Causes of Constipation
The major identifiable causes of constipation are listed in below. Despite the many different possible causes of constipation, most cases seen in clinical practice are functional in origin, and they are often made worse by such factors as inadequate water or fiber intake, or the use of constipating medications. Many cases of constipation may in fact have several contributing factors.
"Functional" means the primary abnormality is in the way the body works.
Constipation can be broadly divided into 3 classes based upon the underlying physiologic cause;
- normal-transit constipation,
- slow transit constipation, and
- pelvic floor dysfunction.
In normal-transit constipation, colonic motility (the way muscles contract and relax to move contents through the colon) is unaltered; stool moves through the colon at a normal rate. However, patients with normal-transit constipation may experience other difficulties in stool passage, for example due to harder stools.
In contrast, in slow-transit constipation colonic motility is decreased and bowel movements are infrequent, leading to more severe symptoms of straining and harder stools.
Pelvic floor dysfunction
The pelvic floor is a group of muscles that supports the organs within the pelvis and lower abdomen and also plays an important role in defecation. Persons with pelvic floor dysfunction have a functional outlet obstruction, a defect in the coordination necessary for stool evacuation. This usually occurs due to the failure of the pelvic floor muscles (including the anal sphincter) to relax appropriately during evacuation efforts. When this happens it makes stool passage much more difficult, regardless of whether stool transit in the colon is normal or delayed.
In some cases, individuals contract their pelvic muscles instead of relaxing them. This condition is known variously as “pelvic floor dyssynergia,” “paradoxical pelvic floor/puborectalis contraction,” or “anismus.”
The majority of persons seen by a doctor have normal-transit constipation, followed by pelvic floor dysfunction, and slow-transit constipation.
As noted, some patients can have a combination of slow transit and pelvic floor dysfunction (functional outlet obstruction).