The pain often begins after eating and goes away after a bowel movement. Other symptoms are bloating, passage of mucus, and a feeling of incomplete emptying. IBS is not caused by structural, biochemical, or infectious abnormalities. Rather, IBS is considered a dysregulation, or abnormality of brain-bowel function. In IBS, diarrhea comes from an increased rate of passage of stool through the colon.
Constipation is the result of a decreased speed of stool passing through the colon.
Increased pain sensitivity results from the increased sensitivity of the nerves. Sometimes, the nerves are so sensitive that normal contractions, even with digesting a normal meal, bring on pain or discomfort. Some patients, depending on their symptoms, age, and general health require diagnostic testing to exclude other medical conditions. If a patient has IBS, the results of these tests will be essentially negative. This does not mean, however, that the symptoms are not real.