Bilirubin Metabolism and Excretion
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Bilirubin Metabolism and Excretion

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Questions and Answers

Which organ is the primary site of bilirubin metabolism and excretion?

  • Pancreas
  • Spleen
  • Liver (correct)
  • Kidney

    • What is the major conjugating group in the glucuronidation of bilirubin?

  • Glucose
  • Glucuronic acid (correct)
  • Glycine
  • Glutamic acid

    • Which enzyme catalyzes the glucuronidation of bilirubin?

  • Uridine diphospho-glucuronosyltransferase (UDPGT) (correct)
  • Heme oxygenase (HO-1)
  • Multidrug resistance protein 2 (MRP2)
  • Biliverdin reductase

    • What is the fate of conjugated bilirubin in the bile?

    <p>It is secreted into the intestinal tract</p> Signup and view all the answers

    What is the color of urobilinogen?

    <p>Colorless</p> Signup and view all the answers

    What is the color of stercobilin?

    <p>Brown</p> Signup and view all the answers

    What is the main clinical laboratory test used to measure serum bilirubin?

    <p>Van den Bergh assay</p> Signup and view all the answers

    Which type of bilirubin does the Van den Bergh assay measure?

    <p>Total bilirubin</p> Signup and view all the answers

    Which type of bilirubin is water-soluble (conjugated) and reacts rapidly in the Van den Bergh assay?

    <p>Conjugated bilirubin</p> Signup and view all the answers

    Which of the following organs is NOT involved in the removal of senescent erythrocytes from circulation?

    <p>Kidney</p> Signup and view all the answers

    Which organ is primarily responsible for the conversion of heme to bilirubin?

    <p>Liver</p> Signup and view all the answers

    What molecule is used in the catabolism of heme to yield bilirubin?

    <p>NADPH</p> Signup and view all the answers

    How is bilirubin normally processed by the liver?

    <p>Excreted in bile</p> Signup and view all the answers

    What is the role of UDP-glucuronyl-transferase in heme catabolism?

    <p>Conversion of heme to bilirubin</p> Signup and view all the answers

    How is conjugated bilirubin converted back into unconjugated bilirubin?

    <p>By intestinal bacteria</p> Signup and view all the answers

    What is the difference between direct and indirect measurements of bilirubin?

    <p>Direct measures the conjugated bilirubin, while indirect measures the total bilirubin</p> Signup and view all the answers

    What is the biochemical basis for problems associated with neonatal jaundice?

    <p>High levels of unconjugated bilirubin</p> Signup and view all the answers

    What are the genetically inherited disorders of hyperbilirubiemia mentioned in the text?

    <p>Gilbert &amp; Crigler-Najjar syndromes (type I and II)</p> Signup and view all the answers

    What effects do genetically inherited disorders of hyperbilirubiemia have on bilirubin lab values?

    <p>Increased bilirubin lab values</p> Signup and view all the answers

    What is the average source of bilirubin?

    <p>Senescent erythrocytes</p> Signup and view all the answers

    Which of the following is a characteristic of unconjugated (indirect) hyperbilirubinemia?

    <p>It is commonly seen in neonatal jaundice</p> Signup and view all the answers

    What is the most common treatment for neonatal jaundice?

    <p>Exposure to blue light</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Gilbert Syndrome?

    <p>It is characterized by decreased hepatic conjugation of bilirubin</p> Signup and view all the answers

    Which disorder is characterized by an inherited deficiency of the MRP2 transporter?

    <p>Dubin-Johnson Syndrome</p> Signup and view all the answers

    Which of the following is a characteristic of Dubin-Johnson Syndrome?

    <p>It is differentiated by urinary coproporphyrin excretion</p> Signup and view all the answers

    What is the underlying mechanism of non-bile acid organic anions in the liver?

    <p>Altered hepatobiliary transport</p> Signup and view all the answers

    Which of the following is a characteristic of obstructive jaundice?

    <p>It is a result of liver or gall bladder damage</p> Signup and view all the answers

    What is the genetic basis of Gilbert-Meulengracht syndrome?

    <p>UGT1A1</p> Signup and view all the answers

    What is the prognosis of Dubin-Johnson Syndrome?

    <p>Benign</p> Signup and view all the answers

    What is the characteristic feature of hepatocellular jaundice?

    <p>Impaired liver capacity to conjugate and excrete bilirubin</p> Signup and view all the answers

    Study Notes

    Bilirubin Metabolism and Excretion

    • The liver is the primary site of bilirubin metabolism and excretion.
    • Glucuronic acid is the major conjugating group in the glucuronidation of bilirubin.
    • The enzyme UDP-glucuronyl-transferase catalyzes the glucuronidation of bilirubin.
    • Conjugated bilirubin is excreted into the bile.

    Fate of Bilirubin in the Body

    • Urobilinogen is yellow.
    • Stercobilin is brown.
    • The main clinical laboratory test used to measure serum bilirubin is the Van den Bergh assay.
    • The Van den Bergh assay measures direct bilirubin.
    • Direct bilirubin is water-soluble (conjugated) and reacts rapidly in the Van den Bergh assay.

    Organ Involvement in Bilirubin Removal

    • The spleen is primarily responsible for the removal of senescent erythrocytes from circulation.
    • The liver is primarily responsible for the conversion of heme to bilirubin.

    Heme Catabolism

    • The molecule biliverdin is used in the catabolism of heme to yield bilirubin.
    • Bilirubin is normally processed by the liver through glucuronidation.

    Enzyme Role in Heme Catabolism

    • UDP-glucuronyl-transferase is involved in the conjugation of bilirubin.

    Conjugation and Deconjugation

    • Conjugated bilirubin is converted back into unconjugated bilirubin through deconjugation.

    Bilirubin Measurement

    • Direct bilirubin is measured directly using the Van den Bergh assay.
    • Indirect bilirubin is measured indirectly through the difference between total bilirubin and direct bilirubin.

    Neonatal Jaundice

    • The biochemical basis for problems associated with neonatal jaundice is the inability of the newborn to efficiently conjugate bilirubin.

    Genetic Disorders of Hyperbilirubinemia

    • The genetically inherited disorders of hyperbilirubiemia mentioned are Crigler-Najjar syndrome and Gilbert-Meulengracht syndrome.
    • These disorders affect bilirubin lab values, leading to elevated levels of bilirubin in the blood.

    Characteristics of Unconjugated Hyperbilirubinemia

    • Unconjugated (indirect) hyperbilirubinemia is characterized by elevated levels of indirect bilirubin in the blood.

    Treatment of Neonatal Jaundice

    • The most common treatment for neonatal jaundice is phototherapy.

    Characteristics of Gilbert Syndrome

    • Gilbert syndrome is NOT characterized by an inherited deficiency of the MRP2 transporter.
    • It is characterized by a mild, chronic unconjugated hyperbilirubinemia.

    Characteristics of Dubin-Johnson Syndrome

    • Dubin-Johnson syndrome is characterized by an inherited deficiency of the MRP2 transporter.
    • It is characterized by a conjugated hyperbilirubinemia.

    Characteristics of Obstructive Jaundice

    • Obstructive jaundice is characterized by a conjugated hyperbilirubinemia.

    Hepatocellular Jaundice

    • The characteristic feature of hepatocellular jaundice is a mixed pattern of unconjugated and conjugated hyperbilirubinemia.
    • The genetic basis of Gilbert-Meulengracht syndrome is a deficiency in the UDP-glucuronyl-transferase enzyme.
    • The prognosis of Dubin-Johnson syndrome is generally good.

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    Description

    Test your knowledge on bilirubin metabolism and excretion with this quiz by Vanessa De La Rosa, PhD. Learn about the catabolism of heme, the conversion of heme to bilirubin, and the liver's role in processing and excreting bilirubin. Gain a deeper understanding of this potential toxin and diagnostic marker for abnormal bilirubin metabolism.

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