Advanced GI management requires the clinician to integrate pathophysiology with evidence-based pharmacotherapy and endoscopic or surgical treatment algorithms. Proton pump inhibitors (PPIs) irreversibly inhibit the hydrogen-potassium ATPase pump on gastric parietal cells, reducing basal and stimulated acid secretion by up to 90% — they are first-line therapy for GERD, peptic ulcer disease, and Zollinger-Ellison syndrome, but long-term use carries risks of Clostridium difficile infection, hypomagnesemia, and bone fracture. Inflammatory bowel disease management follows a step-up approach: 5-aminosalicylates for mild disease, corticosteroids for acute flares, immunomodulators (azathioprine, methotrexate) for steroid-sparing maintenance, and biologic agents (infliximab, adalimumab targeting TNF-alpha; vedolizumab targeting alpha-4-beta-7 integrin) for moderate-to-severe disease. Hepatic encephalopathy in cirrhosis results from ammonia accumulation due to portosystemic shunting and impaired hepatic urea cycle function, managed with lactulose (osmotic cathartic reducing ammonia absorption) and rifaximin (non-absorbable antibiotic reducing ammonia-producing gut bacteria).