The SMA is the second ventral branch of the abdominal aorta. As mentioned above in the discussion of embryology, this artery will supply the distal duodenum, the small intestine, and the large intestine to the mid transverse colon. Given the vitally important structures its supplies and the important collaterals it provides to both the celiac and IMA, there is a very high morbidity associated with SMA occlusions. Anatomically, the SMA origin is about a centimeter distal to the celiac artery and accessible through the lesser sac near the superior border of the pancreas. The SMA comes off at an acute angle in comparison to the celiac artery. In this aortomesenteric angle, the left renal vein and the fourth portion of the duodenum pass. If this angle is too acute, it may lead to either nutcracker syndrome or SMA syndrome. Symptoms include flank pain and hematuria related to renal vein compression for the former and a gastric outlet obstruction syndrome related to the latter.

SMA branches include [2]:

The first branches of the SMA include the inferior pancreaticoduodenal artery. This comes off the right side of the SMA and divides in to an anterior posterior branch that collateralize to the celiac artery via the previously mentioned collateral pathway (Figs. 2.1, 2.2, and 2.3). The middle colic artery arises from the proximal SMA after passing below the pancreas. This artery travels to the transverse mesocolon giving a right and left branch. During an infracolic exposure of the SMA, when this artery is identified within the transverse mesocolon, it can be followed down to identify the SMA. Within the mid SMA, the right colic artery originates. It is the last branch off the right side of the SMA. As the right colic artery traverses behind the parietal peritoneum, its supplies a descending and ascending branch. The ascending branch collateralizing with the middle colic artery and supplies the ascending right colon. The descending branch collateralizes to the ileocolic artery, supplying the more proximal right colon (Figs. 2.4 and 2.5).

The ileocolic artery is the final major branch of the SMA but may share a common origin with the right colic artery. The ileocolic artery vascularizes the terminal ileum, right colon, cecum, and appendix. There are four identifiable branches. These included the descending branch (to the right colon), cecal branch (an anterior and posterior), ileal branch, and the appendicular artery (to the appendix). Finally, on the left aspect of the SMA arise the multiple jejunal and ileal branches. These fan out, forming several arches to create a collateralized network to the small bowel (Figs. 2.4 and 2.5).

The inferior mesenteric artery is responsible for supplying blood flow to the distal third of the transverse colon, descending colon, sigmoid colon, as well as the upper rectum. It originates in an anterior lateral orientation to the left just above the aortic bifurcation, typically between the L2 and L4 vertebral bodies [3]. It travels in a retroperitoneal plane towards the sigmoid colon.

Branches include [2]:

The left colic artery is comprised of an ascending and descending branch. The ascending collateralizes to the middle colic artery, distal transverse colon, and splenic flexure (Griffith’s point [4], Fig. 2.4). This collateralization is important, as this area is at high risk for watershed ischemia in the setting of dehydration or mesenteric occlusive disease. The descending left colic artery branch collateralizes to the sigmoid arteries. These are comprised of two or three sigmoid artery branches within the mesocolon. The uppermost sigmoid artery collateralizes to the left colic artery, whereas the lowermost collateralizes to the superior rectal artery. The superior rectal artery descends into the pelvis dividing into right and left branches. The superior rectal artery collateralizes with both the middle rectal (branch of the internal iliac artery) and the inferior rectal artery (branch of the internal pudendal artery, Fig. 2.4).