Page 227 - Atlas of Histology with Functional Correlations

the reticulocyte becomes a mature erythrocyte (6).

GRANULOCYTE DEVELOPMENT

The myeloblast (7) is the first recognizable precursor in the granulocytic cell

line. The myeloblast (7) is a small cell with a large nucleus, dispersed chromatin,
three or more nucleoli, and a basophilic cytoplasm rim that lacks specific
granules. As development progresses, the cell enlarges, acquires azurophilic
granules, and becomes a promyelocyte (8, 9). The chromatin in the oval nucleus

is dispersed, and multiple nucleoli are evident. In more advanced promyelocytes,
the cells become smaller, the nucleoli become inconspicuous, the number of
azurophilic granules increases, and specific granules with different staining
properties appear in the perinuclear region. Promyelocytes (8, 9) divide to form

smaller myelocytes (10, 13, 14). The cytoplasm of myelocytes (10, 13, 14) is
less basophilic and contains many azurophilic granules. Myelocytes differentiate
into three kinds of granulocytes, which can be recognized only by the increased
accumulation and staining properties of specific granules in their cytoplasm, as

seen in the eosinophilic myelocyte (13) with red or eosinophilic granules and
the rare basophilic myelocyte (14) with blue or basophilic granules. Myelocytes
develop into metamyelocytes. The cytoplasm of a neutrophilic metamyelocyte
(11) contains deep-staining azurophilic granules, lightly stained specific

granules, and an indented, kidney-shaped nucleus. The eosinophilic
metamyelocytes (15) are larger cells, and their specific cytoplasmic granules
stain eosinophilic.

Megakaryoblasts (12) are large cells with a basophilic, homogeneous

cytoplasm. The voluminous nucleus is ovoid or kidney shaped, contains
numerous nucleoli, and exhibits a loose chromatin pattern. Platelets are not
formed at this stage.

During differentiation, megakaryoblasts (12) become very large. Their
nucleus becomes convoluted, with multiple, irregular lobes interconnected by

constricted regions. The chromatin becomes condensed and coarse, and nucleoli
are not visible. In mature megakaryocytes (17), the plasma membrane
invaginates the cytoplasm and forms demarcation membranes that indicates the
areas of the megakaryocyte cytoplasm that is shed into the blood as small cell

fragments in the form of platelets (16).

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