GI Motility Lecture Notes

Overview

• Focus: Motility of the esophagus and stomach
• Brief introduction to fundamentals of GI motility

Types of GI Motility

• Segmentation
  • Function: Mixing and churning
  • Primarily in small and large intestines
  • Aids digestion and absorption by mixing contents with digestive juices
• Propulsion (Peristalsis)
  • Alternating wave of contraction and relaxation
  • Moves GI content along the tract for absorption or elimination
• Reservoir (Storage) Function
  • Large intestine and stomach can hold contents for extended periods
  • Facilitated by sphincters (e.g., upper/lower esophageal, pyloric)

Smooth Muscle Contraction

• Rhythmic Contractions
  • Alternating contraction and relaxation (segmentation and propulsion)
• Tonic Contractions
  • Sustained contraction (sphincters)
• Smooth Muscle Cell Physiology
  • Resting membrane potential: ~-80mV
  • Threshold potential: ~-55mV
  • Slow waves generated by interstitial cells of Cajal
  • Action potentials lead to muscle contraction
  • Influenced by neurotransmitters (e.g., acetylcholine, gastrin)
• Calcium in Contraction
  • Facilitates contraction through cross-bridge cycling

Esophageal Motility

• Primary Function: Peristalsis
  • Moves bolus from oral cavity to stomach
• Sphincters
  • Upper Esophageal Sphincter: Cricopharyngeal muscle, vagal nerve innervation
  • Lower Esophageal Sphincter: Involvement in reflux prevention
• Clinical Correlations
  • Zenker's Diverticulum: Weakening of esophageal wall above upper sphincter
    • Symptoms: Dysphagia, cough, halitosis
  • Achalasia: Absence of myenteric plexus at lower esophageal sphincter
    • Symptoms: Dysphagia, regurgitation, weight loss
    • Diagnostic: Esophageal manometry

Stomach Motility

• Functions
  • Storage (reservoir)
  • Mixing (churning)
  • Emptying into the duodenum
• Phases of Gastric Secretion
  • Cephalic Phase: Thought, sight, smell of food triggers vagal stimulation
    • Receptive relaxation of fundus
  • Gastric Phase: Arrival of food causes distension and gastrin release
    • Adaptive relaxation
  • Intestinal Phase: Enterogastrones released in response to chyme in duodenum
    • Inhibits further gastric emptying (Enterogastric Reflex)
• Mixing and Emptying
  • Pacemaker cells generate rhythmic contractions
  • Peristaltic waves increase in intensity from body to pylorus
  • Particles must be <2mm to pass through pyloric canal
  • Migrating Motor Complex (MMC): Clears residual contents during fasting

Clinical Correlation: Pyloric Stenosis

• Hypertrophic Pyloric Stenosis
  • Hyperplasia/hypertrophy of pyloric sphincter
  • Symptoms: Projectile vomiting, palpable mass, metabolic alkalosis
  • Treatment: Pyloromyotomy

Summary

• Covered motility aspects of esophagus and stomach
• Further discussions on small and large intestine motility in subsequent sessions