Overview Gastric motility functions orad stomach relaxes to receive the food bolus from the esophagus orad stomach = fundus and proximal body caudad stomach contractions reduce size of the food bolus and mix it with gastric secretions to initiate digestion caudad stomach = distal body and antrum gastric emptying propels the chyme into the duodenum of small intestines receptive relaxation distension of the lower esophagus by the food bolus produces relaxation and opening of the lower esophageal (cardiac) sphincter and, simultaneously, relaxation of the orad stomach reduces pressure and increases volume of the orad stomach vagovagal reflex both afferent and efferent limbs of reflex are carried in the vagus nerve afferent fibers deliver sensory information from the periphery to the CNS mechanoreceptors detect distension of the lower esophagus and the orad stomach by the food bolus and relay sensory information to the CNS via afferent fibers of the vagus nerve efferent fibers deliver motor information from the CNS to the periphery CNS relays motor information to the smooth muscle walls of the lower esophagus and the orad stomach via efferent fibers of the vagus nerve postganglionic peptidergic vagal efferent fibers release vasoactive intestinal polypeptide (VIP), which relaxes the lower esophageal (cardiac) sphincter and smooth muscle of the orad stomach mixing and digestion caudad stomach has a thick muscular wall produces contractions necessary for fragmenting and mixing food contractions mix gastric contents and propel contents from the antrum of stomach back into the body of the stomach (“retropulsion”) retropulsion further fragments and mixes gastric contents gastric emptying contractions periodically propel a portion of the gastric contents through the pylorus and pyloric sphincter into the duodenum of the small intestine gastric emptying is closely regulated to allow adequate time for neutralization of gastric acid in the duodenum and adequate time for digestion and absorption H+ receptors in the duodenum detect low pH (high H+) and act via interneurons in the myenteric (Auerbach's) nerve plexus to slow gastric emptying ↓ gastric emptying ensures gastric contents are delivered slowly to the duodenum allows adequate time for neutralization of gastric acid in the duodenum by pancreatic HCO3- necessary for optimal function of pancreatic enzymes arrival of fatty acids in the duodenum stimulates cholecystokinin (CCK) secretion by I cells in the small intestine to slow gastric emptying ↓ gastric emptying ensures gastric contents are delivered slowly to the duodenum allows adequate time for fatty acid digestion and absorption in the small intestine