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The page below is a sample from the LabCE course Bone Marrow Aspiration: Normal Hematopoiesis and Basic Interpretive Procedures. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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The next stage of the myeloid maturation sequence is the myelocyte. The cytoplasm of this cell begins to produce specific, secondary granules. If the cell is destined to be a neutrophil these secondary granules will be pink/tan and will cause the basophilic color to lighten and breakup. At the "dawn" of neutrophilia, these secondary granules are most obvious in the golgi area. As the cell matures closer to a metamyelocyte, they fill the entire cytoplasm.

While the cytoplasm shifts to producing secondary granules it also looses the prominence of its primary granules. In situations where the bone marrow is stressed or forced to make neutrophils quickly, as in sepsis or during certain therapeutic injections, some of these primary granules may persist as "toxic granules".

At the same time the secondary granule production begins, the nucleus is shrinking and condensing. The nucleoli close and disappear, the chromatin gets coarser/denser and more clumped, and the chromatin gets tighter darker and more compact.

The very early myelocyte (red arrow) in the top image to the right still displays its immature features. While the chromatin is not as condensed as in the intermediate and late stage myelocytes in the bottom image, notice how the cytoplasm no longer has the darker basophilic color of a promyelocyte. There are clusters of neutrophil secondary granules that are changing and breaking up the solid basophilic color. Notice too, that you can no longer see any red/purple primary granules. In this cell the cytoplasm is leading the maturational dance and the nucleus is lagging.

The bottom image to the right shows two myelocytes (blue arrows): one intermediate in maturity, one a bit more mature, as well as a metamyelocyte (green arrow). Notice how the size of the cell continues to shrink as the cell matures. It is apparent that both the nucleus and the cytoplasm of the metamyelocyte adjacent has decreased in size and the chromatin has condensed/clumped as the cell matured toward a metamyelocyte.