Detailed Characteristics of the Migrating Motor Complex in Man and Animals

Abstract

During the interdigestive state occurring in monogastric species, the stomach and small intestine are almost empty. The meal consumed during the foregoing period undergoes the digestive and transport processes. Notwithstanding, the relatively small amounts of indigestible food remnants, cellular debris, bacteria and possibly the small portions of ingested liquids and solid foods may remain in the gastrointestinal lumen. The secretion of the digestive juices is not inhibited completely during the fasting state and the presence of the digestive juices in the gastrointestinal lumen appears to be one of the main reasons to maintain the transport of the luminal content during this period. There is no need to retain an uninterrupted mixing of gastrointestinal flow of digesta as it occurs during the postprandial period. Thus, the character of motor activity present in nonfed humans and monogastric animals adapts to the actual conditions and the interdigestive motility exhibits the cyclical character. Therefore, it was defined as cyclic motor activity and these cycles are regarded as the migrating motor complexes (MMCs). The MMC comprises four phases exhibiting the exponential intensity of contractions: phase I was defined as the weakest or with no contractions; during usually the longest phase II, divided sometimes into phase IIa and IIb, the increased frequency and amplitude of contractions are noticed; in the course of phase III, the strongest contractions occur at the maximal frequency; during phase IV, not always observed, the irregular submaximal contractions, similar to those during phase II can be recorded. There are quite precise criteria for MMC identification and it is possible to distinguish normal and abnormal MMCs. This fasting pattern occurring in most mammals and birds, is organized during the fetal life and in some species, like ruminants and other herbivores, is not abolished by feeding. The manometric technique still appears to be the gold standard method in man and promising in animals at least for the gastric and small-intestinal MMC registration to allow more detailed analysis of the interdigestive motility than the other minimally invasive methods used for clinical purposes.