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: