The digestive system has both an upper and a lower digestive tract.
The upper digestive tract breaks down food and the digestion of waste begins in the lower tract small intestine and subsequently the large intestine. Water is removed from the waste as it moves through the large intestine, and the result is solid stool.
A bowel movement (BM) would usually be initiated when enough stool has collected in the rectum, at the end of the large intestine, and the urge to empty the bowels should intensify as the rectum fills with more solid stool.
When finally going to the bathroom, the brain should signal for the release of the anal sphincter muscles, so that the related muscles can push the stool out through the anus.
The frequency between bowel movements tends to differ greatly from person to person. While for some people it is normal to have one or up to three BMs per day, the normal frequency for others can be as few as three times weekly.
The normal consistency of the stool can also vary significantly from person to person. A good general rule: a normal BM should be easy to pass.
Following a Spinal Cord Injury
Following a spinal cord injury (SCI), messages can no longer travel between the body and the brain as they normally would have.
This usually means a loss of the sensation of being full and a lack of the normal urge to empty the bowels.
When this happens as a result of an injury to the nervous system, or spinal nerves, bowel function is referred to as a ‘neurogenic’ bowel.
There are two types of neurogenic bowels that can occur after SCI, and the type of bowel depends on the injury level.
- With injuries above T-12 (Upper Motor Neuron injuries), a reflex bowel is common.
Here, the anal sphincter remains closed, yet a reflex BM can occur at any time without warning once stool has filled the rectum.
- With injuries below T-12 (Lower Motor Neuron injuries), however, there is often a loss of reflex response, called a flaccid bowel.
Although this causes reduced muscle strength that is often coupled with a loss of anal sphincter tightness, the bowel does not usually empty itself. However, the loose sphincter causes another complication, as mucus and other bodily fluids can seep around the stool and leak out the anus.