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Heme Catabolism and Bilirubin
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Heme Catabolism and Bilirubin

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Questions and Answers

What percentage of heme is obtained from hemoglobin in the body?

  • 70%
  • 60%
  • 90%
  • 80% (correct)

    • Which of the following is NOT a source of heme in the body?

  • Myoglobin
  • Cytochrome
  • Chlorophyll (correct)
  • Hemoglobin

    • What is the organic compound found in heme?

  • Carotenoid
  • Porphyrin (correct)
  • Bilirubin
  • Chlorophyll

    • Which bodily substances contain bilirubin?

    <p>Bile, urine, and feces</p> Signup and view all the answers

    What is the term for the structure formed by the connection of four pyrrols rings in heme?

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

    How many pyrrols-like rings are present in bilirubin?

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

    What is the fate of hemoglobin in the spleen?

    <p>It is broken down into its constituent amino acids, iron, and heme</p> Signup and view all the answers

    What is the characteristic of unconjugated bilirubin in terms of solubility?

    <p>It is insoluble in water</p> Signup and view all the answers

    Where is unconjugated bilirubin formed?

    <p>In the spleen</p> Signup and view all the answers

    What is the role of albumin in relation to unconjugated bilirubin?

    <p>It binds to unconjugated bilirubin</p> Signup and view all the answers

    What is the product of heme ring breakdown?

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

    What is the purpose of conjugating bilirubin with glucouronic acid in the liver?

    <p>To make it more water-soluble and readily transported to bile</p> Signup and view all the answers

    What is the eventual destination of conjugated bilirubin in the body?

    <p>The duodenum for fat digestion</p> Signup and view all the answers

    What is the role of the bile duct in the conjugation process of bilirubin?

    <p>It transports conjugated bilirubin to the duodenum</p> Signup and view all the answers

    What is the result of the reaction between bilirubin and glucouronic acid in the liver?

    <p>The formation of bilirubin diglucuronides</p> Signup and view all the answers

    What is the primary function of enterohepatic circulation in the context of bile?

    <p>To allow for the reabsorption of bile from the intestine</p> Signup and view all the answers

    What is the primary contributor to the characteristic brown color of feces?

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

    What is the fate of conjugated bilirubin that remains in the large intestine?

    <p>It is metabolized by colonic bacteria</p> Signup and view all the answers

    What is the significance of elevated levels of bilirubin in blood and urine?

    <p>They indicate certain diseases</p> Signup and view all the answers

    How do indirect and direct bilirubin react with a reagent?

    <p>Indirect bilirubin reacts slowly, while direct bilirubin reacts rapidly</p> Signup and view all the answers

    What is the formula for total bilirubin?

    <p>T = D + ID</p> Signup and view all the answers

    What is the difference between the reaction of indirect bilirubin with a reagent and the reaction of direct bilirubin with a reagent?

    <p>Indirect bilirubin reacts slowly in methanol, while direct bilirubin reacts rapidly in solution</p> Signup and view all the answers

    What is the primary characteristic of jaundice?

    <p>Elevation of bilirubin in blood</p> Signup and view all the answers

    How is jaundice classified according to the cause?

    <p>Into three types: pre-hepatic, hepatic, and post-hepatic</p> Signup and view all the answers

    What is affected by the yellow discoloration in jaundice?

    <p>Skin, sclera, and mucous membrane</p> Signup and view all the answers

    What is the common factor among pre-hepatic, hepatic, and post-hepatic jaundice?

    <p>Elevation of bilirubin in blood</p> Signup and view all the answers

    What is the underlying cause of the yellow discoloration in jaundice?

    <p>Elevation of bilirubin in blood due to various causes</p> Signup and view all the answers

    What is the underlying cause of the elevated level of direct bilirubin in the blood and urine in post-hepatic obstructive jaundice?

    <p>Obstruction of the bile duct, preventing the passage of conjugated bilirubin into the intestine</p> Signup and view all the answers

    Which of the following laboratory tests would confirm a diagnosis of hemolytic anemia as a cause of jaundice?

    <p>Increased reticulocyte count and low haptoglobin levels</p> Signup and view all the answers

    What is the result of an increased rate of RBCs breakdown in the body?

    <p>Increased production of bilirubin in the liver, exceeding the liver's ability to convert it to the conjugated form</p> Signup and view all the answers

    What is the reason behind the high bilirubin level in newborns after 2-3 days?

    <p>The newborn's liver is not fully mature</p> Signup and view all the answers

    What is the consequence of very high unconjugated bilirubin levels?

    <p>It can cause brain damage</p> Signup and view all the answers

    Why is phototherapy used to treat high bilirubin levels?

    <p>It helps to break down bilirubin and convert it to the photo isomer form</p> Signup and view all the answers

    What is the characteristic of the liver in Dubin-Johnson syndrome?

    <p>It is dark brown in color due to the presence of a pigment similar to melanin</p> Signup and view all the answers

    What is the prognosis of Gilbert syndrome?

    <p>Excellent, with no treatment necessary</p> Signup and view all the answers

    What is the characteristic of bilirubin levels in Crigler-Najjar syndrome type 1?

    <p>Bilirubin levels are usually &gt; 20 mg/dl</p> Signup and view all the answers

    What is the characteristic of Crigler-Najjar syndrome type 2?

    <p>A moderate deficiency of glucuronyl transferase</p> Signup and view all the answers

    What is the prognosis of Crigler-Najjar syndrome type 1?

    <p>Poor, with a high risk of kernicterus</p> Signup and view all the answers

    What is the characteristic of bilirubin levels in patients with Gilbert syndrome?

    <p>Usually below 5mg/dl</p> Signup and view all the answers

    What is the difference between Dubin-Johnson syndrome and Rotor syndrome?

    <p>Presence of coarse dark-brown pigment in the liver</p> Signup and view all the answers

    What is the incidence of Gilbert syndrome in the population?

    <p>3-7% of the population</p> Signup and view all the answers

    What is the characteristic of Crigler-Najjar syndrome type 2?

    <p>Moderate deficiency of glucuronyl transferase</p> Signup and view all the answers

    What is the primary reason for performing a bilirubin test in newborns?

    <p>To diagnose jaundice</p> Signup and view all the answers

    How do you convert bilirubin levels from mg/dL to μmol/L?

    <p>Multiply by 17.1</p> Signup and view all the answers

    What is the effect of hemolyzed sample on bilirubin levels?

    <p>Increases indirect bilirubin levels</p> Signup and view all the answers

    What is the normal range of total bilirubin in adults in mg/dL?

    <p>0.3-1.2</p> Signup and view all the answers

    Study Notes

    Bilirubin and Jaundice

    • Bilirubin is a yellow pigment produced during heme catabolism, found in bile, urine, and feces.
    • Heme is composed of iron and an organic compound called porphyrin, and is found in hemoglobin, which is a principal component of RBCs.
    • 80% of heme in the body comes from hemoglobin in old RBCs, and 20% comes from other hemo-proteins such as cytochrome and myoglobin.

    Heme Catabolism

    • Heme is broken down into amino acids, iron, and bilirubin in the spleen.
    • Bilirubin is initially in an unconjugated (indirect) form, which is not soluble in water.
    • Unconjugated bilirubin is bound to albumin and carried to the liver, where it is conjugated with glucouronic acid to produce a water-soluble form.

    Conjugation and Enterohepatic Circulation

    • Conjugated bilirubin is excreted into bile through the bile duct, where it helps with fat digestion.
    • Most of the conjugated bilirubin is reabsorbed from the terminal ileum into the liver through the portal vein, a process known as enterohepatic circulation.
    • The remaining conjugated bilirubin is metabolized by colonic bacteria to produce urobilinogen, which can be further oxidized to urobilin and stercobilin, giving feces its brown color.

    Jaundice and Bilirubin Levels

    • Elevated levels of bilirubin in the blood and urine indicate certain diseases, such as jaundice (icterus).
    • Jaundice is a yellow discoloration of the skin, sclera, and mucous membranes due to elevated bilirubin levels.
    • Total bilirubin levels can be measured, and consist of both direct (conjugated) and indirect (unconjugated) bilirubin.

    Types of Jaundice

    • Pre-hepatic jaundice occurs due to increased RBC breakdown, and is characterized by an increased level of unconjugated bilirubin.
    • Hepatic jaundice occurs due to liver cell damage, and is characterized by a decreased ability to conjugate bilirubin.
    • Post-hepatic jaundice occurs due to obstruction of the bile duct, and is characterized by an increased level of conjugated bilirubin.

    Causes of Jaundice

    • Hemolytic anemia (e.g. thalassemia) can cause pre-hepatic jaundice.
    • Liver cell damage (e.g. hepatitis, cirrhosis) can cause hepatic jaundice.
    • Obstruction of the bile duct (e.g. gallstones, cancer) can cause post-hepatic jaundice.

    Hereditary Hyperbilirubinemia

    • Gilbert syndrome is a type of hereditary indirect hyperbilirubinemia caused by a mild deficiency of glucuronyl transferase.
    • Crigler-Najjar syndrome is a type of hereditary indirect hyperbilirubinemia caused by a severe or moderate deficiency of glucuronyl transferase.
    • Dubin-Johnson syndrome is a type of hereditary conjugated hyperbilirubinemia characterized by a chronic benign jaundice without pruritus or elevation of serum ALP.
    • Rotor syndrome is a type of hereditary conjugated hyperbilirubinemia similar to Dubin-Johnson syndrome.

    Bilirubin Test

    • The bilirubin test is performed to diagnose jaundice, liver or gallbladder problems, and to monitor newborns.
    • Normal bilirubin levels in adults are:
      • Total bilirubin: 0.3-1.2 mg/dL
      • Direct bilirubin: 0.1-0.4 mg/dL
      • Indirect bilirubin: 0.2-0.7 mg/dL

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    Description

    Learn about the breakdown of heme, a key component of hemoglobin, and its product bilirubin, which is present in bile, urine, and feces. Understand the sources of heme in the body, including hemoglobin and other hemo-proteins. Test your knowledge of this important biological process!

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