Platelet (redirected from platelet cofactor I)

platelet /plate·let/ (plat´let) thrombocyte; a disk-shaped structure, 2 to 4 µm in diameter, found in the blood of mammals and important for its role in blood coagulation; platelets, which are formed by detachment of part of the cytoplasm of a megakaryocyte, lack a nucleus and DNA but contain active enzymes and mitochondria.

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plate·let (pltlt)

n.

A minute, irregularly shaped, disklike cytoplasmic body found in blood plasma that promotes blood clotting and has no definite nucleus, no DNA, and no hemoglobin. Also called blood platelet, thrombocyte.

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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

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platelet (plāt´let),

n a disc found in the blood of mammals that is involved in the coagulation and clotting of blood.

platelet ac-globulin,

n See factor, platelet, 1.

platelet activating factor,

n 1-0-alkyl-2-sn-glycero-3-phosphocholine. A phospholipid derivative formed by platelets, basophils, neutrophils, monocytes, and macrophages. It is a potent platelet-aggregating agent and inducer of systemic anaphylactic symptoms, including hypotension, thrombocytopenia, neutropenia, and bronchoconstriction.

platelet aggregation,

n a clumping together of platelets in vitro, and likely in vivo, by a number of agents, such as adenosine diphosphate, thrombin, and collagen, as part of a sequential mechanism leading to the initiation and formation of a thrombus or hemostatic plug.

platelet aggregation inhibitors,

n.pl the drugs or agents that antagonize or impair any mechanism leading to blood platelet aggregation.

platelet cofactor I,

n See factor VIII.

platelet cofactor II,

n See factor IX and plasma thromboplastin component.

platelet count,

n the number of platelets found in 1 mm³ of blood; the normal range is between 200,000 and 300,000 platelets.

platelet-derived growth factors (PDGF),

n a type of protein released by platelets of the blood that aid in the repair and regeneration of connective tissue.

platelet disorder,

n See disorder, platelet.

platelet-rich plasma (PRP),

n See plasma, platelet-rich (PRP).

platelet transfusion,

n 1. the transfer of blood platelets from a donor to a recipient or reinfusion to the donor.
n 2. a treatment modality used in treating hemophilia and other conditions of impaired blood coagulation.

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platelet

a small disk or platelike structure, the smallest of the formed elements in blood. Blood platelets (called also thrombocytes) are disk-shaped, non-nucleated blood elements with a very fragile membrane; they tend to adhere to uneven or damaged surfaces. They average about 250,000 per cubic millimeter of blood and are formed in the red bone marrow by fragmentation of megakaryocytes, the largest of the bone marrow cells. Platelet production is controlled by a hormone, thrombopoietin, and regulatory lymphocytes acting at the stem cell level. 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.

The functions of platelets are related to the clotting of blood. Because of their adhesion and aggregation capabilities platelets can occlude small breaks in blood vessels and prevent the escape of blood. Platelets which have adhered to exposed collagen in damaged vessels release ADP in milliseconds which in turn initiates the synthesis of thromboxane A₂, a very potent prostaglandin which causes platelet aggregation and localized vasoconstriction. Fibrinogen, factors V and VIII, calcium ions, platelet phospholipid (PF-3), associated with the platelet membrane are also released. Substances contained within the platelet granules such as thromboglobulin, heparin neutralizing activity (PF-4) mitogens such as platelet derived growth factor, thrombospondin, ADP, serotonin and calcium ions are also released by aggregated platelets.

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platelet-activating factor (PAF)

see platelet-activating factor.

platelet adhesion

the adherence of platelets to any area with damaged blood vessels; an important component of hemostasis.

platelet aggregation

the progressive accumulation of platelets, attracted by other platelets once adhesion begins. Thromboxane A₂ causes irreversible platelet aggregation.

platelet aggregation test

a known platelet aggregating factor such as collagen, ADP or thrombin is added to a suspension of the platelets under test and the degree of aggregation measured by decrease in turbidity of the suspension.

platelet count

may be performed directly (in a hemocytometer chamber) or indirectly (estimating from the stained blood smear by number per field or in comparison to the number of white blood cells), expressed as number of cells per liter of blood.

platelet-derived growth factor

one of three growth factors released by platelets which undergo the release reaction; the growth factors stimulate endothelial cell proliferation.

platelet distribution width (PDW)

an indication of variation in platelet size which can be a sign of active platelet release.

platelet factor 3 (PF-3) test, platelet release test

test the antiplatelet activity of serum; used to detect circulating antiplatelet antibodies. Antibody-antigen reactions involving platelets cause the release of PF-3 from platelets which in turn shortens the contact-activated clotting time of platelet-rich plasma (PRP).

platelet factors

factors important in hemostasis which are contained in or attached to the platelets: platelet factor 1 is adsorbed clotting factor V from the plasma; platelet factor 2 is an accelerator of the thrombin-fibrinogen reaction; platelet factor 3 is a phospholipid with potent procoagulant activity; platelet factor 4 is capable of inhibiting the activity of heparin (heparin neutralizing activity).

mean platelet volume (MPV)

elevated level is an indication of increased megakaryocyte shedding of platelets and decreased level is seen in thrombocytopenia.

platelet plug formation

see platelet aggregation (above).

platelet release reaction

measured by the degree of secondary ADP-mediated aggregation that occurs. This is assessed by the amount of PF-4, PF-3 or serotonin, etc. released.

platelet retention

tested by testing the adhesiveness of a suspension of the subject platelets to a glass bead column or standard size filter.

platelet rich plasma

plasma prepared by centrifugation to separate out red blood cells but not platelets for transfusion.

platelet storage-pool disease

an inherited autosomal thrombopathia in American foxhounds and cats characterized by a deficiency of platelet storage granules.

platelet transfusion

transfusion of fresh, nonchilled whole blood is the usual method of transfusing platelets to an animal with thrombocytopenia.