3.1 Overview of Motility

• What does the GI tract depend on for movement?

  Inherent motility
• What is the basic movement in the esophagus?

  Peristalsis
• How does the stomach facilitate movement?

  By using three muscle layers for churning
• What process do small intestines use for movement?

  Segmentation
• What movement process is used by large intestines?

  Mass movement
• What are the three primary functions of GI motor activity?

  1. Produces segmental contractions for nonpropulsive movement
  2. Produces propulsion through peristaltic contractions
  3. Allows hollow organs to act as reservoirs
• What is the result of segmental contractions in the GI tract?

  Increased mixing that enhances digestion
• What do peristaltic contractions cause in the GI tract?

  Propagated movement of food in caudal direction
• What is the result of GI motor activity in terms of waste?

  Elimination of nondigested, nonabsorbed material
• How do sphincters contribute to GI motility?

  They separate organs to hold luminal content
• What type of muscle activity primarily accomplishes GI functions?

  Coordinated activity of smooth muscle
• What are the electrical and mechanical properties of intestinal smooth muscle?

  • Tonic (sustained) contractions
  • Rhythmic contractions (alternating contraction & relaxation)
• What neurotransmitter is predominant in excitatory motor neurons?

  ACh (Acetylcholine)
• Which neurotransmitters are associated with inhibitory motor neurons?

  VIP and NO
• How do excitatory and inhibitory neurotransmitters affect smooth muscle?

  They modulate [Ca2+]i and contractility