Neurovasculature of the Small Intestine

00:01 Let's now have a look at the vasculature of the small intestine. And to do this, we need to look at both derivatives of the 4 guts and of the mid gut because part of the duodenum, the first 2 bits really up to where the major duodenal papilla enters into the descending duodenum is supplied by the celiac trunk. So here we can see coming off the celiac trunk, we mentioned it, we looked to the stomach is the common hepatic artery. The common hepatic artery is going to give rise to an artery that's called the gastroduodenal. Remember the common hepatic artery also gave rise to that right gastric that went to the lesser curvature. Once that right gastric is being given off, it gives rise to the gastroduodenal artery. The gastroduodenal artery then runs posterior to the duodenum, but it gives rise to 2 important blood vessels. It gives rise to the superior pancreaticoduodenal artery.

00:59 Here, we can see the posterior version of the superior pancreaticoduodenal artery.

01:04 And it also gives rise to the right gastroepiploic which goes to the greater curvature. So you can see we have a superior pancreaticoduodenal artery which we've also added the posterior and anterior versions to as well. Now, if you were to be lucky enough to look at these arteries in a cadaver or look in different textbooks, you may see slightly different variations of how the blood vessels are giving rise to. But as we can see here in this image coming off the gastroduodenal artery, you really have superior pancreaticoduodenal, which gives rise to posterior and anterior versions and the gastroepiploic artery on the right hand side which goes to the stomach. So these are important branches that are coming off the celiac trunk ultimately because they're supplying the 4 gut.

01:53 The foregut being the stomach and the first bit and a half of the duodenum. And by way of the gastroduodenal, superior pancreaticoduodenal arteries, this part of the foregut is supplied the highest part of the small intestine. Here, we can see the superior mesenteric artery, the superior mesenteric artery is coming off the abdominal aorta. It's the second of the 3 unpaired blood vessels coming off the aorta to go and supply the abdomen and it very much supplies the mid gut, so very much the largest proportion of the small intestine. You can see here the superior mesenteric artery is beginning to give rise to the inferior pancreaticoduodenal artery. Obviously, this would make sense as we have a superior pancreaticoduodenal artery coming from the gastroduodenal coming from the celiac trunk. The superior mesenteric artery which is supplying the mid gut is going to give rise to more inferior pancreaticoduodenal arteries both from the anterior and here we can see the posterior aspect. If we then look on to the jejunum and the ileum, we need to return back to the superior mesenteric artery. So here we can see the superior mesenteric artery and this one we can say really comes from say L1. Again, some textbooks may vary but it's sometimes convenient for celiac trunk to be T12 superior mesenteric artery to be around about L1, but again it can vary from textbook to textbook. Here we can see it's coming pretty much from the lower boundary of L1. But the superior mesenteric artery then runs underneath the pancreas to then run anterior to the duodenum which we can see here. So the superior mesenteric artery is passing from under the pancreas but then running over the duodenum, which we can see here. It runs through that space between the pancreas and the duodenum to then run within the mesentery. So what we can see here is the posterior abdominal wall without any small intestines located.

04:04 What we have is that yellow layer on the posterior abdominal wall. Now that is mesentery. Okay? For the purposes of this topic, that is essentially mesentery. It's actually peritoneum which is going to come together and form the mesentery, but the point is it's the same continuous layer. A layer of connective tissue peritoneum along the posterior abdominal wall, but really it's mesentery because it's coming up together to form a double layer, a mesentery is a double layer of peritoneum. So here we can see that blood vessel which is now running through that space and you will have to imagine those 2 layers of peritoneum that have been split by that superior mesenteric artery and are running up alongside it forming a double layer with the blood vessel running in between it. We can see then coming off the superior mesenteric artery are whole series of blood vessels running between the double layers of mesentery which is taking it to the jejunum and the ileum, taking it to the small intestine. Here, we can see the middle colic artery, we can see the right colic artery, we can see the ileocolic artery. Now, what these blood vessels are, they are really running along the posterior abdominal wall and they go in towards the ascending colon. So here we can see the middle colic and the right colic passing towards the ascending colon. What we can start to see is that transition where these are now running up towards the ileum and we can see the ileocolic artery is giving branches that will go both to the ascending colon and also the ileum, hence ileocolic artery. If we then move around to the jejunal arteries, these are the blood vessels running between that double layer of peritoneum, the mesentery, to go and supply the jejunum and here we can see all of those jejunal branches supplying the ileum. As the jejunum becomes the ileum, we then change the name of the jejunal arteries to ileal arteries as they supply the ileum. To finish up, we need to just briefly look at the nerve supply to the small intestine and again the nerve supply to the small intestine, the principles will be that similar to the stomach and you'll have periarterial branches that run towards the actual structure. So here we have the duodenum, the jejunum, and the ileum again and we have parasympathetic input coming by the vagus nerve, specifically posterior trunk as it says here. But similar principle, the vagi coming down thru the esophageal hiatus surrounding the esophagus and then passing down and spreading over the small intestine. What this does is it increases the activity of the small intestine. The sympathetic input would be by the sympathetic chain which is giving branches to the superior mesenteric plexus and from the superior mesenteric plexus which is formed from greater, lesser, and least splanchnic nerves, we'll cover this in much more detail in a wrap up nerve lecture later on, but the sympathetic innovation is going to increase activity so we rely on the vagal nerve to increase activity of these organs to aid with digestion. The sympathetic nervous system, greater, lesser, least, splanchnic nerves coming from the sympathetic chain decrease activity. And here you can start to see some of how these nerves, sometimes it can be quite difficult to link the conceptual understanding of nerves to what they actually look like but actually passing alongside the various blood vessels to the structures associated with those arteries. So again, you got the gastroduodenal artery and then you have the periarterial plexus following the gastroduodenal artery. It makes sense to piggyback these nerves on to the arteries that are supplying this region. Exactly the same thing happens here. We got superior mesenteric ganglion which is giving rise to those sympathetic nerves passing to the superior mesenteric plexus formed by the greater, lesser, and least splanchnic nerves. And here, you can see the union of those nerves is then passing along the various branches of the superior mesenteric artery that's passing along the ileal and jejunal branches to go and provide innovation to the jejunum and the ileum.