leukocyte


leukocyte
leukocytic /looh'keuh sit"ik/, adj.
/looh"keuh sit'/, n. Immunol.
Also, leucocyte.
[1865-70; LEUKO- + -CYTE]

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Any of several types of blood cells that help defend the body from infection.

The different mature forms
granulocytes, including neutrophils (heterophils), basophils, and eosinophils; monocytes, including macrophages; and lymphocytes
have different functions, including ingesting bacteria, protozoans, or infected or dead body cells; producing antibodies; and regulating the action of other leukocytes. They act mostly in the tissues and are in the bloodstream only for transport. Blood normally contains 5,000–10,000 leukocytes per cu mm.

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also spelled  leucocyte , also called  white blood cell  or  white corpuscle 
 a cellular component of the blood that lacks hemoglobin, has a nucleus, is capable of motility, and defends the body against infection and disease by ingesting foreign materials and cellular debris, by destroying infectious agents and cancer cells, or by producing antibodies (antibody). Leukocytes are found within tissues, where they fight infections, and in circulation. On the basis of their appearance under a light microscope, leukocytes are grouped into three major classes—lymphocytes, granulocytes, and monocytes—each of which carries out somewhat different functions.

 Lymphocytes (lymphocyte), which are further divided into B and T cells, are responsible for the specific recognition of foreign agents and their subsequent removal from the host. B lymphocytes (B cell) secrete antibodies, which are proteins that bind to foreign microorganisms in body tissues and mediate their destruction. Typically, T cells recognize virally infected or cancerous cells and destroy them, or they serve as helper cells to assist the production of antibody by B cells. Also included in this group are natural killer (NK) cells, so named for their inherent ability to kill a variety of target cells. In a healthy person, about 25 to 33 percent of white blood cells are lymphocytes.

      Granulocytes (blood), the most numerous of the leukocytes, rid the body of large pathogenic organisms such as protozoans or helminths and are also key mediators of allergy and other forms of inflammation. These cells contain many cytoplasmic granules, or secretory vesicles, that harbour potent chemicals important in immune responses. They also have multilobed nuclei, and because of this they are often called polymorphonuclear cells. On the basis of how their granules take up dye in the laboratory, granulocytes are subdivided into three categories: neutrophils, eosinophils, and basophils. The most numerous of the granulocytes—making up 50 to 80 percent of all leukocytes—are neutrophils. They are often one of the first cell types to arrive at a site of infection, where they engulf and destroy the infectious microorganisms through a process called phagocytosis. Eosinophils and basophils, as well as the tissue cells called mast cells (mast cell), typically arrive later. The granules of basophils and of the closely related mast cells contain a number of chemicals, including histamine and leukotrienes, that are important in inducing allergic inflammatory responses. Eosinophils destroy parasites and also help to modulate inflammatory responses.

      Monocytes (blood), which constitute up to 7 percent of the total number of white blood cells in the blood, move from the blood to sites of infection, where they differentiate further into macrophages. These cells are scavengers that phagocytose whole or killed microorganisms and are therefore effective at direct destruction of pathogens and cleanup of cellular debris from sites of infection (see video). Neutrophils and macrophages are the main phagocytic cells of the body, but macrophages are much larger and longer-lived than neutrophils. Some macrophages are important as antigen-presenting cells, cells that phagocytose and degrade microbes and present portions of these organisms to T lymphocytes, thereby activating the specific acquired immune response.

      A healthy adult human has between 4,500 and 11,000 leukocytes per cubic millimetre of blood. The blood leukocyte count rises after exercise, convulsions, and strong emotional reactions; during pain, pregnancy, and labour; and also during many disease states, such as infections and intoxications. Specific types of cells are associated with different illnesses and reflect the special function of that cell type in body defense. A fall in leukocyte count, which is called leukopenia, occurs in states such as debilitation, anaphylaxis, and overwhelming infection. In general, newborns have a high white blood cell count that gradually falls to the adult level during childhood. An exception is the lymphocyte count, which is low at birth, reaches its highest levels in the first four years of life, and thereafter falls gradually to a stable adult level. See also blood cell formation.

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Universalium. 2010.

Look at other dictionaries:

  • leukocyte — leukocyte. См. лейкоцит. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • leukocyte — also leucocyte, 1860, via Fr. leucocyte, from Gk. leuko , comb. form of leukos white (see LIGHT (Cf. light) (n.)) + ctye (see CYTO (Cf. cyto )) …   Etymology dictionary

  • leukocyte — [lo͞o′kō sīt΄, lo͞o′kəsīt΄] n. [see LEUCO & CYTE] any of the small, colorless nucleated cells in the blood, lymph, and tissues, which are important in the body s defenses against infection, including granular types such as neutrophils,… …   English World dictionary

  • leukocyte — 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… …   Medical dictionary

  • leukocyte — var. of LEUCOCYTE. * * * leukocyte, cytic etc.: see leucocyte …   Useful english dictionary

  • leukocyte — noun Etymology: International Scientific Vocabulary Date: 1870 white blood cell • leukocytic adjective …   New Collegiate Dictionary

  • leukocyte — (loo ko saīt) Any colorless white blood cell. Can be classified into granular and agranular lymphocytes …   Dictionary of microbiology

  • leukocyte — noun A white blood cell …   Wiktionary

  • leukocyte — Synonyms and related words: Rh factor, Rh negative, Rh positive, Rh type, Rhesus factor, antibody, antigen, arterial blood, blood, blood bank, blood cell, blood count, blood donor, blood donor center, blood group, blood grouping, blood picture,… …   Moby Thesaurus

  • leukocyte — n. white blood cell …   English contemporary dictionary


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