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Hi, everyone. I'm going, I'm a second year medical student here at Ulster University. I've just been asked to teach you guys some anatomy regarding the lower gi system today. Um I'm also part of the Surgical Society Committee and we've been making um a few videos on different systems. So if you're a member of the society, please go check that out. But let's get started. So these are the learning objectives that I'll be talking about today. Basically, I'm going to be focusing on the anatomy structure and a neurovasculature of the small intestine, large intestine and the rectum. Um So those three polyps are really what we're going to focus on when it comes to the lower gi tract. Um I also try to make the slides as simple and straightforward as possible just so you guys can focus on the high yield stuff for the exams. So before we get started, we need to have an overview of what the intestines actually are as well as the rectum. What are their functions and where are they located in the abdomen. So when I'm talking about the lower gi tract, I'm really talking about anything that's lower than the pylori of the stomach. So you can kind of visualize it here in this diagram. Um just below the gallbladder and the small intestine, we have the duodenum, which is the first part and then right off the duodenum, you have the jun and then you have the ilium, which is the next part and the last part of the small intestine and then that ends over at the ileocecal valve which then goes into your caecum. And this is the beginning of your large intestine which goes up your ascending transverse and then descending colons um ends with the sigmoid and then the rectum. So it's pretty straightforward, but we'll go through it again soon. And then, yeah, that's basically the lower gi tract. So the abdominal aorta relations is actually something that kind of comes up in exam sometimes. So I would suggest that you try to know at least some of the main ones. There is actually no mnemonics online that show you how to memorize like the order which goes through, which goes um these throughout. I will say that you don't need to know every single thing here. Um like the fourth lumbar, the lumbar. Um Yeah, it says that's a spinal level, but you don't need to memorize that it's more so the things like renal, inferior supra renal, um even like inferior phrenic that comes up a lot. I think um I would also just know that the IVC kind of runs down the right side of your body next to the abdominal aorta. And the reason why that's important is because in some of the kidney questions, oh, it actually says it here. It says um that the right renal artery goes behind the IVC. So you'd kind of need to know that like if there's a renal question on that, I'm not really doing a renal lecture today, but that's just something that maybe you should know. Um But the three things I want to highlight here is like the three large branches that kind of supply the different guts if you will of the gastrointestinal system. So you have the, the celiac trunk, then you have the sma superior mesenteric artery and then you have your inferior mesenteric artery um comes off at L3 L1 sm at 12 celiac. So this will come off right below the diaphragm because remember the aorta um paras the diaphragm. So that's where that comes off at celiac. We're not going to focus much on it because it's going to be mainly, you know, supplying the f gut, which is like your stomach and esophagus and pancreas and things like that. Um Sma we're gonna be focusing on that a little bit because it's gonna be supplying your mid gut. So everything basically in your small intestine all the way up to your proximal to the, the transverse colon in your large intestine and you have your I MA which just supplies the hi got to the rest of the colon and the rectum. So that's, that's why I brought this up because that is important to know. So we're going to be talking about the small intestine now. So the part, the first part of the small intestine is the duodenum, which is kind of the c shaped structure right here. So this is actually, like I said, you know, the first part of the small intestine, that's where the, the, that's where the full gut ends. And that's where the midgut begins. So that is actually something important to remember, I would say. But yeah, like I said, there's four parts you have the superior part, which I said was covered by the visceral peritoneum. There is a reason why I said this because basically the first and your fourth parts are intraperitoneal organs. Whereas your descending and inferior parts are like located Retroperitoneally just with the first part. Um It's held up by the hepato duodenal ligament, which is, which just means like it's related to the liver. Um It's also a very common site for things like ulcers to happen. I'll talk a little bit about ulcers later. Um But the second part here, that's your descending, that's where the major duodenal papilla is or the um um the um where the pancreatic juice and the bile um juices from the gallbladder. Sorry. So they will drain in that area basically at the ample of bladder as well and then you have your inferior part and then you have your ascending. Um So here it's actually highlighted, that's the duo Jal junction. So that's where the Judum kind of begins. Um arterial supply. I wouldn't worry too much about this one, but I just put it in. It's called the gastroduodenal artery. It's pretty straightforward. Um You have your inferior pancreaticoduodenal artery as well. These two are going to be supplied by the, as a, by the way because like we said, mid gut is always kind of supplied by the S MA. And then all the um kind of drainage goes into the hepatic portal vein, kind of easy to remember because the liver again is over here near the first part of the duodenum. Um lymphatic drainage like, yeah, it exists, but I don't think they really ask much about that. And then you have something called a suspensor muscle of the duodenum that's located around here. And what it does is that it actually suspends that ascending pot up and it actually can contract and help food kind of move down. And I forgot to say this earlier. I'm sorry. But a big, basically a big part of the small intestines like function is to absorb nutrients from foods. Ok. So if there's something wrong with your duodenum or even, you know, you're judging them, even ilium, you're going to have problems with malabsorption. And we might talk about that a bit later. When we come to like things like celiac disease. So the next uh kind of high yield topic that gets brought up a lot does concern the geum and the ilium. Um So these are both intraperitoneal structures and they're both attached to actually the posterior abdominal wall by something called the mesentery. So this like kind of flat structure here between the intestine is the mesentery and you can actually see these arteries run through the mesentery. The mesenteries is made of like fattened peritoneal cells really. Um But they carry a lot of nutrients and they, they're very thin structures and I'm going to talk about the omentum in the next slide. But yeah, the, the mesentery is a very, very big part of what's in between intestines. Um So you have your jejunum, of course, and you have your Du Du Du Jal fracture. Um The thing about the helium and the is that like, they don't really have a very clear division. It kind of just begins. Um like there's a flex show but there isn't really a flap or anything, you know what I mean? Um And then in the ilium, um at the very end of the ilium, you have the ileocecal valve, um we're going to come to the cecum and I'm going to talk a little bit about why this valve is really, really important um in a minute. But you also have arterial supply, like I said, it's just a s and then you have your superior mesenteric vein as well, not that important to know. But yeah, we'll come back to the vas rectal thing as well. So another kind of high yield sort of question that pops up in a lot of exams is what's the difference between Judum and ilium? Um, you know, obviously they're located differently in the abdomen, but the juju tends to have a thicker intestinal wall compared to the ilium. The reason is because the juju tends to absorb more nutrients than the ilium does. So it needs kind of that thicker wall for most surface area um has longer vas orecta, whereas ilium have shorter vas orecta, vas orecta if you don't know, are these like almost like little um parts of the arteries that come off the sa specifically. So this is a only sa kind of feature and it splits off into like 20 or more branches. And the reason it really exists is just to have like coater vasculature really you have arcades which are just like more smaller um sort of a reca connecting together. And then the jun is always going to be darker in color because it has a much richer blood supply than the alium does. So next, the next is the large intestines. So mainly the function of the large intestines is to absorb water while um I guess what, what, what is going to become the um the fecal matter? And the function is to absorb water and nutrients and electrolytes and then eventually it becomes the um fetal fecal matter. Sorry. Um But the first part of the large intestine is your c so remember how I said, there's something called the ileocecal valve. So you can see the ileum kind of popping up here. Here is kind of the the opening and that's where the ileocecal valve is. Why is this important? Well, if you know how the large intestine is kind of structured, there are a lot of enteric bacteria and a lot of microbiota and flora, things like that. Those are natural microflora, but you cannot allow them to go into your ilium because it's going to cause infection. Um Having said that helium actually has a lot of pays patches compared to the j I don't think it was in the previous slide, but it has pays patches specifically for this reason. So it's kind of like an extra layer of protection. Um But yeah, the cecum is kind of the first opening of the large intestine and just in that um kind of middle posterior side is where the appendix sits. So the appendix is a very, very small kind of organ and it kind of looks like this like deflated one of those noodle balloons to me. Um But you know, of course, the purpose of the appendix has been widely debated. It does contain lymphoid tissues and some people think it plays a role in immunity um, it also sits kind of in different positions but the most common position is your retrocecal. Um, and it's held up by something called a mesoappendix which has your appendicular artery coming off it. So that supplies, um, your appendix. Why is the appendix, you know, important to know? Well, you can have pathology now, of course, you can get appendicitis, which I'll talk about a bit a bit later. Um, but yeah, appendix very important to know and just the two functions of the cecum, like I said, it just stops the bacteria from entering. But it's also a very big landmark for colonoscopy. So if a doctor is, you know, doing a colonoscopy on a patient, um they can see where the end or I guess the beginning of the large intestine is all right. Next is the structure of the large intestine. So we talked about how the from the cecum there is the ascending, transverse, descending and the Sigmund column um arterial supply, like I said for so, um midgut is basically the two thirds of your transverse colon, your um ascending colon and your um cecum that's going to be your midgut. Your appendix is also part of the mid gut, by the way. Um So you're going to have the SMA, which is this big vessel here, the sma a splits off into your middle colic artery um which goes more so about like near your hepatic flexure. Then you have your right colic artery. So that's your ascending colon. Um And then you have, of course, the ileo colic artery, I think in the previous slide, um It was written that the ileo colic artery mostly supplies the cecum as well. And like I said earlier, Hind God is just I A so the rest of the colon basically with that one. And then the sigmoid mainly just the sigmoid arteries. Um And then the rectum kind of has three supplies actually, but we'll get to that soon. Innervation wise, midgut is going to be um basically the superior mesenteric plexus. It's kind of easy to remember just given the fact that the sma also supplies the vascular device, hindgut, um parasympathetically, pelvic, slacking nerves in your pelvis, sympathetically, the lumbar slighting nerves that um that set actually runs kind of in the lumbar spine. So like the lower back and just also to know the large intestine has some anatomical features that might be important to know as well. So the first thing I want to talk about is something called a um the omental appendices. They kind of these like small little patches or pouches or peritoneum and fat that kind of reside on the surface of the large intestine. There's also the greater omentum, the greater omentum kind of comes off the greater curvature of the stomach and hangs down like a curtain over your transverse intestine, your colon. Sorry. Um The reason why the omentum exists is it has a lot of lymphoid tissue, carries nutrients, has fat in it as well, vessels and it also drains peritoneal fluid. So it kind of prevents fluid build up in the peritoneum. Um If you didn't know what a peritoneum is, it's just like the inner covering of the abdomen. Um then you have the 10 coli, this is also a very important kind of landmark on the large intestine that just kind of strips of muscle. And when they contract, they cause these little indentations called haustra as well. Next, you have the marginal artery of Drummond. So you can see in this picture here between the middle colic and the left colic artery, it kind of connects and anastomosis over the near the splenic flexure. Um Why is this important? Well, you know, if you get something called ischemic colitis or mesenteric colitis, uh mesenteric ischemia, you know, this kind of plays a bit more relevance in that, but we'll talk about the conditions a bit later. Ok. So rectum anatomy, all right. So the rectum begins around S3 level in the spine. There's three flexors that we really need to know. So the first one is sacral, it's kind of um obvious what that means. It's just following the curve of the sacrum and the coccyx burn. Then you have your inner rectal uh flexure. So that's highlighted here at the bottom, but it's basically running along your puborectalis muscle and it helps with fecal continence then you have your lateral flexors. So in the rectum, you have three kind of rectal folds, the superior intermediate and the inferior folds and these are formed by the lateral flexors. This gets tested quite a lot, I feel like. Um and they're also made of circularis muscle as well. Um Then you have your amlo that's kind of like the dilated portion of the bottom of your rectum. And basically fecal matter will be stored there and it kind of helps expand that muscle a little bit. Um, and one important thing to note is the rectum is mostly retroperitoneal, but the top half of it. So the top third of it has peritoneum attached to it, but the rest of it doesn't. So that's kind of interesting to know. All right. So, neurovascular supply, it's very interesting because the rectum has three supplies. Um, it's pretty well perfused organ. So you have your superior rectal artery comes off your im. So we talked about it's part of the hind gut that makes sense, middle rectal artery that comes of your internal iliac artery. So if you remember your abdominal aortic artery and then splits off into internal, external iliacs and then the internal, uh, sorry, it splits off a deer called an iliacs. And then the internal external iliacs. And those two iliacs kind of meet at the, um, middle part of the rectum, then you have your inferior rectal artery that's going to be coming off your internal pental artery, uh vein drainage, I mean, the superior is just going back to your portal venous, just like the s just like the im sorry, middle and inferior systemic veins. Um goes through your IVC innervation, lumbar splanchnic nerves and superior inferior hypogastric plexus. We talked about how lumbar splanchnic is the same as a sympathetic innervation of the hindgut. So that's an easy way to remember it. Hypogastric are those like set of nerves that kind of sit in front of your uh coccyx, basically below the pelvic brim. Then you have a parasympathetic, which is S two s four of your pelvic spinning nerves. And again, the hypergastric plexus um just to kind of remind you sympathetically the digestive system, you know, gets turned off, whereas parasympathetically is like known as the rest and digest. So that's, that's when you would want to expel that fecal matter because that is the rest and digest part of it. All right. So the next part is mainly talking about some of the things you might see in an exam um or some conditions that might be presented commonly in clinical practice. But I also wanted to ask some questions at the very end as well because that might help you. So this is a very common kind of exam question that could show up, but it's just talking about what organs are behind the peritoneum. So again, the peritoneum is just like covering that's inside your abdomen um there's a mnemonic called sad paco. So you have supraadrenal glands, you have your aorta IVC duodenum. It's only the middle parts, by the way, it's uh the 1st and 4th parts like they're intraperitoneal, pancreas, ureters, colon, you're ascending and descending kidneys, of course. Um esophagus, this is the, I guess American spelling, but they put it in there and then rectum. Um I will say the ureter kidneys and adrenal glands, they're kind of like a unit almost. So you can kind of remember that way. And this is just a diagram kind of showing you the uh positionings of where everything sits as well. All right. So this is mainly for the second years who may be watching this because if you're first year, you probably won't need this as much. But I just wanted to kind of go through some of the cod conditions that might be relevant with the lower gi tract in particular. So, peritonitis is when you're having an inflammation in the peritoneum and it can be due to causes like perforation, surgery, trauma, even peritoneal dialysis. Um there's different types of peritonitis. So you can have spontaneous bacterial peritonitis, which is like where you don't know the origin of it. But that kind of happens like second to ascites or liver disease and you'd have to do like a paracentesis for that. But signs of like rigidity, very being very specific fever, intestinal paralysis, signs of fever infection, absolute bowel sounds appendicitis, like I said, a very common presentation, especially in like younger people. And it's just really when the, when the appendix might burst and it causes inflammation, um, person might feel like white, um iliac fossa pains. You have something called the mcburney's Point Robson sign, Bloomberg sign. So a sign that one has a lot of signs, mild fever and of course, you'd have to do surgery to fix that peptic ulcer disease is when you have like little ulcerative lesions that pop out in the mucosa of either the stomach or the duodenum. I think it's more common in the stomach. Um but it typically happens due to h pylori infections or NSAID use. Um and it has very similar symptoms to gastritis. The next one is gastrointestinal perforation. So I included a chest X ray for this because if you see air trapped under the diaphragm, that's kind of a uh big indicator of this um happening, but perforation can be happening because of trauma, even bowel obstruction due to hernias or um constipation. If you have diverticulitis and the diverticula pop, it can even happen from cancers or tumors or ulcers popping, that causes very painful kind of inflammation in the peritoneum. So it can cause peritonitis and it can cause someone to literally develop abscesses and sepsis, which is obviously very dangerous. Um Colorectal tumors, I don't have an image for that, but you know, you can have um types that come sporadically. So from polyps or it can be more of a genetic thing. So if you have a PC gene mutations or H AND PCC, which is something from microsatellite instability, or if you have familial adenomatosis polyposis, um which is why like younger people will develop polyps that will like most definitely develop into cancer. Eventually, you would do like fit testing as well as like screening programs without ischemic colitis, which is what this P is supposed to show. So, like I said, that marginal kind of artery of Drummond gets um affected and it causes parts of the intestine to not get perfused anymore. And usually things like atrial fibrillation is a big risk factor for this because embolus can develop and cause blockages in the artery. Um places like the watershed area. So, splenic flexor is a watershed area that gets affected. You might see abdominal bruit um weight loss pain while eating. Um depends the pain onset. Kind of depends because there's like three types of ischemic colitis you can get um but I would just search those up yourself diverticular disease. Um Those are just like little muscular weakness or out pouchings on mostly your sigmoid um colon. And it's because the sigmoid colon is really under a lot of strain and pressure, it's also the most flexible part of your colon. So you tend to see that here and then when fecal matter kind of builds up on those diverticuli, you get complications like diverticulitis which is just inflammation. So people might feel that left iliac fossil pain with fevers and things like that. IBD. IBD is just Crohn's and ulcerative colitis. I'm sure like all the first years probably know what that is as well. Um UC presents with more diarrhea, um, or bleeding with diarrhea affects the rectum upwards, usually only affects like the first mucosal layer. Crohn's is all the way through skip lesions, granulomas, um, has more complications like fistula as far as UC might have something called toxic megacolon. Um on the abdominal x rays, celiac disease. Um That's an autoimmune kind of disorder that where um inflammation in the small bowel happens when you eat gluten. So when you eat gluten, it causes something called glid to be attacked by the antibodies in your small bowel. Um, it can cause complications like dermatitis. Hepato form is which is like the little lesions on your elbows, but it can also cause autoimmune disorders like type one diabetes and even infertility in some women. Um IBS is a functional disorder of the bowel. So that one just presents with mainly abdominal pain bloating and changes in bowel habits. Usually you'd see like uh mucus in the diarrhea as well. Um, and travelers diarrhea, mostly an e coli kind of infection and it just makes you have a lot of diarrhea in a day, really a few times a day. So that's, that's kind of like the core conditions in a nutshell obviously, this is like, if you're a second year listening to this, you would need to know way more than what I just said. But I guess that's like a good start. All right. So the first question I want to ask is which of the following is not a branch of the abdominal aorta. So we have these options and I'm just going to like if you want to pause this, you can think about yourself. But I'm just gonna because I'm running out of time, I'm just gonna skip ahead. Superior chronic. So yeah, so if you just look at the like literally just look at the previous diagram um because like I said, inferior phrenic is gonna be that, but the superior phrenic is not really in that. It's kind of more above that. And if you remember the inferior phrenic is one of the first one that shows up as well. 10 year old boy presents to A&E with right iliac fossa pain, low grade fever. I strongly suspect that he might have appendicitis, which of the following embryological structures is the appendix derived from. Um So you kind of need to know the boundaries of each gut. You can kind of rule these two out immediately just because they make no sense. Um But yeah, it is the mid gut. So like I said, midgut is from the beginning of the small intestine all the way to basically the end of your two thirds of the proximal transverse colon. So it has to meet a bit gut. And the last question is 30 year old presents to emergency department acutely unwell. She has tachycardia tachypnea and a low grade fever infection suspected, but the source is unknown. She did a CT scan and they found retroperitoneal collection likely the result from a damaged retroperitoneal structure which of the following structure is most likely involved. Um So if you, this is just another way of them asking you if you know which organs are retroperitoneal or not. So if you just look at the sad PCO mnemonic, I taught you, you would know that is just ureters. Um because it's the only one of these options that is retroperitoneal, spleen isn't even an option. Stomach is not an option, transverse colon. Like we said, it's only the ascending and descending that are retroperitoneal. And we said that the 2nd and 3rd parts are retro peritoneal and the rest are not. So it has to be ureters. But yeah, that's all for today. Um Thank you guys so much for listening. I hope you guys learned something and if you have any questions or if you want to ask me something about this presentation, just let me know you can contact me. But thank you so much for listening and I'll see you later.