Good morning, everybody. My name is Kajali Mishra. I'm one of the IBD doctors at Stroger Hospital under Cook County Health. I'll be giving a brief overview about the basic anatomy and the physiology of the small intestine. So this picture kind of is what you would see if you would just remove the skin from the body of a person if you were looking at them. So over on the right is the large organ, liver, hiding underneath it in a foci is the gallbladder, then kind of going in the middle of the abdomen is your pancreas hiding behind the stomach. So when you put the food in the mouth, it goes to the esophagus and then goes into the stomach. And then from the stomach, it goes into your small intestine, which is kind of in the middle. And then the large intestine is kind of bordering the entire diagram. And then the food is eventually after digestion, hopefully gets pooped out. The liver, gallbladder, pancreas are sort of the organs that are going to help and assist in the digestion process. And they have their specific functions, and we're going to go through those now. So the small intestine is really long. It basically is around 25 feet and takes up most of the space in the abdomen. So kind of fills in between the entire colon as the stomach empties its contents into small intestine. The job of the small intestine is to sort of coordinate that digestion and then absorb the digested elements, absorb the water that's important, and then keep the food moving so that the pipeline doesn't back up. So the small intestine is further divided into three parts. One is the duodenum, followed by the jejunum, and then the ileum. The duodenum is the shortest segment of the small intestine. This is the upper part of the stomach, and then the pylorus is sort of the valve, which controls the exit of the food contents from the stomach into the small intestine. So this part, the C that you're seeing, is the duodenum. It has further divided into four parts, and it's a very important part of the small intestine because the bulb, it receives the food. Then we have our descending part where you see the area marked as the major papilla, which is where the bile and all the gallbladder, liver, and pancreas secretions are going to come. Then in a coordinated manner, the food has to go down to the horizontal portion of the duodenum and then kind of go up against gravity in the ascending portion. While this is happening, when the food enters into the duodenum, there is a hormonal pathway that you don't really have to know much about, but understand that it has to be the release of all the digestive stuff has to be in a coordinated manner so that the digestion process starts right about here. So the duodenum is the C portion of the duodenum and kind of marked the papilla over there where the opening is. What's happening behind the scene is we have this pancreas, which is sort of at an angle in our body, like right about here. I tried to show that in the diagram, in the first diagram that we had, and then we have the gallbladder over here in our body. So what's happening is the liver is producing all the bile and then the gallbladder's job is to store it. What's happening here over in the, if you just kind of track the green ducts, you have common hepatic duct, the gallbladder does the storage. When your food is ready and to be digested, the gallbladder squeezes it out into the cystic duct that comes down into the common bile duct, and then the bile gets released into the, through the ampullavator into the duodenum. And similarly, more important for digestion is the pancreas and what, it also involves two ducts. One is a big duct and other one, as you can see, is a smaller duct. Both of them end up releasing all the contents and through the amp, via the ampullavator into the duodenum. And this is a very coordinated process of helping in the digestion. So then we have, this is kind of just the, you know, what function it does is that the duodenum is responsible for all the enzymes to be released, as I told you, which the enzymes are, some of these enzymes are there in the small intestine, some are coming from the pancreas and the bile is released from the liver and the gallbladder. And then after this breakdown of the digestion part is happening, there is the absorption and the major absorption of most of the nutrition happens here. And the iron portion is absorbed in the duodenum. Now note that this part of digestion does not involve any sort of acid production. The acid production is primarily job of the stomach. And if anything, the acid gets neutralized in this part of the, in this part of the digestive tract. Then we have the next part after the duodenum, the food goes on to the jejunum. And really, you know, there is almost a kind of a continuity between the duodenum, jejunum and ileum. And from the, you can really not tell the difference between where the jejunum stops and where the ileum sort of starts, but the job of this area being so long and giving all the surface area for absorption of all the nutrition from the digestion that has happened earlier. And to aid into that digestion, the absorption, this area is very richly supplied by blood and also with the lymphatic system. And you can see that red connection turning into the blue. That's sort of the blood vessels inside. You have the yellow string, which is the nerve, and then the greens are the green is the lymphatic. The lymphatic system is sort of the immunity barrier because as much as the job of this part to absorb, the lymphatic system kind of also captures, you know, anything that the body has to, you know, recognize as foreign or any infection that it might encounter. And this is the part where the body also kind of sends signals to the immune system. So most of the absorption of the nutrition, carbs, fats, protein, minerals, and vitamins happens in the jejunum. And then if you were to look at the small intestine with a camera, like how we do when we're scoping, this is how the villi look. And you can see there are plenty of them to increase the surface area. And this is kind of present in the entire small intestine and pretty characteristic when we're looking at them in endoscopy. So once we see the villi, we sort of know that we're in the small intestine, whether we go from above or we go from the colon. Once we enter into our ileum portion from the colon, this is kind of the picture we want to see if it's a normal small intestine. Then the ileum, which is sort of the final portion, it's really long, about 15 feet, longest part of the small intestine. And then it is connected to our colon. And there is a valve, which basically serves a very important part of kind of coordinated movement of this digested food into the colon. Ileum again is doing a lot of absorption. The part that it is specializing in is absorption of the fats, olive oil, vitamins. So vitamin A, D, E, and K, and also vitamin B12 are absorbed in this portion of the small intestine. Then we walk over, after all the digestion and the busy part of the small intestine, we come into the colon. The colon is sort of a very compliant part of the intestine and often referred to as large intestine in layman terms. It is further divided into, so we will start from the right bottom. So this is kind of where the cecum, which is where the small intestine will drain all the food, all the digested contents after the absorption. So almost sort of the beginning of a production of the waste material. Then the cecum goes forward to the ascending colon, and there is transverse colon, so laterally, horizontally, and then descending colon, sigmoid, and then in a very coordinated manner, the stooling process happens in the rectum and the anus. This part is not as long as the small intestine, but it's still fairly long, about five feet, depending on the body habitus. The primary job is to absorb water and electrolytes, so most of the nutrition absorption has already happened in the small intestine. The water portion will be absorbed here so that you're not pooping liquid stool. You sort of have a consistency to your stool. And then the elimination of the solid waste will then happen in the rectum and the anus area. The peristalsis is a very important process because the peristalsis is sort of the churning thing. The movement of the entire digestive tract is a very significant part of the digestion process, so the stomach moves a lot, and so does your small intestine and your large intestine. Small intestine moves a lot more than your large intestine. Usually the peristalsis happens in a forward direction, especially because we have to push the contents out, but because we want to make sure that we're churning this really good, there is also a concept of reverse peristalsis just to help things get absorbed really well. And then in the portion of the right colon, some of the reverse peristalsis happens, but when we come into the left colon, which is where we almost body knows that this part has to be discarded, this is going to become the stool eventually, so then there's mass peristalsis and then the stool comes into the rectum and your body's ready to defecate that. So the rectum and the anus area, the sphincter really controls the process of defecation over here. There's an external sphincter and an internal sphincter of your anus area, and then dentate line marks from within. If we were to look at this with a camera like we do in an endoscopy, we know that if we are beyond the dentate line, we're in the rectum, and if we are outside of it, then we're sort of in the anus area. But the anal sphincters really help with the coordinated motion of how the stool is going to come out. So the sphincters have a certain tone, and how it's controlled is that the internal sphincter is involuntary, meaning that it will sense the stool and then it will relax on its own. The external sphincter is what helps you control it. Even though you know you need to go poop after that coffee that you had in the morning, you still won't be able to control it until you get to the bathroom. So the external sphincter's job is to kind of give that coordination, but any trauma or damage to this part will lead to accidents or problems like that. So it's a very complex mechanism of defecation, but just to make it easy, the sphincters are the external anal sphincter and internal anal sphincter are sort of in the bottom, and then in a fashion of sling, a puberectalis muscle kind of holds the rectum portion at an angle. And when you're ready to defecate, when you're sitting on the potty pot, the puberectalis muscle will then coordinate, and your internal anal sphincter and external anal sphincter will go in a coordinated manner where the external anal sphincter will completely relax for the anorectal angle to increase, and then all the stool contents to come down. So it's a very coordinated manner of contraction of certain muscles and relaxation of other certain muscles in the distal area for the stool to come down. And any problems in that, whether the voluntary portion of it gets damaged through trauma or any nerve damage, or due to trauma to the pelvis area, if any of those nerve attachments or muscle attachments don't get damaged, then problems with defecation arise. So this area is often studied better in MRI and kind of in a, we take pictures to see how the stooling process is really happening. So that's all the interesting stuff I got for the anatomy and physiology. Did you guys have any questions? If you have any questions, please feel free to reach out to me, and I'll be happy to

small intestine

digestion

peristalsis

nutrient absorption

Kajali Mishra