Updated: 10/29/2018

Gastric Motility

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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
 

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