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Functional bowel disorders / Irritable bowel syndrome
Irritable bowel syndrome
King et al. (8) have shown a greater gas production (particularly of hydrogen) in IBS patients than in control individuals, which suggests that abnormal fermentation may be responsible for bloating in some IBS patients. Both symptoms and gas production are reduced by an exclusion diet. This reduction may be associated with alterations in the activity of hydrogen-consuming bacteria. Fermentation may be an important factor in the pathogenesis of IBS.
Some studies have shown that abnormal colonic fermentation subsequent to damaged gut flora by antibiotics or gastroenteritis may be an important factor in the development of symptoms in some patients with IBS.
Enteric inflammatory cells may also play an important role in the pathophysiology of IBS. Inflammation may alter intestinal cytokine milieu and motility, both of which can result in an increase in a patient’s pain sensation.
Colonic and rectal hypersensitivity (also called “visceral hyperalgesia”) are also important factors in the causation of symptoms. Patients with IBS have an increased visceral sensitivity to stimuli which causes pain and abdominal discomfort. Studies involving balloon distension of the rectosigmoid colon have shown that patients with IBS experience pain and bloating at pressures and volumes much lower than control subjects (10).
Researchers suspect that the regulatory conduit between the central and enteric pathway in patients suffering from IBS may be impaired. The communication between gut and brain results in reflex responses mediated at three levels: prevertebral ganglia, spinal cord and brainstem. End organ sensitivity, stimulus intensity changes or receptive field size of the dorsal horn neuron and limbic system modulation are the mechanisms involved in visceral hypersensitivity.
Only about 10% of people with symptoms of IBS present to physicians for evaluation or treatment.
Enteric propulsion and sensation are, in part, mediated by acetylcholine and serotonin (5HT). Recent studies associate neurotransmitters with IBS. Serotonin is located in the central nervous system (5%) and the gastrointestinal tract (95%), and when it is released into the body it results in the stimulation of intestinal secretion and peristaltic reflex and in symptoms such as abdominal pain, bloating, nausea, and vomiting. These preliminary studies suggest increased serotonin levels in the plasma and in the rectosigmoid colon of patients with IBS.
