Migrating Motor Complex

The intestines are designed to digest food in liquid form. The achieve this the stomach using powerful contraction to break up the food we eat mix it with digestive juices and force it through a 1 to 2 mm constriction called the pyloric sphincter. This is a muscular 'valve' where the stomach meets the duodenum.

What happens to large pieces of food or even things like keys that we swallow as children? This is dealt with by the migrating motor complex.

The migrating motor complex is a distinct pattern of activity observed in intestinal smooth muscle during the periods between meals. It is thought to serve a "housekeeping" role and sweeps residual undigested material out of the stomach and intestines through the digestive tube. The cycle recurs every 1.5 to 2 hours and last about 2 hours. It consists of 4 phases as follows:

Phase 1. A period of smooth muscle inactivity lasting 45 to 60 minutes, during which there are only rare action extensions and contractions.

Phase 2. A period of roughly 30 minutes in which peristaltic contractions occur and progressively increase in frequency. Peristalsis originates in the stomach and propagates through the small intestine. (Peristalsis is a word that describes the muscular movement in the intestines like waves.)

Phase 3. The phase lasting 5 to 15 minutes in which rapid, evenly spaced peristaltic contractions occur. In contrast to the digestive period, the pylorus remains open during these peristaltic contractions, allowing many indigestible materials to pass into the small intestine.

Phase 4.A short period of transition.

The periodic nature of the migrating motor complex is thought to be controlled from the central nervous system and may be implemented in part by the hormone motilin. Like real housekeeping, the migrating motor complex is readily overridden by "more important" processes like the eating of food.
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