USMLE Step 1 Review 04 07 Anatomy Blood Supply to Large Intestine 2

USMLE Step 1 Review 04 07 Anatomy Blood Supply to Large Intestine 2

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Begin 04 07 Anatomy Blood Supply to Large Intestine 2 Transcription

Now let’s look at the rest of the large intestine.

After the right two-thirds of the transverse colon, what four parts do we have left?

  • The left third of the transverse colon, the descending colon, sigmoid colon, and rectum.

What main artery, arising from the abdominal aorta supplies the left third of the transverse colon, the descending colon, sigmoid colon, and the upper two-thirds of the rectum through its branches?

  • The inferior mesenteric artery.

And at what level does the inferior mesenteric artery arise from the abdominal aorta?

  • At the level of L3.

Does the inferior mesenteric artery arise at the midline?

  • No it does not.

To what side of the midline is the inferior mesenteric artery origin?

  • On the left of midline.

As the inferior mesenteric artery arises from the abdominal aorta, it arises posterior to what structure?

  • Posterior to the horizontal and ascending parts of the duodenum.

Now as the inferior mesenteric artery passes inferiorly and to the left, what other artery does it cross over?

  • The left common iliac artery.

The inferior mesenteric artery divides into its terminal branches within what peritoneal structure?

  • Within the sigmoid or descending mesocolon.

As the inferior mesenteric artery passes down into the mesocolon, what vein lies parallel and to its left or lateral to it?

  • The inferior mesenteric vein.

Now the course of the inferior mesenteric vein is different in quality from the course of the superior mesenteric vein in that, the superior mesenteric vein basically follows the same course as the superior mesenteric artery. However, the inferior mesenteric vein only follows the course of the inferior mesenteric artery until the inferior mesenteric artery moves away to its origin on the aorta.

At that point, as the inferior mesenteric vein continues to ascend, what structure does the inferior mesenteric vein pass lateral to, or to the left of?

  • The ascending portion of the duodenum.

As the inferior mesenteric vein approaches the level of the duodenum and then passes up alongside the ascending portion of the duodenum, what is its relationship to the peritoneum?

  • At this point it is retroperitoneal.

Previously it was intraperitoneal within what structure?

  • The sigmoid or descending mesocolon.

And as the inferior mesenteric vein passes lateral to the ascending portion of the duodenum, it also passes just lateral to the edge of a recess that we have looked at before.

Which recess of peritoneum goes underneath to the left of the inferior mesenteric vein as it passes up alongside the ascending portion of the duodenum?

  • The paraduodenal recess.

Okay, which branch of the inferior mesenteric artery supplies both the left third of the transverse colon and the descending colon?

  • The left colic artery. Now the left colic artery divides into two terminal branches.

Which of these supplies the left third of the transverse colon and the upper half of the descending colon?

  • The superior or ascending branch of the left colic artery.

Which branch of the left colic artery supplies the bottom half of the descending colon?

  • The inferior or descending branch of the left colic artery.

Now what are the three branches of the left colic artery that supply the sigmoid colon?

  • The sigmoid arteries.

Finally, what branch of the left colic artery supplies the rectum down to the dentate line?

  • The superior rectal artery. Okay, let’s review this.

What four parts of the large intestine are supplied by branches from the inferior mesenteric artery?

  • The left third of the transverse colon, the descending colon, the sigmoid colon, and the rectum, down to the dentate line.

And which terminal branch of which main branch of the inferior mesenteric artery supplies the left third of the transverse colon?

  • The superior or ascending branch of the left colic artery.

And again, which terminal branch of which main branch of the inferior mesenteric artery supplies the upper half of the descending colon?

  • The superior or ascending branch of the left colic artery.

Moving on, which terminal branch of which main branch of the inferior mesenteric artery supplies the lower half of the descending colon?

  • The inferior or descending branch of the left colic artery.

Which three branches supply the sigmoid colon?

  • The sigmoid arteries.

And where do these sigmoid arteries arise from?

  • Directly from the inferior mesenteric artery.

And which branch directly from the inferior mesenteric artery supplies the rectum down to the dentate line?

  • The superior rectal artery.

Now before reaching the rectum the superior rectal artery supplies two branches to the rectosigmoid junction.

What are these called?

  • The rectosigmoid arteries.

And through what structure does the superior rectal artery run to reach the rectum?

  • The sigmoid mesocolon or descending mesocolon.

What is the branching pattern that the superior rectal artery uses to supply the rectum down to the level of the dentate line?

  • The superior rectal artery bifurcates and sends a branch to the left and right sides of the rectum.

And again, where does the superior rectal artery arise?

  • Directly from the inferior mesenteric artery.

And at what vertebral level does the inferior mesenteric artery arise from the left side of the anterior face of the abdominal aorta?

  • L3.

And what’s the vertebral level for the origin of the superior mesenteric artery?

  • L1.

****END OF TRANSCRIPTION****

 

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