--- module: 021-02 language: en chapter: 21 title: "Digestion, Absorption, Liver Function, and Nutrition" module_title: "Gut transport, portal integration, and failure of digestive reserve" source_sha256: 6370b601f922a9a3cec3ca5559e9d83aa8505a8447c293e596a7833ef2a57a56 --- # Gut transport, portal flow, and digestive reserve ## Motility as coordinated propulsion ### Slow waves set contraction windows ### Neural and chemical signals reach threshold ### Uncoordinated force worsens pain or obstruction ### Peristalsis: contract behind, relax ahead ### Segmentation improves mucosal contact ### Migrating complex clears between meals #### Loss favours bacterial overgrowth ### Emptying depends on particle size and feedback #### Symptoms track measured delay imperfectly ### Obstruction versus ileus #### Obstruction: transition point, proximal distension #### Ileus: diffuse propulsion failure #### Shared complications, different treatment ## Secretion and mucosal defence ### Proton pump is the final step #### Blocking it overcomes upstream signals #### Review long-term indication and duration ### Barrier: mucus, bicarbonate, prostaglandins, flow ### Anti-inflammatory drugs remove prostaglandin support ### Helicobacter pylori adds inflammation and ulcers ### Premature enzyme activation in pancreatitis #### Severe: capillary leak, necrosis, organ failure ## Absorption needs digestion and surface ### Digestion, bile, surface, transport, lymph, transit ### Coeliac disease damages proximal surface ### Bile-acid loss in two phases #### Modest: colonic secretion and diarrhoea #### Extensive: pool depletion and steatorrhoea #### Fatty acids bind calcium, oxalate stones ### Short bowel depends on remaining segments #### Colon in continuity salvages water and energy #### Parenteral support if autonomy insufficient ### Carbohydrate: osmoles, gas, acidic stool ### Protein loss through inflamed mucosa ## Diarrhoea as transport phenotype ### Osmotic improves with fasting ### Secretory persists during fasting ### Inflammatory adds blood and lost surface ### Rapid transit coexists with each ### Stool osmotic gap #### Low gap supports secretion #### High gap suggests unmeasured osmoles ### High volume: normal-gap acidosis, weakness ### Rehydration via sodium-glucose cotransport ## Portal circulation and zonation ### Portal blood brings nutrients, microbes, drugs ### Periportal: oxidation, gluconeogenesis, urea ### Centrilobular: drug enzymes, low-flow injury ### Portal hypertension from raised resistance #### Splanchnic vasodilation drives sodium retention #### Varices shunt ammonia and drugs #### Splenic congestion lowers platelets ### Ascites is more than low albumin #### Infection without perforation, sample urgently ## Liver tests as compartment signals ### Aminotransferases: membrane injury, not synthesis ### Alkaline phosphatase and others: ductal pattern ### Albumin and clotting reflect synthesis ### Falling enzymes: recovery or hepatocyte loss ### Failure: bilirubin, clotting, glucose, encephalopathy ### Encephalopathy from ammonia and inflammation #### Triggers: bleeding, infection, constipation, sedatives #### Reduce gut nitrogen, protect airway ## Nutrition as functional physiology ### Oedema and ascites conceal weight ### Strength and trajectory beat serum proteins ### Enteral feeding does not end aspiration #### Post-pyloric feeding misses oral secretions ### Parenteral nutrition needs precise composition #### Excess: hyperglycaemia, carbon dioxide, fatty liver #### Underfeeding perpetuates catabolism ### Monitor tolerance, not only delivered intake ### Microbiome ferments fibre to short-chain acids #### Composition rarely proves causation ## Integrated synthesis and red flags ### Name the failing process ### Then cause, consequence, trigger, recovery measure ### Ischaemia: symptoms exceed examination #### Normal lactate does not exclude it #### Do not delay imaging and surgical review ### Jaundice matched to bilirubin pathway #### Haemolysis raises unconjugated load #### Obstruction raises conjugated fraction #### Urinary bilirubin is the conjugated form