Pathology Thread

Note that the mature forms of the myeloid series (neutrophils, eosinophils, basophils), all have lobed (segmented) nuclei. The degree of lobation increases as the cells mature.

Starting with the cell at the LEFT, CLICK on the above images to review WBC maturational morphology.

The earliest recognizable myeloid cell is the myeloblast (10-20m dia) with a large round to oval nucleus. There is fine diffuse immature chromatin (without clumping) and a prominant nucleolus.

The cytoplasm is basophilic without granules. Although one may see a small golgi area adjacent to the nucleus, granules are not usually visible by light microscopy. One should not see blast cells in the peripheral blood.

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The promyelocyte (10-20m) is slightly larger than a blast. Its nucleus, although similar to a myeloblast shows slight chromatin condensation and less prominent nucleoli. The cytoplasm contains striking azurophilic granules or primary granules. These granules contain myeloperoxidase, acid phosphatase, and esterase enzymes. Normally no promyelocytes are seen in the peripheral blood.

At the point in development when secondary granules can be recognized, the cell becomes a myelocyte.

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Myelocytes (10-18m) are slightly smaller than promyelocytes and have eccentric round-oval nuclei, often flattened along one side. The chromatin is fine, but shows evidence of condensation. Nucleoli may be seen in early stages but not in the late myelocyte. Primary azurophilic granules are still present, but secondary granules predominate. Secondary granules (neut, eos, or baso) first appear adjacent to the nucleus. In neutrophils this is the "dawn" of neutrophilia.

Myelocytes are not normally found in the peripheral blood.

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Metamyelocytes (10-18m) are slightly smaller than myelocytes. They have kidney shaped indented nuclei and relatively dense chromatin, especially along the nuclear membrane. The cytoplasm is faintly pink with almost no blue background. Numerous secondary granules (neutro, eos, or baso) clearly outnumber primary granules. Zero to one percent of the peripheral blood white cells may be metamyelocytes (juveniles).

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Bands, slightly smaller than juveniles, are marked by a U-shaped or deeply indented nucleus. Opposite sides or lobes are of roughly equal size or diameter. There is no nuclear constriction > than 1/2 the lobe diameter. The chromatin is heavily clumped and secondary or specific granules either neutrophilic or basophilic predominate.

Normal band counts vary but are usually in the range of 0-6%.

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Segmented (segs) or polymorphonuclear (PMN) leukocytes (average 14 m dia) are distinguished by definite lobation with thin thread-like filaments of chromatin joining the 2-5 lobes. The chromatin of the segmented neutrophil is coarsely clumped and the cytoplasm is pink due to large numbers of secondary granules.

In practice when examining peripheral blood, neutrophils are the only leukocytes to be divided into myelocyte, juvenile, band, and PMN stages. Eosinophils and basophils of all stages are lumped together in most instances.

Normally approximately 45-75% of the peripheral blood white cells are segmented neutrophils.

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Which of the two cells shown here is most likely to be phagocytic ?

A. the monocyte
B. the neutrophil
C. the lymphocyte
D. the basophil
E. the myelocyte

While doing a WBC differential you come across 50 nucleated red blood cells. The automated instrument counted 12.0 x10 /L "WBCs". What is the actual WBC count ?

A. 6,000 / uL
B. 6.0 x 10 /L
C. 4.0 x 10 /L
D. 8.0 x 10 /L
E. 6,000 x 10 /dL