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Questions and Answers
During which stage does hemoglobin synthesis begin?
What is the impact of the mutation in the beta chain of hemoglobin S?
How many molecules of O2 can a single hemoglobin molecule bind?
What is the primary composition of hemoglobin?
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In terms of oxygen affinity, how does fetal hemoglobin (Hb F) compare to adult hemoglobin (Hb A)?
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What happens to sickle cell hemoglobin at low partial oxygen pressure (PaO₂)?
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What causes jaundice as described in the provided content?
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How does sickle cell anemia provide a survival advantage in certain populations?
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Which factor results in a decreased affinity of hemoglobin for oxygen?
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What happens to hemoglobin in carbon monoxide poisoning?
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Which statement about bilirubin is correct?
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What is the final product of the conversion of porphyrin ring after iron is removed from heme?
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Which description applies to urobilinogen?
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How is bilirubin conjugated in the liver?
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What is the role of hemoglobin in buffering H⁺ in red blood cells?
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What is the effect of increased temperature on hemoglobin's affinity for oxygen?
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What would be expected in a laboratory finding for hemolytic jaundice?
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Which type of jaundice is characterized by an increase in conjugated bilirubin in the blood and urine?
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What is the normal range for total bilirubin in mg/dl?
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What laboratory finding is indicative of obstructive jaundice?
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Which situation would most likely increase the unconjugated bilirubin in blood?
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What could be a consequence of obstructive jaundice affecting bile flow?
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Physiological hyper-bilirubinaemia in newborns is mainly due to which factor?
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What is expected during a laboratory examination for urine in a case of hemolytic jaundice?
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Study Notes
Hemoglobin Structure and Synthesis
- Hemoglobin is an iron-containing protein found in red blood cells, responsible for oxygen transport.
- Hemoglobin synthesis begins in the proerythroblast and continues until the reticulocyte stage.
- Hemoglobin synthesis involves the formation of a porphyrin ring, which binds to iron to form heme.
- Four polypeptide chains, two alpha and two beta, combine with heme to form a hemoglobin molecule.
Hemoglobin Abnormalities
- Abnormal hemoglobin arises from gene mutations, often affecting the polypeptide chain.
- Sickle cell hemoglobin (Hb S) is a common example.
- Sickle cell hemoglobin arises from a substitution of valine for glutamate in the beta chain at position 6.
- Hb S has lower oxygen affinity and polymerizes under low oxygen tension, leading to red blood cell sickling, aggregation, and ischemia.
Factors Affecting Oxygen Binding to Hemoglobin
- The affinity of hemoglobin for oxygen is affected by various factors.
- The type of polypeptide chain determines oxygen affinity, with Hb F having higher affinity than Hb A.
- Carbon dioxide, hydrogen ions, temperature, and 2,3-diphosphoglycerate (2,3-DPG) concentration affect oxygen affinity.
- Increased carbon dioxide, hydrogen ions, temperature, and 2,3-DPG decrease oxygen affinity.
Carbaminohemoglobin
- Hemoglobin reversibly binds to carbon dioxide at the amino terminal of the polypeptide chain.
- Carbaminohemoglobin carries approximately 5% of carbon dioxide in the blood.
Methaemoglobin and Carboxyhemoglobin
- Methaemoglobin (Met Hb) is formed when the ferrous ion (Fe2+) in heme is oxidized to ferric ion (Fe3+) by oxidizing agents, preventing oxygen binding.
- Carboxyhemoglobin (Carboxy Hb) arises when carbon monoxide (CO) binds to hemoglobin.
- Carbon monoxide has a much higher affinity for hemoglobin than oxygen, displacing oxygen and rendering hemoglobin unable to carry oxygen.
Hemoglobin Breakdown and Bilirubin Formation
- When red blood cells are destroyed, hemoglobin is broken down.
- The polypeptide portion of hemoglobin is hydrolyzed into amino acids and released into circulation.
- Iron is removed from heme and released back into the plasma bound to transferrin.
- The porphyrin ring is converted to biliverdin, and subsequently to bilirubin.
Bilirubin Metabolism
- Unconjugated bilirubin is insoluble in water and binds to albumin in the plasma.
- In the liver, bilirubin conjugates with glucouronic acid, becoming water-soluble.
- Conjugated bilirubin is secreted into bile and excreted in feces.
- Conjugated bilirubin in bile is converted into stercobilinogen and urobilinogen by intestinal bacteria.
- Stercobilinogen provides the brown color to feces.
- Urobilinogen is colorless and partially reabsorbed into the portal blood.
- Most reabsorbed urobilinogen is re-excreted in bile, while a small percentage is secreted in urine.
Jaundice
- Jaundice refers to a yellow discoloration of the skin, sclera, and mucous membranes, caused by increased bilirubin levels in the blood.
- Jaundice can be classified into three types based on the cause: hemolytic, hepatic, and obstructive jaundice.
Hemolytic Jaundice
- Increased red blood cell destruction leads to increased levels of unconjugated bilirubin in the blood, which cannot be secreted in the urine.
- The liver conjugates and excretes bilirubin at a higher rate.
- Increased production of urobilinogen results in elevated urinary urobilinogen levels.
Hepatic Jaundice
- Liver dysfunction prevents conjugation of bilirubin, causing elevated unconjugated bilirubin levels in the blood and no bilirubin secretion in urine.
- Failure to secrete conjugated bilirubin into bile leads to increased conjugated bilirubin in the blood and urine.
- Conjugated bilirubin predominates in hepatocellular liver disease due to impaired biliary secretion caused by cell injury.
Obstructive Jaundice
- An obstruction to bile flow, such as a tumor or gallstone, prevents secreted conjugated bilirubin from reaching the intestines.
- Conjugated bilirubin leaks back into the bloodstream, resulting in high conjugated bilirubin levels in the blood and urine.
- Bile obstruction leads to pale stools due to absent stercobilinogen, fat malabsorption, and vitamin K deficiency.
- No urobilinogen is detected in urine.
Physiological Hyperbilirubinemia and Jaundice
- During fetal life, bilirubin crosses the placenta and is excreted by the mother's liver.
- The fetus's liver has limited bilirubin conjugation capacity in the first few days after birth.
- Mild unconjugated bilirubin accumulation occurs in newborns, which is usually transient.
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Description
Test your knowledge on the structure, synthesis, and abnormalities of hemoglobin. Explore how hemoglobin's function is influenced by genetic mutations and various factors affecting oxygen binding. This quiz covers crucial concepts crucial for understanding red blood cell physiology.
