One function of the stomach is to grind food into smaller particles and mix it with digestive juices so the food can be absorbed when it reaches the small intestine. The stomach normally empties its contents into the intestine at a controlled rate.
The stomach has three types of contractions:
- There are rhythmic, 3 per minute, synchronized contractions in the lower part of the stomach, which create waves of food particles and juice which splash against a closed sphincter muscle (the pyloric sphincter) to grind the food into small particles.
- The upper part of the stomach shows slow relaxations lasting a minute or more that follow each swallow and that allow the food to enter the stomach; at other times the upper part of the stomach shows slow contractions which help to empty the stomach.
- Between meals, after all the digestible food has left the stomach, there are occasional bursts of very strong, synchronized contractions that are accompanied by opening of the pyloric sphincter muscle. These are sometimes called "housekeeper waves" because their function is to sweep any indigestible particles out of the stomach. Another name for them is the migrating motor complex.
Examples of stomach (gastric) motility disorders include:
- Delayed gastric emptying (gastroparesis)
- Rapid gastric emptying (dumping syndrome)
- Functional dyspepsia
Delayed gastric emptying (gastroparesis)
The symptoms of delayed gastric emptying include nausea and vomiting. Poor emptying of the stomach can occur for several reasons:
- The outlet of the stomach (the pylorus and duodenum) may be obstructed by an ulcer or tumor, or by something large and indigestible that was swallowed.
- The pyloric sphincter at the exit of the stomach may not open enough or at the right times to allow food to pass through. This sphincter is controlled by neurological reflexes to ensure that only very tiny particles leave the stomach and also to insure that not too much acid or sugar leaves the stomach at one time, which could irritate or injure the small intestine. These reflexes depend on nerves that sometimes become damaged.
- The normally rhythmic, 3 per minute contractions of the lower part of the stomach can become disorganized so that the contents of the stomach are not pushed towards the pyloric sphincter. This also usually has a neurological basis; the most common known cause is longstanding diabetes mellitus, but in many patients the cause of delayed gastric emptying is unknown, so the diagnosis given is idiopathic (meaning cause unknown) gastroparesis.
Cyclic vomiting syndrome (CVS)
Cyclic vomiting syndrome (CVS) is a disorder with recurrent episodes of severe nausea and vomiting interspersed with symptom free periods. CVS occurs in all ages. Patients may struggle for many years before a correct diagnosis is made.
Rapid gastric emptying (dumping syndrome)
Rapid gastric emptying, or dumping syndrome, happens when the upper end of the small intestine (jejunum) fills too quickly with undigested food from the stomach.
"Early" dumping begins during or right after a meal. "Late" dumping happens 1 to 3 hours after eating. Many people have both type.
Many patients have pain or discomfort that is felt in the center of the abdomen above the belly button. Some examples of discomfort that is not nonpainful are:
- Early satiety (feeling full soon after starting to eat)
There is no single motility disorder that explains all these symptoms, but about a third of patients with these symptoms have delayed gastric emptying (usually not so severe that it causes frequent vomiting), and about a third show a failure of the relaxation of the upper stomach following a swallow (abnormal gastric accommodation reflex). About half of the patients with these symptoms also have a sensitive or irritable stomach, which causes sensations of discomfort when the stomach is filled with even small volumes.
Adapted from IFFGD Publication: Gastrointestinal Motility Disorders of the Esophagus and Stomach by William E. Whitehead, PhD, Co-Director, Center for Functional GI & Motility Disorders Center; Professor of Medicine, Division of Digestive Diseases; and Professor of Psychology, University of North Carolina, Chapel Hill, NC, and NIH Publication No. 05–4629, December 2004; the text of which is not copyrighted.