What Causes Diverticular Disease?

The circular muscle fibres in the alimentary canal wall contract and relax to move food along its length in a motion known as peristalsis. If the diet is low in roughage, then the muscles of the colon become constantly strained as they try to push along a small amount of material upon which they can get no grip. Over time, the overworked muscles become over-sized and lose their efficiency. When the pressure in the colon is increased during a motion, weak places bulge out between the stiff, thick, muscle fibres to form marble-sized pouches (diverticula). Although fairly small at first, these pouches made only of the slippery, lubricated mucous membrane and peritoneal covering can expand to about 3 cm over time.

Diverticula are most commonly found in the lower portions of the large intestine just above the rectum (the sigmoid colon). If a small amount of faeces becomes trapped in one of these pouches, the area can become infected and inflamed - a condition known as diverticulitis. If the pouch develops a small tear or perforation, the infection may spread to the membrane that covers the intestinal tract and surrounds the organs in the abdomen, resulting in peritonitis.