Myeloblast
Encyclopedia
The myeloblast is a unipotent stem cell, which will differentiate into one of the actors of the Granulocyte
series.
. There is also an intermediate phase between the myeloblast and these primitive reticulum cell, namely the hemocytoblast. At this time several developing blood cell
lines are available, like erythropoiesis
and thrombopoiesis. The granulopoiesis
is regulated by humoral agents, like Colony Stimulating Factor and Interleukin 3
.
. The hematopoiesis takes place in the extravascular cavities between the sinuses of the marrow. The wall of the sinuses is composed with two different types of cells, the endothelial cells and the adventitial reticular cells. The hemopoietic cells are aligned in cords or wedges between these sinuses, the myeloblasts and other granular progenitors are concentrated in the subcortical regions of these hemopoietic cords.
. Their nucleus
is composed of very fine nonaggregated chromatin
and possesses 3 or more nucleoli. The cytoplasm
has basophilic
character and is devoid of granules, which is a major difference with its 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 main features that distinguish a myeloblast from a lymphoblast
upon microscopic examination are the presence of more prominent nucleoli, the nuclear chromatin being less condensed, and cytoplasmic granules are present.
consists of 5 stages, of which the myeloblast is the first recognizable cell. Next in the differentiation sequence is the pro-myelocyte, this one will have ability to turn in one of the three different precursor cells, the neutrophilic, basophilic
or eosinophilic
myelocyte
. This proliferation needs five divisions before the final stage is obtained. These divisions all take place in the first three stages of granulopoiesis.
, hemorrhage and infection as result. There is a progressive accumulation of leukemic cells, because some blast progenitor cells renew themselves and will have a limited differentiated division. Key mediators are the cell-density and Colony Stimulating Factor(CSF). A few acute myeloblastic leukemia can be initiated by earlier hematologic disorder, like pancytopenia
, hypoplasia
of the bone marrow
.
Granulocyte
Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...
series.
Origin
These cells descend from the primitive reticulum cells, which are found in the stroma of the marrowBone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
. There is also an intermediate phase between the myeloblast and these primitive reticulum cell, namely the hemocytoblast. At this time several developing blood cell
Blood cell
A blood cell, also called a hematocyte, is a cell normally found in blood. In mammals, these fall into three general categories:* red blood cells — Erythrocytes* white blood cells — Leukocytes* platelets — Thrombocytes...
lines are available, like erythropoiesis
Erythropoiesis
Erythropoiesis is the process by which red blood cells are produced. It is stimulated by decreased O2 in circulation, which is detected by the kidneys, which then secrete the hormone erythropoietin...
and thrombopoiesis. The granulopoiesis
Granulopoiesis
Granulopoiesis is hematopoiesis of granulocytes.It occurs primarily within bone marrow and involves the following stages:* Pluripotential hemopoietic stem cell* Myeloblast* Promyelocyte* Eosino/neutro/basophilic myelocyte...
is regulated by humoral agents, like Colony Stimulating Factor and Interleukin 3
Interleukin 3
Interleukin 3, also known as IL-3, is a protein that in humans is encoded by the IL3 gene.-Function:Interleukin-3 is an interleukin, a type of biological signal that can improve the body's natural response to disease as part of the immune system...
.
Location in the body
The myeloblasts reside extravascularly in the marrowBone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
. The hematopoiesis takes place in the extravascular cavities between the sinuses of the marrow. The wall of the sinuses is composed with two different types of cells, the endothelial cells and the adventitial reticular cells. The hemopoietic cells are aligned in cords or wedges between these sinuses, the myeloblasts and other granular progenitors are concentrated in the subcortical regions of these hemopoietic cords.
Structure
Myeloblasts are rather small cells with a diameter between 14 and 18μm, from which the major part is occupied by a large oval nucleusCell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
. Their nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
is composed of very fine nonaggregated chromatin
Chromatin
Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. The primary functions of chromatin are; to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene...
and possesses 3 or more nucleoli. The cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
has basophilic
Basophilic
Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues, as seen down the microscope, after a histological section has been stained with a basic dye. The most common such dye is haematoxylin....
character and is devoid of granules, which is a major difference with its successor, the promyelocyte
Promyelocyte
A promyelocyte is a granulocyte precursor, developing from the myeloblast and developing into the myelocyte.-External links: - "18. Bone Marrow and Hemopoiesis: bone marrow smear, promyelocyte and erythroblasts " "Bone marrow" "Bone marrow"* - "Bone marrow smear"...
. The nucleolus
Nucleolus
The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within 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 main features that distinguish a myeloblast from a lymphoblast
Lymphoblast
Lymphoblasts are immature cells which typically differentiate to form mature lymphocytes. Normally lymphoblasts are found in the bone marrow, but in acute lymphoblastic leukemia , lymphoblasts proliferate uncontrollably and are found in large numbers in the peripheral blood.The size is between 10...
upon microscopic examination are the presence of more prominent nucleoli, the nuclear chromatin being less condensed, and cytoplasmic granules are present.
Function
The granulopoiesisGranulopoiesis
Granulopoiesis is hematopoiesis of granulocytes.It occurs primarily within bone marrow and involves the following stages:* Pluripotential hemopoietic stem cell* Myeloblast* Promyelocyte* Eosino/neutro/basophilic myelocyte...
consists of 5 stages, of which the myeloblast is the first recognizable cell. Next in the differentiation sequence is the pro-myelocyte, this one will have ability to turn in one of the three different precursor cells, the neutrophilic, basophilic
Basophilic
Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues, as seen down the microscope, after a histological section has been stained with a basic dye. The most common such dye is haematoxylin....
or eosinophilic
Eosinophilic
Eosinophilic refers to the staining of certain tissues, cells, or organelles after they have been washed with eosin, a dye.Eosin is an acidic dye; thus, the structure being stained is basic....
myelocyte
Myelocyte
A myelocyte is a young cell of the granulocytic series, occurring normally in bone marrow, but not in circulating blood .-Histology:...
. This proliferation needs five divisions before the final stage is obtained. These divisions all take place in the first three stages of granulopoiesis.
Pathology
Most common problem with malfunctioning myeloblasts is the acute myeloblastic leukemia. The main clinical features are caused by failure of the hemopoiesis with anemiaAnemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, hemorrhage and infection as result. There is a progressive accumulation of leukemic cells, because some blast progenitor cells renew themselves and will have a limited differentiated division. Key mediators are the cell-density and Colony Stimulating Factor(CSF). A few acute myeloblastic leukemia can be initiated by earlier hematologic disorder, like pancytopenia
Pancytopenia
Pancytopenia is a medical condition in which there is a reduction in the number of red and white blood cells, as well as platelets.If only two parameters from the full blood count are low, the term bicytopenia can be used...
, hypoplasia
Hypoplasia
Hypoplasia is underdevelopment or incomplete development of a tissue or organ. Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells. Hypoplasia is similar to aplasia, but less severe. It is technically not the opposite of hyperplasia...
of the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
.
See also
- granulopoiesisGranulopoiesisGranulopoiesis is hematopoiesis of granulocytes.It occurs primarily within bone marrow and involves the following stages:* Pluripotential hemopoietic stem cell* Myeloblast* Promyelocyte* Eosino/neutro/basophilic myelocyte...
- hematopoiesis
- pluripotential hemopoietic stem cellPluripotential hemopoietic stem cellHematopoietic stem cells , also spelled Hæmatopoietic stem cells, are multipotent stem cells that give rise to all the blood cell types from the myeloid , and lymphoid lineages...
- Myeloid leukemiaMyeloid leukemiaMyeloid leukemia is a type of leukemia affecting myeloid tissue.Types include:* Acute myeloid leukemia* Chronic myelogenous leukemia...
External links
- Wilson J.D., Braunwald E., Isselbacher K.J., Martin J.B., Fauci A.S., Root R.K. Harrison’s Principles of Internal Medicine 12th edition. McGraw-Hill Inc.(1991).
- Curran R.C., Crocker J. Curran’s Atlas of Histopathology 4th edition. Harvey Miller Publishers LTD. Oxford University Press Inc.(distributor).(2000).
- Bloom W., Fawcett D.W. A Textbook of Histology 12th edition. W.B. Saunders Company
- Murohashi I., Tohda S., Suzuki T., Nagata K., Yamashita Y., Nara N.(1989).Autocrine growth mechanisms of the progenitors of blast cells in acute myeloblastic leukemia. Journal of the American Society of Hematology 74, 35-41
- Villamor N., Zarco M-A., Rozman M., Ribera J-M., Feliu E., Montserrat E.(1998).Acute myeloblastic leukemia with minimal myeloid differentiation: phenotypical and ultrastructural characteristics. Leukemia 12, 1071–1075
- News and views.(1949).Journal of the American Society of Hematology 4, 89-96
- Williams Majorie J.(1955).Myeloblastic Leukemia Preceded by Prolonged Hematologic Disorder. Journal of the American society of hematology 10, 502-509
- Beutler E.,Lichtman M.,Coller B.,Kipps T. Williams Hematology 5th edition. McGraw-Hill Inc.(1995).