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Monocyte

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Definition

noun, plural: monocytes

A type of white blood cell capable of immune functions such as phagocytosis, and can further differentiate into a macrophage or a myeloid dendritic cell


Supplement

Hematopoiesis is the process of forming new blood cellular elements in vertebrates. It begins with a multipotent stem cell, a hemocytoblast, which gives rise to a common myeloid progenitor cell (CMP). The CMP, in turn, gives rise to granulocyte-monocyte colony forming units (CFU-GM), also called granulocyte-macrophage progenitor. The CFU-GM may partially differentiate into CFU-G (precursor in myelocyte-granulocyte series) or CFU-M (precursor in monocyte-macrophage series). The CFU-GM serves as the precursor for monoblasts and myeloblasts.

In the monocytic series, the monoblast is a precursor cell for promonocyte. The promonocyte matures into a monocyte. The monocyte migrates from the bone marrow to the peripheral blood through diapedesis. In humans, it constitutes the 2% to 10% of the white blood cells in the body. A monocyte is capable of immune functions, such as phagocytosis, antigen presentation, and cytokine production. It may leave the bloodstream and enters the connective tissue spaces. When it does, the monocyte divides and/or differentiates into a macrophage. Monocytes may also differentiate into a myeloid dendritic cell. In humans, some of the monocytes are stored in the spleen.

A monocyte is the largest type of white blood cell. Its size may range from 13 to 25 μm in diameter. It may be amoeboid in appearance. Its nucleus is unilobulated. The chromatin has a lacy pattern. When stained with conventional dyes, the cytoplasm appears blue-gray in color with fine, red-blue azurophil granules. Vacuoles are usually present.

As a type of white blood cell (leukocyte), the monocyte belongs to the mononuclear leukocytes as opposed to other white blood cells that are polymorphonuclear.


See also:

Related form(s):

  • monocytic (adjective, of, pertaining to, or relating to a monocyte)