The blood supply of the intestines
The intestines are mainly supplied by the three unpaired branches of the abdominal aortas:
- Coeliac artery
- Superior mesenteric artery
- Inferior mesenteric artery
The coeliac artery emerges immediately after the passage of the aorta through the aortic hiatus of the diaphragm. It divides into a branch to the spleen, the lienal artery, a branch to the stomach, the left gastric artery, and into the common hepatic artery, which somewhat later becomes the right gastric artery.
The superior mesenteric artery supplies the whole small intestine and extends branches up to the middle third of the transverse colon. Up to this point, the innervation is taken over by the vagus nerve (CN X).
The inferior mesenteric artery is responsible for supplying blood to the left third of the transverse colon and to the sigmoid colon. More distally the rectal arteries supply this portion of the intestines with blood. The boundary is clinically relevant because the arterial blood supply and venous draining changes in this region.
The endodermal portion is supplied by the sigmoid artery, a branch of the inferior mesenteric artery, while the ectodermal portion is supplied by the rectal arteries, that stem from the internal iliac artery. Nevertheless anastomosis are also present in between. The venous outflow of the upper part takes place via the portal vein directly into the liver, while the lower part flows out via the internal iliac vein.
The innervation of the descending colon, sigmoid, and rectum takes place via nerves of the sympathetic solar plexus and of the pelvic ganglion (Auerbach's and Meissner's myenteric plexus and pelvic nerves) and via parasympathetic fibers of the spinal cord (S2 - S5).