Okay, this is a tutorial on the Superior Mesenteric Artery. We’re looking here at a view of the abdominal aorta with the inferior vena cava sitting to the right. You can see the celiac axis at the top. And just below it, you’ve got an artery coming off anteriorly and this is the superior mesenteric artery. Just a little bit further down coming off to the side, we’ve got the inferior mesenteric artery.
First, I’ll talk a little bit about the relations of the superior mesenteric artery and then I’ll talk about the branches.
The superior mesenteric artery supplies the midgut. The midgut is the section of the intestine which runs from just below the major duodenal papilla through two-thirds of the way across the transverse colon.
What we can see here is that just above the superior mesenteric artery is this celiac artery. The celiac artery lies at the level of the upper border of L1 lumbar vertebra and the superior mesenteric artery lies at the lower border of L1 lumbar vertebra.
Just underneath it, you can see this vein. This is the left renal vein. This runs underneath the superior mesenteric artery. And then you’ve got the superior mesenteric vein which runs alongside it just to the right of it.
And above the superior mesenteric artery is the splenic vein. The splenic vein is shown slightly out of place there. It should be shown a little bit further down because it crosses anteriorly in front of the superior mesenteric artery just about here.
I’ve just brought some viscera in and you could see the pancreas sitting on top of it. And again, this is shown slightly out of place. It should be shown a bit to the left of what is shown here. The neck of the pancreas actually sits anteriorly over the superior mesenteric artery.
Also at the level of L1, you’ve got the renal arteries. You can see these arteries coming off the side of the aorta just a bit behind the superior mesenteric artery.
And one thing to point out also is that the inferior part of the duodenum – so the duodenum has the C-shape. And the inferior part of the duodenum actually passes underneath the superior mesenteric artery.
The first branch that comes off the superior mesenteric artery is the inferior pancreaticoduodenal artery. This anastomoses with a branch of the gastroduodenal artery which comes off the common hepatic artery of the celiac axis. If you watch the tutorial on the celiac axis, then you’ll see how these arteries anastomose. The inferior pancreaticoduodenal artery is the first artery that branches off the superior mesenteric artery.
What I’m going to do now is I’m going to switch over to a diagram and show you the rest of the branches of the superior mesenteric artery.
We’re looking here at a view of the superior mesenteric artery. You’ve got the super mesenteric vein alongside it to the right. And you’ve got the pancreas sitting over on top of it. You can see how these vessels emerge just under the neck of the pancreas.
The first branch you can see here just after the superior mesenteric artery comes out from underneath the pancreas is the middle colic artery. I’ll come back to talk about the middle colic artery in a moment, but first we’ll look at the vessels that come off the left side of the SMA.
You’ve got jejunal vessels and ileal vessels. And there are lots of these as you can see. What you’ll notice is as these arches or arcades, which are anastomosis between these vessels, so, the vessels join together to form these arches or arcades. You can see that there’s a few sort of levels of these arcades.
If you’ve watched my tutorial on the peritoneal cavity, you’ll know that the small intestine is intraperitoneal. The jejunal and the ileal vessels pass between the two sheets of the mesentery and supply the small intestine. You’ve got these anastomoses forming these arcades and you’ve got several of these arches. And just right at the end distally, you’ve got the straight vessels which supply the surface of the small intestine.
These straight vessels are called vasa recta. In Latin, ‘vasa’ means vessels and ‘recta’ means straight. You’ve got vasa recta in the kidney and it just means ‘straight vessels’. The distal vessels are called vasa recta.
We’ve taken a look at the blood supply to the jejunum and the ileum. And next, we’ll move distally and take a look at the next branch of the superior mesenteric artery.
This is called the ileocolic artery. This is the most distal branch of the SMA. And as you can see here, it has two branches. The ileocolic branch splits into a superior branch and an inferior branch.
the inferior branch is a bit more complicated because it has four branches, but if you think logically of the structures in the right ileac fossa, then you’ll be able to remember the names of the structures that the ileocolic artery supplies.
The inferior branch has four branches. What’s in the right ileac fossa, you’ve got the distal ileum. That’s supplied by the ileal branch. You’ve got the cecum next, which comes off the ileum. That’s supplied by the cecal branch. And you’ve got the appendix which comes off here, so you’ve got the appendicular branch. And you’ve got the start of the ascending colon, so you’ve got a colic branch.
The ileocolic artery has a superior branch which ascends and supplies the ascending colon, but the inferior branches which supply the distal ileum, the cecum, the appendix and the start, the proximal ascending colon.
Moving on to the ascending branch, so the superior branch of the ileocolic artery (and this supplies the ascending colon), it anastomoses with the branch that comes off the next branch of the SMA.
If we look at the next branch coming off the superior mesenteric artery above the ileocolic artery, we’ve got the right colic artery. This name pretty much describes what this artery does. ‘Colic’ refers to colon and right means it’s on the right side. The right side of the colon is the ascending colon. The right colic artery vascularizes the ascending colon.
And again, it’s got two branches. You’ve got a descending branch which anastomosis with the superior branch of the ileocolic artery. And you’ve got an ascending branch, which ascends up and anastomoses with the artery above it, which I’ve mentioned at the start. The middle colic artery has a branch that anastomoses with the branch from the right colic artery.
It’s fairly simple. You’ve got a branch which goes up (so it’s ascending) and you’ve got a branch which goes down (so descending).
The right colic artery supplies the ascending colon. Next, we’ve got the middle colic artery, which emerges on this SMA just after it passes through underneath the pancreas. Like the other two arteries, it splits into two branches. These are left and right branches because they don’t go up or down like the right colic branches or the ileocolic branches. They go left and right, so they’re called left and right branches.
The right branch anastomoses with the ascending branch of the right colic artery and the left branch anastomoses with the branch that comes off the left colic artery. And the left colic artery, I’ll come onto in a tutorial on the inferior mesenteric artery.
The middle colic artery supplies the proximal two-thirds of the transverse colon. Something to point out is that the transverse colon is an intraperitoneal structure. The branches of the middle colic artery pass into the transverse colon, so a transverse mesocolon which wraps around the transverse colon and tethers it to the back, to the posterior abdominal wall.
The right colon artery supplies the ascending colon, which you’ll know is a retroperitoneal structure. The right colic artery goes retroperitoneal and supplies the ascending colon. But the middle colic artery works its way into the transverse mesocolon because it’s an intraperitoneal structure.
I’ve talked a lot about how these different vessels anastomose. You’ve got anastomosis between the right colic, the middle colic and the left colic artery. And these arteries form a margin around the rim of the large intestine. These edges of the arcs of these anastomosing arteries are called the marginal artery. You’ve got this artery which lines the margin of the large intestine and it’s called the marginal artery.