The colon is the last part of the digestive tract and is the part where nutrients and water are absorbed. It is the final part of the digestive process where food is formed into feces before it is excreted from the body through the rectum. Food that is not digested or absorbed needs to be eliminated from the body as well. The digestion of your food begins when you chew it up in your mouth and it travels down to your stomach. From there, it goes to the intestines and the colon. Some things that are eaten, such as certain types of food additives, are not digested but merely pass out of the body. Others remain as undigested waste.

In people with Irritable Bowel Syndrome, a functional disease of the gastrointestinal tract, the normal grinding and mixing of the digestive process are only slightly affected. The body may have the ability to digest more than is needed which prevents the breakdown of the process. The area that may be affected is the transportation of food when it is either slowed down to produce symptoms of nausea, vomiting, bloating, and abdominal enlargement or it is rapid and leads to diarrhea. Using these symptoms to form a diagnosis of IBS is not a simple process.

A functional disease is one which is physiological and can't be observed. When you are suffering from symptoms of diarrhea, you may have rapid transportation of food in your stomach or your sensory nerves may be misinterpreting what they are sensing. It is also possible that the motor nerves are performing the wrong function based on what message they perceive. Processing and perception of messages from the nerves can cause the wrong response to the message.

An increase of mucus around your stools could signal that you have increased or slowed transportation in the colon. You may also have a sense of incomplete elimination after you have a bowel movement. Either of these may be accompanied by constipation or diarrhea to signal that you have rapid or slowed transportation in the colon.

When bacterial growth occurs in the small intestine, slowed transportation of digesting food may be further complicated. Gas-producing bacteria from the colon have the opportunity to move up into the small intestine. The have access to more undigested foods in the small intestine so they can form a lot more intestinal gas. Gas can increase bloating and abdominal distention as well as increase the occurrence of diarrhea.

One of the difficulties of diagnosing IBS is that your body has a limited number of symptoms that it can give as signals. Nausea, vomiting, constipation, diarrhea, abdominal distention and pain are all symptoms that are common to functional diseases as well as non-functional diseases. The only way to effectively diagnose functional diseases such as IBS is to eliminate the non-functional diseases first. The tests that are available for diagnosing functional diseases are not readily available and the results are often wrong. Once you have eliminated a non-functional cause, then your symptoms can be considered for a diagnosis of a functional disease.