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Harrison's Principles of Internal Medicine, 18e
| Part 14. Disorders of the Gastrointestinal System > Section 2. Liver and Biliary Tract Disease > |
Chapter 303. The Hyperbilirubinemias
Sections: Bilirubin Metabolism, Disorders of Bilirubin Metabolism Leading to Unconjugated Hyperbilirubinemia, Disorders of Bilirubin Metabolism Leading to Mixed or Predominantly Conjugated Hyperbilirubinemia, Further Readings.
Topics Discussed: hyperbilirubinemia.
Excerpt:"The details of bilirubin metabolism are presented in Chap. 42. However, the hyperbilirubinemias are best understood in terms of perturbations of specific aspects of bilirubin metabolism and transport, and these will be briefly reviewed here as depicted in Fig. 303-1.Following secretion into bile, conjugated bilirubin reaches the duodenum and passes down the gastrointestinal tract without reabsorption by the intestinal mucosa. An appreciable fraction is converted by bacterial metabolism in the gut to the water-soluble colorless compound urobilinogen. Urobilinogen undergoes enterohepatic cycling. Urobilinogen not taken up by the liver reaches the systemic circulation, from which some is cleared by the kidneys. Unconjugated bilirubin ordinarily does not reach the gut except in neonates or, by ill-defined alternative pathways, in the presence of severe unconjugated hyperbilirubinemia [e.g., Crigler-Najjar syndrome, type I (CN-I)]. Unconjugated bilirubin that reaches the gut is partly reabsorbed, amplifying any underlying hyperbilirubinemia. Recent reports suggest that oral administration of calcium phosphate with or without the lipase inhibitor orlistat may be an efficient means to interrupt bilirubin enterohepatic cycling to reduce serum bilirubin..."
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