Maturation of Blood Cells

General concepts, features of blast cells, and the specific maturation sequences for erythrocytes, leukocytes, and platelets.

Blast cell

A precursor cell that can give rise to all blood cells; typically relatively large (up to $20\,u$ in diameter) with a small amount of cytoplasm relative to the nucleus and no granules.

N:C ratio

The amount of space occupied by the nucleus as to the amount of space occupied by the cytoplasm; this ratio is very high ($20:1$) when the cell is very young.

Basophilia

The affinity of a cell for a basic dye, which is proportional to the cytoplasmic content of ribonucleic acid (RNA); it is lost as the cell matures.

Nucleoli

Small, well-defined pale bodies found in the nuclei of blast cells; the number of these bodies decreases and they eventually disappear as the cell matures.

Primary granules

Also known as azurophilic granules, these are the first granules to appear during cell maturation, specifically during the promyelocyte stage.

Secondary granules

Also called specific granules, these appear during the myelocyte stage and show affinity for specific dyes (acidic, basic, or both).

Eosinophilic granules

Cytoplasmic granules that stain orange-red with acid dye (eosin dye) and are characteristic of eosinophil leukocytes.

Basophilic granules

Cytoplasmic granules that stain blue-black with basic dye and identify the basophil leukocyte.

Neutrophilic granules

Granules that stain violet or purple with a compound of both acid and basic dyes.

Pyknotic

A description of a nucleus that has become coarse, clumped, and non-functional, eventually leading to its extrusion in erythroid cells.

Pronormoblast

The mother cell for the erythrocytic cell line (also known as rubriblast or proerythroblast) which contains one or two nucleoli and an N:C ratio of $8:1$.

Reticulocyte

A polychromatic erythrocyte stage where the cell has no nucleus and contains residual ribosomes appearing as a mesh of blue strands called a reticulum when visualized with a vital stain.

New methylene blue

A vital stain used to visualize residual ribosomes in reticulocytes by staining the cells while they are still alive in suspension.

Erythrocyte

A matured, flattened, biconcave disc with a diameter of $6-8\,\mu\text{m}$ that lacks a nucleus and organelles to maximize space for hemoglobin and oxygen transport.

Megakaryocyte

The large progenitor cell from which platelets are derived; unlike other blood cells, its youngest form is smaller than the fully developed mature form.

Acute Leukemia

A classification of leukemia where the predominating white blood cells belong to the very young or immature types.

Chronic Leukemia

A classification of leukemia characterized by a predominance of white blood cells that are more mature compared to the acute forms.

Polychromatophilic normoblast

A stage in erythroid maturation where the cytoplasm first displays color associated with hemoglobin development; this stage lasts approximately $48\,\text{hours}$.

Orthochromic

A nomenclature term based on the amount of hemoglobin present in a normoblast (a nucleated red blood cell precursor).