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The stages in the normal maturation of the granulocytes are: myeloblast, promyelocyte, myelocyte (neutrophilic, eosinophilic, and basophilic), metamyelocyte (neutrophilic, eosinophilic, and basophilic), band cell (neutrophilic, eosinophilic, and basophilic), and segmented cell (neutrophilic, eosinophilic, and basophilic). As the granulocytes mature, the granules increase in number. These granules later become specific and differ in the affinity for various dyes. Neutrophilic granules do not stain intensely with either dye. Basophilic granules have an affinity for the basic or blue dye. Eosinophilic stain red with an affinity for the acid dye. The criteria for identification of the various stages of the granulocytic series are: size of cell, nucleus-cytoplasm ratio, nuclear shape, number of nucleoli, and the type and size of cytoplasmic granulation.

a. Myeloblast.
(1) Size. Fifteen to 20 microns in diameter.
(2) Nucleus. The nucleus is round or ovoid and stains predominantly reddish-purple. The interlaced chromatin strands are delicate, well defined, and evenly stained. Two or more pale blue nucleoli are demonstrable. The nucleus occupies most of the cell with a nucleus-cytoplasm ratio of 6:1. It is separated from the cytoplasm by a definite nuclear membrane.
(3) Cytoplasm. The cytoplasm is a narrow, deep blue, nongranular rim around the nucleus.

Figure 4-3a. Granulocytic series: Myeloblast.

b. Promyelocyte.

(1) Size. Fifteen to 21 microns in diameter.
(2) Nucleus. The nucleus is round or ovoid with coarse-clumping, purple chromatin material. One to three oval, light-blue nucleoli are usually present. The nucleoli are less distinct than in the myeloblast. This cell has a nucleus-cytoplasm ratio of 4:1.
(3) Cytoplasm. The cytoplasm is light purple and contains varying numbers and sizes of dark nonspecific granules that stain red to purplish-blue. The granules usually overlie the nucleus.

Figure 4-3b. Granulocytic series:
a. Promyelocyte.
b. Promyelocyte with Auer Body.

c. Myelocyte. In the myelocytic stage the granules are definite and so numerous that frequently they obscure nuclear detail. While promyelocytes are sometimes distinguished as neutrophilic, eosinophilic, or basophilic, the differentiation is generally considered as first occurring in the myelocytic stage.

Figure 4-3c. Granulocytic series: Myelocyte.

d. Neutrophilic Myelocyte.
(1) Size. Twelve to 18 microns in diameter.
(2) Nucleus. The nucleus is round, oval, or flattened on one side. The chromatin strands are light purple, unevenly stained, and thickened. Nucleoli are usually absent. The nucleus is smaller than the earlier cells of this series with a nucleus-cytoplasm ratio of 2:1.
(3) Cytoplasm. The cytoplasm is bluish-pink and contains a small relatively light area of ill-defined, pink granules, which develop among the dark, nonspecific, azurophilic granules of the promyelocyte. As the myelocyte ages, the dark granules become less prominent and the light-pink-colored neutrophilic granules predominate.
e. Neutrophilic Metamyelocyte.
(1) Size. Ten to 18 microns in diameter.
(2) Nucleus. The nucleus is indented or kidney-shaped. The nuclear chromatin stains dark purple and is condensed into irregular strands. Nucleoli are absent. The nucleus-cytoplasm ratio is approximately 1.5:1.
(3) Cytoplasm. The cytoplasm is pinkish-blue and covered with many small, light pink granules.

Figure 4-3d. Granulocytic series:
a. Metamyelocyte.
b. Band Neutrophil.

f. Neutrophilic Band.
(1) Size. Ten to 16 microns in diameter.
(2) Nucleus. The nucleus is shaped like a horseshoe with a dark pyknotic mass at each poIe of the nucleus where the lobes develop. The nucleus-cytoplasm ratio is approximately 1: 2.
(3) Cytoplasm. The cytoplasm contains many small, evenly distributed light pink granules.
g. Neutrophilic Segmented Cell.
(1) Size. Ten to 16 microns in diameter.
(2) Nucleus. The nucleus has definite lobes separated by a very narrow filament or strand. The nucleus-cytoplasm ratio is approximately 1: 3.
(3) Cytoplasm. The cytoplasm is light pink and the small, numerous, and evenly distributed neutrophilic granules have a light pink color.
h. Development of the Eosinophilic Group. Cells of the eosinophilic group are characterized by relatively large, spherical, cytoplasmic granules that have a particular affinity for the eosin stain. The earliest eosinophil (myelocyte) has a few dark spherical granules with reddish tints that develop among the dark, nonspecific granules. As the eosinophilic cells pass through their various developmental stages, these granules become less purplish-red and more reddish-orange. The dark blue, nonspecific granules, characteristic of the promyelocyte and the early myelocyte stages, disappear. Because the percentage of eosinophils is usually low in bone marrow peripheral blood smears, no useful clinical purpose is served by routinely separating the eosinophils into their various myelocyte, metamyelocyte, band, and segmented categories. On the other hand, in situations such as eosinophilic leukemia in which the eosinophils are greatly increased, an analysis of the incidence of the various stages would be useful in diagnosis.
i. Mature Eosinophil.
(1) Size. Ten to 15 microns in diameter.
(2) Nucleus. The nucleus has definite lobes separated by a very narrow filament or strand. Seldom does an eosinophil have more than two lobes.
(3) Cytoplasm. The cytoplasm contains bright reddish-orange, distinct granules. The granules are spherical, uniform in size, and evenly distributed throughout the cytoplasm, but rarely overlie the nucleus.

Figure 4-3e. Granulocytic series: Eosinophil.

j. Development of the Basophilic Group. These cells have round, indented, band, or lobulated nuclei and are classified according to the shape of the nuclei, as basophilic rnyelocytes, metamyelocytes, bands, and segmented forms. These cells are so few in peripheral blood and bone marrow that there is little clinical value in differentiation of the various maturation stages.

Figure 4-3f. Granulocytic series:
a. Basophil.
b. Neutrophil: Segmented.

k. Mature Basophils.
(1) Size. Ten to 15 microns in diameter.
(2) Nucleus. The nucleus has definite lobes separated by a very narrow filament or strand. The nuclear details are obscured by the cytoplasmic granulation.
(3) Cytoplasm. The cytoplasm is covered by many blue to black granules. These granules are unevenly distributed and vary in number, size, shape, and color.

Curriculum design: David L. Heiserman
Publisher: SweetHaven Publishing Services

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