27.21 : Gastric Motility

Gastric motility is the coordinated contraction and relaxation of stomach muscles that convert ingested food into chyme, a semi-liquid substance ready for further digestion in the intestines. The process begins with the vagus nerve inducing the relaxation of the smooth muscles in the fundus and body of the stomach, allowing these regions to expand and accommodate up to approximately 1.5 liters of food and liquid.

Peristaltic Waves and Chyme Formation

Upon food entry, the stomach initiates peristaltic waves, which are rhythmic contractions that originate near the gastroesophageal sphincter and intensify as they move toward the pylorus. These waves create a mixing mechanism, with stronger muscular contractions in the pyloric antrum grinding the food into smaller particles. These mixing waves and gastric secretions transform the ingested food into chyme. The upper regions, including the fundus and body, serve as storage areas where the food is less mixed while the antrum vigorously churns the contents, facilitating the blending process.

Enteric Pacemaker Cells and Electrical Rhythms

The enteric pacemaker cells (interstitial cells of Cajal), located in the myenteric plexus, generate spontaneous electrical impulses that establish the stomach's basic electrical rhythm. These impulses propagate through gap junctions, synchronizing the contractions of the stomach wall. This coordination ensures that peristaltic waves occur at regular intervals, effectively moving and mixing the stomach contents. The basic electrical rhythm governs these contractile movements, facilitating effective gastric motility and digestion.

Overall, gastric motility is a complex process regulated by neural and muscular components. It ensures that food is mechanically and chemically prepared for absorption in the intestines. The interplay between the vagus nerve, smooth muscle relaxation, peristaltic waves, and enteric pacemaker cells exemplifies the intricate control mechanisms underlying digestive physiology.