AssessmentsSmall bowel ischemia and infarction
Small bowel ischemia and infarction
USMLE® Step 1 style questions USMLE
A 72-year-old woman is brought by her son to the emergency room for evaluation of rapid-onset abdominal pain. The patient was watching television when her symptoms began suddenly. She describes the pain as constant and rates it as 9 out of 10 in severity. Past medical history is notable for hyperlipidemia and atrial fibrillation. She is currently taking atorvastatin and metoprolol. While in the emergency room, the patient has one episode of non-bilious, non-bloody vomiting. Her temperature is 37.2°C (99.0°F), blood pressure is 122/78 mmHg, and pulse is 86/min and irregular. Physical exam shows diffuse abdominal tenderness. No bruising or signs of trauma are observed. Which of the following best describes the pathophysiology of this patient’s condition?
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.
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.
To reduce the risk of that happening, the mesenteric arteries branch and reconnect at points forming collateral circulation.
That’s protective because if blood flow is reduced in one pathway, then the tissue can still receive blood through another pathway.
Unfortunately, though, that process can cause further injury - called reperfusion injury.
In reperfusion injury, the influx of oxygen into an already damaged cell can be overwhelming and can cause even more oxidative stress, which worsens the cell damage.
As damaged cells release reactive oxygen species, it triggers an inflammatory response which attracts immune cells, like neutrophils.
The immune cells remove dead and damaged cells and release of cytokines, like Tumor necrosis factor-alpha.
Small bowel ischemia and infarction becomes more severe as the damage extends from just the mucosal layer, called a mucosal infarct, to all layers, known as a transmural infarction.