GI Phys 4

• three functional regions of the stomach

  - fundus

  - body

  - antrum
• prevention of reflux


  lower esophageal sphincter
• flexible size, thin, weak, smooth

  fundus of the stomach
• secretes mucus, pepsinogen, and HCl


  body of the stomach
• mixing and grinding; secretes mucus, pepsinogen, and gastrin


  antrum of the stomach
• controls emptying


  pyloric sphincter
• first portion of small intestine

  duodenum
• which region in the stomach has thicker, stronger, and smooth ridges and folds?

  the body
• secrete "gastric juice"


  gastric pits
• _ cell types and _ secretions in the stomach

  6; 8
• juice + bolus =

  chyme
• mucus, bicarbonate secretion


  mucous cells
• acid, intrinsic factor secretion; secrete hydrochloric acid


  parietal cells = exocrine
• histamine secretion


  ECL = paracrine
• pepsinogen secretion; when activated turns into pepsin

  chief cells = exocrine
• somatostatin secretion


  endocrine = D cell
• gastrin secretion


  endocrine = G cell
• exocrine secretions into the stomach lumen, chyme

  acid, intrinsic factor, pepsinogen
• HCl production and secretion by parietal cells


  image:

  
• four factors regulating HCl secretion by parietal cells

  image:

  
• K+ leak channels into the stomach lumen allow the H+/K+ ATPase to happen; what happens in the stomach lumen after this?

  HCl forms
• the pH of blood leaving the stomach capillaries during a meal has an alkaline pH; why?

  HCO3- increases buffering capacity
• what factor inhibits H+ acid secretion?

  somatostatin from D cells
• which drugs treat excess acid production, heartburn, and GERD (gastroesophageal reflux disease)?

  - OTC antacid tablets/solution

  - histamine blockers

  - proton pump inhibitors
• • weakest drug
  • neutralizes HCl but does not inhibit further HCl production
  • TUMS, Rolaids, Peptobismol


  OTC antacid tablets/solution
• • middle drug
  • reduce effects of 2nd messenger cascade and reduce H+ acid secretion
  • Tagamet, Zantac

  Histamine blockers
• • strongest drug
  • inside the apical membrane lumen; inhibits HCl production
  • Prilosec, Nexium

  Proton pump inhibitors
• gastric phase stimuli:


  luminal distension

  amino acids & peptides
• presence of nutrients in the small intestine has an inhibitory effect on BOTH stomach secretion and motility
• stimuli of cephalic phase


  sight, smell, taste, chewing
• stimuli of the gastric phase


  - distension

  - ^ peptides

  - decreased H+ concentration
• stimuli of the intestinal phase

  - distension -> stretching of SI

  - ^ H+ concentration

  - ^ osmolarity

  - ^ nutrient concentrations
• pathway from the cephalic phase


  parasympathetic nerves to enteric nervous system
• pathway of the gastric phase


  long and short neural reflexes and direct stimulation of gastrin secretion
• pathway of intestinal phase


  long and short neural reflexes; secretin, CCK, and other duodenal hormones
• result of the cephalic and gastric phase pathways


  ^ HCl secretion
• result of intestinal phase pathway


  decreased HCl secretion
• regulation of parietal cell secretion


  image:

  
• pepsinogen is an ________ zymogen

  inactive
• pepsin activates pesinogen


  autocatalysis