Bilirubin Metabolism
Macrophage destruction RBC _ Splitting off of globin _ Amino acid pool
Heme (protoporphyrin + iron)
Biliverdin + carbon monoxide
Peripheral blood Unbound bilirubin + albumin (unconjugated bilirubin)
_ Uptake of UCB by carrier proteins
Liver _ Binding of UCB to ligandins
_ UDP-glucuronyl transferase
_ Canalicular transport system (rate-limiting step)
Bile CB in common bile duct
_ Stored and concentrated in gallbladder
Bowel CB in terminal ileum + colon
___ Bacterial reduction by b-glucuronidase
_ Further reduction by bacteria
Urobilinogen (colorless) oxidized to urobilin (color of stool)
Enterohepatic circulation (terminal ileum)