platelet
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platelet
[plāt´let]the smallest of the formed elements in blood, a disk-shaped, non-nucleated blood element with a fragile membrane, formed in the red bone marrow by fragmentation of megakaryocytes. Platelets tend to adhere to uneven or damaged surfaces, and there are an average of about 250,000 per mm3 of blood. The bone marrow produces from 30,000 to 50,000 platelets per mm3 of blood daily, which means that in any ten-day period all the platelets in the body are completely replaced. Called also thrombocyte.
The rate of platelet formation seems to be governed by the amount of oxygen in the blood and the presence of nucleic acid derivatives from injured tissue. At any given time about one-third of the total blood platelets can be found in the spleen; the remaining two-thirds are in the circulating blood. Their primary functions are related to coagulation of blood. Because of their adhesion and aggregation capabilities they can occlude small breaks in blood vessels and prevent escape of blood . They also are able to take up, store, transport, and release serotonin and platelet factor 3. Abnormally high numbers of platelets occur in the presence of malignancy, splenectomy, asphyxiation, polycythemia vera, and acute infections. A very low count can occur as a result of idiopathic thrombocytopenic purpura, pernicious anemia, and allergic conditions, and during cancer chemotherapy. Many drugs can cause a toxic decrease in the number of platelets.
The rate of platelet formation seems to be governed by the amount of oxygen in the blood and the presence of nucleic acid derivatives from injured tissue. At any given time about one-third of the total blood platelets can be found in the spleen; the remaining two-thirds are in the circulating blood. Their primary functions are related to coagulation of blood. Because of their adhesion and aggregation capabilities they can occlude small breaks in blood vessels and prevent escape of blood . They also are able to take up, store, transport, and release serotonin and platelet factor 3. Abnormally high numbers of platelets occur in the presence of malignancy, splenectomy, asphyxiation, polycythemia vera, and acute infections. A very low count can occur as a result of idiopathic thrombocytopenic purpura, pernicious anemia, and allergic conditions, and during cancer chemotherapy. Many drugs can cause a toxic decrease in the number of platelets.
Platelet response to vascular injury. From Malarkey and McMorrow, 2000.
platelet factors factors important in hemostasis which are contained in or attached to the platelets: platelet factor 1 is adsorbed coagulation factor V from the plasma; platelet factor 2 is an accelerator of the thrombin-fibrinogen reaction; platelet factor 3 is a lipoprotein with roles in the activation of both coagulation factor X and prothrombin; platelet factor 4 is capable of inhibiting the activity of heparin.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
plate·let
(plāt'let),An irregularly shaped, disclike cytoplasmic fragment of a megakaryocyte that is shed in the marrow sinus and subsequently found in the peripheral blood, where it functions in clotting. A platelet contains granules in its central part (granulomere) and, peripherally, clear protoplasm (hyalomere), but no nucleus, is about one third to one half the size of an erythrocyte, and contains no hemoglobin.
Synonym(s): Bizzozero corpuscle, blood disc, elementary bodies (2) , elementary particle (1) , third corpuscle, thrombocyte, thromboplastid (1) , Zimmermann corpuscle
[see plate]
Farlex Partner Medical Dictionary © Farlex 2012
platelet
(plāt′lĭt)n.
A minute, nonnucleated, disklike cytoplasmic body found in the blood plasma of mammals that is derived from a megakaryocyte and functions to promote blood clotting. Also called blood platelet, thrombocyte.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
plate·let
(plāt'lĕt)An irregularly shaped, disclike, cytoplasmic fragment of a megakaryocyte that is shed in the marrow sinus and subsequently found in the peripheral blood, where it functions in clotting. Contains granules in the central part (granulomere) and, peripherally, clear protoplasm (hyalomere), but no definite nucleus; is about one third to one half the size of an erythrocyte.
See also: plate
Synonym(s): blood disc, elementary particle (1) , thrombocyte, thromboplastid (1) .
See also: plate
Synonym(s): blood disc, elementary particle (1) , thrombocyte, thromboplastid (1) .
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
platelet
A fragment of the CYTOPLASM of a MEGAKARYOCYTE 2–4 mm in diameter. Each megakaryocyte produces 1000 to 3000 platelets, which are present in large numbers in the blood-50,000 to 300,000 per cu. mm. Platelets survive for about 10 days and play an essential part in blood clotting. Platelet plasma membranes contain a range of glycoproteins by means of which they bind to different materials including collagen, fibrinogen and von Willebrand factor. Platelets are by no means the passive tissue fragments they were formerly thought to be. They carry many granules and a canalicular system by which the granules are released. They also have a dense tubular membrane system in which prostaglandins and thromboxanes are synthesized. Platelet granules contain heparin-neutralizing factor, von Willebrand factor, smooth muscle growth factor and fibrinogen. Deficiency of platelets is known as thrombocytopenia.Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
platelet
see BLOOD PLATELETS.Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
Platelet
An irregularly shaped cell-like particle in the blood that is an important part of blood clotting. Platelets are activated when an injury causes a blood vessel to break. They change shape from round to spiny, "sticking" to the broken vessel wall and to each other to begin the clotting process.
Mentioned in: Anticoagulant and Antiplatelet Drugs, Erythroblastosis Fetalis, Fibrinogen Test, Idiopathic Thrombocytopenic Purpura, Multiple Myeloma, Waldenström's Macroglobulinemia
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
Deetjen,
Hermann, German physician, 1867-1915.Deetjen bodies - a disklike cytoplasmic fragment found in the peripheral blood where it functions in clotting. Synonym(s): platelet
Bizzozero,
Giulio, Italian physician, 1846-1901.Bizzozero corpuscle - an irregularly shaped disklike cytoplasmic fragment of a megakaryocyte found in the peripheral blood; functions in clotting. Synonym(s): platelet
Hayem,
Georges, French physician, 1841-1933.Hayem hematoblast - an irregularly shaped, disklike cytoplasmic fragment of a megakaryocyte found in the peripheral blood where it functions in clotting. Synonym(s): platelet
Hayem solution - a blood diluent used prior to counting red blood cells.
Hayem-Widal syndrome - obsolete term for acquired hemolytic icterus. Synonym(s): Widal syndrome
Zimmermann,
Karl W., German histologist, 1861-1935.polkissen of Zimmermann - mesangial cells that fill the triangular space between the macula densa and the afferent and efferent arterioles of the juxtaglomerular apparatus. Synonym(s): extraglomerular mesangium
Zimmermann corpuscle - Synonym(s): Zimmermann elementary particle
Zimmermann elementary particle - a disklike cytoplasmic fragment found in the peripheral blood where it functions in clotting. Synonym(s): platelet; Zimmermann corpuscle; Zimmermann granule
Zimmermann granule - Synonym(s): Zimmermann elementary particle
Medical Eponyms © Farlex 2012
plate·let
(plāt'lĕt)An irregularly shaped, disclike, cytoplasmic fragment of a megakaryocyte that is shed in the marrow sinus and subsequently found in the peripheral blood, where it functions in clotting.
Synonym(s): blood disc, elementary particle (1) , thrombocyte, thromboplastid (1) .
Synonym(s): blood disc, elementary particle (1) , thrombocyte, thromboplastid (1) .
Medical Dictionary for the Dental Professions © Farlex 2012