Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
As described previously, IBS is believed 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 length of the
gastrointestinal tract from the esophagus to the anus in the muscular walls of
the organs. These nerves communicate with other nerves that travel to and from
the spinal cord. Nerves within the spinal cord, in turn, travel to and from the
brain. (As an organ system, the gastrointestinal tract is exceeded only by the spinal cord and brain
in the numbers of nerves it contains.) Thus, the abnormal function of the
nervous system in IBS may occur in a gastrointestinal muscular organ, the spinal
cord, or the brain.
The nervous system that controls the gastrointestinal organs, as with most
other organs, contains both sensory and motor nerves. The sensory nerves
continuously sense what is happening within the organ and relay this information
to nerves in the organ's wall. From there, information is relayed to the
spinal cord and brain. The information 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 (responses) are sent to the organ through the
motor nerves. Two of the most common motor responses in the intestine are
contraction or relaxation of the muscle of the organ and secretion of fluid
and/or mucus into the organ.
As already mentioned, abnormal function of the nerves of the gastrointestinal
organs, at least theoretically, may occur in the organ, spinal cord, or brain.
Moreover, the abnormalities may occur in the sensory nerves, the motor nerves,
or at processing centers in the intestine, spinal cord, or brain. Some
researchers argue that the cause of functional diseases is an abnormality of the
function of the sensory nerves. For example, normal activities, such as
stretching of the small intestine by food, may give rise to abnormal sensory
signals that are sent to the spinal cord and brain, where they are perceived as
pain.
Other researchers argue that the cause of functional diseases is
an abnormality of the function of the motor nerves. For example, abnormal
commands through the motor nerves may produce a painful spasm (contraction) of
the muscles. Still others 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 may be due to sensory dysfunction, motor dysfunction, or both sensory
and motor dysfunction. One area that is receiving a great deal of scientific
attention is the potential role of gas produced by intestinal bacteria in
patients with IBS. Studies have demonstrated that some patients with IBS produce
larger amounts of gas than individuals without IBS, and the gas may be retained
longer in the small intestine. In patients with IBS, the abdominal size increases
during the day, reaching a maximum in the evening and returning to baseline by the
following morning. In individuals without IBS, there is no increase in the abdominal
size during the day.
There is much controversy over the role that poor digestion
and/or absorption of dietary sugars may play in aggravating 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 many processed foods. Poor
digestion or absorption of these sugars could 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 individuals causes food as well as gas to move more
slowly through the stomach and small intestine. Some patients with IBS may even
respond to dietary fat in an exaggerated fashion with greater slowing. Thus,
dietary fat could--and probably does--aggravate the symptoms of IBS.
Abdominal pain is pain in the belly and can be acute or chronic. Causes include inflammation, distention of an organ, and loss of the blood supply to an organ. Abdominal pain can reflect a major problem with one of the organs in the abdomen such as the appendix, gallbladder, large and small intestine, pancreas, liver, colon, duodenum, and spleen.
Diarrhea is a change is the frequency and looseness of bowel movements. Cramping, abdominal pain, and the sensation of rectal urgency are all symptoms of diarrhea. Absorbents and anti-motility medications are used to treat diarrhea.
Gas or "intestinal gas" means different things to different people. Everyone has gas and eliminates it by belching or farting (passing it through the rectum).
Constipation is defined medically as fewer than three stools per week and severe constipation as less than one stool per week. Constipation usually is caused by the slow movement of stool through the colon. There are many causes of constipation including medications, poor bowel habits, low fiber diets, abuse of laxatives, hormonal disorders, and diseases primarily of other parts of the body that also affect the colon.
Fibromyalgia, formerly
known as fibrositis, causes chronic pain, stiffness, and
tenderness of muscles, tendons, and joints without detectable inflammation. Fibromyalgia patients have an unusually low pain threshold. Symptoms of fibromyalgia include fatigue, abnormal sleep, mental/emotional disturbances, abdominal pain, migraine and tension headaches, and irritable bladder. Treatment of fibromyalgia involves patient education, medication, exercise, and stress reduction.
In lactose intolerance, the digestive system cannot digest lactose (the main sugar in milk). Symptoms of lactose intolerance include diarrhea, flatulence, abdominal pain, abdominal bloating, abdominal distention, and nausea. There are several tests to diagnose lactose intolerance. Treatment is generally made with dietary changes, supplements, and adaptation to small amounts of milk.
Small intestinal bacterial overgrowth (SIBO) refers to a condition in which abnormally large numbers of bacteria (at least 100,000 bacteria per ml of fluid) are present in the small intestine and the types of bacteria in the small intestine resemble more the bacteria of the colon than the small intestine. There are many conditions associated with small intestinal bacterial overgrowth, to include: diabetes, scleroderma, Crohn's disease, and others. There is a striking similarity between the symptoms of irritable bowel syndrome and SIBO. It has been theorized that SIBO may be responsible for the symptoms of at least some patients with irritable bowel syndrome. Symptoms of SIBO include: excess gas, abdominal bloating, diarrhea, and abdominal pain.
Dyspepsia (indigestion) is a functional disease in which the gastrointestinal organs, primarily the stomach and first part of the small intestine, function abnormally. It is a chronic disease in which the symptoms fluctuate infrequency and intensity. Symptoms of dyspepsia include upper abdominal pain, belching, nausea, vomiting, abdominal bloating, early satiety, and abdominal distention (swelling). These symptoms are most often provoked by eating.
Digestion is the complex process of turning food you eat into the energy you need to survive. The digestive process also involves creating waste to be eliminated, and is made of a series of muscles that coordinate the movement of food.
Irritable bowel syndrome (IBS) is a functional disease that can affect the quality of those who suffer from this condition. Individuals with IBS can make lifestyle changes that may modify or control the number and severity of episodes. Certain foods, medications, and hormone levels may trigger IBS episodes. Learn how to prevent the number and severity of IBS episodes of diarrhea and constipation.
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