Overview Product Source Action Regulation Notes Intrinsic Factor (IF) parietal cells (stomach-body) binds vitamin B12 mediate svitamin B12 absorption interminal 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