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Hi, everybody. Thank you so much for joining for this evening's teaching. I'm just gonna give it five minutes to let everybody join and then I will hand over to Keegan for this session. So five minutes. So good evening everybody. Thank you so much for joining our second week of teaching. Um This week we will be focusing on the lower gi and we've got Kegan here with us that will take us through some anatomy. Um Just before we start, I just wanna say a massive thank you to our partners. So the MDU teach me surgery, pass the mcrs um medal and more than skin deep. Um I will send out a feedback form towards the end of the session and if you fill out the form, you'll get access to these slides, um a recording and also some special discount codes from some of our partners. So without further ado, let's hand over to Keegan for this evening's teaching. Sorry. Can you hear me? Yeah, I can hear you all fine. Perfect. Let me just switch on my camera. Uh Can I be seen? Yeah, we can see you as well. Perfect. Perfect. That's brilliant. That's brilliant. Just one second. Yeah. Right. Right. Um, good evening everybody. Um, so my name is Keegan Fernandez. Uh, I'm 1/4 year medical student from the University of Central Lancashire. Uh, welcome to this anatomy of the lower gi teaching session. Uh, just very quickly, something that I wanted to touch up upon. It's, this is something that has been of particular interest to me, uh, especially when I started my, uh, secondary care placements in year three. When I started going into hospital, I started with medicine before moving on to surgery and gastroenterology and general surgery, which basically consists of upper gi and lower gi was something which I found really interesting, something which I spent quite a lot of time on. So I think it's something which I have been able to grasp, wrap my head around quite well. So hopefully, I do justice to this teaching session and I'm able to pop my knowledge uh in this uh teaching session. So without further ado I'd like to get cracking. Um So I have a couple of objective which I am looking to cover. So I'd like to uh in the session identify the anatomy and key features of certain areas of the lower gi tract. So I'd like to, I'd like to cover the appendix, the cecum, the colon, uh the rectum and also the canal as well. Now, all these uh key uh along with these um organs that I've just mentioned also like to describe the arterial supply and the venous drainage of the lower in a bit more detail as well. So those are the objectives that I'm looking to cover. I have a couple of secondary objectives as well which I highly doubt I'll be able to achieve due to time constraints. So I wanted to speak about the abdominal cavity. The callose triangle, speak about peritoneum and me mamma Andries in a bit more detail. Uh the inguinal canal, the heel back triangle and the anterolateral and posterior abdomen. However, due to time, it won't be possible, but I will try my best to touch up all triangle and the heel back strangle as well. So yeah, let's have a go and let's see how we are doing on time and then try and cover it right. So let's just get started. Now, while I was offered the opportunity to do this lower gi anatomy teaching session. And while I started creating this powerpoint, the one thing despite being 1/4 year medical student, which is gonna sound strange. I didn't know exact to start. So obviously, we do know that the gi tract is conventionally given to the upper gi and the lower gi system. So the upper is from your mouth to the ileum and the lower gi is from the anus. He was an interesting in factoid from my side is that when you're considering a gi bleed, the demarcation between the upper and lower gi tract happens to be the duodenal junction, which is the ligament of res. So basically what that means is when you have a bleed above the duodenal genital flexure, it's called an upper G IV and flexure, it's called the lower G IV. So when I found this, I found it really confusing and I didn't know where exactly do I start. So to let things flow chronologically and for my mental sanity, I'm gonna call into Stein in detail as well. So bear with me, right. So I did mention the ligament of triad. So before we go on to the small intestine, just very quickly, it's basically a band of tissue in your abdomen. It's, it's basically in your belly. The purpose of it is to support and anchor the duodenum, which is your first part of the small intestine. And basically what it does is it helps move contents along your gi tract. Now, for those of you who have covered, who have had your pediatrics rotation or have an inx, I'm sure you all must have heard of the condition called intestinal. Now, basically what happens in this condition is you basically have a birth defect involving the ligament of res. Now, what happens is when this is basically a birth defect in this ligament cause twisting of, of your intestine and hence lead to intestinal malrotation. So it's just something that I wanna share with regards to the ligament of re it's not included in the slide, but I just thought it just shit. So, yeah. Right. So, moving on to the small intestine. So it's one of the, it's, it's an organ located within the gastrointestinal tract and has a length of around 6.5 m. It has a function of assisting in digestion and absorption of ingested food. So this was one thing which was of, which was of particular interest to me where I felt that the anatomic medication with regards to the duodenum starts form the pylori of the stomach and then, you know, goes on, but basically, it extends from the duodenal bulb, which is your first part of the duodenum. And it continues to the ileocecal where it meets the large in to sign at the ileocecal valve. So when you move on from the duodenum to the jejunum and to the ileum, which are the three parts of the small bowel, which will be covering in detail. When you reach the ileum, uh you have, then you move on to the large intestine and start with the cecum no, between the ileum and the seal ileocecal valve. Now that ileocecal valve signifies the end of the small intestine and indicates the start of the large inter sign as well. So, yup, that's basically the small intestine starting from the duodenum and ending at the ocal valve. Basically the transition from small intestine to large intestine. So, yeah, anatomically, the small bowel bowel can be divided into these three parts, the duodenum ju and ilium. And we'd be covering the anatomy of the small intestine, the structure of the small intestine and the neurovascular supply of the small intestine. Right? So, with regards to the duodenum, so it's the most proximal portion, the small intestine, it's derived from the Latin digitorum, meaning 12 fingers length. And that's something that I've never covered in phase one over year one and year two. So I thought it might be kinda interesting share, not sure how relevant that's gonna be in the future, but just thought that in there. So it runs from the pylorus of the stomach to the duodenal junction and it can be divided into four parts. So you have your superior, you have your descending part and ascending, which I'll be showing you diagrams and talking about a bit more detail in the next slide. Now, together these parts from form a sort of C shape and it measures around 25 centimeters long and it basically wraps around the head of the pancreas which you're gonna be seeing in the next im right here. So uh one second, I do have a cursor here, right? So here is your entire duodenum and it's basic, it basically divide, it's divided into the four parts that I mentioned in the previous sides. So here in blue, you have your su part of the duodenum. You have your descending part here, you have your inferior part here and you have your ascending part here. Now, as you can see this forms ac shape around and it's 25 centimeters long. And over here, you have your the head of your pancreas over here. So it wraps around the head of the pancreas perfectly over here. Now, with regards to the superior section, it's or two as the gap. So from the, now, just one thing I'd like to mention with regards to this diagram, the liver, the gallbladder and transverse colon has been removed from this picture. So it hasn't been removed in this picture. Now, it's a section of the duodenum, as I said, it's referred to as the gap. It descends upwards from uh the pylori of the stomach and it's connected by it's connected to the liver by the hepatoduodenal ligament. Now, a fun fact with regards to this area, the superior aspect of the human site filtration. So obviously, when you're covering your, when you go in and general ulcers and duodenal ulcers, and we over time learn how to differentiate between the two of them. And apparently this is the site which is most common for duodenal ulcers of the duodenal, moving on to the descending part of the duodenum. You have your descending portion which curves inferiorly around the head of the pancreas. So this is the key part which is responsible for forming the C shape around the, it lies posterior to the transverse colon. As you see over here, you have your transverse colon, which would be covering up in more detail as we go along with the slides. Uh as you see the transverse colon here, it lies posterior to the transverse colon. But still, as you see your right kidney over here, it lies anterior to the right kidney. So these are just a bit, these are just a couple of anatomical relations for us to uh appreciate and yeah, now, internally, the descending duodenum is basically marked by the major duodenal papilla. So it's kind of an opening where bile and panic secretions enter from the anilla of vata or well, hepatopancreatic ulla. So basically what ha the major duodenal PAA is, it's basically of vata. Now, it's a rounded projection in the duodenum into which your common bile duct and your pancreatic duct basically drain. Now, the major do the t is um in most people, the primary mechanism for secretion of bile and other enzymes which basically facilitate digestion. Another fun fact is the initial three centimeters of the superior duodenum that you see here is covered anterior and posteriorly by visceral peritoneal peritoneum. With the remainder just retroperitoneal, which is only covered anteriorly, right. So, moving on, we have the inferior part of the duodenum right here in red. So the inferior duodenum travels laterally to the left. So it goes uh to the left and crossing over the inferior vena cava and the aorta. Um so it is located inferiorly to the pancreas as you can see in this image over here, you have your pancreas over here and inferior to that, you have your inferior duodenum, your inferior aspect of the duodenum. And it basically crosses the inferior vena cava and the aorta s sorry, apologies for that. Oh, sorry. Yeah. Now it is also located posterior to the superior mesenteric artery and the superior mesenteric vein. Now, this diagram over here in the middle is not very clear and indicative of that. So had to get another of mesenteric artery and the superior mesenteric vein, it lies behind these two blood vessels. So that's something to appreciate with regards to the anatomy of the duodenum and and peri per pertaining to uh the inferior part of the duodenum from the inferior part of the descending. Uh yeah, ascending aspect of the duodenum which signified of the duodenum. So after it crosses the aorta, uh it ascends and anteriorly to join the jejunum at a sharp turn, known as the duodena jeal flexion. Now, one thing to appreciate is that at this duodenal gal flexo, you have a slip of muscle called the suspensory muscle duodenum. Now kind of this muscle, uh basically helps with widening of the angle of flexo and just basically aids the movement of inner contents into the jeju. So it's called a suspensor muscle of the, the duodenum. It's something which I've never heard of until, you know, until I recently did a bit of research with regards to it. But yeah, and also if you could see over these two slides, I've also written uh written to the spinal levels at which these uh parts of the duodenum MRI. So you have the superior part of the duodenum one, you have the descending at L1 and L3 and you have the inferior and ascending at L3 and L3 to L2 respectively. So, yeah. OK. Right. So moving on to the histology um for those phase one students out there that are in year one and year two, I would say this is extremely important because uh I think this is one area where I got quizzed, I mean, where me and my colleagues got quizzed a lot in year one and year two with regards to the histology of the small intestine, the duodenum. So it's basically got a villous mucosa as you can see over here on this image in the right. So it's long and thin and it basically aids in absorption um absorption of your digested food. Uh It's distinct from the mucosa of the pylori which directly joins to the duodenum. So like the other structures of the gi tract, as you can see here, it's called mucosa, it's called a submucosal muscularis externa and adventitia image. Over here on the right. As you can see, you have your muscularis mucosa, you have submucosa muis muscular layer and you have your long muscle layer. One thing to appreciate of this time is that uh or or rather commonly asked exam question is how does it, the histology of the small intestine differ, especially the duodenum differ from parts of the gi tracts. Now, the key thing remember is that the glands that line the duodenum are known as brunner's glands. Now, what its function is, it basically secretes mucus and bicarbonate and the function of these glands is neutralized uh the stomach, its or the acidic contents from the stomach and it basically increases your, the ph of your intestinal contents. So, yeah, the the the bre glands. Are you located in the subway? Sorry, apologies, sir. So, the brown glands are located in submucosal over below and it's, it's particularly for the duodenum and you will not find it anywhere else. Now, these are, yeah, it's not found in the ilium or the or the parts of the small intestine right now, moving on to the jejunum and the ileum. So these are the distal two parts of the small intestine, both of them completely intraperitoneal. Uh It's attached to the posterior abdominal wall by knees entry, which is a double layer of peritoneum. There is no clear exact external demarcation between the jejunum and ileum that can be identified by different mesenteric vascular pattern. So, not quite sure where exactly the jejunum and ileum where it's pretty difficult to differentiate between the two of them. Now, they are macroscopically different, which is something that I'd be to touching upon in the upcoming slides. And like I said, beforehand, the ilium ends at the, now at this junction, basically, the ileum invaginate into the. There's one thing, once the intestinal contents pass from the jejunum into the ilium, the ileum invaginate into the caecum to form the ileocecal valve. Now, although it is not enough to control movement of material from the ileum to the cecum, it does prevent the reflux of your abdominal contents back into the ileum basically. So that's I think one thing we can appreciate, I see of, yep, that's exactly what is what, what I spoke about in the image over here. So you have your ileum and then you have your ileocecal valve and your cecum over here. So your abdominal contents, yours are allowed to pass through and it prevents the reflux of all that, all those contents back in. So, yeah, now, with regards to characteristics, features of the Jejunum and ileum, um it's basically, now the jejunum is located in the upper left quadrant where the ileum is located in the lower right quadrant. Uh The jejunum has a thicker intestinal wall, whereas the has a thinner intestinal wall. Um Now the jejunum has low reca now, basal reca basically what that means is straight arteries. So how it looks is basically when you have a particular artery which moves in between of your me into approximately a bunch of that could be around 10 to 20 branches. Now, when these branches anastomosed to form loops, these loop arcades and when from these arcades, you have long and straight arteries that arise that are called erecta. Now, the one appreciate with regards to the Jejunum and the ileum is that the Jejunum had longer straight arteries and the ilium has got short arteries. However, the Jejunum has less loops while helium has more arterial loops. And another thing is that the jejunum is brighter in color. It's like it's red, it's like bright red, whatever, whereas the ilium is color. So, yeah, right. So with regards to the vasculature and the lymphatics of the duodenum, you have the the arterial supply of the duodenum is derived from two sources. Now, you have approximate to the major duodenal papilla, which um you have your gastroduodenal artery. So basically what happens is you have celiac trunk. Now, from the celiac trunk, it gives rise to your common hepatic artery and that further gives rise to your gastroduodenal artery. Now, this is all of this. So basically the arterial supply of the duodenum is the gastro gastroduodenal artery and this is proximal to the major duodenal papilla. Now distal to the major duo artery, you have apologies for that. Sorry, sorry. Just, yeah. So, distal to the major duo, you have your superior mesenteric artery and you have a branch that comes off from that which is the inferior pancreaticoduodenal artery. Now, that provides the blood supply to the distal aspect of the major duodenal PAA. Now, I think this is something which is very important for us to understand because this transition is important. It marks and signifies the change from the embryological fo gut to the hind gut, sorry, mid cut, apologies for that. So yeah, this marks the change from the embryological fore gut to the mid gut. So yeah, now the veins of the duodenum follow the major arteries and drain into the hepatic portal vein. Whereas with regards to the lymphatic drainage, it's directly to the pancreaticoduodenal and superior meso nodes, right. So with regards to the arterial supply to the jejunum is from the superior manic artery. So that's exactly where we, where I mentioned in the previous slide, where you move on from your embryological f gut to gut. You have the arterial supply changes from your celiac trunk to the superior mesenteric artery. So this arises from the aorta and one your L1 vertebrae, which inferior to the. Now, this is the concept I explained with regards to your arterial loops and your vaso reca. So when you have your sma which moves between the layers of the mesentery, this splits into approximately 20 branches. Now, these branches anastomose to form loops called arcades. And from these arcades, you have long and straight arteries that arise called erect. Now, this may not make the most sense, but I have an image in the upcoming slides which explains this in a bit more detail. With regards to the venous drainage of the Jejuni medium, you have your superior mesenteric vein. Now, this unites with neck vein at the neck of the pancreas to form the hepatic portal vein. And with regards to the lymphatic drainage of the Jejunum Andum, it's basically through the superior mesenteric nodes just like over here. But however, the drainage of the duodenum is also via the pancreaticoduodenal no as well. So this basically explains what I was saying in the past 23, couple of slides. So with regards to the difference between the Jejunum and Ileum, uh the Jejunal wall is a bit thicker as you can see over here in this image. Whereas with regards to the ileal wall, it's a bit thinner as you can see here, a cross section of the Jejuni is taken and it's got longer straight arteries of that. You can see it in this image over here and you can see it in this image over here. What with regards to the I it's a lot. And again, over here, there are less arterial loops in comparison to this to this area over here. So that's another thing to appreciate with regards to the an anatomical differences between the Jejunum and the ileum, with regards to the neurovascular supply of the Jejunum and the ileum where the Jejunum has terial loops, whereas the ileal has more as clearly depicted in this picture over here. So, yeah, I think it's important for us to uh appreciate this because other than that, it's very difficult to kind of identify where the jejunum ends and where the ileum starts. So, yeah, right before we move on to the cecum and the large intestine, I think it's very important to talk about the ileocecal valve and the clinical relevance with regards to it. So, like I mentioned, it separates it, you know, it represents a separation between the small and large intestine and it prevents the reflux of eric fluid into the colon uh from the colon into the small intestine. It is also used as a landmark during colonoscopy. So indicating that the colon has uh been reached and that a complete colonoscopy has been performed. Furthermore, it is also important in the setting of the large bowel obstruction. So should the ileocecal valve be incompetent? Uh a closed loop obstruction can occur and cause bowel perforation. Now, should the ileocecal valve be incompetent plus backflow of enteric contents into the small bowel bowel? Then the situation is less emergent and the trajectory of the obstruction can be less rapid. Now, moving on to the cecum on the large intestine, uh the cecum is the most proximal part of the last time. So it's looking the ileum which is the distal small bowel and the ascending colon. Uh it acts as a reservoir for kind which it receives from the ileum and we're gonna be covering the anatomical structure, neurovascular supply and the lymphatic drainage of the cum, apparently one f fun factor. Interesting factor about the C is apparently that many, many, many years ago. It used to serve as for cellulose digestion and something which I came across while do preparing this powerpoint. So just thought I could share that now with regards to the anatomy and relations of the cecum. Uh it's the most proximal part of the large intestine. It's found in the right iliac fossa of the abdomen. It lies inferior to the ileocecal junction. So as you can see over here in this image, sorry, apologies for that. As you can see in this image in the lower right part of the page, um you have your cecum which is inferior to the ileocecal junction over here. Uh It can be palpated due to feces or inflammation or malignancy. So it definitely can be palpated and superiorly. The cecum is incon is continuous with the ascending colon which is over. Yeah, as you can see in this image over here, now all the cum is also an intraperitoneal structure. So that's one thing of note as well. Uh between the cecum and the ileum. You also do have ileocecal valve. And yeah, like I mentioned this, I mentioned there were a bunch of times in this powerpoint that it prevents of the reflux of the intestinal contents from the cecum back to the ilium, right, with regards to the new, with regards to the neurovascular supply of the ki. So this slide from the embryological mid cut. Uh the vascular supply is via branch of the sma just like the ilium. Uh The outline is from the ileocolic artery which is a branch of this sorry for that ton of this sma. Now, this divides into the anterior and posterior cecal arteries. As you can see in this image on the top right of the page. Uh the anterior and posterior cecal arteries directly supply the cecum. And these two arteries are branch of the ileocolic artery, which is furthermore, a branch of the S MA with regards to that, you can better understand it is if you can just have a look at this image on the, the top right part of the page with regards to the venous drainage. Uh This provided by the corresponding iliacs. Furthermore, empties into the superior mesenteric vein. I also like to take a, a bit of a moment to speak about the innervation. So the sympathetic and parasympathetic branches of uh I'm sorry, the sympathetic and sympathic branches of the autonomic nervous system innovate the cecum and the appendix. This is achieved by the ileocolic branch of the superior mesenteric plexus. So this follows the same course as the ileo artery uh which uh which is a neovascular supply of the cecum. So this carries both vagal and sympathetic nail fiber. So I thought that's something offer elements which I'd like to state to you guys with regards to the lymphatic drainage of the cecum. There's nothing much to say over here. It's just that the lymph from the cecum drains directly into the ileocolic lymph nodes which surrounds the ileocolic art. So you have your upper group of ileocolic nodes over here and you have your low group of ileocolic nodes over here. So, so basically, these two structures are responsible for the lymphatic drainage of both and the appendix as well. Another thing to uh take note of with regard to your cecum is that it's 10% of all intestinal wall. So as we know that the sigmoid volvulus is one of the most common uh volvulus that there is. But however, the cecal cecal volvulus is does account for 10% of ovulation is present. Uh So common, clinical features include colicky, abdominal pain, abdominal distension and absolute constipation. When you take an X ray, you'd be able to demonstrate a large a loop of large bowel. Basically that is distended and that uh the pain which originates from the right quadrant and the distended loop of uh uh large bowel can be seen in the right lower quadrant onwards. Anyways, this is something of clinical relevance of the cum that I thought I'd like to share. But this will be covered in further detail in future sessions. So I wouldn't want to draw too much on it, moving on to the appendix. Um So it's a narrow blind ended tube that is attached to the posterior medial end of the cecum. Uh it contains a large amount of lymphoid tissue but is not thought to have any vital functions whatsoever. It's basically a vestigial organ. So again, gonna touch up upon the ana anatomical structure and relations, the neurovascular supply and the lymphatic drainage. Now, with regards to the anatomy and its relation, you have your appendix which originates from the posteromedial aspect of the cecum. Now, it is supported by the mesoappendix. Now, what the mesoappendix is is basically is you have of mesentery which suspends the appendix from the term terminal ilium basically. So that's what allows these to hang from the terminal ileum. Basically, that's the mesoappendix. The position of the free end of the appendix is highly variable from person to person. And this can be categorized into a bunch of main locations, into seven main locations uh depending on its relationship to the ilium cum or pelvis. The most common position is retro cecal. However, the different location be remembered by their relationships to a clock face, so which we will be covering up in the next slide. So as you can see over here, you have the preileal, the postileal subileal pelvic, subcecal, paracecal and retrocecal um uh relations. So over here. So as you can see over here, you have your pre ileal which is in green over here, which is in like dark green. Over here. It's at a one or two o'clock position, you have your post ileal, which is behind the ILIM again at the one or two o'clock position. Furthermore, you have the sub allele position isn't mentioned over here, but it's parallel with the termin ileum at a three o'clock position. So it be around here, you have your pelvic, which is over here. So it's descending over the pelvic brim. So that's at a five o'clock position. You have your subsequent position at a six o'clock position. So it's basically just below the sequence. Unfortunately, I wasn't able to get a picture of the pa cecal location, which is basically alongside the board of the cecum and you have your retro cecal position, which is, yeah, basically behind the cecum at 1111 o'clock position. So I think the reason why I put this over, it's important for us to just um appreciate the fact that the appendix can have. It's not situated in one area and then it could vary from person to person and it could anatomically different from one person to the other, right. So with regards to the neovascular supply of the appendix, it's basically derived from the embryological mid gut. So the vascular supply is via branches of the sma. And it's basically where you have your sma, which gives rise to your ileocolic artery and that further gives rise to your appendicular artery. So it's very similar to the blood supply of the cecum, venous drainage is responding, appendicular vein. So nothing too fancy and both are contained within the measles, which I explained in the previous slide, sympathetic and parasympathetic em, uh the autonomic nervous system which innervate the appendix. And this is by the ileocolic branch of the superior plexus and it accompanies the ileocolic artery to reach the appendix. So, yeah, and just a fun fact or something to note of clinical relevance. Uh the sympathetic fibers of the appendix originate from T 10. So at 10 of the spinal cord, basically. Now this explains why when you have the pain early on in appendicitis, it's usually felt centrally in the abdomen before spreading to the right iliac fossa. That's because the sympathetic affair, afferent fibers start of of the appendix arise from TD of the spinal cord. So this is just a picture to appreciate the arterial supply to both the cecum and the appendix via the ileocecal artery. So you have your ileocecal artery here and thus gives rises to your both the appendicular artery and everything. Everything. So, right. So, moving on to the lymphatic drainage of the appendix, um lymphatic fluid from the appendix drains into the lymph nodes within the mesoappendix. So this is fairly similar to the cecum as well. So, yeah, it basically leads into the upper lobe, the ileocolic lymph nodes which again surround the ileocolic artery, right. So, move the colon, which is the large intestine. Um Basically, you have uh this 1 50 centimeter in length. It's basically 150 centimeters in length and can be divided into four parts. So you have your ascending, transverse, descending and sigmoid. So you, it's the most distal part. It's one of the most distal parts of the gi tract extending from the cecum to the anal canal. So it receives digested food from the small intestine from which it had water and electrolytes to form feces. And yeah, it's divided into these four parts. So I just realized I'm just running a bit short on time. So I'm probably just gonna go a bit faster. So, starting with the ascending colon, uh that's where that's the beginning part of the colon. And it is a retroperitoneal structure. So, in contrast to the cecum, which is an intraperitoneal structure, now we're moving Retroperitoneally. So this ascends with it ascends purely from the cecum where it meets the right lobe of the liver. Now, from the right lobe of the liver, basically, you have your ascending colon which goes at a 90 degree angle and then it makes with the right lobe of the liver, it turns 90 degrees and moves horizontally. This turn is known as the right colic flexure or the hepatic flexure. And this marks the start of the transverse. So the hepatic flexure uh this where it, where your ascending colon meets the edge of the liver, it turns 90 degrees mm starting the transverse colon. And because it makes that turn at the, from there on the right lobe of the liver it's referred to as the hepatic flexure. Then you have your transverse colon which extends from the right colic flexure, the hepatic flexure towards the spleen. And that's where it makes another 90 degree down inferiorly. This area is known as your splenic flexure. Over here, the colon is attached to the diaphragm by the phrenic uh sorry phren phrenicocolic ligament. Now unlikely, ascending and descending colon. The transverse colon is intraperitoneal uh just like the cecum and is enclosed by the transverse mesocolon. Right. Now, here's a very fun fact with regards to the trunk is that it's the least fixed part of the colon and it's very well in position and it can dip into the pelvis in a tall and thin individual. So that's one fun fact to appreciate. So, moving on to the descending colon uh after the left colic flexure, after the splenic flexure, the colon moves inferiorly towards the pelvis. And this is called the descending colon intraperitoneal in the majority of individuals. And it's located anteriorly to the left kidney, passing over the lateral border. And when the colon begins to turn immediately, that's when that's the end of the and thus becomes the sigmoid colon. So, moving on to the sigma called you have your sigmoid colon, which is 40 centimeters long and it, it's located in the lower left quadrant or extending from the left iliac fossa to the level of the estra, the entire journey of the sigmoid colon from the descending colon gives its characteristic s shape. So now the sigmoid colon is attached to the posterior pelvic wall by the Sigma sigmoid meso mesocolon. So, like we saw on the previous slide, you have your mesocolon with your transverse colon, which is basically enclosed by the transverse mesocolon. You have your sigmoid colon, which is basically uh attached to the posterior pelvic wall by the sigmoid Musicola. So yeah, this is the image of the dialogue Argentine or of the colon over here, your cecum over here which then you have your ascending colon, you have your hepatic flexure, which signifies the start of the transverse colon before you reach your splenic flexure. And then this descends inferiorly forming the descending colon and that goes immediately forming your sigmoid colon. So, yeah, that disc which stands from your cecum all the way to the rectum and then eventually the anus which will be covered in the upcoming slides. So, with regards to this uh slide, we, I'd also like to mention something called paracolic gutters. So I don't know if you guys have heard of this, but it's basically uh two spaces between the ascending and descending colon and the posterolateral abdominal wall. Really how it functions is it allows material that has been released. You have your inflamed or infected abdominal organs to accumulate elsewhere in the abdomen. Basically. So just thought of mentioning now it's regards to clinical features of the large in design, just very quickly to touch up upon. You have attached to the surface of the large in design, you have your omental uh appendices which are small pouches of peritoneum filled with fat. Now longitudinally along the surface of the large bowel are three strips of muscles known as T coli. The three types are called mesocolic tia. You have free tia coli and you also have omental tia coli. So these are the three strips of muscles which basically run along the surface of the large bowel. Now, these are known to contract and basically shorten the wall of the bowel producing circulations known as Haustra. Now, these characteristics features are basically distinguish the large intestine from the small intestine. So it is important to know about stuff like the omental appendices and the tia coli and hos, which is why I've highlighted it in bold. Furthermore, the large intestine also has a much, much wider diameter compared to the small intestine. As we hear, these are the images of the appendices. So these are the small pouches of the peritoneum which is filled with fat. And y you have your ta coli which is running over here and your heart as you can see, basically, it's when the TNA coli contract and shorten giving rise to the circulations. So, yeah. Furthermore, with regards to the anatomical relations, just wanted to quickly touch up upon this. So, anterior to the ascending colon, you have your in small intestine, your great omentum your anterior abdominal wall. Whereas posteriorly, you have your iliac and your lumborum, your right kidney and your iliohypogastric and ilioinguinal lobes uh under the transverse colon, you have your great, your anterior abdominal wall and posteriorly, you have your duodenum and the head of the pancreas and Jejuni men. So I think these are anatomical relations, which I think it's just important for us to appreciate. And obviously, if we're your upper g lower gi surgery, I think it's something which we definitely need to know in more detail. Then you have your descending colon where anteriorly to the descending colon, you have your small intestine, your great omentum and your anterior abdominal wall. And posteriorly, you have your ilio quadrati lumbar, your left kidney and also your iliohypogastric, iliohypogastric and ilioinguinal lobes with regards to the sigmoid sigmoid colon because it's a bit more inferior. You have the urinary bladder, you have your, you have urinary bladder, inferior. You have your uterus and the upper vagina in females only basically which is anterior to the sigmoid colon, posteriorly to the sigmoid colon. You have your rectum, your sacrum and your ilium, right. So, with regards to the neurovascular supply of the colon. Um Sorry. Yeah, you have uh so it's closely linked to its embryological origin. So you have your ascending colon and your, so you have your ascending colon and you have your transverse colon. Now, the proximal two third of the transverse colon and the ascending colon basically are derived from the mid gut. Now, the distal one third of the transverse colon. So if you have a straight line and if you have the approximal two thirds and your distal one third, so your distal one third of the transverse colon, your descending colon and sigmoid colon are derived from your, from your embryological hindgut. I think this is very important for us to appreciate so that we can understand the arterial supply in a bit more detail in the upcoming slides. So the ascending colon receives its arterial supplies from two branches of the S MA, the ileocolic and the right colic arteries. Now, these are ee colic, anterior cecal and posterior cecal branches. All apply the ascending colon. Now, as a general rule, midgut derived structures are supplied from the S MA. Whereas hindgut structures are derived from the I MA, which is your inferior mesenteric artery. Now, the transverse colon is derived from both mid gut, high and hi gut and midgut and hindgut structures. So you have uh branches of the sma and the eye both supplying the transverse colon. So you have your right colic and middle colic arteries which basically are derived from your SMA, which supply the slide, the transverse colon and you have the left colic artery, which is basically derived from your I MA, which also supplies the transverse colon. Now, the left colic artery supplies the distal one third of the transverse colon. Whereas you have your right colic and middle colic artery, which is derived from the SMA, which we apply the approximate two thirds of the transverse colon. Yeah. Uh The descending colon is supplied by the left colic artery which again, like I mentioned is a branch of the I MA. And the sigmoid colon receives its arterial supply by the sigmoid arteries, which is again another branch of the I MA. So you just very quickly to touch up upon the marginal artery of drum. And I wouldn't wanna go make you read all of this because this is just way too much information, but it anatomically variable blood supply that forms a ma like a major, an uh an network, uh superior and inferior mesenteric artery. So what it does is it vascular the trauma and the descending colon and is a major contributor to the collateral circulation of the left colic structures. That's just basically what it is. It provides a collateral blood supply to all the left colic structures and it vascularise the trans and descending colon basically, right. So, moving on to the, yeah, this is just so that you can appreciate the marginal artery of dr right. And with regards to the venous drainage, the superior and mesenteric, superior mesenteric and inferior mesenteric veins ultimately empty into the hepatic portal vein. So this allows all the toxins to be absorbed and from the colon and just basically be toxified by the liver with regards to the venous drainage of the colon. Um the sending colon, uh you have your ileocolic and the right colic veins which empty in the s into the superior mesenteric vein. You have your transverse colon, which basically um has its venous supply from the middle colic vein which empties into the superior mesenteric vein again and then again, with regards to the descending colon and your sigmoid colon, you have your left colic and sigmoid veins respectively which drain into the eye in your inferior mesenteric vein. So this is just an image to we just appreciate the venous drainage of the colon. Basically great with regards to the innovation of the colon. Uh you have your midgut derived structure. So you have your ascending colon and the approximate two thirds of the trials colon which received there. Sorry, excuse me, which basically received a sympathetic and parasitic uh innervation and sensory supply via nerve from the superior mesenteric plexus. Whereas your hi gut derived structures uh you your distal one third of the transverse colon, the descending colon and your sigmoid colon, which uh received a sympathetic parasympathetic and sensory supply via nose from the inferior me. Now, the parasympathetic innervation is why your p splanchnic doves or your sympathetic innervation is why your lumbar spinus splanchnic tos. So, yeah, with regards to the lymphatic drainage of the colon, you have a where they basically dra your ascending and transverse colon drain into your superior mesenteric nodes, your descending colon and your sigmoid colon drain into the inferior mesenteric nodes. Now, most of the lymph from the superior and inferior mesenteric nodes passes i into the intestinal lymph trunks and then eventually onto the cisterna chyli, which ultimately empties into the thoracic duct. Right. So, moving on to the rectum, which is the most dis distal segment of the large intestine. So its role is its most important role is to temporarily store feces. Now, this continues approximately with the sigmoid colon and terminates at the anal canal. Now, the rectum begins at the level of uh S3. So it is, it goes on in continuation with the sigmoid colon and it is macroscopically different from the colon with an absence of tinea coli haustra and omental appendix. Now, the course of the rectum is marked by two major flexors. So you have your sacral flexure and you have your anorectal flexure. Now, the sacral sacral flexure is an anterior anteroposterior curve with concavity. So it follows the curve of the sacrum and the coccyx. Whereas with regards to the anorectal flexure, it's ba basically an anterior posterior again with convexity anteriorly. So you have your sacral flexure, which is uh which basically is an anteroposterior curve which with concavity anteriorly. Whereas the anorectal flexure is basically an anteroposterior curve with convexity anteriorly. So this flex, the anorectal flexure is basically formed by the tone of the puber rectalis muscle and contributes significantly to fecal continence. So it allows you basically prevents the passage of your feces and you know, helps you contain it there, you know, no, there are additionally three lateral flexors. So you have your superior intermediate and your inferior lateral flexors. Now, these are transverse folds from the uh transverse folds of the internal rectum wall, the final segment of the rectum, which is the impala relaxes to accumulate and temporary store feces, feces until defecation occurs. Now, this is in continuation with the anal canal which passes through the pelvic floor to end as the anus basically. So this is the sacral flexure and the anorectal flexure that I was mentioning before. So yeah, again, this is the level of S S3. I think I'm gonna skip over peritoneal covering, seeing that we have uh we're just a bit short of time right now. And again, these are just a couple of uh again, if you get these slides, I think these are just some and uh structures which are anti and posture directum for you all to just appreciate in a bit more detail. So I don't wanna rush through this. I think it's something that you guys can go through during your own time, right? So with regards to the neurovascular supply of the rectum, you have uh your superior rectal artery. So it basically receives arterial supply to three main arteries. So you have your superior rectal artery, which is basically a terminal continuation of the inferior mesenteric artery. You have the middle rectal artery, which is a branch of the internal iliac artery. And you have your inferior rectal artery, which is a branch of the internal peridental artery. So you have these three art arteries over here, your superior middle and inferior rectal artery which both supply the which both are responsive. All three are responsible for the arterial supply of the rectum. With regards to the venous drainage, you have your superior middle and inferior rectal vein. And I think the one thing which is important to remember with regards to the venous drainage of the rectum is you have your superior rectal vein which keys directly into the portal venous system, whereas you have your middle and inferior recal vein which they need to be carried back up. Now, anastomose sorry. Now, anastomosis between um the portal and systemic veins are located in the wall of the anal canal. So this is what makes this a pretty common uh making this a sign of portal anastomosis. So I think that's 11 more thing to appreciate. The rectum is also closely um anatomically associated with the rectal venous plexus. However, the rectal venous plexus has more of an influence with regards to the anal canal which I will touch up upon later, right. So with regards to the innovation of the rectum, you have sensory and autonomic innervation. So you have a sympathetic nervous supply to the rectum, which is from the lumbar splanchnic nerves and superior and inferior hypogastric plexus, you have your parasympathetic supply, which is from S to NS four wide, the pelvic splanchnic nerves to plexuses. Whereas your visceral afferent fibers just follow the parasympathetic supply. So, yeah, this is just a diagram to uh show you the superior rectal artery supplying the upper aspect of the rectum. Basically. And with regards to the lymphatic drainage you have of the rectum which is via the pararectal lymph nodes which drain into the inferior mesenteric nodes. And then lymph from the lower aspect of the rectum drains directly into the internal iliac lymph nodes. So, yeah, that's so you have your inferior, so you have your pararectal lymph nodes which drain into the inferior me nodes and flow aspect of the rectum. This just drains directly into the internal iliac lymph nodes. Sorry. Before I go ahead, I think there's one thing which I'd like to say with regards to clinical relevance of the rectum. Uh It's very important to mention uh with regards to AD R which is a digital rectal examination. So you have your anterior wall of the rectum which has a number of closed anatomical structures. So these palpated digitally via the rectum. So, most significant are the prostate and the seminal vesicles in males and cervix in females. Basically. So bony structures such as the sacrum and coccyx as well may be palpated in both sexes. So I think that's something that uh that I should with regards to the clinical relevance of the dre. Right now, we're gonna be touching upon final segment of the gastrointestinal tract. So you have the anal canal which has just one important role in defecation and maintaining fetal continence, right. So the anal canal is located within the anal triangle of the peri between the right and left fossa. It is the final segment of the gi tract and it's around two centimeters in length and the canal begins as a continuation with the rectum and passes inferiorly and determinate at the anus. So you, you have your anal sphincters, the anal canal has your anal sphincters and the anal canal is surrounded by both internal and external anal sphincters which both play an important role in the maintenance of free continence. So you have your internal anal sphincter which surround the upper two third of the anal canal and it is formed by a thickening of the involuntary circular smooth muscle in now. And you have your external anal sphincter, which is basically a voluntary muscle that surrounds the lowest, the anal canal. Basically the one that we can control and it overlaps with the internal sphincter at the same time as well as well. Now with the puber rectalis muscle of the pelvic floor. So this is external anal sphincter is the one which we have voluntary control over. And it basically surrounds the lower two thirds of the anal canal and is extremely crucial and that it overlaps with the internal SPHC sphincter crucial in the maintenance of fecal continence, right. So, yeah, this is just the image of the anal sphincters, right? And yep, this is just with regards to the superior ain structures of the anal canal. So you have the superior aspect of the anal canal which has me epithelial lining as the rectum. Oh uh It's there is mark called helium. And however, in the anal canal, the mucosa is organized into longitudinal folds known as anal canal. So I think it is important to appreciate the fact that when you are at the rectum, when you are the uh the cells are shaped in a columnar epithelium. And then when you move on to the anal canal, they are more organized into anal columns. Now, these are joined at the inferior ends by anal valves which will be shown in the upcoming image above the anal valves are small s which are referred to as anal sinuses. Now, these contain glands that basically secrete mucus and allow passage of your fecal matter. I think I'm gonna skip this. Yup. So this is basically yeah, what I was explaining in the previous slide, right. Again, anatomical structure, an anatomical relations of the anal canal to you know, uh that are anterior to the anal canal and posterior to the anal canal. Be much better if you take your time and go through this rather than me rushing through this, right. So you have the arterial supply and the arterial supply and the venous drainage of the anal canal. So the pectinate line which is mentioned over here in the previous image. So this is the pectinate line. So the arterial supply and the venous drainage depends on where you are with in relation to the pec net line. So above the pec net line, basically, you have your superior rectal artery which supplies the anal canal which is a branch of the I MA. Uh And you also have the anastomosis from the middle rectal artery, which also supplies your anal canal above the pectinate line. Now, below the PEC line, you have your in inferior rectal artery, which is a branch of the internal nerve. And as well, you have anastomosing branches from the middle that supply the anal canal below the line. Your, with regards to the venous venous drainage, you have your superior rectal vein which empties the inferior mesi mesenteric vein. And basically, it's part of the portal venous system. Now, this is responsible for the venous drainage above the PEC line and you have your inferior recal empties into the internal pental vein and then eventually into the subvenous system. Now, this is below the pec midline. So I think it is important for us to appreciate the fact that the arterial supply and the venous drainage uh really does depend on whether you are above or below the line. So, yeah, I'm gonna skip the nerve supply and lymphatics due to time constraints. But yeah, uh I think we're almost done right now. So with regards to Callos triangle, um basically, it's a cystohepatic triangle, a small anatomical space in the abdomen. And it is located at the porta hepatis of the liver where the hepatic ducts and neurovascular structures enter and exit the liver. So we're just gonna quickly touch up on the border and the contents of the callus angle. So you have three B borders, you have the medial border, inferior border and border. So it's oriented in such a way. Callos angle is oriented in such a way that the apex is directed at the liver and the borders are as follows. So you have your common hepatic duct, which is the medial border. You have your cystic duct, which is the inferior border and you have your superior duct, superior border, which is the inferior surface of the liver. So, yeah, there we go. So as you can see over here, this is Callow triangle. So uh the i it's oriented in such a way so that the apex is directed towards the liver as you can see over here and immediately you have your common hepatic duct. So that's your, you have your inferior border, which is your cystic duct. And you have the inferior surface of the liver, which is basically your superior border. So that's the callus triangle. Uh There's one thing which I really wanna touch up upon with regards to a callus triangle. Um a most likely place where it's clinically irrelevant to remember. This is uh called laparoscopic cholecystectomy because uh basically the removal of a gallbladder because in this, the triangle is carefully affected by the surgeon and its contents and B orders are identified. So this allows us to account any anatomical variation and permits basically safe ligation and division of the cystic duct and the cystic artery. So I think, um with regards to Callos triangle, I think it's very important to remember with regards to laparoscopic cholecystectomies. And anytime you are witnessing a removal of a gallbladder, it is very important to take Callos Triangle into con consideration last. Yeah, sorry. So with regards to the contents of callus triangle, you have your right hepatic artery, you have your cystic artery, you have your lymph node of lung, which is the first lymph node of the gallbladder. And you have a bunch of lymphatics that run through the triangle. Last but not the least. We have uh the Inguinal triangle, which is Hesselbach triangle. So it's part of the anterior abdominal wall. It is also known as the medial inguinal fossa. And yeah. So the inguinal canal, the inguinal has the back strangle, uh basically has three borders. So you have your inguinal inguinal triangle, which is located in the inferior medial aspect of the abdominal wall. So it has three boundaries again. So you have your sorry marrow, you have your medial border, which is the lateral border of the rectus abdominal muscle. You have your lateral border, which is your inferior epigastric vessels. And last but not least you have your inferior the border, which is basically the inguinal ligament hernia. I think it is important to identify it lies within the tri whereas an indirect hernia, it usually lies laterally. Yeah, this is just uh the image of the inguinal triangle and I think that's about it. It completes uh I think we're just 10 minutes over it. But yeah, thank you so much for uh attending the session. I really apologize. I had to rush through the slides at the end and I really hope you enjoyed the teaching session. And yeah, thank you so much, Keegan. That was incredibly comprehensive and I have definitely learned stuff that I didn't even learn in first year. So really thank you so much for that. It was really helpful going through the so of the you split it up nicely into different parts of each section. So thank you so much. Thank you so much. Thank you so much. And also I'm really sorry because it did involve a lot of things that I personally haven't covered myself and I had to find and I had to rush through it at the end as well. So really sorry for that, really sorry for having to do, rush through it at the end. But yeah, thank you so much for listening and thank you so much for the Florence. You're very welcome. I've sent the feedback form in the chat if everyone wants to fill that in who attended and you'll get a certificate as well. Um Unfortunately, we have had to cancel our teaching on Thursday due to some illness, but that's going to be um rearranged for, I think the week beginning 18th of March. So keep your eyes peeled on our socials for that. So Instagram, Facebook and also medal um and next week we are doing upper gi as well. So we're gonna be doing a bit of anatomy and clinical cases again as well. So keep an eye on our socials for that information and that's it. Thank you so much, everybody for attending and again a massive thank you to Keegan as well for such an amazing talk so well and everybody and enjoy your evenings. Thank you so much, everyone. Thank you so much, Florence. Take care. You're very welcome. Take care. Bye bye.