Bilirubin metabolism

Question 1

What is bilirubin

Answer 1

Yellow pigment produced through the breakdown of red blood cells - known as haemolysis

Question 2

Describe unconjugated bilirubin

Answer 2

Insoluble in water

Can only travel in the bloodstream if bound to albumin

Cannot be directly excreted from the body

Question 3

Describe conjugated bilirubin

Answer 3

Water soluble

Allows it to travel through the blood stream without requiring transport proteins like albumin

Can be excreted out of the body

Question 4

Describe the creation of bilirubin

Answer 4

Reticuloendothelial cells - macrophages

Take up red blood cells and metabolise the haemoglobin into haem and globin

Globin - broken down into amino acids - recycled

Haem - into iron and biliverdin - catalysed by haem oxygenase

Iron gets recycled

Biliverdin - reduced to create unconjugated bilirubin

Question 5

Describe the conjugation of bilirubin

Answer 5

Blood stream - unconjugated bilirubin binds to albumin to facilitate its transport to the liver

Liver - glucuronic acid + unconjugated bilirubin (glucocuronyl transferase)

= conjugated bilirubin (soluble)

Excreted into the duodenum in bile

Question 6

Describe bilirubin excretion

Answer 6

Colon - colonic bacteria deconjugate bilirubin - urobilinogen

80% - further oxidised by intestinal bacteria = stercobilin - excreted to faeces

20% - reabsorbed into blood stream (enterohepatic circulation) - recycled in the liver, some reaches kidney - urobilin - urine

Question 7

What are the three steps of bilirubin

Answer 7

Creation

Conjugation

Excretion