2013B06 Briefly describe the breakdown of haemoglobin after red cell lysis.



·         Hb structure

·         In the RES

·         In the blood

·         In the liver

·         Enterohepatic circulation and excretion


Haemoglobin (Hb) structure:

·         Complex protein in RBCs

·         4 x haem (protoporphyrin with central Fe2+)

·         4 x globin (polypeptide, mostly α2β2 in adult)


In the reticulo-endothelial system (RES):

·         i.e. spleen red pulp, lymph nodes

·         RBC destroyed after ~ 120 days

·         Iron transported via ferritin to the bone marrow for re-incorporation

·         Globin degraded into amino acids for recycling

·         Protoporphyrin converted into bilirubin and excreted


In the blood:

·         Bilirubin is unconjugated, lipid-soluble

·         Diffuses into blood

·         Bound to albumin


In the liver:

·         BR taken up by hepatocyte

·         BR-DG (water-soluble) secreted into bile (NOTE: rate limiting step), enters intestine


Enterohepatic circulation and excretion:


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