In the large intestine, one distinguishes the caecum with the vermiform appendix, the ascending colon, transverse colon, descending colon, sigmoid colon, and the rectum.
The colon begins in the right iliac fossa and passes into the rectum at the level of the second sacral vertebra. The colon forms a frame around the loops of the small intestine.
Vessels
The arterial supply for the ascending and transverse colon is provided by the ileocolic artery, right colic artery, and middle colic artery, which arise from the right side of the superior mesenteric artery. The middle colic artery connects on the right with a branch of the right colic artery, and on the left with a branch of the left colic artery.
The descending and sigmoid colon and the greater part of the rectum are supplied by the inferior mesenteric artery via the left colic, sigmoid, and superior rectal arteries.
Riolan's Anastomosis
It is an anastomosis that does not occur regularly, between the middle colic artery and the left colic artery, and thus ultimately between the superior and inferior mesenteric arteries. It can ensure the collateral supply of the colon in the event of an occlusion of one of the two mesenteric vessels.
Veins
Running parallel to the arteries are the veins of the same name, which drain the blood into the superior and inferior mesenteric veins. Both vessels open into the hepatic portal vein.