- lymphoid tissue
Cells, tissues, and organs composing the immune system, including the bone marrow, thymus, spleen, and lymph nodes.The most highly organized components are the thymus and lymph nodes, and the least organized are the cells that wander in the loose connective-tissue spaces under membranes lining most body systems, where they can establish lymph nodules (local lymphocyte production centre) in response to antigens. The most common lymphoid tissue cell is the lymphocyte. Others are macrophages, which engulf foreign materials and probably alter them to initiate the immune response, and reticular cells, which produce and maintain thin networks of fibres as a framework for most lymphoid organs. See also immunity; lymphatic system.
* * *▪ anatomycells and organs that make up the lymphatic system, such as white blood cells (leukocytes (leukocyte)), bone marrow, and the thymus, spleen, and lymph nodes (lymph node).Lymphoid tissue has several different structural organizations related to its particular function in the immune response. The most highly organized lymphoid tissues are in the thymus and lymph nodes, which are well-defined encapsulated organs with easily identifiable architectures. In the spleen (a soft, purplish organ lying high in the abdomen), the lymphoid tissue is a cylinder of loosely organized cells surrounding small arteries. In the bone marrow this tissue is mixed with the blood-forming cells, and no organization is apparent. The most diffuse lymphoid tissue is found in the loose connective-tissue spaces beneath most wet epithelial (epithelium) membranes, such as those that line the gastrointestinal tract and the respiratory system. In these spaces many cells of the lymphatic system wander and become exposed to invading microorganisms and foreign material. They can establish localized centres of cell production in response to such invasions. These are referred to as nodules (lymph nodule) and are not to be confused with nodes, an entirely different structure. Some nodules become relatively permanent structures, such as the tonsils (tonsil), appendix, and Peyer's patches (Peyer patch), which are in the lining of the small intestine. Most nodules appear and disappear in response to local needs.Several types of cells are included in the lymphoid system—for example, reticular cells and white blood cells such as macrophages and lymphocytes (lymphocyte). Reticular cells provide structural support, since they produce and maintain the thin networks of fibres that are a framework for most lymphoid organs. Macrophages (blood) help eliminate invaders by engulfing foreign materials and initiating the immune response. These cells may be fixed in one place, such as lymph nodes, or they may wander in the loose connective-tissue spaces. The most common cell type in the lymphoid tissue is the lymphocyte. Like macrophages, lymphocytes are formed from stem cells in the bone marrow and then circulated in the blood to the lymphoid tissue. T lymphocytes mature in the thymus before proceeding to the other lymphoid organs, such as the spleen. B lymphocytes mature in the bone marrow and proceed directly to the lymphoid organs. Both kinds play a key role in immune responses to infectious microorganisms.
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Lymphoid tissue — A part of the body s immune system that helps protect it from bacteria and other foreign entities. Lymphoid tissue is rich in lymphocytes (and accessory cells such as macrophages and reticular cells). The lymphoid tissue includes the lymph nodes … Medical dictionary
lymphoid tissue — noun tissue making up the lymphatic system • Syn: ↑lymphatic tissue • Hypernyms: ↑animal tissue • Hyponyms: ↑tonsil, ↑palatine tonsil, ↑faucial tonsil, ↑ … Useful english dictionary
lymphoid tissue — Tissue that is particularly rich in lymphocytes (and accessory cells such as macrophages and reticular cells), particularly the lymph nodes, spleen, thymus, Peyer s patches, pharyngeal tonsils, adenoids, and (in birds) the Bursa of Fabricius … Dictionary of molecular biology
lymphoid tissue — a tissue responsible for the production of lymphocytes and antibodies. It occurs as discrete organs, in the form of the lymph nodes, tonsils, thymus, and spleen, and also as diffuse groups of cells not separated from surrounding tissue. See also … The new mediacal dictionary
Mucosa-associated lymphoid tissue — MALT redirects here. For germinated cereal grains, see Malt. The mucosa associated lymphoid tissue (MALT) (also called mucosa associated lymphatic tissue) is the diffusion system of small concentrations of lymphoid tissue found in various sites… … Wikipedia
Mucosa-associated lymphoid tissue — Les (MALT) (mucosa associated lymphoid tissue), ou tissus lymphoïdes associés aux muqueuses, forment une partie des organes lymphatiques secondaires qui se situent de manière diffuse dans différents organes du corps, par exemple dans le tube… … Wikipédia en Français
Gut-associated lymphoid tissue — The digestive tract s immune system is often referred to as gut associated lymphoid tissue (GALT) and works to protect the body from invasion. GALT is an example of mucosa associated lymphoid tissue. FunctionAbout 70% of the body s immune system… … Wikipedia
peripheral lymphoid tissue — Secondary lymphoid tissue, not necessarily located peripherally. See lymphoid tissue … Dictionary of molecular biology
bronchial-associated lymphoid tissue — bronchus associated lymphoid tissue (BALT) lymphoid tissue associated with the lungs … Medical dictionary
gut-associated lymphoid tissue — (= GALT) Peripheral lymphoid organ consisting of lymphoid tissue associated with the gut (Peyer s patches, tonsils, mesenteric lymph nodes, and the appendix) … Dictionary of molecular biology