Describe the physiology of bilirubin production, metabolism and clearance (70% of marks).

Outline the changes in blood and urine of the products of bilirubin metabolism with intra and post hepatobiliary disease (30% of marks).

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College Answer

A good answer for this question required the description of the pathway of bilirubin
production beginning with the breakdown of haemoglobin breakdown, then haem to
biliverdin by biliverdin reductase, biliverdin to bilirubin, bilirubin transported to liver bound
to plasma proteins, bilirubin monoglucuronide and diglucuronide by conjugation, secreted
into bile. Secretion into bile is dependent on active transport and is the first to be impaired in
inflammation of the liver. Bilirubis metabolized to stercobilinogen which is absorbed and
excreted in urine as urobilinogen. The remaining part to this question flowed on from this
point, ie Intrahepatic disease – increased conjugated bilirubin, urobilinogen and urine
bilirubin, Posthepatic disease – increased conjugated bilirubin, no urobilinogen, increased
urine bilirubin
Syllabus: I2c
Reference Text: Guyton Ch 70