3.2 Segments of the GI

• What type of muscle primarily composes the GI tract?

  Smooth muscle
• What is the exception to the smooth muscle composition in the GI tract?

  Striated muscle of upper esophageal sphincter
• Which part of the GI tract contains striated muscle?

  Upper esophageal sphincter
• What is the function of the circular muscle layer in the intestine?

  It causes segmentation through contraction
• What does the longitudinal muscle layer in the intestine do?

  It causes wave-like contractions
• What are the characteristics of segments of the GI tract?

  • Hollow, low-pressure organs
  • Separated by circular muscles or sphincters
  • Maintain positive resting pressure
• What is the function of sphincters in the GI tract?

  Regulate antegrade and retrograde movement
• How does the resting pressure of the pyloric sphincter function?

  It controls emptying of gastric contents
• What does the resting pressure of the lower esophageal sphincter (LES) prevent?

  Prevents gastric contents from refluxing
• What happens to the sphincter when stimuli are proximal to it?

  It causes sphincteric relaxation
• What is the effect of stimuli distal to the sphincter?

  It induces sphincteric contraction
• How do sphincters function in the GI tract?

  They serve as one-way valves
• What occurs during the act of deglutition regarding the UES and LES?

  UES relaxes while LES remains contracted
• When does the LES begin to relax after deglutition?

  Approximately 3 seconds after UES pressure returns
• How many sphincters are present in the GI tract?

  • Six sphincters
  • Each has different resting pressures
  • Each responds differently to stimuli
• What is the function of the Sphincter of Oddi?

  Regulates movement of bile into duodenum