White blood cell
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"White Blood Cells" redirects here. For the White Stripes album, see White Blood Cells (album).
White blood cells or leukocytes are cells which form a component of the blood. They are produced in the bone marrow and help to defend the body against infectious disease and foreign materials as part of the immune system.
There are normally between 4×109 and 1.1×1010 white blood cells in a litre of healthy adult blood. In conditions such as leukaemia this may rise to as many as 50,000 white blood cells in a single drop of blood. As well as in the blood, white cells are also found in large numbers in the lymphatic system, the spleen, and in other body tissues.
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[edit] Nomenclature
The name "white cells" derives from the fact that after centrifugation of a blood sample, the white cells are found in the Buffy coat, a thin layer of nucleated cells between the sedimented red blood cells and the blood plasma, which is white in color (or sometimes green, if there are large amounts of neutrophils in the sample, which are high in green. This green colour is due to neutrophils having MPO. myeloperoxidase).
[edit] Types
There are many different types of white blood cells. One primary technique to classify them is to look for the presence of granules, which produces the categories "granulocytes" and "agranulocytes".
- Granulocytes: As Granular Leucocytes and polymorphonuclear leucocytes (informally, "PMNS" or "Polys"), Granulocytes are a category of white blood cells, characterised by the fact that all types have differently staining granules in their cytoplasm on light microscopy. These granules are related to lysosomes found in some regular cells and primarily act in the digestion of engulfed invaders. There are three types of granulocytes: neutrophils, basophils, and eosinophils (named according to their staining properties).
- Agranulocytes: Agranulocytes are a category of white blood cells which are characterized by the absence of granules in their cytoplasm. There are two types of agranulocytes: lymphocytes and monocytes.
These categories can be further broken down as follows:
Type | Image | Diagram | Approx. % in humans | Description |
Neutrophil | 65% | Neutrophils deal with defense against bacterial infection and other very small inflammatory processes and are usually first responders to bacterial infection; their activity and death in large numbers forms pus. | ||
Eosinophil | 4% | Eosinophils primarily deal with parasitic infections and an increase in them may indicate such. | ||
Basophil | <1% | Basophils are chiefly responsible for allergic and antigen response by releasing the chemical histamine causing inflammation. | ||
Lymphocyte | 25% | Lymphocytes are much more common in the lymphatic system. The blood has three types of lymphocytes:
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Monocyte | 6% | Monocytes share the "vacuum cleaner" (phagocytosis) function of neutrophils, but are much longer lived as they have an additional role: they present pieces of pathogens to T cells so that the pathogens may be recognised again and killed, or so that an antibody response may be mounted. | ||
Macrophage | (see above) | Monocytes are also known as macrophages after they migrate from the bloodstream and enter tissue. |
[edit] Other tissue cells
- Histiocytes, found in the lymphatic system and other body tissues, but not normally in blood:
- Mast cells
- Allergies can also change your white blood cell count.
[edit] Additional images
[edit] See also
[edit] External links
- Dorlands/Elsevier l_07/12485996
- Dictionary at eMedicine leukocyte
- MeSH Leukocytes
- Animation of leucocyte adhesion Animation with some great images of actin and microtubule assembly and dynamics.
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Adaptive immune system | Innate immune system | Humoral immune system | Cellular immune system | Immunological tolerance | Lymphatic system | White blood cells | Antibodies | Antigen (MHC) | Complement system | Inflammation |