The superior mesenteric artery (SMA) supplies blood to most of the small intestine and the right side of the large intestine. It branches from the front of the abdominal aorta just below the celiac trunk and is responsible for feeding roughly half the digestive tract, from the lower part of the duodenum all the way to about two-thirds of the way across the transverse colon.
Small Intestine: The SMA’s Largest Territory
The bulk of the SMA’s job is keeping the small intestine alive. It sends off multiple jejunal and ileal branches to the left side, which fan out through the tissue that suspends the intestines (the mesentery). These branches don’t simply dead-end at the intestinal wall. Instead, they form a series of looping arches called arcades that connect to each other, creating backup pathways for blood to reach the gut.
From those arcades, small straight vessels extend to the intestinal wall itself. The pattern differs along the length of the small intestine in a way that’s useful to know: the jejunum (the midsection) has fewer arcades but longer straight vessels reaching the gut wall, while the ileum (the final section) has more arcades but shorter vessels. This structural difference means the jejunum has a richer direct blood supply, which matches its role as the primary site for nutrient absorption.
Large Intestine: Cecum to Mid-Transverse Colon
On its right side, the SMA gives off three named branches that supply the large intestine:
- Ileocolic artery: feeds the cecum (the pouch where the small and large intestines meet), the appendix, and the terminal ileum.
- Right colic artery: supplies the ascending colon, which runs up the right side of the abdomen.
- Middle colic artery: supplies the transverse colon, the segment that crosses the upper abdomen from right to left.
The SMA’s territory ends partway across the transverse colon. From there, the inferior mesenteric artery takes over to supply the left side of the colon, the sigmoid colon, and most of the rectum.
The Vulnerable Transition Zone at the Splenic Flexure
Where the SMA’s territory ends and the inferior mesenteric artery’s begins, near the splenic flexure (the sharp bend where the transverse colon becomes the descending colon), there’s an important weak spot in the blood supply. This junction, known as Griffiths’ point, depends on small connecting vessels to bridge the two arterial systems. In a study of arteriographic images, a reliable connection at this point was present in only 48% of people. It was weak or absent in the other 52%.
This matters because if blood flow drops for any reason, whether from a clot, low blood pressure, or surgery that interrupts the inferior mesenteric artery, the splenic flexure is one of the first places to lose adequate circulation. People without a dependable connection at Griffiths’ point are especially vulnerable to a condition called ischemic colitis, where part of the colon is damaged by insufficient blood flow.
A Common Anatomical Variation
In about 10 to 20% of people, the SMA does something it’s not “supposed to” do on the textbook diagram: it gives off the right hepatic artery, which supplies the right lobe of the liver. Normally, the liver gets all its arterial blood from branches of the celiac trunk, but this variant (called a replaced right hepatic artery) is common enough that surgeons actively look for it before any operation involving the pancreas, bile ducts, or liver. Accidentally cutting an artery you didn’t expect to find can have serious consequences.
What Happens When the SMA Is Blocked
Because the SMA feeds such a large stretch of intestine, a sudden blockage is a surgical emergency. Acute mesenteric ischemia occurs when blood flow through the SMA drops sharply, usually from a blood clot. The hallmark symptom is severe abdominal pain that seems out of proportion to what a doctor finds on physical exam. The reason for this mismatch is that damage starts on the inner lining of the intestine and works outward, so the belly can feel soft and unremarkable to the touch even while the patient is in agony.
In one large review, 95% of patients with acute mesenteric ischemia presented with abdominal pain, while 44% had nausea, 35% had vomiting, and 35% had diarrhea. About one-third showed a triad of abdominal pain, fever, and blood in the stool. More than 90% had elevated white blood cell counts, and 88% showed signs of metabolic acidosis with high lactate levels, both markers that tissue is being starved of oxygen. If the condition isn’t caught early, it can progress to intestinal necrosis, where sections of bowel die, and eventually septic shock.
SMA Syndrome: When the Artery Compresses the Intestine
The SMA doesn’t just supply the gut. Its physical position also matters. The artery passes over the third part of the duodenum, and the angle it makes with the aorta normally sits between 45 and 60 degrees, with about 10 to 20 millimeters of space. In some people, particularly after rapid weight loss, that angle narrows below 22 to 28 degrees and the gap shrinks to 2 to 8 millimeters. When this happens, the SMA can physically compress the duodenum like a clamp, blocking food from passing through. This is called SMA syndrome, and it causes nausea, vomiting, and pain after eating, especially when lying flat. Weight gain or nutritional support often relieves the compression by restoring the fat pad that normally keeps the angle open.