Blood Supply of Small and Large Intestines
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| ARTERIES OF SMALL INTESTINE |
The blood supply to the small and large intestines is extremely variable and unpredictable. The variations concerning the origin, course, anastomoses, and distribution of the intestinal vessels are so frequent and so significant that conventional textbook descriptions are inadequate and, in many respects, even misleading, a situation much the same as that of the blood supply of the upper abdominal organs. Because of this variability, the surgeon should have an intimate acquaintance with the entire spectrum of the gut’s arterial supply in order to avoid operative errors, such as devascularization of intestinal sections, which might inadvertently induce necrosis leading to rupture and peritonitis. In this overview, we will review the most typical branching patterns of the vessels associated with the small and large intestines. In the sections devoted to each organ, we will consider the complex variations that may be encountered.
The digestive tract within the abdominal cavity receives nearly all
of its blood supply from three unpaired branches of the abdominal aorta. The
foregut organs (distal esophagus, stomach, liver, gallbladder, spleen,
pancreas, and proximal duodenum) are supplied by the celiac trunk, a
large artery that leaves the abdominal aorta shortly after passing through the
diaphragm. The small and large intestines receive their blood supply from the
other two unpaired vessels of the aorta, the superior mesenteric and inferior
mesenteric arteries.
The superior mesenteric artery arises from the anterior wall of the
abdominal aorta immediately inferior to the celiac trunk. It supplies the
midgut organs (distal duodenum, part of the head of the pancreas, jejunum,
ileum, cecum, vermiform appendix, ascending colon, and transverse colon) before
forming anastomoses with the inferior mesenteric artery. One of the first
arteries to arise from the superior mesenteric artery is the middle colic
artery, which supplies the most distal midgut structure, the transverse
colon. The position of the transverse colon is a remnant of the rotation and
extreme elongation of the embryonic gut tube that occurs as it reaches its
mature state. We will revisit this artery again as it anastomoses with the
blood supply to the ascending colon.
Another proximal branch of the superior mesenteric artery is the inferior
pancreaticoduodenal artery. It splits into an anterior branch and a
posterior branch that sandwich the inferior aspect of the head of the pancreas.
These vessels, as their name implies, also supply the distal duodenum as it transitions to become the
jejunum. The anterior and posterior branches of the pancreaticoduodenal artery
anastomose with two adjacent branches of the celiac trunk, the anterior and
posterior branches of the superior pancreaticoduodenal artery. The
inferior pancreaticoduodenal artery also forms an anastomosis with the next
branch off of the superior mesenteric artery that supplies the jejunum.
The next branches from the superior mesenteric artery are 15 to 18
intestinal branches that are either jejunal
arteries or ileal arteries. These exit the left side of
the superior mesenteric artery and travel within the intestinal mesentery until
they reach the jejunum and ileum. The point at which these vessels become
covered by the two peritoneal folds that become the small intestine’s mesentery
is termed the root of the mesentery. As these vessels approach the small
intestine, they inter-connect to form a series of loops, or arterial arcades.
These arcades ensure redundancy in the blood supply to the small intestine so
that a blockage in one region will
not cause ischemia of the nearby intestine. The arterial arcades give off straight
arteries (vasa recta) that actually reach the gut tube. Although there is
no clear transition between the jejunum and ileum, the appearance of the
arterial arcades and straight arteries can assist in differentiating one from
the other. The jejunum tends to have simple arcades with one loop between
adjacent jejunal arteries and fairly elongated straight arteries. In contrast,
the ileum has more complex arcades with two or more loops and relatively short
straight arteries that reach the ileum.
Exiting the right side of the superior mesenteric artery are the
ileocolic and right colic arteries. The ileocolic artery travels
inferiorly and to the right, branching into an ileal branch and a colic
branch. The ileal branch anastomoses with the arterial arcades of the ileal
artery, supplying the terminal ileum. The ileal branch also typically gives off
the important appendicular artery, which travels posteriorly to the
ileal arterial arcades, through the mesoappendix, and finally to the vermiform
appendix itself. In the vicinity of the appendicular artery, the ileal branch
of the ileocolic artery gives off an anterior cecal artery and a posterior
cecal artery, which supply blood to their respective sides of the cecum.
The right colic artery exits the superior mesenteric artery superior to
the ileocolic artery and travels transversely toward the ascending colon. It
forms significant anastomoses with the colic branch of the ileocolic and middle
colic arteries. The anastomosis occurs primarily through a large artery, the marginal
artery (of Drum-mond), which parallels the entire large colon and receives
blood from the ileocolic, right colic, middle colic, left colic, and sigmoid
arteries. The marginal artery is a vessel that allows blood to reach the entire
length of the colon even if one of the feeder arteries is compromised. From the
marginal artery, blood reaches the colon itself via straight arteries (vasa
recta).
The inferior mesenteric artery is the last of the three unpaired vessels that supply the
digestive tract. It arises from the left anterior aspect of the abdominal aorta
approximately 3 to 5 cm above the bifurcation of the right and left common
iliac arteries. It quickly gives off several branches, the left colic, sigmoid,
and superior rectal arteries. The left colic artery travels transversely
to the left, giving off an ascending artery that travels toward the left
colic flexure to anastomose with branches of the middle colic artery. The rest
of the left colic artery contributes blood primarily to the descending colon
via the marginal artery and straight arteries. The sigmoid arteries are
a series of three to four arteries branching off of the inferior mesenteric artery which travel
within the sigmoid mesocolon to reach the sigmoid colon. The branches of
the sigmoid artery form interconnecting arterial arcades before giving off
straight arteries that enter the sigmoid colon itself. Typically, the marginal
artery does not continue as a distinct structure into the sigmoid mesocolon.
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| ARTERIES OF LARGE INTESTINE |
The final direct branch of the inferior mesenteric artery is the superior
rectal artery. It communicates with the sigmoid arterial arcades and may
also supply some distinct
branches to the sigmoid colon, termed the rectosigmoid arteries. The
sigmoid mesocolon disappears as the sigmoid colon transitions to become the
retroperitoneal rectum. As this transition occurs, the superior rectal artery
bifurcates into two lateral rectal arteries that parallel the rectal wall and
supply blood to the organ. These branches of the superior rectal artery
anastomose with the middle rectal artery, a branch of the internal iliac
artery, and to a lesser degree, the inferior rectal artery, a branch of
the internal pudendal artery.
