Two orthrochromatophilic erythrocytes are seen in this micrograph. Their nuclei have become even smaller and the nucleus exhibits a compact, dense staining. The cytoplasm is
Polychromatophilic erythrocyte, bone marrow smear, human, Giemsa, ×2,200.
A polychromatophilic erythrocyte (PE) is seen in this micro-graph. Its nucleus has been extruded and the cytoplasm exhibits a slight basophilia. In proximity are a number of mature erythrocytes (E). Compare the coloration of the polychromatophilic erythrocyte with that of the mature red blood cells. Polychromatophilic erythrocytes can also be readily demonstrated with special stains that cause the remaining ribosomes in the cytoplasm to clump and form a visible reticular network, hence the polychromatophilic erythrocyte is also commonly called a reticulocyte.
KEY E, erythrocytes N, nucleoli PE, polychromatophilic erythrocyte 308 Granulopoiesis is the process by which the granulocyte blood cells (neutrophils, eosinophils, and basophils)  differentiate and mature in the bone marrow. The earliest recognizable stage is the myeloblast, which is followed consecutively by the promyelocyte, myelocyte, metamyelo-cyte, band cell, and finally, the mature granulocyte. It is not possible to differentiate eosinophil, basophil, or neutrophil precursors morphologi-cally until the myelocyte stage is reached – when specific granules characteristic of each cell type appear. The cells of the basophil lineage are extremely difficult to locate in a marrow smear because of the minimal number of these cells in the marrow. The myeloblast is characterized by a large euchromatic, spherical nucleus with three to five nucleoli. The cell measures 14 to 20 m in di-ameter. The cytoplasm stains deeply basophilic. The presence of a light or poorly staining area indicates a Golgi apparatus. The promyelocyte exhibits a similar size range, 15 to 21 m; nucleoli are present. Promyelocyte cytoplasm stains similarly to that of the myoblast, but it is distin-guished by the presence of large, blue/black, primary azurophilic granules, also called nonspecific granules. The myelocyte ranges from 16 to 24 m. Its chromatin is more condensed than its precursor and nucleoli are absent. The cytoplasm of the neutrophilic myelocyte is character-ized by small, pink-to-red specific granules with some azurophilic granules present. The eosinophilic lineage has a similar appearing nucleus, but its specific granules are large. The metamyelocyte ranges from 12 to 18 m. The nuclear-cytoplasmic ratio is further decreased and the nu-cleus assumes a kidney shape. There are few azurophilic granules at this stage in cells, and there is a predominance of small, pink-to-red spe-cific granules. The eosinophilic metamyelocyte shows an increased number of specific granules compared to the neutrophilic metamyelocyte. The band cells are further reduced in size, 9 to 15 m. The chromatin of the nucleus exhibits further condensation and has a horseshoe shape. In the neutrophilic band cell, the small, pink-to-red specific granules are the only granule type present. The eosinophilic band cell shows little or no change relative to the specific granules, but the nucleus exhibits a kidney shape. Mature granulocytes are shown on Plate 17.
Myeloblast, bone marrow smear, human, Giemsa, ×2,200.
The myeloblast shown here exhibits a deep blue cytoplasm with a lighter region that represents the Golgi area (G). The nucleus is-round. Several nucleoli (N) are evident.