Gastrointestinal Motility

• Large intestine motility


  • Plays a big role in peristaltic activity
  • Involves mass peristalsis (mass movements)
  • Involves haustral contractions (segmentation)
• Mass peristalsis (mass movements)


  Propulsive peristaltic contractions that move contents towards the rectum
• Haustral contractions (segmentation)


  Mixing and absorption-focused contractions that increase contact between contents and mucosal surface
• Haustral contractions


  1. Stretch reflex activated

  2. Myenteric nervous system initiates contraction

  3. Tenia coli muscles contract to create constriction points and pouches (haustra)

  4. Increases contact between contents and mucosal surface for absorption
• Tenia coli


  • Bands of smooth muscle in large intestine wall that contract to create haustra
• Haustral contractions primarily occur in ascending and transverse colon
• Mass movements primarily occur in transverse and descending colon
• Triggers for mass movements


  • Stretch/distension of intestinal wall
  • Irritants in intestinal contents
  • Gastrocolic reflex
• Gastrocolic reflex


  Neural reflex where stomach distension/contents triggers contractions in colon to evacuate
• Mass movements occur 3-5 times per day, often after meals
• Gastrocolic reflex


  1. Emptying the colon

  2. Refilling the colon

  3. Ileal reflux occurring
• Propulsion


  Movement of contents through the colon towards the rectum
• Defecation reflex


  Mechanism to move feces from the rectum out of the body
• Defecation contractions occur 3-5 times per day
• Triggers for defecation contractions


  • Food in stomach
  • Stretch
  • Irritants
  • Can occur during or after meals
• Defecation contractions


  • Powerful
  • Contract over 20cm of large intestine
• Movement of feces


  1. From transverse colon to descending colon

  2. From descending colon to sigmoid colon

  3. From sigmoid colon to rectum
• Feces reach the rectum


  Initiates stretch and defecation reflex
• Defecation reflex


  1. Stretch receptors in sigmoid colon and rectum activated

  2. Sensory signals to spinal cord

  3. Parasympathetic motor signals to contract sigmoid colon and rectum

  4. Parasympathetic signals relax internal anal sphincter

  5. Voluntary control of external anal sphincter
• Internal anal sphincter


  Smooth muscle, involuntary
• External anal sphincter


  Skeletal muscle, voluntary
• Voluntary control of defecation


  1. Cerebral cortex sends signals down corticospinal tracts

  2. Activates pudendal nerve to relax external anal sphincter

  3. Levator ani muscle contracts to lift anal canal
• Valsalva maneuver


  Closing glottis to increase intra-abdominal pressure and aid defecation