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SMA / IMA

(SMA – Ryan p.168, 172f, 173; IMA Ryan p.173f, 174f, 174)

Arterial supply of the small intestine

  • The entire small intestine is supplied by the superior mesenteric artery, which arises from the aorta at the L1 vertebral level.
  • Jejunal and ilea branches arise from the left of the main trunk.
  • These branches link with one another in a series of arcades, which are usually single in the jejunum but number up to 5 in the distal ileum.
  • The arteries that enter the intestinal wall – the vasa recta – are end arteries.

The arterial supply of the colon

  • The part of the colon derived from the midgut (i.e. caecum to the midtransverse colon) is supplied by the superior mesenteric artery as follows:
    • The ileocolic artery (the lowest right-sided branch of the main trunk of the superior mesenteric artery) supplies the caecum, appendix and the beginning of the ascending colon
  • The right colic artery (arising about the midway down right side of the SMA, occasionally from a common trunk with ileocolic artery) supplies the remainder of the ascending colon
  • The middle colic artery (arising from SMA just below pancreas) supplies the transverse colon to its midpoint
  • The inferior mesenteric artery supplies the colon as far as the upper rectum as follows:
    • The left colic artery to the descending colon;
    • The sigmoid artery to the sigmoid colon; and
    • The superior rectal (superior haemorrhoidal) artery to the upper rectum

Each of these vessels anastomoses with its neighbor, forming a marginal artery (of Drummond) close to the colon. The vessels that enter the bowel are, however, end arteries