Food and beverages move through the digestive tract at different speeds. This is largely determined by the motion within the gut, that is generated by small muscles that contract and relax in a rhythmic coordination. It ensures that the food you eat travels down your throat, through your esophagus, then into the stomach, small intestine and large intestine before unabsorbed nutrients and wastes are passed out as stool. Gravity may help and so does being mobile, but the tiny muscles within the bowels are responsible for pushing food and wastes along. When this motion within the bowels is disturbed for whatever reason, a host of problems can arise.
What are bowel motility disorders?
Also known as intestinal motility disorders, this is a group of conditions that cause abnormalities in movement inside the bowels. As a result it affects the passage of food, water and wastes in the gut. Rapid motility is seen in diarrheal conditions such IBS with diarrhea. However, the concern is often more on bowel motility disorders where movement is too slow or so disrupted that it causes the contents to become backed up as if there is a blockage in the bowels although there is no physical obstruction (pseudo-obstruction).
The causes of bowel motility disorders can vary – some may arise within the digestive tract, others may be arise from outside of the gut. Whatever the cause and wherever the origin of the problem, it ultimately leads to abnormal muscle contractions within the bowel wall. This can include spasm of these muscles and in some instances even paralysis of the muscles. As a result portions of the bowel cannot contract and relax in a rhythmic manner to push food, wastes and water along its course.
Movement Inside The Bowels
It is important to first understand how movement occurs within the bowels. The term peristalsis refers to the pushing motion within the bowels. Embedded in the bowel walls are tiny smooth muscles. These muscles are not under voluntary control. Although the basic mechanism of gastrointestinal motility applies to the entire digestive tract, there is some variation in the type of movement within the small intestine (small bowel) and large intestine (large bowel). This has been discussed in detail under intestinal motility for the small intestine and colonic motility for the large intestine.
Types of contractions
There are two main types of movements within the small and large bowel:
- Mixing contractions to churn the food (small intestine) or expose the mush (chyme) so that water and electrolytes can be absorbed. It is also known as segmentation contractions.
- Propulsive contractions to push the food, mush and stool forward. These are also known as peristaltic waves.
Both types of contractions are stimulated by stretching of the intestinal wall, which occurs when food, chyme or stool enters a portion of the small or large intestine. It is also stimulated by the events in other parts of the digestive tract, as well as externally input from the brain and spinal cord. Slowly the contents are churned and pushed forward in this manner.
Other factors can also influence movement within the bowels, such as:
- Psychological stress
- Time of day
Causes of Intestinal Motility Disorders
Intestinal motility disorders are a result of a disturbance in the coordination of bowel muscle contractions. It does not mean that these contractions do not occur entirely. Sometimes it does not. But often the problem lies with disrupted coordination.
Nerve and muscle disorders
If the nerves and muscles do not function properly, then the signals needed to coordinate bowel muscle contractions (nerves) and the actual contractions (muscles) will be affected. This is seen in degenerative nerve and muscle diseases.
A number of drugs can contribute to intestinal motility disorders. Anesthesia and opioid analgesics (painkillers) are among the more well known drugs that can “shut down” movement within the bowels. Other drugs that may also be responsible include tricyclic antidepressants diuretics, laxatives, lithium and chemotherapeutic agents.
Intestinal motility disorders are also associated with endocrine disorders such as hypothyroidism (myxedema) and diabetes (diabetic neuropathy), although the problem is nerve-related in diabetic neuropathy.
A number of conditions are known to cause intestinal motility disorders, and are at times even caused by underlying intestinal motility disorders that arise for other reasons.
- Constipation may be due to age, diet, fluid intake, pregnancy and a host of other causes.
- Fecal incontinence seen with aging, nerve injury and diseases, diabetes and certain food intolerances.
- Irritable bowel syndrome may be due to intestinal motility disorders although the exact cause is unknown.
Sometimes the cause of an intestinal motility disorder is unknown. This is referred to as idiopathic.
Signs and Symptoms
When bowel motility is affected, digestion and absorption of nutrients is compromised and movement of the intestinal contents are hampered. This results in a host of signs and symptoms such as:
- Abdominal distension
- Bloating (sensation of fullness)
- Discomfort or abdominal pain
- Diarrhea or constipation
- Loss of appetite
- Weight loss
These signs and symptoms can vary greatly depending on the nature and cause of the intestinal motility disorder. It may also vary from one person to another.
The approach to treatment depends on the underlying cause once it has been identified. Sometimes there is no clear cause of the intestinal motility disorder.
Certain medication may be used such as:
- Cholinergic agonists which allows the parasympathetic nervous system to have a greater effect on the bowel muscles.
- Prokinetic agents which increases peristaltic contractions which is useful for slow bowel motility.
- Opioid reversal agents like methylnaltrexone to undo the effects of opioid analgesics (painkillers).
- Antidiarrheal drugs like loperamide to slow down contractions which is useful for rapid bowel motility.
- Antibiotics like erythromycin can speed up gastric emptying.
Sometimes invasive procedures may be considered. Endoscopic decompression is usually the first procedure to be considered in severe acute cases which does not respond to medication. In chronic cases, surgery may be considered. This can include surgically removing (resecting) a portion of the bowels. If the remaining ends of the bowels are not surgically connected then a ostomy made also be done. This procedure creates an opening on the abdominal wall where the end of the bowel is then connected.