Secondary Condition: Bowel Management
by J. Glen House, MD
Spinal Cord Injury Secondary Condition: Bowel Management
Anatomy
The gastrointestinal tract, also called the GI tract, is a continuous tube which includes the mouth, esophagus, stomach, small intestine, large intestine (bowel), rectum and anus. Its function is to store food and absorbed nutrients from the food we eat.
The gastrointestinal tract is controlled by two nervous systems, the enteric nervous system and the autonomic nervous system. The enteric nervous system is unique to the gastrointestinal tract and is further divided into the myenteric plexus and the Meissner plexus.
The myenteric plexus is located between two layers of the muscles that exist in the gastrointestinal tract, a layer that travels parallel to the intestine and a circular layer that is positioned perpendicularly. It functions involuntarily without input from the brain. The myenteric plexus is responsible for sustained (tonic) contractions that give tone to the gastrointestinal tract and rhythmic (intermittent) contractions.
The Meissner plexus is located in the submucosa (an inner layer of the bowel) and is responsible for absorption of nutrients.
Normal bowel function before a spinal cord injury
Food enters the mouth and travels down the esophagus to the stomach. The stomach then produces enzymes and hydrochloric acid to help break down the food content. The food then travels into the small intestine and eventually the large intestine. During this time the nutrients of the food are continuously being absorbed while waste products are being continuously moved through the gastrointestinal tract towards the rectum and anal canal. The muscular layers of the gastrointestinal tract move the food material by a process called peristalsis. In the anal canal there is an internal and an external sphincter. The internal anal sphincter is under involuntary control and is continuously contracted (tight) at all times. The external anal sphincter is under voluntary control and receives its nerve supply from the pudendal nerve, which comes from the spinal cord levels S2-S4. When stool enters the rectum it causes a reflex relaxation of the internal anal sphincter. Individuals then have the urge to defecate or have a bowel movement. It is at this time that the external anal sphincter is required to prevent stool from exiting the body until in an appropriate location.
Bowel function after a spinal cord injury
The enteric nervous system continues to function normally after a spinal cord injury. Therefore, food material is normally moved along the gastrointestinal tract from the mouth to the rectum. The voluntary control of the external anal sphincter is lost, however. The amount of tone in the external anal sphincter is dependent on the specific level of spinal cord injury. Individuals who have a spinal cord injury at T12 or above have a bowel that is described as an upper motor neuron bowel and the anal sphincter is spastic (continuously contracted and tight). Individuals who have a spinal cord injury at L1 or below have a bowel that is described as a lower motor neuron bowel and the anal sphincter is flaccid (loose without tone).
