[Role of motility in intestinal transit and absorption]

The relationships between small intestinal motility, transit of digestive content and absorption of nutrients have been examined at two levels: intestinal contraction and motor profile mainly characterized by the cyclic occurrence of migrating motor complexes (MMC). The propulsive efficacy of a contraction depends upon several parameters such as amplitude, orientation, distance of propagation, and is modulated by the nature and the amount of digestive contents. The most rapid transit and the highest flow of digesta appear during the postprandial state and the phase 2 of MMC. Both contractions and MMC are correlated with increases in transmucosal potential difference which corresponds in part to the ionic permeability of the mucosa. Using analogic models or anesthetized animals, it has been shown that intestinal contractions are associated with water absorption. Simultaneous measurements of duodenal motility and glycemia in awake animals indicate that glucose absorption mainly occurs during periods of activity of the MMC and is minimum during the phases of quiescence. Such relations have also been determined between intestinal motility and arterial blood flow, but then are dependent upon the presence of nutrients or bile in the intestinal lumen. Finally, the complexity of the relationships between motility, transit and absorption is mainly due to the numerous parameters which characterize an intestinal contraction and to the nature of the intestinal contents.