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Overview of Gastrointestinal Motility
Food needs to be moved through the gut, to places where it can be broken down (stomach and small intestine), and absorbed (small intestine and colon). Waste needs to be moved out of the body. These movements are caused by muscles in the wall of the gut, and controlled by the enteric nervous system (ENS), with input from the brain though peripheral nerves (vagus and spinal nerves). The ENS also regulates secretion and sensation within the gut. The overall process of moving food, liquids, and waste through the gut is called gastrointestinal motility.
The Enteric Nervous System
The ENS is a self-contained system within the gut with its own reflexes and control of movement. It controls motility, secretion, and sensation. The main "movement" of the gut is called peristalsis, the progressive wave of contraction and relaxation of the muscular gut tube, by which the contents are forced through the system.
Sensations from the gut are typically not perceived most of the time unless pain receptors are stimulated. These receptors are usually activated by stretching of the gut wall (called distension), cramping, or inflammation. Usually when the insult subsides, the pain does as well. In certain cases, silent pain receptors (called nociceptors) are activated that do not “turn off” after the insult has gone away, and the patient is left with a chronic pain situation. The reasons for this happening are not known, but this concept underlies many disorders of hypersensitivity, such as post-infectious Irritable Bowel Syndrome (IBS).
Abnormalities of gut motility, secretion, and sensation can lead to a wide range of diseases and disorders. These disorders can be from damage to nerves, muscle, or both of these ENS components. Very often motility problems may be due to drug side-effects, for example diarrhea from the antibiotic erythromycin which stimulates gut motility, or constipation from narcotics which suppress gut motility. Many motility disorders have no known cause but are very common (such as IBS). Some are less common but can be life-threatening, such as gastroparesis or intestinal pseudo-obstruction.
Gut Motility Disorders: