The myeloblast is a

unipotent In mathematics, a unipotent element ''r'' of a ring ''R'' is one such that ''r'' − 1 is a nilpotent element; in other words, (''r'' − 1)''n'' is zero for some ''n''. In particular, a square matrix ''M'' is a unipote ...

white blood cell White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...

which differentiates into the effectors of the

granulocyte Granulocytes are cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear, that i ...

series. It is found in the

bone marrow Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...

. Stimulation of myeloblasts by

G-CSF Granulocyte colony-stimulating factor (G-CSF or GCSF), also known as colony-stimulating factor 3 (CSF 3), is a glycoprotein that stimulates the bone marrow to produce granulocytes and stem cells and release them into the bloodstream. Function ...

and other

cytokine Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...

s triggers maturation, differentiation, proliferation and

cell survival Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as di ...

Structure

Myeloblasts reside extravascularly in the

Hematopoiesis Haematopoiesis (; ; also hematopoiesis in American English, sometimes h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. In a healthy adult human, roughly ten ...

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 oval

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

composed of very fine nonaggregated

chromatin Chromatin is a complex of DNA and protein found in eukaryote, eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important r ...

and possessing 3 or more

nucleoli The nucleolus (; : nucleoli ) is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis. The nucleolus also participates in the formation of signal recognition particles and plays a ro ...

. The

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

has a

basophilic Basophilic is a technical term used by pathologists. It describes the appearance of cells, tissues and cellular structures as seen through the microscope after a histological section has been stained with a basic dye. The most common such dye ...

character and is devoid of granules, which is a major difference from the myeloblast's successor, the

promyelocyte 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 Cell nucleus, nucleus of a promyelocyte is approximately the ...

. The

nucleolus The nucleolus (; : nucleoli ) is the largest structure in the cell nucleus, nucleus of eukaryote, eukaryotic cell (biology), cells. It is best known as the site of ribosome biogenesis. The nucleolus also participates in the formation of signa ...

is the site of assembly of

ribosomal Ribosomes () are macromolecular machines, found within all cells, that perform biological protein synthesis (messenger RNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA molecules to fo ...

proteins, which are located in various particles dispersed over the cytoplasm.

Mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

are present but have a rather small size. The main features that distinguish a myeloblast from a

lymphoblast __NOTOC__ A lymphoblast is a modified naive lymphocyte with altered cell morphology. It occurs when the lymphocyte is activated by an antigen and increased in volume by nucleus and cytoplasm growth as well as new mRNA and protein synthesis. The ly ...

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.Figure 12-14 in:

Development

These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these primitive reticulum cells, namely the

hemocytoblast Hematopoietic stem cells (HSCs) are the stem cells that give rise to other blood cells. This process is called haematopoiesis. In vertebrates, the first definitive HSCs arise from the ventral endothelial wall of the embryonic aorta within the (m ...

. At this time several developing

blood cell A blood cell (also called a hematopoietic cell, hemocyte, or hematocyte) is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...

lines are available, like

erythropoiesis Erythropoiesis (from Greek ''erythro'', meaning ''red'' and ''poiesis'', meaning ''to make'') is the process which produces red blood cells (erythrocytes), which is the development from erythropoietic stem cell to mature red blood cell. It is s ...

and thrombopoiesis.

Granulopoiesis Granulopoiesis (or granulocytopoiesis) is a part of haematopoiesis, that leads to the production of granulocytes. A granulocyte, also referred to as a polymorphonuclear leukocyte (PMN), is a type of white blood cell that has multi lobed nuclei, u ...

is regulated by humoral agents, like

colony-stimulating factor Colony-stimulating factors (CSFs) are secreted glycoproteins that bind to receptor proteins on the surfaces of committed progenitors in the bone marrow, thereby activating intracellular signaling pathways that can cause the cells to proliferate ...

(CSF) and

interleukin 3 Interleukin 3 (IL-3) is a protein that in humans is encoded by the ''IL3'' gene localized on chromosome 5q31.1. Sometimes also called colony-stimulating factor, multi-CSF, mast cell growth factor, MULTI-CSF, MCGF; MGC79398, MGC79399: after remo ...

Function

consists of 5 stages, in which the myeloblast is the first recognizable cell. Next in the differentiation sequence is the

monoblast Monoblasts are the committed progenitor cells that differentiated from a committed macrophage or dendritic cell precursor (MDP) in the process of hematopoiesis. They are the first developmental stage in the monocyte series leading to a macrophage. ...

and the

, which can develop into one of three different precursor cells: the

neutrophilic Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in different ...

eosinophilic Eosinophilic (Greek suffix '' -phil'', meaning ''eosin-loving'') describes the staining of tissues, cells, or organelles after they have been washed with eosin, a dye commonly used in histological staining. Eosin is an acidic dye for stainin ...

myelocyte A myelocyte is a young cell of the granulocytic series, occurring normally in bone marrow (can be found in circulating blood when caused by certain diseases). Structure When stained with the usual dyes, the cytoplasm is distinctly basophili ...

. This proliferation takes five divisions before the final stage is obtained. These divisions all take place in the first three stages of granulopoiesis. File:Leukopoiese.JPG File:Granulopoiesis.jpg

Clinical significance

The most common problem with malfunctioning myeloblasts is acute myeloblastic leukemia. The main clinical features of acute myeloblastic leukemia are caused by failure of

hemopoiesis Haematopoiesis (; ; also hematopoiesis in American English, sometimes h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. In a healthy adult human, roughly ten b ...

with

anemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, ...

and infection as a result. There is a progressive accumulation of leukemic cells, because some blast

progenitor cells A progenitor cell is a Cell (biology), biological cell that can Cellular differentiation, differentiate into a specific cell type. Stem cell, Stem cells and progenitor cells have this ability in common. However, stem cells are less specified than ...

renew themselves and have a limited differentiated division. Sometimes acute myeloblastic leukemia can be initiated by earlier hematologic disorders, like

myelodysplastic syndrome A myelodysplastic syndrome (MDS) is one of a group of cancers in which blood cells in the bone marrow do not mature, and as a result, do not develop into healthy blood cells. Early on, no symptoms typically are seen. Later, symptoms may includ ...

pancytopenia Pancytopenia is a medical condition in which there is significant reduction in the number of almost all blood cells (red blood cells, white blood cells, platelets, monocytes, lymphocytes, etc.). If only two parameters from the complete blood cou ...

, or

hypoplasia Hypoplasia (; adjective form ''hypoplastic'') is underdevelopment or incomplete development of a tissue or organ.bone marrow Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...

Structure

Development

Function

Clinical significance

See also

References

Further reading