Last reviewed 01/2018

Granulopoiesis is the formation of granulocytes within the bone marrow. It is controlled by a number of substances including granulocyte colony stimulating factors.

The cell differentiation is sequentially:

  • stem cell progenitor
  • promyelocyte:
    • relatively large nucleus
    • basophilic cytoplasm
  • myelocytes, divided into cell lines distinguishable by granule staining within cytoplasm:
    • basophilic myelocyte
    • neutrophilic myelocyte
    • eosinophilic myelocyte
  • metamyelocyte cell lines:
    • granules are becoming more concentrated within cell
    • cell nucleus becomes more lobulated
    • gives rise to:
      • mature basophil
      • mature eosinophil
      • band cell

The band cell is an immature neutrophil that develops in the bone marrow by further lobulation of its nucleus.

The mature neutrophils, or band cells if a left shift has occurred, along with mature basophils and eosinophils, pass through the sinus endothelium in bone marrow through to blood.