Anatomy

Red Blood Cell Physiology

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Red Blood Cell Physiology, Hemoglobin Production, Hemoglobin A2, Hemoglobin A, Hemoglobin F, Hemoglobin H, Hemoglobin Bart

  • See Also
  1. Iron
  2. Heme
  3. Bilirubin
  1. Primary Hormone regulator of RBC production
  2. Erythropoietin sources
    1. Fetus: Monocyte and Macrophage system in liver
    2. Postnatal: Peritubular cells in Kidney
  1. Hemoglobin produced until amounts to 90% of RBC mass
  2. Red Blood Cells start as Reticulocytes in Bone Marrow
    1. Reticulocytes are juvenile Red Blood Cells
      1. Nucleus extruded once RBC has matured
      2. Reticulocytes contain ribosome remnants
        1. Immature Reticulocytes contain most ribosomes
        2. Mature Reticulocytes contain least ribosomes
    2. Reticulocytes have 4 day life span
      1. Bone Marrow: 3 days (less if Erythropoietin high)
      2. Peripheral blood: 1 day
  3. Red Blood Cell survival
    1. Normal RBC: 120 days
    2. Abnormal RBC: May survive as little as 15 days
    3. Following transfusion: RBC survival 2-3 weeks
  1. Normal Hemoglobin is composed of 4 Protein-Heme complexes
    1. Two pairs of polypeptides (4 total)
      1. A pair of alpha chains are found in every normal Hemoglobin type
      2. A pair of other identical polypetides depending on Hemoglobin type (Gamma, Beta, Delta)
    2. Central iron-containing heme ring
      1. Attached to each of the 4 polypeptides
    3. Images
      1. hemoglobin.jpg
  2. Six types of normal Hemoglobin
    1. Embryonic
    2. Gower I
    3. Gower II
    4. Portland
    5. Fetal Hemoglobin (HbF): Alpha2-Gamma2
      1. Primary Hemoglobin in fetus
      2. Replaced by Adult Hemoglobin by age 6-12 months
    6. Adult Hemoglobin (HbA): Alpha2-Beta2
    7. Adult Hemoglobin (HbA2): Alpha2-Delta2
  3. Thalassemia related Hemoglobins
    1. Hemoglobin Bart's: Gamma4
      1. Seen in Alpha Thalassemia
    2. Hemoglobin H: Beta4
      1. Seen in Beta Thalassemia
  4. Sickle Cell Related Hemoglobin (Hb S)
    1. Hemoglobin S (Hb S) replaces the normal Hemoglobin A
      1. Deoxygenated Hemoglobin-S assumes a sickle shape deforming Red Blood Cells
      2. Deoxygenated HbS aggregates under low oxygen tension
        1. Molecules polymerize into a gelatinous network
        2. Deforms Red Blood Cells into a sickle shape
      3. Red cells with sickle shape are less deformable
        1. Results in microvascular Occlusion, ischemia and acidosis from sludging within arterioles
        2. Results in Hemolysis due to red cell fragility
    2. Chromosome 11 Mutation: Substitution of Amino AcidValine for Glutamic Acid
      1. Occurs at the 6th position of the Hemoglobin beta-chain
      2. Results in a "sticky" Hemoglobin that forms a rigid chain when deoxygenated
      3. Sickle cell gene is inherited in Autosomal Recessive pattern
        1. Heterozygotes have Sickle Cell Trait and Homozygotes have Sickle Cell Anemia
        2. Sickle Cell Trait is protective against Malaria, resulting in up to 40% trait Prevalence in some African regions
  5. Hemoglobin Metabolism
    1. Hemoglobin breakdown occurs when Red Blood Cells are destroyed (e.g. in Spleen at the end of their roughly 120 day life cycle)
    2. Hemoglobin is converted into Biliverdin and ultimately into Bilirubin for excretion
    3. See Bilirubin
  • References
  1. (1998) MMWR Morb Mortal Wkly Rep 47:1-29 [PubMed]
  • Resources
  1. MMWR Iron Deficiency Anemia Prevention
    1. http://www.cdc.gov/mmwr/pdf/rr/rr4703.pdf