Superior mesenteric artery syndrome is when the first part of the small intestine—which is the duodenum—gets squeezed between two large arteries: the abdominal aorta and the superior mesenteric artery.
So, when the duodenum gets squashed, food can’t easily pass by, and it leads to intestinal obstruction.
Normally, blood heading toward the lower parts of the body exits the heart, swoops through the aortic arch, and then flows downward through the descending aorta, which is a large, muscular blood vessel about as wide as a thumb.
The descending aorta runs along the back of the abdominal wall in front of the spine, and that part is called the abdominal aorta.
The abdominal aorta then forks into the common iliac arteries near the fourth lumbar vertebra, or L4.
Along the way, it gives rise to a number of paired arteries like the renal arteries, as well as three unpaired arteries—the celiac trunk, the superior mesenteric artery, and the inferior mesenteric artery—all of which come off of the anterior or front wall of the aorta and supply blood to the stomach and intestines.
Usually, the angle between the aorta and the superior mesenteric artery as it branches off—the aortomesenteric angle—is around 45 degrees.
It turns out that the duodenum, which is the C-shaped first section of the small intestines - passes through this little archway.