More about IBS Diagnosis

In case of irritable bowel syndrome (IBS) there is no blood test or any special examination, which could be used to straightly diagnose this disease.
IBS shares the same general symptoms with some other bowel diseases, but it lacks symptoms that are specific for it. Therefore, IBS diagnosis is based on general symptoms excluding the symptoms specific for other abdominal diseases, found in course of appropriate investigations. For example, an experienced physician can easily distinguish IBS from colorectal cancer as the latter has its specific symptoms.
It is reasonable for the patient to let their doctor decide which tests should be made to find out the real disease. Here are common bowel diseases that  share symptoms with irritable bowel syndrome.
Lactose intolerance occurs in patients whose small intestine can’t digest milk sugar, which results in bloating and diarrhea. Obviously, these symptoms are pretty much similar to those occurring in case of IBS. To make proper diagnosis a patient sticks to a strict milk-free diet for two weeks. If it relieves symptoms significantly, it usually indicates that he has lactose intolerance. Otherwise, the probability of irritable bowel syndrome is very high.
Celiac disease, is a disease of small intestine that is caused by a reaction to gliadin and other proteins found in wheat and other crops. It common symptoms are abdominal inflammation, diarhhea, fatigue, etc. IBS is diagnosed in case of negative results in course of gluten-free diet.
Inflammatory bowel diseases (IBD) such as Crohn’s disease and ulcerative colitis also have symptoms similar to IBS: abdominal pain, bloody stools, diarhhea, vomiting, weight loss, etc. Diagnosis is made after colonoscopy with biopsy.

More About Constipation and Diarrhea

We have already learned that there are two most common types of irritable bowel syndrome: constipation predominant and diarrhea predominant. Let’s speak about those two in more detail.

Constipation is the condition in which defecation is delayed for a variety of reasons. It may be due to consciously ignoring or preventing defecation or to decreased colonic motility, which most commonly is secondary to aging, emotion, or a low-bulk diet. Bulk refers to the content of cellulose or other undigested materials in the diet, the volume of which is not decreased by absorption. The longer fecal material remains in the large intestine, the more water is reabsorbed, and the harder and drier the feces become, making defecation more difficult and sometimes painful. During this period additional material from the small intestine continues to enter the colon, progressively increasing the volume of its contents.

Many people have a mistaken belief that unless there is a bowel movement every day retention of fecal material and bacteria in the large intestine will somehow poison the body because of toxic products produced by the bacteria. Attempts to isolate such toxic agents from intestinal bacteria have been totally unsuccessful. In unusual cases where defecation has been prevented for a year or more by blockage of the rectum no ill effects from accumulated feces were noted except for the discomfort of carrying around the extra weight of 50 to 100 lb of feces retained in the large intestine. The symptoms of nausea, headache, loss of appetite, and general feeling of discomfort sometimes accompanying constipation appear to come from the distension of the rectum and large intestine. Experimentally inflating a balloon in the rectum of a normal individual produces similar sensations. Thus, there is no physiological necessity for having bowel movements regulated by a clock; whatever maintains a person in a comfortable state is physiologically adequate, whether this means a bowel movement after every meal, or once a day, or once a week.

Cathartics, or laxatives, are sometimes necessary to relieve constipation. Several types are in common use. Cellulose in vegetable matter is a natural cathartic because of its ability to increase intestinal motility by providing bulk which stretches the smooth muscle of the intestinal wall, increasing its sensitivity to the basic electrical rhythm, and thus increasing its contractile activity. Castor oil acts by irritating the smooth muscle of the intestinal tract, increasing its motility. Some cathartics, such as mineral oil, act by lubricating hard, dry fecal material, thus easing defecation. Such agents as milk of magnesia are not absorbed or absorbed only slowly by the intestinal wall; the presence of nonabsorbable solute causes water to be retained in the intestinal tract and along with the increased motility resulting from the in-creased volume helps to flush out the large intestine.

Diarrhea, the opposite of constipation, is characterized by frequent defecation, usually of highly fluid fecal matter. A primary cause is greater intestinal motility with less time for absorption and thus the delivery of a large volume of fluid to the large intestine overloading its capacity to absorb salt and water. Certain foods, such as prunes, stimulate intestinal motility and tend to produce diarrhea. Disease-producing bacteria often irritate the intestinal wall, increase motility of the intestinal tract, and lead to diarrhea. Prolonged diarrhea can result in a serious loss of fluid and salt, especially potassium, from the body as well as upsetting the acid-base balance of the body due to loss of bicarbonate.

The Colon And Irritable Bowel Syndrome

In order to understand the etiology of irritable bowel syndrome (IBS) one needs to learn more about the functioning of the colon.

The colon (large intestine), a tube about 2.5 in. in diameter, forms the last 4 ft of the gastrointestinal tract. The cecum forms a blind-ended pouch below the junction of the small and large intestines. The appendix, a small fingerlike projection from the end of the cecum, has no known function. The colon is not coiled but consists of three relatively straight segments, the ascending, transverse, and descending portions. The terminal portion of the descending colon is S-shaped, forming the sigmoid colon, which empties into a short section of tubing, the rectum. Although the large intestine has a greater diameter than the small intestine and is about half as long, its epithelial surface area is only about 1/30 that of the small intestine because the mucosa of the large intestine lacks villi and is not convoluted. The large intestine secretes no digestive enzymes and is responsible for the absorption of only about 4 percent of the total intestinal contents per day. Its primary function is to store and concentrate fecal material prior to defecation.

Chyme enters the colon through the ileocecal sphincter separating the ileum from the colon. This sphincter is normally closed, but after a meal when the gastroileal reflex increases the contractile activity of the ileum, the sphincter relaxes each time the terminal portion! of the ileum contracts, allowing chyme to enter the large intestine. Distension of the colon, on the other hand, produces a reflexive contraction of the sphincter, preventing further material from entering.

About 500 ml of chyme from the small intestine enters the colon each day. Most of this material is derived frame the secretions of the small intestine, since most of the ingested food has been absorbed before reaching the large intestine. The secretions of the colon are very scanty and consist mostly of mucus.

The primary absorptive process in the large intestine is the active transport of sodium from the lumen to blood with the accompanying osmotic reabsorption of water. If fecal material remains in the large intestine for a long time, almost all the water is reabsorbed, leaving behind dry fecal pellets. The cells lining the large intestine are unable to actively transport either glucose or аmino acids. There is a small net leakage of potassium into the colon, and severe depletion of total body potassium can occur as a result of repeated enemas and diarrhea.

The large intestine also absorbs some of the products synthesized by the bacteria in it. For example, small amounts of vitamins are synthesized by intestinal bacteria and absorbed into the body. Although this source of vitamins generally provides only a small part of the normal vitamin requirement per day, it may make a significant contribution when dietary intake of vitamins is low. The intestinal bacteria digest cellulose and utilize the glucose released for their own growth and reproduction.

Other bacterial products contribute to the production of intestinal gas (flatus). This gas is a mixture of nitrogen and carbon dioxide with small amounts of the inflammable gases hydrogen, methane, and hydrogen sul-fide. Bacterial fermentation produces gas in the colon at the rate of about 400 to 700 ml/day. In the cow, where bacterial fermentation makes a major contribution to the digestive process, as much as 300 to 600 liters of flatus may be produced each day.

The longitudinal smooth muscle in the human colon is incomplete, and the walls of the large intestine are folded into sacs called haustra by the contraction of the circular smooth muscle. Contractions of the circular smooth muscle produce a segmentation motion which is not propulsive. This movement is considerably slower than in the small intestine, and a contraction may occur only once every 30 min. Because of this slow movement, material entering the colon from the small intestine remains for 18 to 24 hr. Bacteria have time to grow and accumulate in the large intestine because of its slow movements; in the small intestine they do not have sufficient time to accumulate before being swept into the large intestine. During sleep and most of the day there is generally little or no movement in the large intestine, but three to four times a day, generally after meals, a marked increase in motility occurs. This usually coincides with the gastroileal reflex, described earlier, and probably has similar reflex mechanisms. This increased motility may lead to the phenomenon known as mass movement, in which large segments of the ascending and transverse colon contract simultaneously, propelling fecal material one-third to three-fourths of the length of the colon in a few seconds.