platelet aggregation

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1. massing or clumping of materials together.
2. a clumped mass of material.
familial aggregation the occurrence of more cases of a given disorder in close relatives of a person with the disorder than in control families.
platelet aggregation platelet agglutination.

platelet aggregation

platelet cohesion, mediated by glycoprotein membrane receptors and fibrinogen, part of a sequential mechanism leading to the initiation and formation of a thrombus or hemostatic plug. Aggregation is used as an in vitro platelet function assay, and is induced by adenosine diphosphate, arachidonic acid, thrombin, and collagen.

plate·let ag·gre·ga·tion

(plāt'lĕt ag'rĕ-gā'shŭn)
The clumping together of platelets in the blood; part of the sequence of events leading to the formation of a thrombus (clot) or hemostatic plug.

Platelet aggregation

The clumping together of blood cells, possibly forming a clot.


1. massing or clumping of materials together.
2. a clumped mass of material.

familial aggregation
the occurrence of more cases of a given disorder in close relatives of an animal with the disorder than in control families.
platelet aggregation
platelet agglutination.


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.

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.
References in periodicals archive ?
We measured the inhibition of platelet aggregation (using WBA aggregometer) in these patients.
The results of preliminary in vitro studies have shown that Allicor produces a direct effect on platelet aggregation and plasma fibrinolytic activity.
Patients with this syndrome will have normal platelet aggregation studies but abnormal platelet procoagulant activity and decreased microparticle formation.
Phosphatidylinositol 3-kinase inhibitor, wortamannin, inhibits 5-hydroxytryptamine mediated potentiation of platelet aggregation induced by epinephrine.
Provexis looked at the multiple end-points of platelet aggregation and numerous pathways in every single one of those studies, and decided to measure pathways A, B, C and D and show that this fruit compound was having an effect.
24), clopidogrel in vitro reduced ADP-induced platelet aggregation and increased endothelial NO production depending on dose.
Two out of the five subjects who showed a significant difference with the 5[micro]M concentrations of ADP also showed a difference in platelet aggregation with administration of collagen and arachidonic acid.
Privitera confirmed that platelet aggregation was the most common problem observed in both groups of patients.
Analysis of the same data with platelet aggregometry showed a highly significant reduction of platelet aggregation in response to activation with arachidonic acid (p=0.
Reconciling their findings with earlier scientific evidence that cGMP inhibits platelet aggregation, the researchers believe that cGMP initially causes platelets to clump to seal a wound, but later reverses to stop an excessive buildup of cells that might block a blood vessel.
asper venom in order to investigate the possible presence of inhibitors of platelet aggregation.
Medicure has focused its anti-thrombotic program on the design of novel structures that inhibit platelet aggregation, which is one of the causes of clot formation in the blood vessels, as well as Factor Xa inhibition (the coagulation factor).

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