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2. Bilirubin metabolism Physiology and Biochemistrywww.medicinemcq.com2www.medicinemcq.com 3. Questions Where is bilirubin formed? Which is the rate-limiting step in bilirubin metabolism? Why is bilirubin normally absent in the urine? Why does bilirubin appear in the urine in liver diseases? 3www.medicinemcq.com 4. Questions What is delta bilirubin? Where is the enzyme glucoronidase present? When is urobilinogen absent in urine? www.medicinemcq.com4www.medicinemcq.com 5. Bilirubin formation 80% of bilirubin Degradation of the hemoglobin 5Old or injured RBCswww.medicinemcq.com 6. 20% Breakdown of hemoproteins in the liver Catalases Cytochrome oxidases www.medicinemcq.com6www.medicinemcq.com 7. Ineffective erythropoiesis Destruction of newly formed erythrocytes 7Bone marrow itselfwww.medicinemcq.com 8. Major source of bilirubin Old RBCs 80%www.medicinemcq.com8www.medicinemcq.com 9. How much bilirubin is produced daily? 9250 to 300 mgwww.medicinemcq.com 10. Site of bilirubin synthesis Mononuclear phagocyte systemOlder term Reticuloendothelial systemConsists primarily of monocytes and macrophageswww.medicinemcq.com10www.medicinemcq.com 11. Mononuclear phagocyte system Spleen 11Largest unitLiver Bone marrowwww.medicinemcq.com 12. Macrophages Remove old erythrocytes from the circulation Lifespan of RBCs =120 daysHemoglobin broken down into Iron Globin Degraded and returned to the amino acid poolProtoporphyrin 12ReutilizedConverted to bilirubin and excreted from the body.www.medicinemcq.com 13. Synthesis of bilirubin HemeHeme ---------------------- Biliverdin ( green color) + CO + Iron oxygenase Biliverdin reductase Bilirubin (released into blood)www.medicinemcq.com13www.medicinemcq.com 14. Bilirubin Not soluble in water Potentially toxic 14Made soluble and less toxic by its reversible, binding to albuminwww.medicinemcq.com 15. Normal serum concentration of bilirubin < 1.5 mg/dL Almost entirely bilirubin (unconjugated) Tightly but reversibly bound to albuminFor rest of the slides, visit> Video Lectures > Liver15www.medicinemcq.com