| Myeloblast | |
|---|---|
 Myeloblast | |
| Identifiers | |
| TH | H2.00.04.3.04002 |
| FMA | 83524 |
| Anatomical terms of microanatomy | |
Themyeloblast is aunipotent stem cell which differentiates into the effectors of thegranulocyte series. It is found in thebone marrow. Stimulation of myeloblasts byG-CSF and othercytokines triggers maturation, differentiation, proliferation andcell survival.[1]
Myeloblasts reside extravascularly in thebone marrow.Hematopoiesis takes place in the extravascular cavities between the sinuses of the marrow. The wall of the sinuses is composed of two different types of cells, endothelial cells and adventitial reticular cells. The hemopoietic cells are aligned in cords or wedges between these sinuses, with myeloblasts and other granular progenitors concentrated in the subcortical regions of these hemopoietic cords.
Myeloblasts are rather small cells with a diameter between 14 and 18μm. The major part is occupied by a large ovalnucleus composed of very fine nonaggregatedchromatin and possessing 3 or morenucleoli. Thecytoplasm has abasophilic character and is devoid of granules, which is a major difference from the myeloblast's successor, thepromyelocyte. Thenucleolus is the site of assembly ofribosomal proteins, which are located in various particles dispersed over the cytoplasm.Mitochondria are present but have a rather small size.
The main features that distinguish a myeloblast from alymphoblast upon microscopic examination are the presence of cytoplasmic granules, the lesser degree of condensation in the nuclear chromatin, and the increased prominence of the nucleoli.[2]
These cells descend from the primitive reticulum cells, which are found in the stroma of themarrow. There is also an intermediate phase between the myeloblast and these primitive reticulum cells, namely thehemocytoblast. At this time several developingblood cell lines are available, likeerythropoiesis and thrombopoiesis.Granulopoiesis is regulated by humoral agents, likecolony-stimulating factor (CSF) andinterleukin 3.
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Granulopoiesis consists of 5 stages, in which the myeloblast is the first recognizable cell. Next in the differentiation sequence is themonoblast and thepromyelocyte, which can develop into one of three different precursor cells: theneutrophilic,basophilic oreosinophilicmyelocyte. This proliferation takes five divisions before the final stage is obtained. These divisions all take place in the first three stages of granulopoiesis.
The most common problem with malfunctioning myeloblasts isacute myeloblastic leukemia.[3][4] The main clinical features of acute myeloblastic leukemia are caused by failure ofhemopoiesis withanemia,hemorrhage and infection as a result. There is a progressive accumulation of leukemic cells, because some blastprogenitor cells renew themselves and have a limited differentiated division. Sometimes acute myeloblastic leukemia can be initiated by earlier hematologic disorders, likemyelodysplastic syndrome,pancytopenia, orhypoplasia of thebone marrow.