Small bowel refers to the small intestine and infarction is when ischemia, which is an inadequate blood supply, causes necrosis, or tissue death.
So, a small bowel infarction happens when there’s a reduced blood supply to the small intestine causing parts of the intestinal wall to necrose or die which can be life threatening.
Now, the small intestine is made of several layers.
The innermost layer is the mucosal layer and it’s composed of a few of its own layers.
The first layer is the epithelial lining and it faces the lumen; next is the lamina propria, which is rich with blood and lymph vessels; and finally the muscularis mucosae, which has smooth muscle.
Deep to this mucosal layer is the submucosal layer, which has connective tissue with proteins like collagen and elastin, as well as glands, and additional blood vessels.
The submucosal layer also contains the Meissner plexus which is a part of the enteric nervous system.
Below the submucosal layer is the muscularis propria which is basically two layers of smooth muscle with the myenteric plexus, another part of the enteric nervous system, sandwiched between them.
These muscles are particularly important in helping to move food through the bowel.
Finally, there’s the serosal layer which is the outermost layer of the small intestines that faces the abdominal cavity.
The superior mesenteric artery is the main supplier of blood to the small intestine.
Branches of the artery spread through the mesentery - called mesenteric arteries - and penetrate the serosa layer and travel to the submucosa where they branch further into arterioles.
Because the small intestine has a high demand for oxygen and nutrients to sustain digestion, it is highly susceptible to tissue injury from ischemia.