Causes Of Irritable Bowel Syndrome
Irritable bowel syndrome is thought to be due to the abnormal function (dysfunction) of the muscles of the organs of the gastrointestinal tract or the nerves controlling the organs. The nervous control of the gastrointestinal tract, however, is complex. A system of nerves runs the entire distance of the gastrointestinal tract from the esophagus to the anus in the muscular walls of the organs. These nerves intercommunicate with other nerves that journey to and from the spinal cord. Nerves inside the spinal cord, in turn, locomote to and from the brain. (The gastrointestinal tract is exceeded in the numbers of nerves it bears only by the spinal cord and brain.) Thus, the abnormal function of the nervous system in IBS might occur in a gastrointestinal muscular organ, the spinal cord, or the brain.
The nervous system that controls the gastrointestinal organs, as with many other organs, contains both sensory and motor nerves. The sensory nerves continuously sense what is happening within the organ and relay this info to nerves in the organ’s wall. From there, data can be relayed to the spinal cord and brain. The data is received and processed in the organ’s wall, the spinal cord, or the brain. Then, based on this sensory input and the way the input is processed, commands (replies) are sent to the organ across the motor nerves. Two of the most basic motor responses in the intestine are contraction or relaxation of the muscular tissue of the organ and secretion of fluid and/or mucous secretion into the organ.
As already mentioned, abnormal function of the nerves of the gastrointestinal organs, at least in theory, might occur in the organ, spinal cord, or brain. Furthermore, the abnormalities may occur in the sensory nerves, the motor nerves, or at processing centers in the intestine, spinal cord, or brain. Some investigators argue that the cause of functional diseases is abnormalities in the function of the sensory nerves. For example, normal activities, like stretching of the small intestine by food, could give rise to abnormal sensory signals that are sent to the spinal cord and brain, where they are sensed as pain.
Other researchers debate that the cause of functional diseases is abnormalcies in the function of the motor nerves. For instance, abnormal commands through the motor nerves might bring on a painful muscle spasm (contraction) of the muscles. Still other people argue that abnormally functioning processing centers are responsible for functional diseases because they misinterpret normal sensations or send abnormal commands to the organ. In fact, some functional diseases might be due to sensory dysfunction, motor dysfunction, or both sensory and motor dysfunction. Still other people might be due to abnormalities inside the processing centers One area that’s receiving a good deal of scientific attention is the potential function of gas produced by intestinal bacteria in patients with IBS. Studies have demonstrated that patients with IBS produce greater amounts of gas than people without IBS, and the gas can be preserved longer in the small intestine. Among patients with IBS, abdominal size increases over the daytime, reaching a maximum in the evening and falling to baseline by the following morning. In people without IBS, there is no gain in abdominal size during the day.
There has been a good deal of controversy over the role that poor digestion and/or absorption of dietary sugars might play in intensifying the symptoms of IBS. Poor digestion of lactose, the sugar in milk, is very common as is poor absorption of fructose, a sweetener found in a lot of processed foods. Poor digestion or assimilation of these sugars may aggravate the symptoms of IBS since unabsorbed sugars often cause increased formation of gas.
Although these abnormalities in production and transport of gas may give rise to some of the symptoms of IBS, much more work will need to be done before the role of intestinal gas in IBS is clear.
Dietary fat in healthy people causes food as well as gas to move more slowly through the stomach and small intestine. Some patients with IBS might even respond to dietary fat in an exaggerated fashion with greater slowing. Thus, dietary fat could—and probably does—aggravate the symptoms of IBS.
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