Video: Arteries of the large intestine
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Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial on the arteries of the large intestine. Before we look at the arteries that supply the large intestine, let's first familiar... Read more
Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial on the arteries of the large intestine. Before we look at the arteries that supply the large intestine, let's first familiarize ourselves with the structure and function of this organ.
The large intestine extends from the distal end of the ileum to the anus covering a length of almost one and a half meters in adults. Its role is to absorb salts and fluids from the gut contents converting it into feces. The large intestine consists of the vermiform appendix, the cecum and the colon which consists of the ascending colon, the transverse colon, the descending colon and the sigmoid colon. Distal to the colon are the final parts of the large intestine – the rectum and the anal canal.
Approximately, the first half of the large intestine which includes the vermiform appendix, the cecum, the ascending colon and part of the transverse colon is supplied by blood derived from this artery here – the superior mesenteric artery. The superior mesenteric artery is the second main branch of the abdominal aorta arising about one centimeter below the origin of the celiac trunk at the level of the intervertebral disc between the first and second lumbar vertebrae. The blood supply of the small intestine is also derived from this artery through the numerous intestinal arteries that we can see stemming from its left hand side.
This image here which is an anterior view of the abdominal cavity we'll feature throughout the tutorial. In this illustration, most of the small intestine has been removed and the transverse colon has been reflected upwards. This has been done to give us a clearer view of the blood supply of the large intestine. The superior mesenteric artery has three main branches that are involved in the blood supply to the large intestine. These are the ileocolic artery, the right colic artery and the middle colic artery. This artery branching off the right side of the superior mesenteric artery is the ileocolic artery. As the name suggests, this artery supplies both the ileum and the large intestine.
The ileocolic artery has an ileal branch and a colic branch, the first of which we can see here. This is the ileal branch of the ileocolic artery which supplies the ileum. Superior to the ileal branch is the colic branch of the ileocolic artery. The colic branch supplies the ascending colon and so it's often called the ascending colic branch. The ileal and colic branches anastomose together via this connection here which is known as an arcade. These arcades occur throughout most of the length of the large intestine and are essential to the efficient blood supply of the large intestine as they ensure that if one artery is blocked or damaged, another artery can compensate.
If we zoom in to take a closer look at the arcade in the bottom left of this image, we can see a small green artery branching from it. This artery is known as the anterior cecal artery and supplies the anterior part of the cecum. Inferior to the anterior cecal artery is the posterior cecal artery that also branches off the arcade that we talked about before. The posterior cecal artery supplies the posterior aspect of the cecum. It also often gives rise to the appendicular artery which supplies the vermiform appendix. The anterior and posterior cecal arteries can have varying origins arising as either a common trunk or as separate branches. They usually arise from either the ileocolic artery or the right colic artery which we'll have a look at soon. Here they're both arising from an arcade formed by the ileocolic artery. When studying anatomy, it's important to keep in mind that anatomical variations is common with a lot of structures found in the human body.
Superior to the ileocolic artery we can see another main branch of the superior mesenteric artery – the right colic artery. Like the anterior and posterior cecal arteries, the right colic artery has a variable origin. It can also arise from the ileocolic artery or as a common trunk with the middle colic artery. The right colic artery supplies the ascending colon. The right colic artery has two main branches known as the ascending branch and the descending branch. The descending branch of the right colic artery anastomoses with the ileocolic artery to form this arcade here. The descending branch functions to supply the lower part of the ascending colon. The other branch of the right colic artery – the ascending branch – anastomoses with the right branch of the middle colic artery. The ascending branch supplies the upper part of the ascending colon.
Moving superiorly, we can see another artery arising from the superior mesenteric artery which is the middle colic artery. Here the artery arises separately and anterolaterally but it can alternatively arise as a common trunk with the right colic artery. The middle colic artery supplies the proximal two-thirds of the transverse colon. Like the right colic artery, the middle colic artery splits into two main branches but these branches are instead called the right branch and the left branch. The right branch anastomoses with the right colic artery whereas the left branch anastomoses with the left colic artery.
The middle colic artery and its branches run within this structure highlighted in green which is the transverse mesocolon. The transverse mesocolon is a mesentery which is a double-layered peritoneum that attaches the transverse colon to the posterior abdominal wall.
Now we'll move on to have a look at the blood supply the rest of the large intestine which includes the left one-third of the transverse colon, the descending colon, the sigmoid colon and the rectum. Blood supply to these areas is derived from the inferior mesenteric artery. The inferior mesenteric artery arises from the left part of the abdominal aorta at the level of the third lumbar vertebra about three to four centimeters above the bifurcation of the abdominal aorta.
The inferior mesenteric artery has three main branches, the most superior of which is known as the left colic artery. The left colic artery supplies the left third of the transverse colon as well as the descending colon. Like the right and middle colic arteries, the left colic artery splits into two branches – an ascending branch and a descending branch. The ascending branch of the left colic artery runs superiorly to supply the distal third of the transverse colon. The other branch of the left colic artery – the descending branch – runs transversely within the retroperitoneum to supply the descending colon.
Inferior to the left colic artery, we can see the sigmoid arteries stemming from the inferior mesenteric artery. In this illustration, we can see two sigmoid arteries and usually they're between two and five. Regardless of how many there are, they are collectively considered to be the second main branch of the inferior mesenteric artery. The sigmoid arteries supply the distal part of the descending colon and of course the sigmoid colon. Like the middle colic artery, the sigmoid arteries travel within a mesentery which is highlighted here in green. This mesentery is known as the sigmoid mesocolon and it attaches the sigmoid colon to the posterior wall of the pelvis.
The final branch of the inferior mesenteric artery that supplies the large intestine is the superior rectal artery. The superior rectal artery runs inferiorly to supply the upper part of the rectum as well as the anal canal. The rectum is also supplied by two other rectal arteries which arise from the artery we can see here – the internal iliac artery. These are the middle rectal artery and the inferior rectal artery. We'll go over the blood supply of the rectum in more detail in another tutorial.
As I mentioned earlier in this tutorial, a lot of the arteries that supply the large intestine anastomose together to form arcades which ensures that there are multiple blood supplies to each region of the large intestine. The arcades of the ileocolic, right colic, middle colic, and left colic arteries collectively form a plexus of arteries that surround the large intestine. This plexus is known as the marginal artery of the colon. It can also be referred to as the marginal artery of Drummond and as we can see here, it sometimes contains the arcades of the sigmoid colon. This system is known as a collateral blood supply and is of huge clinical importance because it helps prevent ischemia in the event of an arterial occlusion.
Branching off from the marginal artery throughout most of the length of the large intestine are multiple small arteries which supply the large intestine directly. These arteries are known as the straight arteries.
So that brings us to the end of our tutorial on the arteries of the large intestine. Learning the arterial supply of an organ can be very difficult especially with anastomosis and anatomical variation. The most important thing to take away from this tutorial is that the blood supply of the large intestine is derived from branches of the superior and inferior mesenteric arteries. It's good to know the names of these branches as well as the sections of the large intestine that they supply.
I hope you enjoyed the tutorial and thank you for listening.
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Now, good luck everyone, and I will see you next time.