Overview Gastric secretion cells of gastric mucosa secrete gastric juice composed of hydrochloric acid (HCl), pepsinogen, intrinsic factor (IF), and mucus login to view 3 more bullets Gastric Glands Oxyntic glands body of stomach contains oxyntic glands oxyntic glands empty secretory products via ducts into lumen of stomach login to view 1 more bullet oxyntic glands contain parietal cells and chief cells login to view 2 more bullets Pyloric glands antrum of stomach contains pyloric glands pyloric glands empty secretory products via ducts into lumen of stomach login to view 1 more bullet pyloric glands contain G cells and mucosal neck cells login to view 7 more bullets Gastric Parietal Cell Gastric Parietal Cell Parietal cell polarity apical membrane contains H+-K+ ATPase and Cl- channels basolateral membrane contains Na+-K+ ATPase and Cl-/HCO3- exchanger Parietal cell secretion parietal cells secrete HCl and IF into oxyntic ducts that empty into lumen of stomach HCl acidifies gastric contents 1 ≤ pH ≤ 2 login to view 2 more bullets Mechanism of HCl secretion aerobic metabolism of gastric parietal cell produces CO2 intracellularly, CO2 combines with H2O to form H2CO3, which dissociates into H+ and HCO3- CO2 + H2O → H2CO3 → H+ + HCO3- carbonic anhydrase catalyzes hydration of CO2 at apical membrane, H+ is secreted into lumen of stomach via H+-K+ ATPase H+ secretion inhibited by omeprazole, a proton pump inhibitor and an antacid at apical membrane, Cl- "follows" H+ and is secreted into lumen of stomach via Cl- channels at basolateral membrane, HCO3- is absorbed from cell into bloodstream via Cl-/HCO3-exchanger HCO3- moves out of cell and into bloodstream login to view 2 more bullets Cl- moves out of bloodstream and into cell Activation of HCl secretion stimuli smelling, tasting, and conditioned reflexes in anticipation of food login to view 2 more bullets distension of stomach login to view 2 more bullets presence of breakdown products of protein (small peptides and amino acids) login to view 2 more bullets vagal stimulation direct pathway login to view 5 more bullets indirect pathway login to view 3 more bullets atropine login to view 6 more bullets histamine histamine is released from enterochromaffin-like (ECL) cells in gastric mucosa histamine diffuses to nearby gastric parietal cells login to view 1 more bullet histamine binds H2 receptors coupled to Gs proteins on gastric parietal cells login to view 3 more bullets gastrin gastrin is released from G cells of antrum of stomach into systemic circulation login to view 1 more bullet gastrin is delivered back to stomach via systemic circulation login to view 1 more bullet gastrin stimulates HCl secretion via gastric parietal cells by 2 mechanisms login to view 7 more bullets Zollinger-Ellison syndrome login to view 5 more bullets Inhibition of HCl secretion occurs when chyme is propelled along gastrointestinal tract from stomach to duodenum of small intestine HCl is no longer required to activate pepsinogen zymogen to active pepsin enzyme ↓ pH gastric contents acidify (pH lowers) when chyme is propelled along gastrointestinal tract from stomach to duodenum of small intestine login to view 7 more bullets somatostatin somatostatin is secreted by D cells of gastric mucosa somatostatin binds receptors coupled to Gi proteins on gastric parietal cells login to view 2 more bullets somatostatin antagonizes stimulatory effect of histamine on HCl secretion prostaglandins prostaglandins bind receptors coupled to Gi proteins on gastric parietal cells login to view 2 more bullets prostaglandins antagonizes stimulatory effect of histamine on HCl secretion IF secretion IF is required for vitamin B12 absorption in ileum IF is only essential secretion of stomach IF deficiency causes pernicious anemia Gastric Chief Cell Chief cell function chief cells secrete pepsinogen into oxyntic ducts that empty into lumen of stomach pepsinogen is a zymogen (inactive enzyme) that must be activated through cleavage increased concentration of H+ in gastric contents provides the low pH signal low pH converts inactive pepsinogen zymogen to active pepsin enzyme login to view 1 more bullet activation of pepsinogen secretion stimuli vagal stimulation → ↑ pepsinogen secretion via chief cells ↑ H+ → ↑ pepsinogen secretion via chief cells