GI Phys 2

• where do short reflexes occur?

  within the GI tract
• where do long reflexes occur?

  the central nervous system
• stimulus in the GI lumen

  food or water
• feed-forward system stimulus

  sight, smell, taste of food
• stimulus from the limbic system

  emotional states/hunger
• gastrointestinal hormones

  gastrin, CCK, secretin, GIP
• • chemical class: peptide
  • site of production: antrum of the stomach
  • stimuli for hormone release: amino acids, peptides in stomach; parasympathetic nerves
  • factors inhibiting hormone release: acid in stomach; somatostatin


  gastrin
• • chemical class: peptide
  • site of production: small intestine
  • stimuli for hormone release: amino acids, fatty acids in small intestine


  CCK
• • chemical class: peptide
  • site of production: small intestine
  • stimuli for hormone release: acid in small intestine


  secretin
• • chemical class: peptide
  • site of production: small intestine
  • stimuli for hormone release: glucose, fat in small intestine


  GIP (glucose-dependent insulinotropic peptide hormone)
• feedforward hormone stimulates insulin into the plasma after moving to the pancreas

  GIP
• phases of GI control (named where stimulus originates)

  1.) cephalic

  2.) gastric

  3.) intestinal
• cephalicphase


  stimuli is in your head, lots of feed-forward
• gastricphase


  stimuli is the presence of ingested material in the stomach
• intestinal phase


  stimuli is the presence of chyme in small intestine
• stimulated by sight, smell, taste, chewing, emotional states; increases secretory and contractile activity mainly by parasymp - feedforward


  cephalic phase
• stimulated by

  • stretch, acidity, amino acids, peptides

  mediated by

  • short and long reflexes
  • ^ motility, ^ secretion or change secretion
  • hormone gastrin


  gastric phase
• stimulated by

  • stretch, acidity, osmolarity, digestive products

  mediated by

  • short and long reflexes (neural and hormonal controls)
  • hormones:
  • secretin
  • CCK
  • GIP


  intestinal phase
• on plate/in cup

  food, nutrients, liquid
• in mouth/esophagus

  bolus
• in stomach/small intestine

  chyme
• in large intestine/rectum

  chyme/feces