Heme Degradation And Jaundice Flashcards
What is jaundice?
Clinical sign characterized by yellowish discoloration of skin, mucous membranes, sclera, and nail beds.
• Binding of bilirubin (Bile pigment) to connective tissue
• Occurs when serum bilirubin levels are greater than 2 mg/dL (hyperbilirubinemia
What are the stages of heme degradation?
- Formation of bilirubin from heme in reticuloendothelial system
- Transport of bilirubin in blood from RES to liver
- Uptake and conjugation in liver and excretion into bile
- Formation of urobilinogen in large intestine
- Formation of stercobilin and loss in feces
- Absorption of urobilinogen and excretion of urobilinogen in urine
What is the purpose of heme degradation?
- RBC lifespan about 120 days
• RES (Spleen, Kupffer cells of liver, macrophages) removes old RBC
• Hemoglobin = Heme + Globin (amino acid pool)
• Heme proteins like myoglobin and cytochromes release heme and forms bilirubin
Describe bilirubin formation in macrophages
• Heme oxygenase – Fe2+ released
– Porphyrin ring cleaved
– CO formed
– Biliverdin: Green pigment
• Biliverdin reductase
– Bilirubin (bile pigment): Orange- yellow colo
Explain the transport of bilirubin in blood to liver
- Unconjugated (NOT water soluble)
- Binds albumin for transport in blood
- Albumin binding prevents excretion in urine
• Drugs (salicylates, sulfonamides) displace
bilirubin from albumin
• Administration of drugs displaces bilirubin
from albumin and free unconjugated bilirubin crosses blood-brain barrier and cause kernicterus in infants
Explain the uptake of bilirubin by liver
• Unconjugated bilirubin enters liver by specific transporters on hepatocyte
Describe the conjugation of bilirubin in the liver
- Bilirubin converted to conjugated bilirubin (more water soluble)
- Addition of two molecules of glucuronic acid
- Enzyme: Microsomal UDP-glucuronyl transferase
- Induction by phenobarbital
Explain the secretion of conjugated bilirubin into bile
- Conjugated bilirubin actively transported into bile canaliculus by specific ABC transporters
- Conjugated bilirubin (Bile pigment) contributes to the Orange-yellow color of bile
- Bile released into second part of duodenum via common bile duct
Explain formation of urobillinogen in large. Intestine
• Conjugated bilirubin acted upon by bacterial flora in large intestine
• Undergoes deconjugation and…
Urobilinogen
converted to urobilinogen
(colorless)
• Urobilinogen not same as unconjugated bilirubin
Explain formation of stercobilin and loss in feces
- Bacterial action on urobilinogen forms stercobilin (brown color)
- Lost in feces and gives feces a characteristic brown color
- Some urobilinogen is absorbed from the gut into portal blood
Describe the absorption of urobillinogen and excretion of urobillinogen in urine
- 10% of urobilinogen in intestine absorbed into portal blood and goes to liver
- Small part re-excreted into bile canaliculus
- Majority of urobilinogen lost as urine urobilin (light yellow color)
- Urobilinogen and Urobilin synonymous
What is jaundice? What are the findings of jaundice?
• Yellowish discoloration of skin, mucous membranes, sclera, nail beds
• Bilirubin (Bile pigment) binds connective tissue
• Serum bilirubin levels more than 2 mg/dL
(hyperbilirubinemia)
• Normal total serum bilirubin: <1mg/dL; – Unconjugated (80%)
– Conjugated (20%)
• Normal URINE findings:
– Bilirubin absent;
– Urobilinogen (urobilin) is present (Dipstick)
What are the lab tests to detect type of bilirubin?
• Van den Bergh reaction
– Bilirubin with diazo reagent forms red colored complex
• Conjugated bilirubin (direct reacting) water soluble reacts rapidly with reagent
• Total bilirubin
– Reaction in presence of methanol, both conjugated and unconjugated bilirubin react
• Unconjugated bilirubin (indirect reacting) water insoluble and reacts in presence of methanol
• Total bilirubin – Direct (conjugated) bilirubin = Indirect (unconjugated) bilirubin
What are the classifications of jaundice?
Classification of jaundice (hyperbilirubinemia)
• Based on etiology (cause)
– Prehepatic (hemolytic) jaundice: Increased breakdown of RBCs (Decreased lifespan of RBC)
– Hepatic jaundice: Decreased conjugation capacity of liver and decreased excretion of bilirubin
– Posthepatic (obstructive/ cholestatic) jaundice: Decreased excretion of bilirubin via bile
Describe prehepatic (hemolyric) jaundice
Lab findings: serum total bilirubin: increased alot
Serum conjugated bilirubin: N
Serum unconjugated bilirubin: increased alot
Urine bilirubin: absent (acholuric jaundice)
Urine urobilinogrn: increased
What are the changes in bilirubin metabolism in hepatic jaundice
- RBC Breakdown (hemolysis)
- Formation of bilirubin
- Increased unconjugated bilirubin in circulation (albumin-bound)
- Decreased uptake and conjugation of bilirubin by liver & decreased secretion of conjugated bilirubin (increased conjugated bilirubin in circulation due to regurgitation, leading to loss of bilirubin in urine)
- Decreased excretion of conjugated bilirubin into bile and intestine
- Decreased formation of urobilinogen in intestine
- This leads to decreased excretion of urobilin in urine. Decreased stercobilin in feces
What are the changes in bilirubin metabolism in hepatic jaundice
- RBC Breakdown (hemolysis)
- Formation of bilirubin
- Increased unconjugated bilirubin in circulation (albumin-bound)
- Decreased uptake and conjugation of bilirubin by liver & decreased secretion of conjugated bilirubin (increased conjugated bilirubin in circulation due to regurgitation, leading to loss of bilirubin in urine)
- Decreased excretion of conjugated bilirubin into bile and intestine
- Decreased formation of urobilinogen in intestine
- This leads to decreased excretion of urobilin in urine. Decreased stercobilin in feces
Describe the changes in bilirubin metabolism in preheoatic (hemoltyic ) jsundice
- Increased RBC breakdown (hemolysis)
- Increased bilirubin formation
- Increased unconjugated bilirubin in circulation (albumin- bound) – Exceeds conjugation capacity of liver
- Increased bilirubin uptake and conjugation by liver
- Increased excretion of conjugated bilirubin into bile and intestine
- Increased formation of urobilinogen in intestine
- Increased urobilin in urine+ increased stercobilin in urine
What are the laboratory findings in hepatic jaundice?
- Serum conjugated bilirubin elevated due to reduced secretion of conjugated bilirubin into biliary canaliculus. Conjugated bilirubin regurgitates into plasma
- Serum unconjugated bilirubin elevated: Hepatocellular damage results in lower uptake of unconjugated bilirubin. Also, liver damage reduces conjugating capacity of liver.
- Additional lab findings: Elevated serum ALT and AST levels (refer Liver function tests lecture)
What are the lab findings of posthepatic (obstructivr/cholestatic) jaundice?
- Serum conjugated bilirubin elevated as excretion into biliary canaliculus is reduced due to biliary obstruction. Conjugated bilirubin regurgitates into plasma (Cannot be excreted into bile)
- Urine urobilinogen absent/ low (indicates extent of obstruction)
- Additional lab findings: Elevated serum ALP and GGT levels (refer Liver function tests lecture)
What are the physiological jaundice in newborn?
• Reasons for Jaundice in newborn
– Low hepatic UDP-glucuronyl transferase (premature infants more risk)
• Jaundice 2nd or 3rd day clears by 7th day
• Which type of bilirubin is increased??
Unconjugated bilirubin
- Phototherapy (about 450nm)
- Light converts bilirubin to polar, water-soluble isomers (basis of bili-lights)
What is the significance of Kernicterus?
• Serum bilirubin >25mg/dL
• Unconjugated bilirubin (Lipid soluble) crosses
blood-brain barrier (not developed) deposits in
basal ganglia of brain ‘kernicterus’
• Hypoalbuminemia, low pH, drugs (salicylates,
sulfonamides) increase unconjugated unbound
bilirubin (Increase risk of kernicterus)
• Lethargy, altered muscle tone, high pitched cry
• Severe permanent neurologic symptoms
(choreoathetosis, spasticity, muscular rigidity, ataxia, intellectual impairment)
What syndromes lead to inherited unconjugated hyper bilirubinemia?
- Crigler-Najjar syndromes I and II, Gilbert syndrome
- Varying deficiency of bilirubin UDP-glucuronyl transferase • Unconjugated hyperbilirubinemia
- Crigler-Najjar syndrome I
- Most severe; Very low enzyme activity (<5%)
- Jaundice in neonate or infancy
- Serum bilirubin levels up to 50 mg/dL (Unconjugated)
- Kernicterus and developmental delay
- Daily phototherapy, exchange transfusion to prevent kernicterus • Do NOT respond to phenobarbital
- Usually fatal (if not treated) due to kernicterus
Explain arias syndrome
• Crigler-Najjar syndrome II (Arias syndrome)
– Lower activity of bilirubin glucuronyl transferase (10-20%)
– Jaundice, but less severe than type I (serum unconjugated bilirubin levels 6-22mg/dL)
– Respond to phenobarbital (induces enzyme)
– Regular phototherapy in patients with high bilirubin levels
What is Gilbert syndrome?
Inherited unconjugated hyperbilirubinemia
• Gilbert syndrome
– Present in 3-7% of population
– Adolescents and young adults
– Mild jaundice (2-5 mg/dL) following illness or stress or starvation – Bilirubin UDP-glucuronyl transferase activity 50% of normal
– Mild increase in unconjugated bilirubin
– Normal AST, ALT and ALP levels
What is Dubin-Johnson syndrome?
• Dubin-Johnson syndrome
– Inherited deficiency of ABC transporter (secretes conjugated bilirubin into biliary canaliculus)
– Adolescents and young adults
– Elevated conjugated (direct) bilirubin – Normal AST, ALT and ALP levels
