Metabolism - Recirculation
Bilirubin metabolism
Enteric recirculation
After excretion into the bile, conjugated bilirubin enters the intestinal lumen. In the adult, the normal GI tract bacterial flora act on it by various reduction and oxygenation reactions to form a family of related compounds known as urobilinoids. These include urobilin, urobilinogen, stercobilinogen and stercobilin. The latter is excreted in the stool giving it its characteristic pigmentation. Some urobilinogen is reabsorbed into the portal circulation and subsequently excreted in the urine, imparting to it its characteristic color.Under normal circumstances in the non-neonate, the conversion of bilirubin in the gut to urobilinoids prevents its reabsorption, so there is little to no enteric recirculation of bilirubin. However, this is not the case in the newborn where there is an active and extensive enterohepatic recirculation of bilirubin. This is discussed fully in the section on physiologic jaundice. Return to top of page