Degradation of Heme
Start with the big picture
Heme oxygenase initiates breakdown of heme, producing biliverdin while releasing iron and carbon monoxide. Biliverdin is reduced to unconjugated bilirubin, which travels in plasma bound to albumin. The liver takes up bilirubin and uses UGT1A1 to conjugate it, increasing its water solubility; MRP2 then transports conjugated bilirubin into bile. In the intestine, bacteria deconjugate bilirubin and convert it to urobilinogen. Most proceeds toward stercobilin, which colors stool, while smaller amounts are recycled or excreted in urine as urobilin. The sequence also clarifies clinical distinctions: increased heme load can cause pre-hepatic jaundice, impaired hepatic handling can cause hepatic jaundice, and biliary obstruction can cause post-hepatic jaundice.
What you'll learn
- Trace heme breakdown from heme to biliverdin and unconjugated bilirubin.
- Explain how bilirubin is transported in plasma and handled by the liver.
- Describe bilirubin conjugation, biliary secretion, and intestinal processing.
- Relate urobilinogen products to stool and urine color.
- Distinguish major mechanisms underlying pre-hepatic, hepatic, and post-hepatic jaundice.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
