Bowel obstruction pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Hadeel Maksoud M.D.[2]
Overview
It is thought that bowel obstruction is the result of an obstruction that may occur extrinsically, intrinsically or intraluminally.
Pathophysiology
Pathogenesis
- Normally, the small intestine functions to pass gastrointestinal contents for absorption. The large surface area provided by the villi, plicae circularis and valvulae conniventes allow for this exchange to happens.
- In addition, the small bowel is free of microbes, in comparison to the large bowel that houses commensal flora that facilitate digestion and vitamin synthesis, namely vitamin K.
- Continuous transit throughout the bowel is important to prevent bowel dilatation, ischemia and necrosis.
- Obstruction of the bowel can occur functionally (due to abnormal anatomy) or mechanically, which can be acute or chronic.
- Obstructions can be extrinsic, intrinsic or intraluminal obstruction.
- Extrinsic obstructions can happen as the result of a tumor, post-operative adhesions or hernias.
- Intrinsic obstructions can happen as a result of a tumor, stenosis or hematoma.
- Intraluminal obstructions are sometimes referred to intramural obstructions and include, foreign bodies, intussusception and gallstones.
- However an obstruction occurs, proximal to the blockage there will be a dilated segment, whilst distal to the obstruction the segment of bowel will collapse as the contents cannot pass.
- Bowel distention occurs as air that is swallowed and gases produced by the commensal flora begins to accumulate.
- Eventually, the bowel wall becomes edematous and fluid gathers inside the lumen of the bowel. This disrupts the absorptive properties of the gut.
- Some fluid may be lost to the peritoneal cavity, moreover, the proximal obstruction causes severe emesis which will lead to further loss of fluid that contains several electrolytes. This process may result in metabolic alkalosis and hypovolemia.
- The obstruction also causes the normally sterile proximal bowel to become overgrown with bacteria and vomitus may contain feces.
- When a massive dilation of the bowel occurs, the vessels that perfuse the walls of the bowel become compressed and will not be able to supply the bowel loop
adequately. This leads to ischemia.
- If ischemia is not reversed within a timely manner, then necrosis, volvulus and perforation may ensue.
Genetics
- [Disease name] is transmitted in [mode of genetic transmission] pattern.
- Genes involved in the pathogenesis of [disease name] include [gene1], [gene2], and [gene3].
- The development of [disease name] is the result of multiple genetic mutations.
Associated Conditions
Gross Pathology
- On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
Microscopic Pathology
- On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].