Erythropoiesis Simplified

Hemoglobin Switching mnemonics

1st to appear: Embryonic hemoglobin (Gower and Portland)

Switch from fetal hemoglobin to adult hemoglobin:Gamma goes, Beta becomes, Alpha always”

  • Fetal hemoglobin: α2γ2
  • Adult hemoglobin: α2β2
ζ chainα chain
ε chainHbE Gower 1HbE Gower 2
γ chainHbE Portland IHbF
β chainHbE Portland IIHbA
δ chainN/AHbA2

hemoglobin switching

Mnemonic for 4 sites of erythropoiesis

Young Liver Synthesizes The Blood”

  1. Yolk sac: 3-8 weeks
  2. Liver: 6-30 weeks
  3. Spleen and Thymus: 9-28 weeks
  4. Bone marrow: 28 weeks to adult

Erythropoiesis Stages Mnemonic

Powerful Businesses Pollute Our Reeling Environment” OR

Just remember “PB PORE”

  1. Proerythroblast or Pronormoblast (Rubriblast)
  2. Basophilic normoblast (Macroblast or Early normoblast or rubricyte)
  3. Polychromatic normoblast (Intermediate normoblast)
  4. Orthochromatic normoblast (Normoblast or Late normoblast or metarubricyte)
  5. Reticulocyte (Polychromatic erythrocyte)
  6. Erythrocyte


Remember the duration of erythropoiesis from proerythroblast to erythrocyte is 6-8 days (average 7 days).

  • Proerythroblast to Reticulocyte = 4 days (1 day for each)
  • Reticulocyte to erythrocyte = 2 to 4 days (reticulocyte spends 1-2 days in marrow and circulates for 1-2 days in peripheral blood before maturing to erythrocyte)


As the cell matures the following morphological changes take place progressively:

  1. Cell Size: Decreases
  2. Nucleus: Size decreases, chromatin becomes more clumped and the nucleoli disappear
  3. Cytoplasm: Shrinks
  4. Cytoplasmic basophilia decreases:
    • Ribosome (basophilic because of RNA content, i.e. stains blue) appears first
    • Ribosome synthesizes Hemoglobin (acidophilic, i.e. stains pink)
    • As the haemoglobin content approaches the desired levels the number of ribosomes decreases.
    • As erythropoiesis progressess the cytoplasm changes from deep blue (mainly ribosomes) in basophilic normoblast to polychromatophilic (ribosomes and haemoglobin) in polychromatophilic normoblast and resembling that of a erythrocyte (mainly haemoglobin) in orthochromatophilic normoblast.
  5. Cell number: The earliest nucleated stages are least numerous and the later stages the most numerous.

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