Red blood cell

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Basics

  • Red blood cells have a biconcave disc shape
    • This provides them the flexibility to negotiate the microcirculation
    • It also maximizes surface area for gas exchange
  • The primary carriers of gases for cellular respiration
  • Carry:
    • Oxygen
    • Carbon dioxide
    • Nitric oxide
  • These gases are bound to hemoglobin

Life cycle

  • Born in the marrow as a stem cell
    • This is a common predecessor for both white and red blood cells
  • Stem cells differentiate (under the influence of erythropoietin) into:
    • erythroblasts, normoblasts, reticulocytes, and finally erythrocytes.
  • During this progression:
    • size decreases
    • mitotic competence is lost
    • the size of the nucleus decreases (and it disappears completely)
    • Mitochondria and ribosomes are still present in reticulocytes, but are absent in mature red blood cells
  • Generate energy through the glycolytic and phosphogluconate pathways
  • Biconcave in appearance
  • Exist in circulation for ~120 days
  • Eventually removed by mononuclear phagocyte system
    • product of this catabolism is iron and amino acids (reutilized)
    • another product is bilirubin, which is excreted in bile
  • A mature red blood cell has no nucleus, mitochondria, or ribosomes, and uses the glycolytic and phosphogluconate pathways for metabolic energy

Erythropoiesis

  • See Hematopoiesis
  • The normal life span of a red blood cell is 120 days
  • 1% of the RBC pool is replaced daily
  • Production is increased in response to decreased tissue oxygenation
  • The major growth factor is erythropoietin
  • produced by peritubular cells in the kidney

Anemia

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