Porth's Essentials of Pathophysiology, 4e

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Gastrointestinal and Hepatobiliary Function

U N I T 8

U N D E R S T A N D I N G Intestinal Motility Motility of the small intestine is organized to optimize the digestion and absorption of nutrients and the propulsion of undigested material toward the colon. Peristaltic movements mix the ingested foodstuffs with digestive enzymes and secretions and circulate the intestinal contents to facilitate contact with the intestinal mucosa.The regulation of motility results from an interplay of input from the (1) enteric and (2) autonomic nervous (ANS) systems and the intrinsic pacemaker activity of the (3) intestinal smooth muscle cells.

Enteric Nervous System Innervation. The gastrointestinal system has its own nervous system, called the enteric nervous system . The enteric nervous system is composed mainly of two plexuses: (1) the outer myenteric (Auerbach) plexus that is located between the longitudinal and circular layers of smooth muscle cells and (2) an inner submucosal (Meissner) plexus that lies between the mucosal and circular muscle layers. The myenteric plexus controls mainly intestinal movements along the length of the gut, whereas the submucosal plexus is concerned mainly with controlling the function within each segment of the intestine. Fibers in the submucosal plexus also use signals originating from the intestinal epithelium to control intestinal secretion and local blood flow. 1

Villi

Submucosa Submucosal plexus

Circular

Muscular coat

Longitudinal

Myenteric plexus Serosa

Mesentery