platelet

platelet:

see blood clottingblood clotting,
process by which the blood coagulates to form solid masses, or clots. In minor injuries, small oval bodies called platelets, or thrombocytes, tend to collect and form plugs in blood vessel openings.
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Platelet

(also thrombocyte), a formed element found in the blood of vertebrate animals and man that plays an important role in blood coagulation. The platelets of vertebrate animals (except mammals) are small ovoid cells with a solid nucleus and weakly basophilic cytoplasm. In mammals, including man, platelets are anuclear bodies 2–5 µ in diameter. The platelets normally number about 250,000–350,000 per cubic mm of blood. They have granules containing serotonin and substances involved in blood coagulation, as well as mitochondria, microtubules, glycogen granules, and sometimes ribosomes. In mammals, platelets originate in the blood-forming organs when fragments of the cytoplasm of megakaryocytes separate from the megakaryocytes. The life-span of the platelets of mammals, including man, is about five to nine days.

REFERENCE

Markosian, A. A. Fiziologiia trombotsitov. Leningrad, 1970.

platelet

[′plāt·lət] (histology) thrombocyte (hydrology) A small ice crystal which, when united with other such crystals, forms a layer of floating ice, especially sea ice, and serves as seed crystals for further thickening of the ice cover.

platelet

a minute cell occurring in the blood of vertebrates and involved in clotting of the blood

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" >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.

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.

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]

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.

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) .

platelet

(plat'let) [Gr. plate, flat]

PLATELET PLUG FORMATION AND CLOTTINGA round or oval disk, 2 to 4 µm in diameter, found in the blood of vertebrates. Platelets number 130,000 to 400,000/mm³. They are fragments of megakaryocytes, large cells found in the bone marrow. Synonym: thrombocyte See: illustration; blood for illus.; megakaryocyte for illus.; thrombopoietin

Function

Platelets contribute to chemical blood clotting and to other aspects of hemostasis. Platelet factors are the chemicals released by platelets to initiate the first stage of (intrinsic pathway) chemical clotting. When a capillary ruptures, platelets adhere to each other and to the cut edges of the vessel, forming a platelet plug. Blood clotting may be beneficial (e.g., in preventing blood loss from wounds) or may be harmful when it occurs within arteries or veins inside the body (e.g., during coronary thrombosis). Blood clotting is a positive feedback cascade that may continue and occlude an unbroken vessel.

Disorders

Thrombocytopenia (reduced platelet count) occurs in acute infections, anaphylactic shock, and certain hemorrhagic diseases and anemias. Thrombocytosis (increased platelet count) occurs after operations, esp. splenectomy, and after violent exercise and tissue injury.

illustration

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.

platelet

see BLOOD PLATELETS.

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

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): plateletHayem 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 mesangiumZimmermann corpuscle - Synonym(s): Zimmermann elementary particleZimmermann elementary particle - a disklike cytoplasmic fragment found in the peripheral blood where it functions in clotting. Synonym(s): platelet; Zimmermann corpuscle; Zimmermann granuleZimmermann granule - Synonym(s): Zimmermann elementary particle

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REFERENCE

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Function

Disorders

platelet

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Deetjen,

Bizzozero,

Hayem,

Zimmermann,

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Synonyms for platelet

noun tiny bits of protoplasm found in vertebrate blood

Synonyms

Related Words