Superior mesenteric artery

Structure

Origin

In the adult, the SMA arises anterior to inferior border of vertebra L1 (transpyloric plane). It is usually 1 cm lower than the celiac trunk.

Course and relations

It initially travels in an anterior/inferior direction, passing behind/under the neck of the pancreas and the splenic vein. Located under this portion of the superior mesenteric artery, between it and the aorta, are the following:

• left renal vein - travels between the left kidney and the inferior vena cava (can be compressed between the SMA and the abdominal aorta at this location, leading to nutcracker syndrome).
• the third part of the duodenum, a segment of the small intestines (can be compressed by the SMA at this location, leading to superior mesenteric artery syndrome).
• uncinate process of pancreas - this is a small part of the pancreas that hooks around the SMA.

The SMA typically runs to the left of its associated vein, the superior mesenteric vein. After passing the neck of the pancreas it starts giving off its branches.

Branches

The number of arterial arcades in the ileum is more than the number of arcades in the jejunum.

The middle, right, and ileocecal branches anastomose with each other to form a marginal artery along the inner border of the colon. This artery is completed by branches of the left colic which is a branch of the inferior mesenteric artery.