White blood cell

Definition
noun, plural: white blood cells
Any of the nucleated blood cells that lack hemoglobin, with a primary role in the body’s immune system, protecting the body against invading microorganisms and foreign particles
Supplement
Blood is the circulating fluid in the body of eukaryotic animals. It is primarily composed of plasma and cellular elements (blood cells and platelets). The blood cells may be classified as either a red blood cell or a white blood cell. The white blood cell is also referred to as leukocyte.
White blood cells include lymphocytes, granulocytes, monocytes, mast cells, macrophages and dendritic cells. Elevated counts of white blood cells indicate inflammation or infection. In adult humans, the normal range of white blood cell counts is 4500 to 11 000 per mm³.
The name, white blood cell, originates from the fact that centrifugation of blood sample results in the formation of a thin layer of cells which are generally white in color between the sedimented red blood cells and the blood plasma.
In humans, the white blood cells arise from multipotent stem cells (hemocytoblasts) of the bone marrow. The hemocytoblasts are stem cells that give rise to various cellular elements of the blood from the myeloid and the lymphoid lineages. The primary function of the white blood cells is to mount an immune response against non-self particles and tumour or cancerous cells.
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