myelocyte

1. A young cell of the granulocytic series, occurring normally in bone marrow, but not in circulating blood (except in certain diseases). When stained with the usual dyes, the cytoplasm is distinctly basophilic and relatively more abundant than in myeloblasts or promyelocytes, even though m.'s are smaller cells; numerous cytoplasmic granules ( i.e., neutrophilic, eosinophilic, or basophilic) are present in the more mature forms of m.'s, and the first two types are peroxidase-positive. The nuclear chromatin is coarser than that observed in myeloblasts, but it is relatively faintly stained and lacks a well defined membrane; the nucleus is fairly regular in contour ( i.e., not indented), and seems to be “buried” beneath the numerous cytoplasmic granules. 2. A nerve cell of the gray matter of the brain or spinal cord. SYN: medullocell. [myelo- + G. kytos, cell]

- m. A the youngest form of m., characterized by only a few (not more than ten) cytoplasmic granules, which are most reliably demonstrated by means of staining with neutral red; the mitochondria are numerous, and resemble those of the myeloblast.

- m. B the intermediate form of m., characterized by approximately 30–100 (or more) cytoplasmic granules scattered among the mitochondria; the latter are less numerous than in myelocytes of the A stage, and they are frequently displaced toward the periphery of the cell.

- m. C the most mature of the myelocytes characterized by numerous cytoplasmic granules that are recognizable as neutrophilic, eosinophilic, and basophilic; with neutral red these are stained, respectively, red, bright yellow, and deep maroon; C myelocytes are frequently larger than earlier forms; if the nucleus is indented, the m. is maturing into a metamyelocyte.

* * *

my·e·lo·cyte 'mī-ə-lə-.sīt n a bone marrow cell esp a motile cell with cytoplasmic granules that gives rise to the blood granulocytes and occurs abnormally in the circulating blood (as in myelogenous leukemia)

my·e·lo·cyt·ic .mī-ə-lə-'sit-ik adj

* * *

n.

an immature form of granulocyte having an oval nucleus (compare metamyelocyte) and neutrophil, eosinophil, or basophil granules within its cytoplasm (compare promyelocyte). It is normally found in the blood-forming tissue of the bone marrow, but may appear in the blood in a variety of diseases, including infections, infiltrations of the bone marrow, and certain leukaemias. See also granulopoiesis.

* * *

my·elo·cyte (miґə-lo-sīt) [myelo- + -cyte] a precursor in the granulocytic series, being a cell intermediate in development between a promyelocyte and a metamyelocyte; in this stage, differentiation of cytoplasmic granules has begun, so that they are specifically basophilic, eosinophilic, or neutrophilic. myelocytic adj

Neutrophilic myelocyte (arrow).