A myelocyte is a young cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 of the granulocytic
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, occurring normally in 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...

, but not in circulating blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 (except when caused by certain diseases).


When stained with the usual dyes, the 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...

 is distinctly 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....

 and relatively more abundant than in myeloblast
The myeloblast is a unipotent stem cell, which will differentiate into one of the actors of the Granulocyte series.- Origin :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...

s or 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"...

s, even though myelocytes are smaller cells.

Numerous cytoplasmic granules
Specific granules
Specific granules are secretory vesicles found exclusively in cells of the immune system called granulocytes. They are also known as secondary granules....

 are present in the more mature forms of myelocytes. Neutrophilic and eosinophilic granules are peroxidase
Peroxidases are a large family of enzymes that typically catalyze a reaction of the form:For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides...

-positive, while basophilic granules are not.

The nuclear 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...

 is coarser than that observed in myelocyte, 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
A metamyelocyte is a cell undergoing granulopoiesis, derived from a myelocyte, and leading to a band cell.It is characterized by the appearance of a bent nucleus, cytoplasmic granules, and the absence of visible nucleoli...



There is an internationally agreed method of counting blasts, with results from M1 upwards.

External links

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