Understanding GP

Normal Digestion

Intro / Digestion / Who gets GP / What happens / Symptoms / Dx / Mild forms / Tx

Digestion:

We will start with where food enters your body after it leaves your mouth. Once food is chewed and swallowed, it passes through the upper esophageal sphincter. (A sphincter is like a valve. It is a ring of muscle surrounding and serving as a guard to open and close a tube). Food then travels into a hollow muscular tube called the esophagus. The upper part of the esophagus is different from the rest of the gastrointestinal (GI) tract, since the upper section muscles are made up of skeletal muscle, that is, muscles that are under voluntary control of the brain. We can control the movement of these muscles if we wish.

Once food or liquids hit below this section, however, the muscles become like the rest of the GI tract, that is, smooth muscle. (Smooth muscles are those over which we have no conscious control). Food or liquid dilates the tube of the esophagus; this triggers a wave action (peristalsis/motility) of the smooth muscle that propels the contents downward. It takes about five to ten seconds for food to reach the stomach. So food does not merely slip down to the stomach. At the base of the esophagus is the lower esophageal sphincter (LES). The esophagus is very active in its role. Swallowed food passes down the esophagus, and a leading wave of relaxation is transmitted through the esophageal wall. This is what opens the door to the stomach—a brief relaxation of the usually tense LES sphincter
 

Copyright^© 2000 by Houghton Mifflin Company. Adapted and reproduced by permission from The American Heritage Dictionary of the English Language, Fourth Edition.

Your Tummy
Food enters the upper section of the stomach, or FUNDUS. The fundus must relax and accommodate the food to prevent pressure from building up. The upper part of the stomach then acts as a reservoir to store the food for processing. The food triggers weak, rippling waves (peristalsis/motility) that pass along the stomach wall approximately once every twenty seconds. These waves, called slow waves, are thought to be induced by specialized cells in a region of the stomach called the pacemaker region. These peristaltic waves continuously roll out from the upper body of the stomach and spread toward the lower region of the stomach, or ANTRUM. These rippling waves gradually move food out of the fundus area toward the antrum. As the waves spread toward the antrum they become stronger, mixing the food with gastric secretions and kneading the food down to smaller, unrecognizable particles. This food and gastric juice mixture is called chyme.

The PYLORUS is another sphincter muscle. It guards the opening between the antrum, and the beginning of the small intestine called the DUODENUM. The pylorus keeps things in the tummy for a really good mixing. Pressure must be created for the antrum to push the chyme past the pylorus. In other words, the antrum must create waves of even higher pressure in order to overcome the slightly constricted pylorus valve to deliver squirts of chyme to the duodenum.

The rate of stomach emptying (gastric emptying) is regulated by many factors, one of which is the presence of fats in the small intestine. The duodenum lining is a sensory organ; it can taste what is presented to it. If a high-fat content enters, the cells of the duodenum are stimulated to release chemical messengers via the blood stream. These chemicals tell the stomach to slow down its emptying. That is, these chemical messengers inhibit antral peristalsis (waves moving food through the antrum).

For healthy tummies, this is good news; it means that the tummy will slow down the release of calorie-rich fats and keep you working longer between meals.

In an illness state like gastroparesis, however, even this normal slowing of stomach emptying can increase symptoms.

This is a very simplistic overview of the upper gastrointestinal (GI) system. The science of physiology still has not unravelled all the mysteries of how the stomach and other various parts communicate, and generate these slow waves. There is controversy surrounding some of the theories. Research is ongoing. It is hoped this research will lead to discovering the nature and origin of  motility disorders.

Motility
Gut MOTILITY consists of the muscular activity necessary to transport food and contents along the hollow tube of the GI tract. It is the muscular action of squeezing a segment while relaxing the segment just below; the action of kneading, pumping, pushing, and rippling waves. This motility is a symphony of players and enormously complex. Chemicals (digestive hormones), wires (nerves and their chemical transmitters), muscles, and electrical activity all co-ordinate in harmony which, under normal circumstances, is outside your conscious awareness. Motility fulfills the purpose of nourishing your body. As well, the activity of eating brings a great deal of psychological pleasure and provides social and cultural cohesiveness.

However, when discordant notes start to play, our gut comes front and centre to our awareness! In motility disorders, failure or dysfunction in any one component—nerves, muscles, electrical generation (pacemaker cells), or chemical transmitters, for example— can create havoc.