Hepatobiliary Physiology — Bilirubin

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2008B Q18

Exam question

Describe the physiology of bilirubin production, metabolism and clearance (70% of marks). Outline the changes in blood and urine of the products of bilirubin metabolism with intra and post hepatobiliary disease (30% of marks).

CICMWrecks answer

Master answer

RBC Destruction

Globin chains → AA’s
Haem → Biliverdin, Fe²⁺, CO

Biliverdin
- Haeme + Haem oxygenase → biliverdin
- Biliverdin + biliverdin reductase → bilirubin
- Free bilirubin + albumin → transported to hepatocytes
- Conjugated with glucuronide to ↑ water solubility
- Excreted to bile canniliculus
- Secreted to gut at D2 (duodenum)
- Intestinal flora hydrolyse and reduce → urobilinogen
- 3 fates:
  1. Gut bacteria form the dark pigment stercobilin, which is egested in the faeces
  2. Urobilinogen reabsorbed unchanged by the portal system and recycled by the liver
  3. Remainder is reabsorbed by the portal system and then excreted in the urine
Fe2+ → oxidised to Fe3+ → recycled
CO (only endogenous source of CO)

Hepatic Disease:

Intrahepatic disease
- ↓’d conj billi secretion
  - ↑d plasma conjugated bilirubin
  - ↑ urobilinogen in stool
  - ↑ urine bilirubin,
Posthepatic disease (complete obstruction)
- ↑ conjugated bilirubin
- No urobilinogen in stool
- ↑ urine bilirubin

Gladwin 2016

Answer by Gladwin

Past papers

Exam appearances

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Exam	Exact exam wording	Candidate success
2008B Q18	Describe the physiology of bilirubin production, metabolism and clearance (70% of marks). Outline the changes in blood and urine of the products of bilirubin metabolism with intra and post hepatobiliary disease (30% of marks).	—