatrites, which is over here, and that would be the so-called fourth portion of the duodenum. So when we are talking about the duodenum in endoscopy, we'll often separate it into what we call the bulb, D1, D2, D3, and D4, so we use terms like that during endoscopy to describe the position of things. So it's only about eight to ten inches long. You can see the four sections, and you can see it's got this C shape, so that's what we call it, it's called the C loop, and it cradles the pancreas, and a lot of interesting things are going on in this area, and I remember when I was in fellowship, we had a team of research scientists that totally focused on all of the very interesting endocrine, hormonal things that are going on in this section of the duodenum. It's extraordinarily complicated, but the basic anatomy is simple, and I don't want to steal from later on, but this is the basic hepatobiliary anatomy, so you have your gallbladder, which empties through something called the cystic duct, into the common bile duct, here you can see the pancreatic duct coursing through the pancreas, we're going to hear all about that in a minute, and this is the thing called the ampulla. Well, that was fancy. I didn't have the animations when I was just looking at my static slides, I had no idea about the technical expertise that ASG was going to demonstrate. So the bile duct and the pancreas empty into the duodenum, and there's this, there's bile, that basically serves the purpose of saponification, saponification means to dissolve fats, okay, so I'll think about it like Dawn dishwashing liquid, so it kind of makes fats go into solution so that they may be readily absorbed across the surface of the small intestine. And the pancreas, it was stupid, it took me a long time to realize that the pancreas is just another salivary gland, it just happens to be in your stomach, abdomen. It's retroperitoneal, and I'm sure we'll hear about the anatomic relationship of the pancreas in a few minutes, I spend a lot of time dealing with pancreatic disorders. So the function of the duodenum is the initial, well, it's not the initial, it's the second phase, if you will, in the breakdown of food. So in that pancreas, we have these cells that produce enzymes, and those enzymes are the ones that Dr. Lightdale alluded to earlier, one of those enzymes is amylase and one's called lipase, and these enzymes begin to act upon the triterated small one millimeter particles that enter the duodenum, okay, so a lot's happening right now. And then the bile's coming in there, so if I was at, I went to this place one time called Black's Barbecue in Texas, has anybody ever been to Black's Barbecue in Texas? If you like meat, it's a pretty amazing place. And so we went to Black's Barbecue when I was at Christmas a couple years ago, my daughter's in the Air Force, she's a surgeon, so we all said, we're gonna go have Christmas with you because you take call, we were a supportive family, she was a surgery intern. And so my son says, hey, we gotta go to Black's, I said, what's that, he goes, I'll show you. So we went and we got this stuff called brisket, and we brought it home and we had this brisket buffet, which was unbelievable. It was so delicious, I can't tell you what, I mean, it was unbelievable, it's fantastic. And we had leftovers, so we put them in the refrigerator. So the next morning I thought, hey, I got a good idea, I'm gonna break this stuff out for breakfast and make an omelet with it. So I pulled it out, and little did I realize the fat content of brisket, it's really up there. It looked like Crisco is what it looked like. So be aware, if you get barbecue brisket from Black's, it's almost pure lard. But if you eat that brisket and it gets triturated in your stomach and gets down to your duodenum, then the bile and the pancreatic juices can act on that brisket and break it down so you can have more brisket. But that's what it does. It's kind of interesting when you think about it, fat goes into water and all of a sudden it's absorbed? How does that happen? It doesn't happen in my sink, right? My wife tells me that all the time, don't put that down the sink. I'm not alone, I can tell. So you learn something everywhere, and I did not realize the baby's esophagus was eight centimeters long, which is kind of, I did that when I was sitting there, I was like, wow, that's pretty incredible. And then I guess I didn't realize that iron is mostly absorbed in the duodenum. I guess I do that one time and forgot it, and I'll learn it this time and I'll forget it again. That is where iron is absorbed, apparently, and then it's the beginning of the absorption of other nutrients, okay? But the jejunum is a very interesting place, and that's the mid-portion of the small intestine. It's about eight feet, 12 feet, 10 feet. These numbers start changing as we go through the slides. You'll see it's because we don't really, everybody's different, and there's no sharp demarcation between the jejunum and the ileum. So it's kind of hard to say, hey, are you in the jejunum? Some people do this thing called small intestinal endoscopy, and there's some techniques that maybe you'll hear about in a little bit where you use balloons to get further, further down. So someone will say, hey, are you in the jejunum or are you in the ileum? And it all looks kind of the same when you're looking through a scope, so you can't really say. And even in the OR, this demarcation's not very clear. Now I'm going to spend a little bit of time on this slide, because most of my slides don't have many details, but this one does. And so in the small intestine, there are these things called villi. And I'm going to go to the, whoa, wrong way. I thought I was going to, oh, I see how it works. So I'm going to fast forward, but then go back. So here are these little villiform appendages that come off of the jejunum, and it looks really cool, like you're looking at a coral reef or something. And this is, I think, a good example of something that's called underwater endoscopy. I do a lot more underwater endoscopy now, so I fill the lumen with fluid, and you can sometimes see a lot better. And certainly in this view, you can see the villiform appendages very well. And they're only present in the small intestine. They're not present in the stomach, and they're not present in the colon. Colon has different surface, different purpose. And you can see, if it's stretched out, it would be the surface of a tennis court. But then I Googled this, because I was told different. I was told it was the surface of a football field. And then, it depends if you're European or North American, like football, like how about a soccer field? So it could be another football field. So it's a big damn thing, okay? So imagine this whole room, and so it rains like it did last night, and it absorbs all of that stuff. When it's stretched out, because of this wonderful design, which is amazing. So we'll go back. And then here, you can see that the, it wasn't supposed to, oh, it's supposed to be this way. So here you can see the villus, and you can see it sticking out like an appendage, like I said. And it's got some things in there. It's got these veins and arteries, because it has to have proper circulation to function. And then here in the middle, you can see that there's this thing called a lymphatic vessel or a lacteal. And sometimes you can see those endoscopically, but this is where all the fat goes, okay? And all the protein and all the sugars go into the venous system, okay? And all of this is headed back to the liver for processing. So all this absorption is going on. Now, we'll also point out that you can see there's a nerve in there. So that nerve is the electrical system, if you will, for the small intestine. And that's what allows it to have the stimulus to move and have what's called peristalsis. So all this triteration, peristalsis is going on over this huge absorptive surface to allow us to gather every calorie out of every bit of brisket that we eat, unfortunately. That's the way that goes. And my system works great. And so the ileum is the final section of the small intestine. It connects to the colon at the ileocecal valve. Everything has to work in harmony. If there was a problem with the veins in the small intestine, everything falls apart. If there's a problem with the arteries in the small intestine, everything falls apart. If there's a problem with the nerves, it doesn't work. If the villi are gone, you've got problems. If your ileocecal valve's gone, you've got trouble. So everything's working in symphony, if you will, to allow for all of this process of digestion to occur. So the function continues with the absorption of nutrients. And we also have these specialized areas of the ileum that work on the absorption of bile salts and vitamin B12. So now we know that iron is absorbed in the duodenum, and B12 is absorbed in the ileum. And this actually is relevant, because if part of your ileum's gone, then you would be prone to having B12 deficiency. And if part of your ileum or ileocecal valve's gone, then you might have a problem called bile salt-induced diarrhea, which I see with relative frequency. And that's kind of a cool stuff there, if you will. We could go on a bit. It's called the enterohepatic circulation, and we could spend a long time talking about that, but we're going to move on to the colon, which is, if you talk to the average gastroenterologist, I was looking at my endoscopy schedule coming up on Friday, about 75% of the time, when I'm doing endoscopy, I'm doing colonoscopy work. I'm in general practice. Dr. Martin's hanging around the pancreas and the bile duct all day long. I do that too sometimes. But when I'm having an average day, about 75% of the time, I'm doing colonoscopy. So when you're visiting doctors, and we'll talk about this later, when we get to the day in the life, colonoscopy's a big, big part of our practice. Big deal. So this is the colon, and you've got the ascending, you've got the transverse, you've got the descending sigmoid and rectum, and you can see it's about four to five feet long, and so it's shorter than the small intestine. And the primary, there's two things the colon does, a big one, okay, is that's where the water is absorbed. There's not a whole lot of water absorption going on in the small intestine. That small intestinal stuff is coming through, all the glucose is gone, all the proteins are gone, all the fat's gone, but now we have this leftover stuff, a lot of fiber, and water. And all that water is absorbed in the colon, and obviously the colon's going to be involved with defecation. So it relies on peristalsis, it occurs throughout the GI tract, important in mixing and propelling things downstream. You've got this coordinated contraction and relaxation of smooth muscle, and you can see that little cartoon that I've, there it goes, oh, and there's reverse peristalsis. Sometimes things go back and forth, that happens sometimes. And then it propels things along, and then there's this mass peristalsis, or a, what is it called, a mass movement, and perhaps you've had one. And the, so then, and then things are delivered, right, to the sigmoid colon in the rectum. Now the process of deferring defecation is very important. I think we would all agree on that. And so this is where all the magic happens, because things hit the sigmoid colon and you go like, okay, we've got some, I need to take a break. And so the rectum and the sigmoid is a reservoir to give you a moment to gather your things and get to where you need to be. And then we have this thing called the internal and external sphincter, which when they work properly are invaluable. And you can imagine, and we take care of patients who don't have that luxury, where they have problems with this, and we spend a lot of time working with people because it tremendously affects their quality of life. Perhaps injuries that occurred during childbirth, multi-peris women, patients with neurologic disorders, tough patient population when we start dealing with problems in the anorectal area. Once again, the rectum retains stool, and then we have this internal sphincter, which is involving involuntary control, it's always on, thank you. And then the external, which then voluntarily you can expel gas if you choose to in the appropriate location. And so then there's this thing called the anorectal angle, so there are people who spend their literally clinical careers focused on these issues, because you're going to be dealing with doctors talking to them about esophageal disorders, and we're going to begin to see folks come into my office to talk to me about esophageal disorders of the esophagus and new developments. Some of your colleagues in other parts of the industry spend a lot of time in our office talking about constipation, and there are a number of constipation drugs that come out, so one day you might drop by my office on Tuesday, and then on Wednesday and Thursday it'll be the constipation people coming by to talk to us, because it's a big, big problem and a big issue, and we have an aging population. Anyways, so this angle is very important for the process of defecation. Okay, I got eight more seconds, Dr. Turney.

small intestine

large intestine

digestion

nutrient absorption

colon

constipation