Liver Physiology 5- Hepatic Metabolism Of Lipids

Question 1

Haemoglobin and biliverdin metabolism and excretion

Answer 1

1. RBC is ingested by macrophage (phagocyte, Kupffer cell, etc),
   To release Hb –> heme and globin (initiates heme catabolism)
2. Globin broken down into –>amino acids,used in bone marrow to form new RBC
3. Heme broken down into –>biliverdin,catalysed by hemeoxygenase, also liberating Fe2+ and CO2
4. Fe2+ is shuttled to –> bone marrow using plasma transferrin to be again incorporated → new RBC
5. Biliverdin converted to–>unconjugated bilirubin,catalysed by biliverdin reductase
6. Unconjugated bilirubin undergoes biotransformation (glucuronidation) to form bilirubin (occurs in the liver, detoxification)
7. Bilirubin can then dissolve in bile (more water soluble), and thus during digestive processes will end up in the small intestine, where the glucuronic acid is removed by bacteria to form urobilinogen
8. Urobilinogen is either recycled to liver via the ETC (enterohepatic system) or go to the kidneys forming urinary urobilin or oxidised by a different type of intestinal bacteria to form stercobilin
9. Stercobilin is excreted in faeces and is what gives the characteristic brown colour