Page 222 - Atlas of Histology with Functional Correlations

erythrocytic line, early basophilic erythroblasts (7, 21) are recognized by a

large but not very dense nucleus and basophilic cytoplasm. These cells give rise
to the smaller polychromatophilic erythroblasts (8, 22) with a more condensed
nuclear chromatin and a more variable color of the cytoplasm, with the
cytoplasm becoming more eosinophilic. The most recognizable and most
abundant cells of the erythrocytic line are normoblasts (2, 23). They are

characterized by small, dark-staining pyknotic nuclei and a reddish, or
eosinophilic, cytoplasm. Early normoblasts (2, 23) exhibit mitotic activity (6) in
the bone marrow. As normoblasts (2, 23) mature, the cells lose the ability to

divide and extrude their densely staining pyknotic nuclei to become
erythrocytes (3). Cells of the erythrocytic lineage do not display any granules in
their cytoplasm. Erythrocytes (3) are abundant in red bone marrow and are seen
in the numerous sinusoids (1, 12), venule (14), and arteriole (15) as they are
released into systemic circulation.

The early granulocytes initially exhibit numerous primary, or azurophilic,
granules in their cytoplasm. As a result, the immature forms of neutrophils,
eosinophils, and basophils are morphologically indistinguishable and become
recognizable only in the myelocyte stage, when specific granules appear in

recognizable quantities in their cytoplasm that can be stained for recognition. In
neutrophilic cells, the specific granules are only faintly stained, and the
cytoplasm appears clear or neutral. These granules are clearly recognized with
electron microscope. In the eosinophilic line, the specific granules stain deep red,

or eosinophilic. Basophilic granulocytes are rarely observed in the bone marrow
because of their small numbers. The cytoplasm of mature basophils exhibits a
bilobed nucleus and dense blue, or basophilic, granules.

The granulocytic myelocytes (13, 19) exhibit a large spherical nucleus and a

cytoplasm with many azurophilic granules. The myelocytes (13, 19) give rise to
metamyelocytes (4, 11, 20), whose nuclei are bean or horseshoe shaped. The
neutrophilic metamyelocytes (17) exhibit a deeply indented nuclei and
cytoplasm with azurophilic granules and faintly stained specific granules. In
contrast, a cell with bright-staining red (eosinophilic) granules in the cytoplasm

is an eosinophilic myelocyte (18).

The stroma of the reticular connective tissue in the bone marrow is almost
obscured by hematopoietic cells. In less dense areas, the reticular connective
tissue with the elongated reticular cells (16) is visible. Also, numerous thin-

walled sinusoids (1, 12) and different types of blood vessels (14, 15) containing
erythrocytes and leukocytes are present in the bone marrow. Also conspicuous

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