Learn / Metabolism
Metabolic pathways
Every FMK pathway as a clickable map. Pick one pathway to hammer it — next step, enzyme, regulator, cofactor, and the facts that get tested (NADPH and who needs it, rate-limiting steps, deficiencies) — or set it to all pathways for a mixed drill. Every answer says which enzyme and which pathway.
Heme degradation & bilirubin (jaundice)
Bile → small intestine
Made from Bilirubin diglucuronide (conjugated, 'direct') by Canalicular excretion (MRP2, active transport) ★
Canalicular excretion (MRP2, active transport) ★ rate-limiting — Heme degradation & bilirubin (jaundice)
Deficiency: Dubin-Johnson syndrome (AR, MRP2) — benign conjugated hyperbilirubinemia with a grossly BLACK liver
Rate-limiting for hepatic bilirubin handling and the step most easily overwhelmed by obstruction — conjugated bilirubin backs up into blood and urine (dark urine, bilirubinuria).
Condition cards:Intrahepatic cholestasis →Dubin-Johnson syndrome →
Becomes Urobilinogen (colon, colourless) via Colonic bacteria (deconjugate & reduce)
Colonic bacteria (deconjugate & reduce) — Heme degradation & bilirubin (jaundice)
No bile reaching the gut (complete obstruction) → no urobilinogen → pale/clay-coloured (acholic) stool and absent urine urobilinogen.
Condition cards:Post-hepatic (obstructive) jaundice →Gallstone obstruction of the common bile duct (choledocholithiasis) →Pancreatic head cancer (malignant biliary obstruction) →Biliary atresia →Cholangiocarcinoma / primary sclerosing & biliary cholangitis →