Knowing how the bowel works can help us understand the causes of constipation. The body is like an engine; it takes in fuel and discharges waste. During the process of digestion, much of the food we eat is broken down so that the nutrients it contains can be absorbed into the body. Digestion and absorption of nutrients takes place mainly in the stomach and small intestines. Certain parts of food, especially fibre (roughage), cannot be broken down and digested and therefore passes unchanged through the small intestine to the large intestine, which is also known as the colon. When this matter first enters the colon, water is extracted from it and is re-absorbed back into the body. As the matter, which is known as faeces, loses water it becomes more solid. The faeces are propelled along the colon by rhythmic contractions of the muscles of the colon. When faeces enter the largest part of the colon, known as the rectum, we get the signal that we need to empty our bowels. This act of emptying the bowel is known as defecation. Normally we can delay defecation until it is convenient for us to go to the toilet.

Constipation and incontinence

A chronically distended bowel and more importantly, straining to empty the bowel, can weaken and damage the muscles of the pelvic floor. These muscles are important for normal bladder and bowel control (see pages on Pelvic Muscle Exercises).

An additional factor is involved in constipation – induced faecal incontinence. When the stools become very hard they may get stuck in the rectum. This is known as faecal impaction. Faecal material builds up behind the impacted stools and decomposes, giving rise to irritation of the lining of the rectum. As a result of this irritation, the rectum produces mucus (slime) and water, both of which mix with the decomposing faecal material. The foul smelling liquid so produced seeps around the impacted stools and leaks from the anus, giving rise to unpleasant faecal incontinence.

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