Superior mesenteric artery
Arteria mesenterica superior
Also known as: SMA
The superior mesenteric artery (SMA) is the second unpaired branch from the front of the abdominal aorta, arising at L1 about 1 cm below the coeliac trunk. It runs through the root of the mesentery and supplies the midgut, from the second part of the duodenum to the distal transverse colon.
Overview
Course. The SMA arises behind the neck of the pancreas and the splenic vein. It descends in front of the left renal vein, the uncinate process of the pancreas and the third part of the duodenum. It then enters the root of the mesentery and runs down toward the right iliac fossa. The superior mesenteric vein lies on its right.
Intestinal branches. The jejunal and ileal branches form arcades of connecting loops, from which straight vessels (vasa recta) run to the bowel wall. The jejunum has few arcades and long vasa recta, while the ileum has many arcades and short vasa recta. This difference helps surgeons tell them apart.
Colonic connection. Along the inner edge of the whole colon, the marginal artery (of Drummond) links the SMA and IMA territories.
Anatomy
- Branches
In order: the inferior pancreaticoduodenal artery, the jejunal and ileal arteries (from its left side), the middle colic artery, the right colic artery, and the ileocolic artery (which gives the caecal, appendicular and ileal branches).
Function
- Supplies the midgut: the distal duodenum, jejunum, ileum, caecum, appendix, ascending colon and proximal two-thirds of the transverse colon.
- Supplies the head of the pancreas, together with the coeliac trunk.
Clinical significance
Acute mesenteric ischaemia
An embolus (often from atrial fibrillation) usually lodges a few centimetres down the SMA, beyond the middle colic origin. Thrombosis of an atherosclerotic SMA is the other main cause. The patient has severe abdominal pain that is out of proportion to the findings on examination, with a raised lactate. The diagnosis is made by CT angiography, and urgent revascularisation and removal of dead bowel are needed. Mortality is high.
SMA syndrome and nutcracker syndrome
When the angle between the SMA and the aorta becomes very narrow, typically after rapid weight loss, the third part of the duodenum is squeezed between them (Wilkie syndrome), causing vomiting. The left renal vein can be compressed in the same angle (nutcracker syndrome), causing blood in the urine and a left varicocele.
Midgut volvulus
In intestinal malrotation, the midgut can twist around the axis of the SMA. In a newborn this presents with bilious (green) vomiting and is a surgical emergency.
Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.