leukocyte

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leukocyte

 [loo´ko-sīt]
a type of blood cell that lacks hemoglobin and is therefore colorless. Leukocytes are larger in size and fewer in number than erythrocytes; normally the blood has about 8000 of them per mm3. In contrast to erythrocytes, leukocytes can move about under their own power with ameboid movement. Their chief functions are to act as scavengers and to help fight infections. Called also white cell or corpuscle and white blood cell or corpuscle. adj., adj leukocyt´ic.

Leukocytes may be classified in two main groups: the granular leukocytes are the basophils, eosinophils, and neutrophils, and the nongranular leukocytes are the lymphocytes and monocytes. About 63 per cent of all leukocytes are neutrophils; 2.5 per cent are eosinophils; and the remaining types constitute less than 1 per cent each.

Leukocytes are actively engaged in the destruction or neutralization of invading microorganisms and are quickly transported to the vicinity of infection or inflammation, so that they can move through the blood vessel wall to reach the site of injury. For this reason, their life span in the blood is usually very short. When infection is present their numbers are greatly increased and they also become more mobile and move back and forth between the blood, lymph, and tissues. The granulocytes and monocytes are phagocytic, swallowing or ingesting the foreign particles with which they come in contact. During the process of phagocytosis the phagocytes themselves are destroyed. The two types of lymphocytes involved in immunity are B lymphocytes (B cells), which play a role in humoral immunity, and T lymphocytes (T cells), which are important in cell-mediated immunity. Plasma cells are activated B cells that secrete antibodies. Monocytes are also involved in some immune processes.
Types of leukocytes.
agranular l's nongranular leukocyte.
basophilic leukocyte basophil (def. 2).
eosinophilic leukocyte eosinophil.
granular l's leukocytes containing abundant granules in the cytoplasm, including neutrophils, eosinophils, and basophils. Called also granulocyte.
neutrophilic leukocyte neutrophil (def. 2).
nongranular l's leukocytes without specific granules in the cytoplasm, including lymphocytes and monocytes. Called also agranular leukocytes.
polymorphonuclear leukocyte any fully developed, segmented granular leukocyte whose nuclei contain multiple lobes joined by filamentous connections, especially a neutrophil.

leu·ko·cyte

(lū'kō-sīt),
A type of cell formed in the myelopoietic, lymphoid, and reticular portions of the reticuloendothelial system in various parts of the body, and normally present in those sites and in the circulating blood (rarely in other tissues). Under various abnormal conditions the total numbers or proportions, or both, may be characteristically increased, decreased, or unaltered, and leukocytes may be present in other tissues and organs. Leukocytes represent three lines of development from primitive elements: myeloid, lymphoid, and monocytic series. On the basis of features observed with various methods of staining with polychromatic dyes (for example, Wright stain) cells of the myeloid series are frequently termed granular leukocytes, or granulocytes; cells of the lymphoid and monocytic series also have granules in the cytoplasm, but owing to their tiny size and varied properties (frequently not clearly visualized with routine methods), lymphocytes and monocytes are sometimes termed nongranular or agranular leukocytes. Granulocytes are commonly known as polymorphonuclear leukocytes (also polynuclear or multinuclear leukocytes), inasmuch as the mature nucleus is divided into two to five rounded or ovoid lobes that are connected with thin strands or small bands of chromatin; they consist of three distinct types: neutrophils, eosinophils, and basophils, named on the basis of the staining reactions of the cytoplasmic granules. Cells of the lymphocytic series occur as three types, based on the identity of their surface receptors: B lymphocytes, T lymphocytes, and null cells. Morphologically, there are two, somewhat arbitrarily designated, normal varieties: small and large lymphocytes; the former represent the ordinary forms and are conspicuously more numerous in the circulating blood and normal lymphoid tissue; the latter may be found in normal circulating blood but are more easily observed in lymphoid tissue. The small lymphocytes have nuclei that are deeply or densely stained (the chromatin is coarse and bulky) and almost fill the cells, with only a slight rim of cytoplasm around the nuclei; the large lymphocytes have nuclei that are approximately the same size as, or only slightly larger than, those of the small forms, but there is a broader, easily visualized band of cytoplasm around the nuclei. Cells of the monocytic series are usually larger than the other leukocytes, and are characterized by a relatively abundant, slightly opaque, pale blue or blue-gray cytoplasm that contains myriad extremely fine reddish-blue granules. Monocyte nuclei are usually indented, reniform, or horseshoe shaped, but are sometimes rounded or ovoid; their nuclei are usually large and centrally placed and, even when eccentrically located, are completely surrounded by at least a small band of cytoplasm.
Synonym(s): white blood cell
[leuko- + G. kytos, cell]

leukocyte

also

leucocyte

(lo͞o′kə-sīt′)
leu′ko·cyt′ic (-sĭt′ĭk) adj.
leu′ko·cy′toid′ adj.

white blood cell

A cell in the general circulation that is whitish to the naked eye when centrifuged.
 
Types
Nonspecific immune response cells—e.g., monocytes and granulocytes (neutrophils, basophils and eosinophils)—and specific immune response cells—B and T lymphocytes.

leu·ko·cyte

(lū'kō-sīt)
A type of cell formed in the myelopoietic, lymphoid, and reticular portions of the reticuloendothelial system in various parts of the body, and normally present in those sites and in the circulating blood. Under various abnormal conditions, the total number of leukocytes may be increased or decreased or their relative proportions altered, and they may appear in other tissues and organs. Leukocytes represent three lines of development from primitive elements: myeloid, lymphoid, and monocytic series. On the basis of features observed with various methods of staining with polychromatic dyes, cells of the myeloid series are frequently termed granular leukocytes, or granulocytes; because the cytoplasmic granules of lymphocytes and monocytes are smaller and frequently not clearly visualized with routine methods, these cells are sometimes termed nongranular or agranular leukocytes. Granulocytes are commonly known as polymorphonuclear leukocytes (also polynuclear or multinuclear leukocytes), because in a mature cell the nucleus is divided into two to five rounded or ovoid lobes that are connected with thin strands or small bands of chromatin; they consist of three distinct types: neutrophils, eosinophils, and basophils, named on the basis of the staining reactions of the cytoplasmic granules. Cells of the lymphocytic series are smaller than other leukocytes and have relatively large, darkly staining, eccentrically placed nuclei. Cells of the monocytic series are usually larger than the other leukocytes and are characterized by a relatively abundant, slightly opaque, pale blue or blue-gray cytoplasm that contains many fine reddish-blue granules. Monocytes are usually indented, reniform, or shaped similarly to a horseshoe, but are sometimes rounded or ovoid; their nuclei are usually large and centrally placed and, even when eccentrically located, are completely surrounded by at least a small band of cytoplasm.
Synonym(s): white blood cell, leucocyte.
[leuko- + G. kytos, cell]

Leukocyte

A white blood cell protects the body against infection and fight infection when it occurs. They are bigger than red blood cells.

leu·ko·cyte

(lū'kō-sīt)
Cell formed in myelopoietic, lymphoid, and reticular portions of the reticuloendothelial system in various parts of the body, and normally present in those sites and in the circulating blood.
Synonym(s): white blood cell, leucocyte.
[leuko- + G. kytos, cell]

Patient discussion about leukocyte

Q. can i get a short explanation about white blood cells and their job? what does it mean if i have a insafition

A. White blood cells (WBC's) are the ones responsible for the immune system in the body. The white blood cell count rises in cases of infection, steroid use and other conditions. A low white blood cell count can have many causes, which need to be further evaluated by a doctor.

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