White Blood Cell
White blood cells, or leukocytes (also spelled "leucocytes"; from the Greek word leuko- meaning "white"), are cells of the immune system involved in defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell. They live for about three to four days in the average human body. Leukocytes are found throughout the body, including the blood and lymphatic system.
The number of leukocytes in the blood is often an indicator of disease. There are normally approximately 7000 white blood cells per microliter of blood. They make up approximately 1% of the total blood volume in a healthy adult. An increase in the number of leukocytes over the upper limits is called leukocytosis, and a decrease below the lower limit is called leukopenia. The physical properties of leukocytes, such as volume, conductivity, and granularity, may change due to activation, the presence of immature cells, or the presence of malignant leukocytes in leukemia.
Read more about White Blood Cell: Etymology, Types, Medication Causing Leukopenia, Fixed Leukocytes
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—Bible: Hebrew Leviticus 20:13.
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—Julie Burchill (b. 1960)