2. Catabolism of heme
Heme
Bile pigments ( Bilirubin and Biliverdin)
Sites
Reticulo-
endothelial cells of
liver, spleen and
bone marrow.
Sources
• Senescent RBC’s (80%)
• Other heme containing proteins
(Myoglobin, cytochromes) (10%)
• Ineffective erythropoiesis (10%)
Heme degraded
per day – 6gm
3. Steps of Heme degradation
Formation of bilirubin
Uptake of bilirubin by liver
Conjugation of bilirubin
Fate of bilirubin
• Secretion of bilirubin into bile
• Formation of urobilins in the intestine
• Excretion in urine and stool
4. Formation of Bilirubin
Heme
Heme
oxygenase
O2, NADPH +
H+
NADP+
Fe3+, CO
Biliverdin
Biliverdin
reductase
NADPH + H+
NADP+
Bilirubin
Alb Alb
Alb
Alb
Bil
Alb
RBC
Bilirubin-Albumin
Complex
Macrophage
FORMATION OF BILIRUBIN
5. UPTAKE & CONJUGATION OF BILIRUBIN IN LIVER
Alb Bil
Bilirubin
Bilirubin
diglucuronide
Liver
Intestine
Bile
Rate limiting step
Mediated by Multispecific Organ Anion
Transporter (MOAT)
Induced by phenobarbitone
Bilirubin-glucuronyl
transferase
2 UDP-
glucuronic
acid
2 UDP