Hemoglobin Metabolism

• What percentage of the cytoplasmic content of RBCs does hemoglobin comprise?


  Approximately 95%
• What happens to free hemoglobin generated from hemolysis?


  It is rapidly salvaged to preserve iron
• What is the concentration of hemoglobin within RBCs?


  34 g/dL
• What is the molecular weight of hemoglobin?


  64,000 Daltons
• What are the main functions of hemoglobin?


  • Transport oxygen from lungs to tissues
  • Transport carbon dioxide from tissues to lungs
  • Contribute to acid-base balance
  • Transport nitric oxide for vascular regulation
• What is the structure of hemoglobin composed of?


  • Two pairs of polypeptide chains
  • Four heme groups
  • Can carry up to four oxygen molecules
• What is the most predominant hemoglobin in adults?


  HbA
• What percentage of HbA circulates as HbA1c?


  1. 6%
• What does heme consist of?


  A ring of carbon, hydrogen, nitrogen, and iron
• What happens when ferrous iron is oxidized to ferric state?


  It can no longer bind oxygen
• What is oxidized hemoglobin also known as?


  Methemoglobin
• What is the structure of globin in hemoglobin?


  • Two identical pairs of unlike polypeptides
  • Each chain designated by a Greek letter
• How many structural genes code for globin chains?


  Six
• Which chromosomes code for α and ζ globin chains?


  Short arm of chromosome 16
• Which chromosomes code for ε, γ, δ, and β globin chains?


  Short arm of chromosome 11
• What are the hemoglobin percentages in a newborn and a one-year-old?


  • Newborn: 80% HgbF, 20% HgbA1
  • 1 Year old: 95% HgbA1, 3.5% HgbA2, 1-2% HgbF
• What causes hypoxia?


  Insufficient hemoglobin quantity or defective molecule
• Where is hypoxia detected in the body?


  In the kidneys
• What do the kidneys produce in response to hypoxia?


  Erythropoietin to increase RBC production
• What are the reference intervals for hemoglobin concentration?


  • Individuals at high altitudes have higher hemoglobin
• What is the main function of hemoglobin in oxygen transport?


  To readily bind oxygen molecules in the lung
• How much oxygen is bound by each gram of hemoglobin?


  Approximately 1.34 mL
• What does the partial pressure of oxygen (PO2) represent?


  Amount of oxygen needed to saturate 50% of hemoglobin
• What does the hemoglobin-oxygen dissociation curve plot?

  • Percent oxygen saturation of hemoglobin versus PO2
• What shape is the hemoglobin-oxygen dissociation curve?

  Sigmoidal
• What does a left shift in the hemoglobin-oxygen dissociation curve indicate?

  Higher affinity for oxygen
• What does a right shift in the hemoglobin-oxygen dissociation curve indicate?

  Lower affinity for oxygen
• What triggers a left shift in the hemoglobin-oxygen dissociation curve?

  Multiple transfusions and lower body temperature
• What triggers a right shift in the hemoglobin-oxygen dissociation curve?

  Hypoxia and increased body temperature
• What is the P50 of Hb F?

  19-21 mmHg
• Why does Hb F have increased affinity for oxygen compared to Hb A?

  Weakened ability to bind 2,3-BPG
• What is the Bohr effect?

  A shift in the curve due to pH change
• What are the advantages and disadvantages of Hb F?

  Advantages:

  • High affinity for oxygen
  • More effective O2 withdrawal from maternal circulation

  
  

  Disadvantages:

  • Delivers O2 less readily to tissues
  • Compensated by increased RBC production
• What happens to RBC count and hemoglobin concentration in newborns compared to adults?

  Higher in newborns than in adults
• What happens to RBC count and hemoglobin concentration by 6 months of age?

  They decrease to normal physiologic levels
• What is the role of nitric oxide in the body?

  • Causes relaxation of vascular wall smooth muscle
  • Induces vasodilation
• How does nitric oxide bind in hemoglobin?

  It binds to cysteine in the beta chain
• What are dyshemoglobins?

  • Hemoglobins unable to transport oxygen
  • Includes methemoglobin, sulfhemoglobin, carboxyhemoglobin
• What is methemoglobin characterized by?

  Oxidized ferric (Fe3+) state of iron
• What color is methemoglobin and what happens if it accumulates?

  Brownish/bluish; causes cyanosis and hypoxia