Overview Product Source Action Regulation Notes Intrinsic Factor (IF) parietal cells (stomach-body) binds vitamin B12 mediates vitamin B12 absorption in terminal ileum autoimmune destruction of parietal cells causes (1) chronic gastritis and (2) pernicious anemia gastrectomy results in loss of parietal cells and loss of IF; patient requires B12 injection to prevent pernicious anemia Gastric Acid (HCl) parietal cells (stomach-body) ↓ stomach pH ↑ by vagal stimulation (ACh), gastrin, histamine ↓ by somatostatin, GIP, prostaglandin, secretin gastrinoma is a gastrin-secreting tumor that causes (1) continuous high levels of HCl secretion and (2) gastric ulcers Pepsin chief cells (stomach-body) protein digestion ↑ by vagal stimulation (ACh) chief cells secrete inactive pepsinogen, coverted to active pepsin at low pH HCO3- mucosal cells (stomach, duodenum, salivary glands, pancreas) Brunner's glands (duodenum) acid neutralization ↑ pancreatic secretion by secretin HCO3- is trapped in mucus that covers the gastric epithelium