A pouch that forms in the wall of the large intestine is called a diverticulum. When this pouch becomes infected or swollen, it is called diverticulitis.

Diverticulitis
diverticulitis
Infected pouches along the colon.
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It is not clear why the pouches form. It may be due to a constant build up of pressure when food moves too slowly through the bowel. This pressure increases and pushes along the sidewalls of the bowel creating pouches. Digested food or stool can become trapped in one of the pouches. This leads to swelling and infection.

The following may contribute to diverticulitis:

  • Low-fiber diet—Fiber softens stools and makes them pass through the bowel more easily
  • Increased pressure in the bowel from straining to pass a hard stool
  • Defects in the colon wall
  • Chronic constipation