GI Phys 6

• 1. cecum (w/ appendix)
  2. ascending colon
  3. transverse colon
  4. descending colon
  5. sigmoid colon
  6. rectum


  pathway of large intestine

  
• function of the large intestine

  storing and drying feces

  • 3x wider than the small intestine
  • yet shorter in length
• keeps bacteria out of small intestine ileum

  ileocecal valve/sphincter
• (good) bacteria cell # =


  total # of cells in body
• antibiotics damage gut bacteria, and damaging gut bacteria can lead to obesity, immune dysfunction including allergies, depression, and much more
• this keeps a colony of healthy bacteria to repopulate your gut in cases when disaster (or antibiotics) wipes them out

  the appendix
• protective alkaline mucus with bicarb and K+


  secretion of the large intestine

  • explains why excessive diarrhea can lead to acidosis and/or K+ depletion
• bacterial breakdown of complex polysaccharides


  digestion of the large intestine

  • can lead to flatulence
• • products of bacterial metabolism
  • vitamin K
  • NaCl
  • 1.4 L/day of water


  absorption of the large intestine
• motility 1 of the large intestine

  segmentation, aka haustrations

  • occurs every 30 min
  • shuffling back and forth motility
  • aids with drying function
• wall bulges of the LI that can shrink in and expand back out

  haustral sacs
• motility 2 of the large intestine

  mass movement

  • long ranging peristaltic wave in smooth muscle
  • starts at ascending colon and rapidly travels to rectum
  • stimulated by:
  • gastrin in gastric phase of regulation
  • occurs during a meal as part of the "gastrocolic reflex"
  • ultimately:
  • packs rectum w/ feces
  • leads to defecation reflex
  • bowel movements within 30 min of eating a regularly occurring large meal during day
• motility 3 of the large intestine

  defecation (regulated very similar to micturition)

  • rectal stretch leads to stimulation and contraction of smooth muscle
  • the internal anal sphincter relaxes
  • opens, smooth muscle
  • the external anal sphincter reflexively contracts
  • closes, skeletal muscle
  • you are now aware of the urge to defecate...
  • ... if place and time are appropriate
  • external sphincter is voluntarily relaxed
  • opens
• what increases pressure in abdomen and aids with expulsion of feces?

  a "Valsalva Maneuver" (sometimes utilized)
• if reduced motility occurs, then ____________ may result

  constipation