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Let’s continue our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.
Play USMLE Audio MP3 04 08 Anatomy Blood Supply to Large Intestine 3 Below
Begin 04 08 Anatomy Blood Supply to Large Intestine 3 Transcription
What artery runs in a loop inside the loop of the colon?
- The marginal artery.
Now the marginal artery is fed by these branches we’ve been talking about from the superior and inferior mesenteric artery to the different parts of the colon and it is the means of anastomosis between these different branches to the colon.
What is the name for the many small arteries connecting the marginal artery to the different parts of the colon?
- The many small straight arteries.
And again, what is the term for the combination of marginal and straight arteries that spread out to the entire large intestines?
- The arcades.
Now ligating any but one of the branches of the mesenteric arteries would not normally endanger a section of bowel because of the many anastomoses created by the arcades. There is one branch, however, below its last anastomosis which, if ligated, may cause a section of bowel to necrose.
Which branch is this and below which anastomosis?
- The superior rectal artery below its anastomosis with the closest sigmoid artery in the sigmoid mesocolon.
If the superior rectal artery is ligated below its anastomosis with the closest sigmoid artery branch, what section of bowel is likely to necrose?
- The upper rectum, perhaps as far down as the dentate line.
And if the superior rectal artery is ligated below its anastomosis with the closest sigmoid artery, what arteries, one on each side, will save the lower part of the rectum just above the pelvic floor?
- The middle rectal arteries.
And where do the middle rectal arteries come from?
- The internal iliac artery.
And where do the internal iliac arteries arise?
- From the common iliac arteries, which are the two forks of bifurcation of the abdominal aorta. Now there is also a separate blood supply to the rectum below the pelvic floor which includes the anus.
What arteries supply this area, one on each side?
- The inferior rectal arteries.
Where do the inferior rectal arteries arise from?
- The internal pudendal arteries.
And where do the internal pudendal arteries come from?
- Again, the internal iliac artery.
Why is it that the middle and inferior rectal arteries cannot save the upper rectum if the superior rectal artery is ligated after its anastomosis with the nearest sigmoid since the superior rectal artery does extend into the lower areas supplied by the middle and inferior rectal arteries?
- It is simply that they do not anastomose with the superior rectal artery adequately.
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