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A promyelocyte (or progranulocyte) is a granulocyte precursor, developing from the myeloblast and developing into the myelocyte. Promyelocytes measure 12–20 microns in diameter. The nucleus of a promyelocyte is approximately the same size as a myeloblast but their cytoplasm is much more abundant. [1]
There are four types of granulocytes (full name polymorphonuclear granulocytes): [3] Basophils; Eosinophils; Neutrophils; Mast cells; Except for the mast cells, their names are derived from their staining characteristics; for example, the most abundant granulocyte is the neutrophil granulocyte, which has neutrally staining cytoplasmic granules.
In this process it first transforms from a common myeloblast (myeloid progenitor) to a common promyelocyte. This promyelocyte gives rise to a unique myelocyte that for the first time can be classified as an eosinophil, basophil, or neutrophil progenitor based on the histological staining affinity (eosinophilic, basophilic, or neutral granules). [3]
The cytoplasm has a basophilic character and is devoid of granules, which is a major difference from the myeloblast's successor, the promyelocyte. The nucleolus is the site of assembly of ribosomal proteins, which are located in various particles dispersed over the cytoplasm. Mitochondria are present but have a rather small size.
The nuclear chromatin is coarser than that observed in a promyelocyte, but it is relatively faintly stained and lacks a well-defined membrane. The nucleus is fairly regular in contour (not indented), and seems to be 'buried' beneath the numerous cytoplasmic granules. (If the nucleus were indented, it would likely be a metamyelocyte.)
Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells. [1]
Committed granulopoiesis consists of maturation stages of unipotent cells. The first cell that starts to resemble a granulocyte is a myeloblast.It is characterized by large oval nucleus that takes up most of the space in the cell and very little cytoplasm.
The GM-CSF and IL-3 both work together to stimulate production of all lines. When erythropoietin (EPO) is present, red blood cell production from the CFU-GEMM will be activated. G-CSF, M-CSF, IL-5, IL-4, and IL-3 stimulate the production of neutrophils, monocytes, eosinophils, basophils, and platelets, respectively. [4]