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School of Medicine
Normal Bowel Function
The bowel serves three important functions related to nutrition:
- Separation of the non-useful portions of food from the nutritious components.
- Extraction of the valuable nutrients from food
- Timely evacuation of the unused portion including the ability to store until a convenient time for evacuation occurs
Process of Elimination
Most of the absorption of the useful nutrients occurs in the small bowel. Therefore, most of the material that enters the colon is waste. The material entering the colon is normally liquid, and one of the functions of the colon is to absorb some of the water to make it more solid. The other function is to move the waste to the rectum where it is stored until defecation. This occurs through a series of coordinated contractions of the colon wall muscle that resemble a wave. This wave like contraction is referred to as peristalsis.
Once the waste reaches the rectum, it is held there until convenient evacuation is possible. Keeping the waste in the rectum is the function of the anus. The anus has two circular muscles that squeeze the anus closed when contracted. The internal muscle is closed all the time while the external or outer muscle contracts when stool enters the rectum. The pelvic floor muscles also help to keep the stool in the rectum by creating enough pressure in the anus to keep stool in the rectum.
Abnormal Bowel Function
Abnormal bowel function includes:
- Fecal Incontinence
- Irritable Bowel Syndrome