Liver Physiology and Bilirubin Metabolism
Key facts on hepatic blood supply, zonation, the liver's metabolic, synthetic and excretory roles, and the bilirubin pathway.
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Questions Covered in This Set
11 cards to master
What is the liver's dual blood supply and proportions?
~75% from the portal vein (nutrient-rich, oxygen-poor, draining gut/spleen/pancreas) and ~25% from the hepatic artery (oxygen-rich).
What is first-pass metabolism and one clinical consequence?
Orally absorbed drugs pass through the liver via the portal vein before reaching systemic circulation, so oral doses are larger than IV; drugs like glyceryl trinitrate are given sublingually to bypass it.
What do Zone 1 (periportal) hepatocytes do, and what injures them?
Oxygen-rich: gluconeogenesis, β-oxidation, urea synthesis. Damaged first by viral hepatitis and ingested toxins.
What do Zone 3 (pericentral) hepatocytes do, and what injures them?
Hypoxic, rich in cytochrome P450: drug metabolism, glycolysis, lipogenesis. Damaged first by ischaemia/shock and paracetamol toxicity.
Contrast Phase I and Phase II drug metabolism.
Phase I: CYP450 oxidation/reduction/hydrolysis. Phase II: conjugation with glucuronide, sulphate or glutathione — both make lipophilic molecules water-soluble and excretable.
Why is PT/INR the earliest marker of acute liver failure?
Factor VII has the shortest half-life (~4–6 h), so its loss prolongs PT/INR quickly; albumin (t½ ~20 days) only falls in chronic disease.
Which clotting factor is NOT made by the liver?
Von Willebrand factor (made by endothelium/platelets); the liver makes all the others, including vitamin-K-dependent II, VII, IX, X, protein C and S.
Describe the enterohepatic circulation of bile acids.
~95% of bile acids are reabsorbed in the terminal ileum and returned to the liver via the portal vein, recycling the pool 6–10 times daily; ileal loss causes bile-acid diarrhoea and gallstones.
Outline the enzymatic steps of bilirubin production.
Splenic macrophages break down senescent RBCs: haem → (haem oxygenase) → biliverdin + CO + Fe → (biliverdin reductase) → unconjugated bilirubin (~250–350 mg/day).
Why does unconjugated hyperbilirubinaemia cause jaundice without dark urine?
Unconjugated bilirubin is water-insoluble and travels bound to albumin, so it is not filtered by the kidney — jaundice is acholuric.
How does the liver handle ammonia?
Ammonia from gut bacteria and amino-acid deamination is converted to urea via the urea cycle (mainly Zone 1 hepatocytes).
