In blood bilirubin is with -

Ans. is 'a' i.e., Protein Bilirubin metabolismo Bilirubin is the end product of heme degradation,o The heme is derived from -Senescent erythrocytes by mononuclear phagocytic system in the spleen, liver and bone marrow (major source).Tturnover of hemoproteins (e.g. cytochrome p.450).o Heme is oxidized to biliverdin by heme oxygenase.o Biliverdin is then reduced to bilirubin by biliverdin reductase,o Bilirubin is transported to liver in bound form with albumin,o There is carrier mediated uptake of bilirubin in the liver.o This bilirubin is conjugated with glucuronic acid by UDP glucuronyl transferase (UGT1 Al) to from conjugated bilirubin (bilirubin glucronides).o Conjugated bilirubin is excreted into bile.o Most of the conjugated bilirubin is deconjugated and degraded to urobilinogen.o The most of the urobilinogen is excreted in the feces.o Approximately 20% of the urobilinogen is reabsorbed in the ileum and colon and is returned to the liver, and promptly rexcreied into bile - Enterohepatic circulation,o The small amount that escapes this enterohepatic circulation is excreted in urine.