Okay, so this tutorial is an introduction to the blood supply to the abdominal organs. I'm going to talk about the arterial supply and the venous drainage of the abdominal viscera.
We’re looking here at a model of the circulatory system and we're looking at the abdominal region.
Here you can see the abdominal aorta and to the right of it, you can see the inferior vena cava. First, let's just talk about the arterial supply to the abdominal viscera. I'll get rid of the veins.
I got rid of the inferior vena cava and the veins. We're looking at the abdominal aorta. The abdominal aorta begins at the aortic hiatus of the diaphragm and it ends when it bifurcates into the common ileac arteries. The beginning of the abdominal aorta is roughly at the level of T12 and the end of the aorta is roughly at the level of lumbar vertebra L4.
You’ve got quite a few branches coming off the abdominal aorta, but it's the anterior branches which supply the gut and the accessory organs in the abdomen. There are three branches which supply the abdominal organs. Right at the top, you've got this branch here called the celiac axis or the celiac artery or the celiac trunk. You'll hear it called by different things.
And then you've got the superior mesenteric artery just below it. And right at the bottom, you've got the inferior mesenteric artery.
Remembering what these branches supply is fairly straightforward. The top branch supplies the foregut, that's the celiac axis. The next branch down, the superior mesenteric artery supplies the midgut. And the bottom artery, the inferior mesenteric artery supplies the hindgut structure.
You might have noticed that there's a lot of branching from these arteries and I'll talk about these in a lot more detail in separate tutorials. This is just an introduction to the blood supply to the guy. For the purposes of this tutorial, just remember that the top branch is the celiac axis and you've got the superior mesenteric artery and the inferior mesenteric artery. They supply the foregut, the midgut and the hindgut respectively. We’ll just bring these structures in and show you what they are exactly.
The foregut runs from the abdominal esophagus down to the major duodenal papilla where the bile duct empties into the descending part of the duodenum, so roughly mid-way down the duodenum.
The abdominal esophagus is the bit of esophagus distally just after it perforates the diaphragm. The foregut runs from this part of the esophagus. It contains the stomach, the first part of the duodenum and it ends at the major duodenal papilla.
The foregut also includes the pancreas (which you can see lying behind the stomach here) and it also includes the liver and the gallbladder as well as the spleen over here. The spleen isn't part of the gut, but embryologically, it develops with these structures.
The foregut runs from the abdominal esophagus down to the major duodenal papilla in the descending part of the duodenum and it also includes the accessory organs of digestion – the liver, the gallbladder and the pancreas and it also includes the spleen. These structures are supplied by the celiac trunk or celiac artery.
The celiac trunk lies in the transpyloric plane. That's the level of L1. It lies at the upper border of L1, almost T12 level. You can see this vertebra here, that's thoracic vertebra T12. Just at the upper border of L1/T12.
The celiac artery has three branches. You've got the splenic artery, the left gastric artery and the common hepatic artery. It's worth knowing these branches.
Next down, we've got the superior mesenteric artery, which supplies midgut structures. You can see here, it lies at the lower border of L1, just below the celiac trunk. The midgut runs from where we left off, so just at the level of the major duodenal papilla and it covers all the small intestine and extends to two-thirds of the length of the way across the transverse colon.
The midgut extends from just below the major duodenal papilla. It includes the jejunum and the ileum and it encompasses the cecum and the appendix. It includes the ascending colon and then it includes two-thirds of the transverse colon. It ends about this point here. It covers the proximal two-thirds of the transverse colon. That's the midgut and it's supplied by the superior mesenteric artery.
Then we've got the inferior mesenteric artery, which supplies the hindgut structures. You can see it here, the inferior mesenteric artery. You can see this is lumbar vertebra L3. It lies at the inferior border of lumbar vertebra L3 and it supplies the hindgut structures.
I just switched back to this view. We're going to start off from two-thirds of the way along the transverse colon. the hindgut includes the distal third of the transverse colon, the descending colon as you can see here, then you've got the sigmoid colon, the rectum and midway down the anal canal. That’s the hindgut supplied by the inferior mesenteric artery.
Okay. So now we're going to take a look at the venous drainage of the abdominal organs. So the blood doesn't return to the inferior vena cava and then into the right side of the heart. It actually passes through the liver, through the portal system.
You’ve got this deoxygenated, nutrient-rich blood, which passes through the portal system into a second vascular bed inside the liver and then the liver has hepatic veins, which drains into the inferior vena cava.
The venous drainage of the gut is through the portal system. I'll just show you the hepatic portal vein, which is the final common pathway for the blood of the gut.
You can see all the veins in blue here, which are draining the gut. They drain into this one, portal vein here. you can see this common pathway for this blood. This is the portal vein.
The portal vein splits into these two branches. It's got a right and a left branch, which passes into the substance of the liver. This drains into sinusoids. And the sinusoids drain into the hepatic veins. you can see these two veins up here. And these drain into the inferior vena cava just before the inferior vena cava perforates the diaphragm.
I'll just put the diaphragm in for reference. You can see the hepatic veins draining into the inferior vena cava just before the IVC passes through the diaphragm.
The important thing to know here is you've got this venous blood draining the abdominal organs and it drains into this hepatic portal vein, which passes through a second capillary vascular bed in the liver. And then the liver drains via hepatic veins into the inferior vena cava. the blood doesn't just drain straight into the IVC. It passes through this portal system, which passes through the liver.
There are a few main tributaries which lead to the portal vein. you can see this branch coming off here, which drains into the portal vein and this is the splenic vein.
I just want to orientate you a bit with regard to the other structures in this area. If I just bring in the other viscera, you can see where the splenic vein lies and the hepatic portal vein lie. just fading away the stomach, you can see the pancreas underneath the stomach. The splenic vein underneath the pancreas. if I just fade that away, you can see the portal vein here and the splenic vein runs along the length of the pancreas on its posterior surface.
If I just zoom a little bit, you can see (and just fade it in a little bit more), you can see the bile duct in front of the portal vein. That was just to give you an idea of the relationship of these structures.
The splenic vein and this vessel here, which is the superior mesenteric vein meet and form the hepatic portal vein.
The splenic vein receives various different tributaries. you can see there are a lot of different branches coming off the splenic vein, but the big one here joining into the splenic vein is the inferior mesenteric vein.
And then you've got other smaller branches which come from the stomach and the pancreas and that sort of thing.
The superior mesenteric vein just runs alongside the superior mesenteric artery, which you're aware of now. it just runs to the right of it. It drains blood from the small intestine, the cecum, ascending colon and transverse colon.
The inferior mesenteric vein drains blood from the splenic flexure area, the descending colon, the sigmoid colon and the rectum.
The take home message is that venous drainage goes through the portal system through the liver and then into the systemic circulation. The portal vein receives branches from the splenic vein and the superior mesenteric vein. It's got some other tributaries, which I'll talk about. And then the splenic vein receives the inferior mesenteric vein.
That’s a little introduction to the blood supply to the abdominal viscera.