Red Blood Cell Destruction kau

1. Red blood cell Red blood cell
destructiondestruction

2. Recommended ReadingsRecommended Readings
Wills’ Biochemical basis of Medicine. Wills’ Biochemical basis of Medicine.
Chapter 25 Chapter 25
Lippincott’s illustrated reviews biochemistry. Lippincott’s illustrated reviews biochemistry.
Chapter 21Chapter 21

3. Learning objectivesLearning objectives
Know the main location and site of haem breakdownKnow the main location and site of haem breakdown
Outline the pathway for haem degradationOutline the pathway for haem degradation
Compare/contrast types of Plasma Bilirubin & types of Compare/contrast types of Plasma Bilirubin & types of
HyperbilirubinemiaHyperbilirubinemia
Understand the biochemical basis of different types of Understand the biochemical basis of different types of
jaundice.jaundice.

4. Content Content
Main location and site of haem breakdownMain location and site of haem breakdown
Pathway for haem degradationPathway for haem degradation
1.1.Formation of bilirubin in reticuloendothelial system Formation of bilirubin in reticuloendothelial system
2.2.Uptake, conjugation & secretion of bilirubin by liverUptake, conjugation & secretion of bilirubin by liver
3.3.Catabolism of bilirubin in the gutCatabolism of bilirubin in the gut
Types of Plasma BilirubinTypes of Plasma Bilirubin
Definition & types of HyperbilirubinemiaDefinition & types of Hyperbilirubinemia
Jaundice Jaundice
Definition &Definition &
Types & characteristics of each typeTypes & characteristics of each type
Physiological JaundicePhysiological Jaundice
Genetic causes of JaundiceGenetic causes of Jaundice

5. Degradation of hemeDegradation of heme
Red blood cells are degraded by the cells of the Red blood cells are degraded by the cells of the
reticuloendothelial system particularly in the liver and reticuloendothelial system particularly in the liver and
spleen after 120 days in the circulation (RBC life span)spleen after 120 days in the circulation (RBC life span)
Therefore, The principal sites of heme catabolism are Therefore, The principal sites of heme catabolism are
the spleen & the liverthe spleen & the liver
Bilirubin is the end product of heme catabolism:Bilirubin is the end product of heme catabolism:
75% from hemoglobin of old RBCs, 75% from hemoglobin of old RBCs,
the rest from hemoglobin of immature RBCs & from the rest from hemoglobin of immature RBCs & from
cytochromes from extra-erythroid tissuescytochromes from extra-erythroid tissues
250-350 mg bilirubin /day is produced in normal adults250-350 mg bilirubin /day is produced in normal adults

6. Heme catabolism is classified into 3 stages:Heme catabolism is classified into 3 stages:
2.2.Formation of bilirubin in reticuloendothelial Formation of bilirubin in reticuloendothelial
systemsystem (RES)(RES)
3.3.Uptake, conjugation and secretion of Uptake, conjugation and secretion of
bilirubin by the liverbilirubin by the liver
4.4.Catabolism of bilirubin in the gutCatabolism of bilirubin in the gut
Pathway for haem degradationPathway for haem degradation

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10. 2.2.Formation of bilirubin in reticuloendothelial Formation of bilirubin in reticuloendothelial
systemsystem (RES):(RES):
In reticuloendothelial system (RES), hemoglobin is degraded In reticuloendothelial system (RES), hemoglobin is degraded
into heme and globin.into heme and globin.
Globin is either degraded to amino acids or reused for Globin is either degraded to amino acids or reused for
synthesis of hemoglobin.synthesis of hemoglobin.
Heme is converted to biliverdin by the microsomal heme Heme is converted to biliverdin by the microsomal heme
oxygenase (a P450 cytochrom) using NADPH and Ooxygenase (a P450 cytochrom) using NADPH and O
22 . Ferric . Ferric
iron & carbon monoxide are released. iron & carbon monoxide are released.
Biliverdin is water soluble green pigmentBiliverdin is water soluble green pigment
Biliverdin is converted to bilirubin by biliverdin reductase. Biliverdin is converted to bilirubin by biliverdin reductase.
Bilirubin is water insoluble yellow pigmentBilirubin is water insoluble yellow pigment
Bilirubin is transported in blood to the liver carried by plasma Bilirubin is transported in blood to the liver carried by plasma
albumin (it is termed indirect or unconjugated bilirubin).albumin (it is termed indirect or unconjugated bilirubin).
•Certain drugs as salicylates & sulfonamides can displace Certain drugs as salicylates & sulfonamides can displace
bilirubin from albumin, allowing bilirubin to enter the CNS bilirubin from albumin, allowing bilirubin to enter the CNS
causing neural damage in infantscausing neural damage in infants

11. 1.1.Uptake, conjugation and secretion of bilirubin by Uptake, conjugation and secretion of bilirubin by
the liver:the liver:
a)a)Uptake of bilirubin:Uptake of bilirubin:
-Bilirubin leaves albumin & is taken by the hepatocytes Bilirubin leaves albumin & is taken by the hepatocytes
-Hepatic uptake of bilirubin is mediated by a carrier, & may Hepatic uptake of bilirubin is mediated by a carrier, & may
be competitively inhibited by other organic anionsbe competitively inhibited by other organic anions
b)b)Synthesis of bilirubin-diglucuronide (Conjugation):Synthesis of bilirubin-diglucuronide (Conjugation):

-By UDP glucuronyl transferase enzyme, bilirubin is By UDP glucuronyl transferase enzyme, bilirubin is
conjugated with glucuronic acid, to form bilirubin conjugated with glucuronic acid, to form bilirubin
diglucuronide (it is termed direct or conjugated bilirubin diglucuronide (it is termed direct or conjugated bilirubin
& it is water soluble) & it is water soluble)
-UDP-glucuronate acts as donor for glucuronate group to UDP-glucuronate acts as donor for glucuronate group to
form bilirubin monoglucuronide then bilirubin form bilirubin monoglucuronide then bilirubin
diglucuronidediglucuronide
c)c)Conjugated bilirubin is actively secreted by hepatocyte Conjugated bilirubin is actively secreted by hepatocyte
into the biliary canaliculiinto the biliary canaliculi (with(with bile) to small intestinebile) to small intestine
-Secreation is the rate limiting step in bilirubin metabolismSecreation is the rate limiting step in bilirubin metabolism

12. 1.1.Catabolism of bilirubin in the gut:Catabolism of bilirubin in the gut:
a)a)Conjugated bilirubin is converted by Conjugated bilirubin is converted by bacteria to urobilinogenbacteria to urobilinogen: :
-Conjugated bilirubin is deconjugated and reduced by Conjugated bilirubin is deconjugated and reduced by
intestinal bacteria forming urobilinogen.intestinal bacteria forming urobilinogen.
b)b)Most of urobilinogen is oxidized in colon to a brown pigment, Most of urobilinogen is oxidized in colon to a brown pigment,
urobilin urobilin (stercobilin(stercobilin)), which , which is excreted in fecesis excreted in feces giving feces its giving feces its
color. color.

d)d)Some urobilinogenSome urobilinogen (water soluble) is absorbed from gut into (water soluble) is absorbed from gut into
portal blood and re-excreted by liver in bile (enterohepatic portal blood and re-excreted by liver in bile (enterohepatic
circulation). circulation).
f)f)Traces of this urobilinogen reach the systemic blood & are Traces of this urobilinogen reach the systemic blood & are
excreated by kidneys in urineexcreated by kidneys in urine

14. Plasma Bilirubin
Normal plasma bilirubin level is <1 mg/dL
(<17 μmol/L)
Plasma bilirubin is present in 2 forms:
Unconjugated bilirubin (Indirect bilirubin)
Conjugated bilirubin (Direct bilirubin)

15. Unconjugated bilirubin (Indirect bilirubin)
Main bilirubin present in plasma normally
Water insoluble
Transported in blood as Bilirubin-albumin complex
Not excreted in urine
Increases in blood in cases of:
•Hemolysis
•Liver disease: liver fails to uptake or conjugate it.
Termed Indirect bilirubin because its estimation by
van den Bergh reaction needs addition of methanol
to react with the diazo reagent

16. Conjugated bilirubin (direct bilirubin)
Bilirubin-diglucuronide which escapes from the liver
to the systemic blood
Water-soluble
Excreted in urine:
Bilirubinuria is due to conjugated bilirubin and is
always pathological
Increases in blood in cases of:
•Liver disease: liver fails to secrete bilirubin
•Obstruction in the biliary system
Termed direct bilirubin because it reacts directly with
the diazo reagent of van den Bergh

17. Hyperbilirubinemia
Increased plasma bilirubin level more than
1mg/dL (17 μmol/L)
According to the type of bilirubin increased in
plasma, hyperbilirubinemias are classified into 2
types:
Unconjugated hyperbilirubinemia
Conjugated hyperbilirubinemia
According to the underlying defect,
hyperbilirubinemias may be:
Unconjugated ,
Conjugated
Both

18. Unconjugated hyperbilirubinemia
High level of unconjugated bilirubin in blood.
Unconjugated bilirubin can cross the blood-brain
barrier & cause severe brain damage (kernicterus)
Unconjugated bilirubin is not excreted in urine
Causes:
Hemolysis
Immaturity of the enzyme of bilirubin conjugation in
neonates (physiological)
Genetic defect in the enzyme of bilirubin conjugation
Gilbert's syndrome

Crigler-Najjar syndrome
Most common causes are Hemolysis & Gilbert's
syndrome

19. Conjugated hyperbilirubinemia
High level of conjugated bilirubin in blood.
Due to leakage of conjugated bilirubin from hepatocytes or
biliary system into blood
Conjugated bilirubin is water soluble, so it is excreted in urine
and darkens urine color to deep orange brown
Causes:
Biliarry obstruction
Decreased hepatic secretion of conjugated bilirubin
Dubin-Johnson Syndrome
Unknown cause
Rotor’s Syndrome.
Most common cause is biliary obstruction

20. JaundiceJaundice
Jaundice is clinically seen as yellow color of skin, Jaundice is clinically seen as yellow color of skin,
nail beds & sclera (due to deposition of bilirubin) nail beds & sclera (due to deposition of bilirubin)
when plasma bilirubin concentration exceeds when plasma bilirubin concentration exceeds
3 mg/dL (50 μmol/L) due to 3 mg/dL (50 μmol/L) due to
imbalance between bilirubin production and imbalance between bilirubin production and
excretion.excretion.
Types of jaundice are: Types of jaundice are:
Prehepatic (hemolytic) Prehepatic (hemolytic)
HepaticHepatic
Posthepatic (obstructive) Posthepatic (obstructive)

21. Prehepatic (hemolytic) Prehepatic (hemolytic)
jaundice:jaundice:
Due to excess production of Due to excess production of
unconjugated bilirubin after unconjugated bilirubin after
hemolysis which exceeds the hemolysis which exceeds the
capacity of liver to conjugate it capacity of liver to conjugate it

Characterized by the following:Characterized by the following:
High levels of indirect High levels of indirect
(unconjugated) bilirubin in (unconjugated) bilirubin in
plasma i.e., Unconjugated plasma i.e., Unconjugated
hyperbilirubinemia hyperbilirubinemia
Dark urine caused by high levels Dark urine caused by high levels
of urobilinogen in urine of urobilinogen in urine
Dark stool caused by high levels Dark stool caused by high levels
of Fecal urobilinof Fecal urobilin

22. Posthepatic (obstructive) Posthepatic (obstructive)
jaundice jaundice
Due to biliary obstruction Due to biliary obstruction
Characterized by the following:Characterized by the following:
•High levels of direct (conjugated) High levels of direct (conjugated)
bilirubin in plasma i.e., conjugated bilirubin in plasma i.e., conjugated
hyperbilirubinemia hyperbilirubinemia
•Dark urine due to presence of Dark urine due to presence of
conjugated bilirubin. conjugated bilirubin.
•Urine urobilinogen is absent Urine urobilinogen is absent
•Very pale stool (white, clay) due to Very pale stool (white, clay) due to
absence of Fecal urobilinabsence of Fecal urobilin

23. Hepatic jaundice: Hepatic jaundice:
Due to hepatocyte dysfunction that Due to hepatocyte dysfunction that
cause impaired hepatic bilirubin cause impaired hepatic bilirubin
uptake, conjugation, or secretion: uptake, conjugation, or secretion:
•impaired uptake → increased impaired uptake → increased
unconjugated bilirubin in blood), unconjugated bilirubin in blood),
•impaired conjugation → decreased impaired conjugation → decreased
conjugated bilirubin formation in liver→ conjugated bilirubin formation in liver→
decreased urobilinogen formation in gut) decreased urobilinogen formation in gut)
•impaired secretion→increased conjugated impaired secretion→increased conjugated
bilirubin in blood & secretion in urine)bilirubin in blood & secretion in urine)
Characterized by the following: Characterized by the following:

•High levels of direct (conjugated) & High levels of direct (conjugated) &
indirect (unconjugated) bilirubin in indirect (unconjugated) bilirubin in
plasma i.e., conjugated & plasma i.e., conjugated &
Unconjugated hyperbilirubinemiaUnconjugated hyperbilirubinemia
•Dark urine due to the presence of Dark urine due to the presence of
conjugated bilirubin & urobilinogen conjugated bilirubin & urobilinogen
•Pale stool due to decreased Fecal Pale stool due to decreased Fecal
urobilinurobilin

24. increased

25. Neonatal (physiologic) jaundice:Neonatal (physiologic) jaundice:
Transient jaundice, common in neonates (50% of normal Transient jaundice, common in neonates (50% of normal
babies) particularly in premature infants babies) particularly in premature infants
Due to immaturity of the enzymes of bilirubin conjugation Due to immaturity of the enzymes of bilirubin conjugation
leading to unconjugated hyperbilirubinemialeading to unconjugated hyperbilirubinemia
Unconjugated bilirubin is toxic to the immature brain, it may Unconjugated bilirubin is toxic to the immature brain, it may
cause kernicterus cause kernicterus if it exceeds 20-25 mg/dl, if it exceeds 20-25 mg/dl,
kernicterus may result in mental retardation.kernicterus may result in mental retardation.
Treatment:Treatment:
to avoid kernicterus, if plasma bilirubin is too to avoid kernicterus, if plasma bilirubin is too
high:high:
•Phenobarbital: inducer for UDP-glucuronyl transferase Phenobarbital: inducer for UDP-glucuronyl transferase
•Phototherapy: converts bilirubin to more soluble derivatives Phototherapy: converts bilirubin to more soluble derivatives
that are easily excreted in bile (detoxifies bilirubin) that are easily excreted in bile (detoxifies bilirubin)
•Exchange blood transfusion to remove excess bilirubinExchange blood transfusion to remove excess bilirubin

26. Neonatal jaundice
phototherapy

27. Genetic causes of jaundiceGenetic causes of jaundice::
1.1.Gilbert's syndromeGilbert's syndrome


2.2.Crigler-Najjar syndromeCrigler-Najjar syndrome
3.3.Dubin-Johnson syndromeDubin-Johnson syndrome


4.4.Rotor's syndromeRotor's syndrome

28. Gilbert's syndromeGilbert's syndrome::

Affect up to 5% of population Affect up to 5% of population

Due to decreased conjugation of bilirubin & Due to decreased conjugation of bilirubin &
decreased uptake in some cases decreased uptake in some cases
Decreased conjugation of bilirubin is due to moderate Decreased conjugation of bilirubin is due to moderate
deficiency in UDP glucuronyl transferase activity deficiency in UDP glucuronyl transferase activity
Mild intermittent Mild intermittent unconjugated hyperbilirubinemiaunconjugated hyperbilirubinemia
which is noticed after fasting or infection which is noticed after fasting or infection
Harmless & asymptomatic → normal lifespanHarmless & asymptomatic → normal lifespan

29. Crigler-Najjar syndrome:Crigler-Najjar syndrome:

Type 1: Type 1:
•Severe Severe unconjugated hyperbilirubinemiaunconjugated hyperbilirubinemia at birth at birth
•Due to absence of conjugating enzymesDue to absence of conjugating enzymes
•Fatal due to kernicterusFatal due to kernicterus
•Partial response to phototherapy, non to Phenobarbital Partial response to phototherapy, non to Phenobarbital
Type 2:Type 2:
•Severe Severe unconjugated hyperbilirubinemiaunconjugated hyperbilirubinemia at birth at birth
•Due to partial defect of conjugating enzymes Due to partial defect of conjugating enzymes
•Survive to adulthoodSurvive to adulthood
•Good response to phototherapy & PhenobarbitalGood response to phototherapy & Phenobarbital

30. Dubin-Johnson syndrome:Dubin-Johnson syndrome:

Due to decreased hepatic secretion of conjugated Due to decreased hepatic secretion of conjugated
bilirubin bilirubin
Mild intermittent Mild intermittent conjugated hyperbilirubinemiaconjugated hyperbilirubinemia
Bilirubinuria Bilirubinuria
Normal lifespanNormal lifespan
Rotor's syndrome:Rotor's syndrome:

Cause is unknownCause is unknown

Mild intermittent Mild intermittent conjugated hyperbilirubinemiaconjugated hyperbilirubinemia
BilirubinuriaBilirubinuria
Normal lifespanNormal lifespan