14.6 Biochemistry: The bilirubin pathways and bile production Flashcards
What is the structure of bilirubin?
Open chain of four pyrrole rings (tetrapyrrole)
Where is bilirubin usually produced?
Spleen (as a breakdown product of blood)
_______ break down senescent _______ and transform the haem into _____ that normally reduces to free _____
Macrophages break down senescent erythrocytes and transform the haem into biliverdin that normally reduces to free bilirubin
What colour is bilirubin?
Yellow
Why is phototherapy used in jaundiced newborns?
Some double bonds in bilirubin isomerize (when exposed to light). E,E-isomer that results is more soluble than the Z,Z-isomer
What are the chemical forms of bilirubin?
Unconjugated (indirect), conjugated (direct)
What is bilirubin excreted as in bile?
Glucuronide (conjugated)
What does bilirubin at high levels in a newborn present as? What can this result in?
Kernicterus, is neurotoxic
What gives rise to jaundice?
Hyperbilirubinemia
What are 2 genetic causes of elevated levels of bilirubin?
Dubin-Johnston syndrome (failure to secrete diglucuronide) and Crigler-Najjar syndrome (failure to make diglucuronide)
Both are autosomal recessive
What are 3 (not necessarily genetic) causes of elevated levels of bilirubin?
Neonatal hyperbilirubinaemia, severe liver failure with cirrhosis, chronic/acute blockage of the bile duct (choledocholithiasis)
What is urobilinogen?
A colourless product of bilirubin excretion
Where is urobilinogen formed?
In the intestines by bacterial action
What is the enterohepatic urobilinogen cycle?
Some urobilinogen is reabsorbed from the gut and excreted by the kidney
