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

 

List:

·         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: