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[HAP-06] Gastrointestinal & Hepatobiliary Physiology: Parietal Cell Secretion, Enteric Nervous System & Liver Metabolism
HAP-06 • 1. Anatomy & PhysiologyLearning Objectives
Trace the three neurohumoral pathways stimulating gastric parietal cell acid secretion (Histamine H2 via cAMP, Acetylcholine M3 via Ca2+, Gastrin CCK2 via Ca2+) converging on H+/K+-ATPase.; Explain hepatobiliary bilirubin metabolism (unconjugated vs conjugated hyperbilirubinaemia), Child–Pugh scoring, and enterohepatic recycling.; Correlate intestinal SGLT1 sodium–glucose cotransport with the life-saving physiology of WHO Low-Osmolarity ORS ([5.18]).
Chapter Overview & Core Explanation
The digestive tract breaks down food and absorbs nutrients using acid in the stomach, bile and pancreatic enzymes in the small intestine, and specialized sugar-salt transporters in the gut lining that remain intact even during severe cholera or rotavirus diarrhoea.
Key Exam & Clinical Takeaways
- WHO Low-Osmolarity ORS ([5.18]) has a total osmolarity of 245 mOsm/L with an equimolar 75 mmol/L Sodium : 75 mmol/L Glucose ratio to drive brush-border SGLT1 water absorption.
- In hepatic encephalopathy, oral [5.21] Lactulose is fermented by colonic bacteria into lactic and acetic acids, lowering colonic pH to trap diffusible NH3 as non-absorbable ammonium ion (NH4+).