platelets information
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Platelet
Image from alight microscope(40) from a peripheralblood smearsurrounded byred blood cells. One
normal platelet can be seen in the upper left side of the image (purple) and is significantly smaller in size
than thered blood cells(stained pink). Twogiant platelets(stained purple) are also visible.
Platelets, or thrombocytes(from Greek , "clot" and , "cell"), are small, disk shaped clear
cell fragments (i.e. cells that do not have a nucleus), 23 m in diameter,[1] which are derived from
fragmentation of precursormegakaryocytes. The average lifespan of a platelet is normally just 5 to 9
days. Platelets are a natural source ofgrowth factors. They circulate in thebloodofmammalsand are
involved inhemostasis, leading to the formation ofblood clots.
If the number of platelets is too low, excessivebleedingcan occur. However, if the number of platelets is
too high, blood clots can form (thrombosis), which may obstruct blood vessels and result in such events
as astroke,myocardial infarction,pulmonary embolismor the blockage of blood vessels to other parts
of the body, such as the extremities of the arms or legs. An abnormality or disease of the platelets is
called a thrombocytopathy,[2] which could be either a low number of platelets (thrombocytopenia), a
decrease in function of platelets (thrombasthenia), or an increase in the number of platelets
(thrombocytosis). There are disorders that reduce the number of platelets, such as heparin-induced
thrombocytopenia (HIT) or thrombotic thrombocytopenic purpura (TTP) that typically cause
thromboses, or clots, instead of bleeding.
Platelets release a multitude of growth factors includingplatelet-derived growth factor(PDGF), a potent
chemotacticagent, andTGF beta, which stimulates the deposition ofextracellular matrix. Both of these
growth factors have been shown to play a significant role in the repair and regeneration ofconnective
tissues. Other healing-associated growth factors produced by platelets include basic fibroblast growth
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/Hemostasishttp://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Growth_factorshttp://en.wikipedia.org/wiki/Megakaryocytehttp://en.wikipedia.org/wiki/Platelet#cite_note-1http://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Giant_platelethttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Blood_filmhttp://en.wikipedia.org/wiki/Light_microscope 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factor, insulin-like growth factor 1, platelet-derivedepidermal growth factor, andvascular endothelial
growth factor. Local application of these factors in increased concentrations through Platelet-rich
plasma(PRP) has been used as an adjunct towound healingfor several decades.[3][4][5][6][7][8][9]
Kinetics
HSC=hematopoietic stem cell, Progenitor=progenitor cell, L-blast=lymphoblast,lymphocyte, Mo-
blast=monoblast,monocyte,myeloblast, Pro-M=promyelocyte,myelocyte, Meta-M=metamyelocyte,neutrophil,eosinophil,basophil, Pro-E=proerythroblast, Baso-E=basophilic erythroblast, poly-
E=polychromatic erythroblast, Ortho-E=Orthochromatic erythroblast,erythrocyte,promegakaryocyte,
megakaryocyte, platelet.
The physiological range for platelets is (150 400) 103 per mm3. Platelets are produced in blood cell formation (thrombopoiesis) inbone marrow, by budding off
frommegakaryocytes.
Megakaryocyte and platelet production is regulated by thrombopoietin, a hormone usuallyproduced by theliverandkidneys.
Eachmegakaryocyteproduces between 5,000 and 10,000 platelets. Around 1011 platelets are produced each day by an average healthy adult. Reserve platelets are stored in the spleen, and are released when needed by sympathetically
induced splenic contraction.
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t.jpghttp://en.wikipedia.org/wiki/Megakaryocytehttp://en.wikipedia.org/wiki/Kidneyhttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Thrombopoietinhttp://en.wikipedia.org/wiki/Megakaryocyteshttp://en.wikipedia.org/wiki/Bone_marrowhttp://en.wikipedia.org/wiki/Thrombopoiesishttp://en.wikipedia.org/wiki/Megakaryocytehttp://en.wikipedia.org/wiki/Promegakaryocytehttp://en.wikipedia.org/wiki/Erythrocytehttp://en.wikipedia.org/w/index.php?title=Orthochromatic_erythroblast&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Polychromatic_erythroblast&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Basophilic_erythroblast&action=edit&redlink=1http://en.wikipedia.org/wiki/Proerythroblasthttp://en.wikipedia.org/wiki/Basophilhttp://en.wikipedia.org/wiki/Eosinophilhttp://en.wikipedia.org/wiki/Neutrophilhttp://en.wikipedia.org/wiki/Metamyelocytehttp://en.wikipedia.org/wiki/Myelocytehttp://en.wikipedia.org/wiki/Promyelocytehttp://en.wikipedia.org/wiki/Myeloblasthttp://en.wikipedia.org/wiki/Monocytehttp://en.wikipedia.org/wiki/Monoblasthttp://en.wikipedia.org/wiki/Lymphocytehttp://en.wikipedia.org/wiki/Lymphoblasthttp://en.wikipedia.org/wiki/Progenitor_cellhttp://en.wikipedia.org/wiki/Hematopoietic_stem_cellhttp://en.wikipedia.org/wiki/Platelet#cite_note-9http://en.wikipedia.org/wiki/Platelet#cite_note-7http://en.wikipedia.org/wiki/Platelet#cite_note-7http://en.wikipedia.org/wiki/Platelet#cite_note-5http://en.wikipedia.org/wiki/Platelet#cite_note-5http://en.wikipedia.org/wiki/Platelet#cite_note-3http://en.wikipedia.org/wiki/Platelet#cite_note-3http://en.wikipedia.org/wiki/Wound_healinghttp://en.wikipedia.org/wiki/Platelet-rich_plasmahttp://en.wikipedia.org/wiki/Platelet-rich_plasmahttp://en.wikipedia.org/wiki/Vascular_endothelial_growth_factorhttp://en.wikipedia.org/wiki/Vascular_endothelial_growth_factorhttp://en.wikipedia.org/wiki/Epidermal_growth_factorhttp://en.wikipedia.org/wiki/Insulin-like_growth_factor_1http://en.wikipedia.org/wiki/Fibroblast_growth_factor 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The lifespan of circulating platelets is 5 to 9 days. Old platelets are destroyed byphagocytosisin thespleenand byKupffer cellsin theliver.
Thrombus formation
Aggregation of platelets. Platelet rich human blood plasma (left vial) is a turbid liquid. Upon addition of
ADP, platelets are activated and start to aggregate, forming white flakes (right vial).
The function of platelets is the maintenance ofhemostasis. This is achieved primarily by the formation
of thrombi, when damage to the endothelium of blood vessels occurs. On the converse, thrombus
formation must be inhibited at times when there is no damage to the endothelium.
Activation
The inner surface of blood vessels is lined with a thin layer of endothelial cells that, in normal
hemostasis, acts to inhibit platelet activation by producing nitric oxide, endothelial-ADPase, and
PGI2. Endothelial-ADPase clears away the platelet activator,ADP.
Endothelial cells produce a protein called von Willebrand factor (vWF), a cell adhesion ligand, which
helps endothelial cells adhere tocollagenin thebasement membrane. Under physiological conditions,
collagen is not exposed to the bloodstream. vWF is secreted constitutively into the plasma by the
endothelial cells, and is stored in granules within the endothelial cell and in platelets.
When the endothelial layer is injured, collagen, vWF and tissue factor from the subendothelium is
exposed to the bloodstream. When the platelets contact collagen or vWF, they are activated (e.g. to
clump together). They are also activated bythrombin(formed with the help of tissue factor). They can
also be activated by a negatively charged surface, such as glass. Non-physiological flow conditions
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(especially high values of shear stress) caused by arterial stenosis or artificial devices (Mechanical Heart
Valves, blood pumps etc) can also lead to platelet activation.[10]
Platelet activation further results in the scramblase-mediated transport of negatively charged
phospholipidsto the platelet surface. These phospholipids provide a catalytic surface (with the charge
provided by phosphatidylserine and phosphatidylethanolamine) for the tenase and prothrombinasecomplexes. Calcium ions are essential for binding of these coagulation factors.
Shape change :
Scanning electron micrograph of blood cells. From left to right: human erythrocyte, activated
thrombocyte (platelet),leukocyte.
Activated platelets change in shape to become more spherical, and pseudopods form on their
surface. Thus they assume astellateshape.
Granule secretion :
Platelets containalphaanddense granules. Activated platelets excrete the contents of these granules
into theircanalicular systemsand into surrounding blood. There are three types of granules:
dense (or delta) granules(containingADPorATP,calcium, andserotonin) lambda granules similar to lysosomes and contain several hydrolytic enzymes. Alpha granules(containingP-selectin,platelet factor 4,transforming growth factor-1,platelet-
derived growth factor,fibronectin,B-thromboglobulin,vWF,fibrinogen, andcoagulation factors
VandXIII).
Thromboxane A2 synthesis :
Platelet activation initiates thearachidonic acidpathway to produceTXA2. TXA2 is involved in activating
other platelets and its formation is inhibited byCOXinhibitors, such asaspirin.
http://en.wikipedia.org/wiki/Platelet#cite_note-10http://en.wikipedia.org/wiki/Platelet#cite_note-10http://en.wikipedia.org/wiki/Platelet#cite_note-10http://en.wikipedia.org/wiki/Scramblasehttp://en.wikipedia.org/wiki/Scramblasehttp://en.wikipedia.org/wiki/Phospholipidhttp://en.wikipedia.org/wiki/Phospholipidhttp://en.wikipedia.org/wiki/Phosphatidylserinehttp://en.wikipedia.org/wiki/Phosphatidylserinehttp://en.wikipedia.org/wiki/Phosphatidylethanolaminehttp://en.wikipedia.org/wiki/Phosphatidylethanolaminehttp://en.wikipedia.org/wiki/Tenasehttp://en.wikipedia.org/wiki/Tenasehttp://en.wikipedia.org/wiki/Prothrombinasehttp://en.wikipedia.org/wiki/Prothrombinasehttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Leukocytehttp://en.wikipedia.org/wiki/Leukocytehttp://en.wikipedia.org/wiki/Leukocytehttp://en.wikipedia.org/wiki/Pseudopodshttp://en.wikipedia.org/wiki/Pseudopodshttp://en.wiktionary.org/wiki/stellatehttp://en.wiktionary.org/wiki/stellatehttp://en.wiktionary.org/wiki/stellatehttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/w/index.php?title=Canalicular_system&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Canalicular_system&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Canalicular_system&action=edit&redlink=1http://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Calciumhttp://en.wikipedia.org/wiki/Calciumhttp://en.wikipedia.org/wiki/Calciumhttp://en.wikipedia.org/wiki/Serotoninhttp://en.wikipedia.org/wiki/Serotoninhttp://en.wikipedia.org/wiki/Serotoninhttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wikipedia.org/wiki/P-selectinhttp://en.wikipedia.org/wiki/P-selectinhttp://en.wikipedia.org/wiki/P-selectinhttp://en.wikipedia.org/wiki/Platelet_factor_4http://en.wikipedia.org/wiki/Platelet_factor_4http://en.wikipedia.org/wiki/Platelet_factor_4http://en.wikipedia.org/wiki/TGF_beta_1http://en.wikipedia.org/wiki/TGF_beta_1http://en.wikipedia.org/wiki/TGF_beta_1http://en.wikipedia.org/wiki/TGF_beta_1http://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/B-thromboglobulinhttp://en.wikipedia.org/wiki/B-thromboglobulinhttp://en.wikipedia.org/wiki/B-thromboglobulinhttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/Fibrinogenhttp://en.wikipedia.org/wiki/Fibrinogenhttp://en.wikipedia.org/wiki/Fibrinogenhttp://en.wikipedia.org/wiki/Coagulation_factorhttp://en.wikipedia.org/wiki/Coagulation_factorhttp://en.wikipedia.org/wiki/Coagulation_factorhttp://en.wikipedia.org/wiki/Factor_Vhttp://en.wikipedia.org/wiki/Factor_Vhttp://en.wikipedia.org/wiki/Factor_XIIIhttp://en.wikipedia.org/wiki/Factor_XIIIhttp://en.wikipedia.org/wiki/Factor_XIIIhttp://en.wikipedia.org/wiki/Arachidonic_acidhttp://en.wikipedia.org/wiki/Arachidonic_acidhttp://en.wikipedia.org/wiki/Arachidonic_acidhttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/File:Red_White_Blood_cells.jpghttp://en.wikipedia.org/wiki/File:Red_White_Blood_cells.jpghttp://en.wikipedia.org/wiki/File:Red_White_Blood_cells.jpghttp://en.wikipedia.org/wiki/File:Red_White_Blood_cells.jpghttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Arachidonic_acidhttp://en.wikipedia.org/wiki/Factor_XIIIhttp://en.wikipedia.org/wiki/Factor_Vhttp://en.wikipedia.org/wiki/Coagulation_factorhttp://en.wikipedia.org/wiki/Fibrinogenhttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/B-thromboglobulinhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/TGF_beta_1http://en.wikipedia.org/wiki/Platelet_factor_4http://en.wikipedia.org/wiki/P-selectinhttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wikipedia.org/wiki/Serotoninhttp://en.wikipedia.org/wiki/Calciumhttp://en.wikipedia.org/wiki/Adenosine_triphosphatehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/w/index.php?title=Canalicular_system&action=edit&redlink=1http://en.wikipedia.org/wiki/Dense_granulehttp://en.wikipedia.org/wiki/Platelet_alpha-granulehttp://en.wiktionary.org/wiki/stellatehttp://en.wikipedia.org/wiki/Pseudopodshttp://en.wikipedia.org/wiki/Leukocytehttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Prothrombinasehttp://en.wikipedia.org/wiki/Tenasehttp://en.wikipedia.org/wiki/Phosphatidylethanolaminehttp://en.wikipedia.org/wiki/Phosphatidylserinehttp://en.wikipedia.org/wiki/Phospholipidhttp://en.wikipedia.org/wiki/Scramblasehttp://en.wikipedia.org/wiki/Platelet#cite_note-10 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Adhesion and aggregation :
Platelets clumping from a blood smear. May Grunwald-Giemsa. Light Microscopy, oil immersion 100x.
Platelets aggregate, or clump together, using fibrinogen and von Willebrand factor (vWF) as a
connecting agent. The most abundant platelet aggregation receptor is glycoprotein IIb/IIIa (gpIIb/IIIa);
this is a calcium-dependent receptor for fibrinogen,fibronectin,vitronectin,thrombospondin, and vWF.Other receptors include GPIb-V-IX complex (vWF) andGPVI(collagen).
Activated platelets will adhere, viaglycoprotein(GP) Ia, to the collagen that is exposed by endothelial
damage. Aggregation and adhesion act together to form the platelet plug. Myosinandactinfilaments in
platelets are stimulated to contract during aggregation, further reinforcing the plug.
Platelet aggregation is stimulated by ADP, thromboxane, and 2 receptor-activation, but inhibited by
other inflammatory products like PGI2 and PGD2. Platelet aggregation is enhanced by exogenous
administration of anabolic steroids.
Wound repair :
Main article:Wound repair
The blood clot is only a temporary solution to stop bleeding; vessel repair is therefore needed. The
aggregated platelets help this process by secreting chemicals that promote the invasion of fibroblasts
from surrounding connective tissue into the wounded area to completely heal the wound or form a scar.
The obstructing clot is slowly dissolved by the fibrinolytic enzyme,plasmin, and the platelets are cleared
byphagocytosis.
ADP (purinergic/P2) receptors:
Human platelets have three types of P2 receptors:P2X(1),P2Y(1) and P2Y(12). Although abnormalities in
all three genes have been documented, but clinical correlation is available only for P2Y(12) .[11]Patients
with P2Y(12) defects have a mild to moderate bleeding diathesis, characterized by mucocutaneous
bleeding and excessive post-surgical and post-traumatic blood loss. A defects in P2Y(12) should be
suspected when ADP, even at concentrations 10 micro molar, is unable to induce full, irreversible
platelet aggregation. Confirmation of the diagnosis is with tests that evaluate the degree of inhibition of
adenylyl cyclaseby ADP.
http://en.wikipedia.org/wiki/Fibrinogenhttp://en.wikipedia.org/wiki/Fibrinogenhttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/Glycoprotein_IIb/IIIahttp://en.wikipedia.org/wiki/Glycoprotein_IIb/IIIahttp://en.wikipedia.org/wiki/Glycoprotein_IIb/IIIahttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Vitronectinhttp://en.wikipedia.org/wiki/Vitronectinhttp://en.wikipedia.org/wiki/Vitronectinhttp://en.wikipedia.org/wiki/Thrombospondinhttp://en.wikipedia.org/wiki/Thrombospondinhttp://en.wikipedia.org/wiki/Thrombospondinhttp://en.wikipedia.org/wiki/GPVIhttp://en.wikipedia.org/wiki/GPVIhttp://en.wikipedia.org/wiki/GPVIhttp://en.wikipedia.org/wiki/Collagenhttp://en.wikipedia.org/wiki/Collagenhttp://en.wikipedia.org/wiki/Collagenhttp://en.wikipedia.org/wiki/Glycoproteinhttp://en.wikipedia.org/wiki/Glycoproteinhttp://en.wikipedia.org/wiki/Glycoproteinhttp://en.wikipedia.org/wiki/Myosinhttp://en.wikipedia.org/wiki/Myosinhttp://en.wikipedia.org/wiki/Myosinhttp://en.wikipedia.org/wiki/Actinhttp://en.wikipedia.org/wiki/Actinhttp://en.wikipedia.org/wiki/Actinhttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/%CE%912_receptorhttp://en.wikipedia.org/wiki/%CE%912_receptorhttp://en.wikipedia.org/wiki/%CE%912_receptorhttp://en.wikipedia.org/wiki/PGI2http://en.wikipedia.org/wiki/PGI2http://en.wikipedia.org/wiki/PGD2http://en.wikipedia.org/wiki/PGD2http://en.wikipedia.org/wiki/Wound_repairhttp://en.wikipedia.org/wiki/Wound_repairhttp://en.wikipedia.org/wiki/Wound_repairhttp://en.wikipedia.org/wiki/Fibroblastshttp://en.wikipedia.org/wiki/Fibroblastshttp://en.wikipedia.org/wiki/Fibroblastshttp://en.wikipedia.org/wiki/Plasminhttp://en.wikipedia.org/wiki/Plasminhttp://en.wikipedia.org/wiki/Plasminhttp://en.wikipedia.org/wiki/Phagocytosishttp://en.wikipedia.org/wiki/Phagocytosishttp://en.wikipedia.org/wiki/Phagocytosishttp://en.wikipedia.org/wiki/P2Xhttp://en.wikipedia.org/wiki/P2Xhttp://en.wikipedia.org/wiki/P2Xhttp://en.wikipedia.org/wiki/P2Y_receptorhttp://en.wikipedia.org/wiki/P2Y_receptorhttp://en.wikipedia.org/wiki/P2Y_receptorhttp://en.wikipedia.org/wiki/Platelet#cite_note-Cattaneo2011-11http://en.wikipedia.org/wiki/Platelet#cite_note-Cattaneo2011-11http://en.wikipedia.org/wiki/Platelet#cite_note-Cattaneo2011-11http://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Adenylyl_cyclasehttp://en.wikipedia.org/wiki/Adenylyl_cyclasehttp://en.wikipedia.org/wiki/File:Platelets.jpghttp://en.wikipedia.org/wiki/File:Platelets.jpghttp://en.wikipedia.org/wiki/File:Platelets.jpghttp://en.wikipedia.org/wiki/File:Platelets.jpghttp://en.wikipedia.org/wiki/Adenylyl_cyclasehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Platelet#cite_note-Cattaneo2011-11http://en.wikipedia.org/wiki/P2Y_receptorhttp://en.wikipedia.org/wiki/P2Xhttp://en.wikipedia.org/wiki/Phagocytosishttp://en.wikipedia.org/wiki/Plasminhttp://en.wikipedia.org/wiki/Fibroblastshttp://en.wikipedia.org/wiki/Wound_repairhttp://en.wikipedia.org/wiki/PGD2http://en.wikipedia.org/wiki/PGI2http://en.wikipedia.org/wiki/%CE%912_receptorhttp://en.wikipedia.org/wiki/Thromboxanehttp://en.wikipedia.org/wiki/Adenosine_diphosphatehttp://en.wikipedia.org/wiki/Actinhttp://en.wikipedia.org/wiki/Myosinhttp://en.wikipedia.org/wiki/Glycoproteinhttp://en.wikipedia.org/wiki/Collagenhttp://en.wikipedia.org/wiki/GPVIhttp://en.wikipedia.org/wiki/Thrombospondinhttp://en.wikipedia.org/wiki/Vitronectinhttp://en.wikipedia.org/wiki/Fibronectinhttp://en.wikipedia.org/wiki/Glycoprotein_IIb/IIIahttp://en.wikipedia.org/wiki/Von_Willebrand_factorhttp://en.wikipedia.org/wiki/Fibrinogen -
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Other functions :
Clot retraction Procoagulant Inflammation Cytokinesignalling Phagocytosis[12]
Cytokine signaling :
In addition to being the chief cellular effector ofhemostasis, platelets are rapidly deployed to sites of
injury or infection, and potentially modulate inflammatory processes by interacting withleukocytesand
by secretingcytokines,chemokines, and other inflammatory mediators.[13][14][15][16]Platelets also secrete
platelet-derived growth factor(PDGF).
Role in disease:
Diagram of the internal structure of a platelet
High and low counts :
A normal platelet count in a healthy individual is between 150,000 and 450,000 per L (microlitre) of
blood ((150450)109/L).[17] Ninety-five percent of healthy people will have platelet counts in this
range. Some will have statistically abnormal platelet counts while having no demonstrable abnormality.
However, if it is either very low or very high, the likelihood of an abnormality being present is higher.
Both thrombocytopenia and thrombocytosismay present with coagulation problems. In general, low
platelet counts increase bleeding risks; however there are exceptions (such as immune-mediated
heparin-induced thrombocytopeniaorparoxysmal nocturnal hemoglobinuria). High counts may lead to
thrombosis, although this is mainly when the elevated count is due tomyeloproliferative disorder.
http://en.wikipedia.org/wiki/Clot_retractionhttp://en.wikipedia.org/wiki/Clot_retractionhttp://en.wikipedia.org/wiki/Inflammationhttp://en.wikipedia.org/wiki/Inflammationhttp://en.wikipedia.org/wiki/Cytokinehttp://en.wikipedia.org/wiki/Cytokinehttp://en.wikipedia.org/wiki/Platelet#cite_note-12http://en.wikipedia.org/wiki/Platelet#cite_note-12http://en.wikipedia.org/wiki/Platelet#cite_note-12http://en.wikipedia.org/wiki/Hemostasishttp://en.wikipedia.org/wiki/Hemostasishttp://en.wikipedia.org/wiki/Hemostasishttp://en.wikipedia.org/wiki/Leukocyteshttp://en.wikipedia.org/wiki/Leukocyteshttp://en.wikipedia.org/wiki/Leukocyteshttp://en.wikipedia.org/wiki/Cytokineshttp://en.wikipedia.org/wiki/Cytokineshttp://en.wikipedia.org/wiki/Cytokineshttp://en.wikipedia.org/wiki/Chemokineshttp://en.wikipedia.org/wiki/Chemokineshttp://en.wikipedia.org/wiki/Chemokineshttp://en.wikipedia.org/wiki/Platelet#cite_note-13http://en.wikipedia.org/wiki/Platelet#cite_note-13http://en.wikipedia.org/wiki/Platelet#cite_note-15http://en.wikipedia.org/wiki/Platelet#cite_note-15http://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Litrehttp://en.wikipedia.org/wiki/Litrehttp://en.wikipedia.org/wiki/Litrehttp://en.wikipedia.org/wiki/Platelet#cite_note-Kumar.26Clark-17http://en.wikipedia.org/wiki/Platelet#cite_note-Kumar.26Clark-17http://en.wikipedia.org/wiki/Platelet#cite_note-Kumar.26Clark-17http://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Paroxysmal_nocturnal_hemoglobinuriahttp://en.wikipedia.org/wiki/Paroxysmal_nocturnal_hemoglobinuriahttp://en.wikipedia.org/wiki/Paroxysmal_nocturnal_hemoglobinuriahttp://en.wikipedia.org/wiki/Thrombosishttp://en.wikipedia.org/wiki/Thrombosishttp://en.wikipedia.org/wiki/Myeloproliferative_disorderhttp://en.wikipedia.org/wiki/Myeloproliferative_disorderhttp://en.wikipedia.org/wiki/Myeloproliferative_disorderhttp://en.wikipedia.org/wiki/File:Platelet_structure.pnghttp://en.wikipedia.org/wiki/File:Platelet_structure.pnghttp://en.wikipedia.org/wiki/File:Platelet_structure.pnghttp://en.wikipedia.org/wiki/File:Platelet_structure.pnghttp://en.wikipedia.org/wiki/Myeloproliferative_disorderhttp://en.wikipedia.org/wiki/Thrombosishttp://en.wikipedia.org/wiki/Paroxysmal_nocturnal_hemoglobinuriahttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Platelet#cite_note-Kumar.26Clark-17http://en.wikipedia.org/wiki/Litrehttp://en.wikipedia.org/wiki/Platelet-derived_growth_factorhttp://en.wikipedia.org/wiki/Platelet#cite_note-15http://en.wikipedia.org/wiki/Platelet#cite_note-15http://en.wikipedia.org/wiki/Platelet#cite_note-13http://en.wikipedia.org/wiki/Platelet#cite_note-13http://en.wikipedia.org/wiki/Chemokineshttp://en.wikipedia.org/wiki/Cytokineshttp://en.wikipedia.org/wiki/Leukocyteshttp://en.wikipedia.org/wiki/Hemostasishttp://en.wikipedia.org/wiki/Platelet#cite_note-12http://en.wikipedia.org/wiki/Cytokinehttp://en.wikipedia.org/wiki/Inflammationhttp://en.wikipedia.org/wiki/Clot_retraction -
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Transfusion is generally used only to correct unusually low platelet counts (typically below (10
15)109/L). Transfusion is contraindicated inthrombotic thrombocytopenic purpura(TTP), as it fuels the
coagulopathy. In patients undergoing surgery, a level below 50109/L is associated with abnormal
surgical bleeding, and regional anaesthetic procedures such asepidurals are avoided for levels below
80109/L.[18]
Normal platelet counts are not a guarantee of adequate function. In some states, the platelets, while
being adequate in number, are dysfunctional. For instance,aspirinirreversibly disrupts platelet function
by inhibitingcyclooxygenase-1 (COX1), and hence normal hemostasis. The resulting platelets are unable
to produce new cyclooxygenase because they have no DNA. Normal platelet function will not return
until the use of aspirin has ceased and enough of the affected platelets have been replaced by new
ones, which can take over a week. Ibuprofen, anotherNSAID, does not have such a long duration effect,
with platelet function usually returning within 24 hours,[19] and taking ibuprofen before aspirin
sometimes may prevent the irreversible effects of aspirin.[20] Uremia, a consequence of renal failure,
leads to platelet dysfunction that may be ameliorated by the administration ofdesmopressin.
Medications :
Oral agents often used to alter/suppress platelet function include aspirin, clopidogrel, cilostazol,
ticlopidine,ticagrelorandprasugrel.
Intravenous agents often used to alter/suppress platelet function include: abciximab, eptifibatide,
tirofiban.
In addition to platelet transfusion, hematopoetic agents such as Oprelvekin, Romiplostim, and
Eltrombopagcan be used to increase platelet counts.
Diseases :Disorders leading to a reduced platelet count:
Thrombocytopeniao Idiopathic thrombocytopenic purpura also known as immune thrombocytopenic
purpura (ITP)
o Thrombotic thrombocytopenic purpurao Drug-induced thrombocytopenic purpura (for example heparin-induced
thrombocytopenia(HIT))
Gaucher's disease Aplastic anemia Onyalai
Alloimmunedisorders
http://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Coagulopathyhttp://en.wikipedia.org/wiki/Coagulopathyhttp://en.wikipedia.org/wiki/Surgeryhttp://en.wikipedia.org/wiki/Surgeryhttp://en.wikipedia.org/wiki/Regional_anaesthetichttp://en.wikipedia.org/wiki/Regional_anaesthetichttp://en.wikipedia.org/wiki/Regional_anaesthetichttp://en.wikipedia.org/wiki/Epiduralhttp://en.wikipedia.org/wiki/Epiduralhttp://en.wikipedia.org/wiki/Epiduralhttp://en.wikipedia.org/wiki/Platelet#cite_note-18http://en.wikipedia.org/wiki/Platelet#cite_note-18http://en.wikipedia.org/wiki/Platelet#cite_note-18http://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Ibuprofenhttp://en.wikipedia.org/wiki/Ibuprofenhttp://en.wikipedia.org/wiki/NSAIDhttp://en.wikipedia.org/wiki/NSAIDhttp://en.wikipedia.org/wiki/NSAIDhttp://en.wikipedia.org/wiki/Platelet#cite_note-19http://en.wikipedia.org/wiki/Platelet#cite_note-19http://en.wikipedia.org/wiki/Platelet#cite_note-19http://en.wikipedia.org/wiki/Platelet#cite_note-20http://en.wikipedia.org/wiki/Platelet#cite_note-20http://en.wikipedia.org/wiki/Platelet#cite_note-20http://en.wikipedia.org/wiki/Uremiahttp://en.wikipedia.org/wiki/Uremiahttp://en.wikipedia.org/wiki/Renal_failurehttp://en.wikipedia.org/wiki/Renal_failurehttp://en.wikipedia.org/wiki/Renal_failurehttp://en.wikipedia.org/wiki/Desmopressinhttp://en.wikipedia.org/wiki/Desmopressinhttp://en.wikipedia.org/wiki/Desmopressinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Clopidogrelhttp://en.wikipedia.org/wiki/Clopidogrelhttp://en.wikipedia.org/wiki/Cilostazolhttp://en.wikipedia.org/wiki/Cilostazolhttp://en.wikipedia.org/wiki/Ticlopidinehttp://en.wikipedia.org/wiki/Ticlopidinehttp://en.wikipedia.org/wiki/Ticagrelorhttp://en.wikipedia.org/wiki/Ticagrelorhttp://en.wikipedia.org/wiki/Ticagrelorhttp://en.wikipedia.org/wiki/Prasugrelhttp://en.wikipedia.org/wiki/Prasugrelhttp://en.wikipedia.org/wiki/Prasugrelhttp://en.wikipedia.org/wiki/Abciximabhttp://en.wikipedia.org/wiki/Abciximabhttp://en.wikipedia.org/wiki/Eptifibatidehttp://en.wikipedia.org/wiki/Eptifibatidehttp://en.wikipedia.org/wiki/Tirofibanhttp://en.wikipedia.org/wiki/Tirofibanhttp://en.wikipedia.org/wiki/Oprelvekinhttp://en.wikipedia.org/wiki/Oprelvekinhttp://en.wikipedia.org/wiki/Romiplostimhttp://en.wikipedia.org/wiki/Romiplostimhttp://en.wikipedia.org/wiki/Eltrombopaghttp://en.wikipedia.org/wiki/Eltrombopaghttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Idiopathic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Idiopathic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Drug-induced_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Drug-induced_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Gaucher%27s_diseasehttp://en.wikipedia.org/wiki/Gaucher%27s_diseasehttp://en.wikipedia.org/wiki/Aplastic_anemiahttp://en.wikipedia.org/wiki/Aplastic_anemiahttp://en.wikipedia.org/wiki/Onyalaihttp://en.wikipedia.org/wiki/Onyalaihttp://en.wikipedia.org/wiki/Alloimmunehttp://en.wikipedia.org/wiki/Alloimmunehttp://en.wikipedia.org/wiki/Alloimmunehttp://en.wikipedia.org/wiki/Onyalaihttp://en.wikipedia.org/wiki/Aplastic_anemiahttp://en.wikipedia.org/wiki/Gaucher%27s_diseasehttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Heparin-induced_thrombocytopeniahttp://en.wikipedia.org/wiki/Drug-induced_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Idiopathic_thrombocytopenic_purpurahttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Eltrombopaghttp://en.wikipedia.org/wiki/Romiplostimhttp://en.wikipedia.org/wiki/Oprelvekinhttp://en.wikipedia.org/wiki/Tirofibanhttp://en.wikipedia.org/wiki/Eptifibatidehttp://en.wikipedia.org/wiki/Abciximabhttp://en.wikipedia.org/wiki/Prasugrelhttp://en.wikipedia.org/wiki/Ticagrelorhttp://en.wikipedia.org/wiki/Ticlopidinehttp://en.wikipedia.org/wiki/Cilostazolhttp://en.wikipedia.org/wiki/Clopidogrelhttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Desmopressinhttp://en.wikipedia.org/wiki/Renal_failurehttp://en.wikipedia.org/wiki/Uremiahttp://en.wikipedia.org/wiki/Platelet#cite_note-20http://en.wikipedia.org/wiki/Platelet#cite_note-19http://en.wikipedia.org/wiki/NSAIDhttp://en.wikipedia.org/wiki/Ibuprofenhttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Platelet#cite_note-18http://en.wikipedia.org/wiki/Epiduralhttp://en.wikipedia.org/wiki/Regional_anaesthetichttp://en.wikipedia.org/wiki/Surgeryhttp://en.wikipedia.org/wiki/Coagulopathyhttp://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpura 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Fetomaternal alloimmune thrombocytopenia Some transfusion reactions
Disorders leading to platelet dysfunction or reduced count:
HELLP syndrome Hemolytic-uremic syndrome Chemotherapy Dengue
Disorders featuring an elevated count:
Thrombocytosis, including essential thrombocytosis (elevated counts, either reactive or as anexpression ofmyeloproliferative disease); may feature dysfunctional platelets
Disorders of platelet adhesion or aggregation:
Bernard-Soulier syndrome Glanzmann thrombasthenia
Disorders of platelet granule amount or release
Hermansky-Pudlak Syndrome Gray platelet syndrome
Disorders of platelet metabolism
Decreasedcyclooxygenaseactivity, induced or congenital Storage pool defects, acquired or congenital
Disorders that compromise platelet signaling:
WiskottAldrich syndromeDisorders in which platelets play a key role:
Atherosclerosis Coronary artery disease, CAD andmyocardial infarction, MI Cerebrovascular diseaseandStroke, CVA (cerebrovascular accident) Peripheral artery occlusive disease(PAOD)
http://en.wikipedia.org/wiki/Fetomaternal_alloimmune_thrombocytopeniahttp://en.wikipedia.org/wiki/Fetomaternal_alloimmune_thrombocytopeniahttp://en.wikipedia.org/wiki/HELLP_syndromehttp://en.wikipedia.org/wiki/HELLP_syndromehttp://en.wikipedia.org/wiki/Hemolytic-uremic_syndromehttp://en.wikipedia.org/wiki/Hemolytic-uremic_syndromehttp://en.wikipedia.org/wiki/Chemotherapyhttp://en.wikipedia.org/wiki/Chemotherapyhttp://en.wikipedia.org/wiki/Denguehttp://en.wikipedia.org/wiki/Denguehttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Essential_thrombocytosishttp://en.wikipedia.org/wiki/Essential_thrombocytosishttp://en.wikipedia.org/wiki/Essential_thrombocytosishttp://en.wikipedia.org/wiki/Myeloproliferative_diseasehttp://en.wikipedia.org/wiki/Myeloproliferative_diseasehttp://en.wikipedia.org/wiki/Myeloproliferative_diseasehttp://en.wikipedia.org/wiki/Bernard-Soulier_syndromehttp://en.wikipedia.org/wiki/Bernard-Soulier_syndromehttp://en.wikipedia.org/wiki/Glanzmann_thrombastheniahttp://en.wikipedia.org/wiki/Glanzmann_thrombastheniahttp://en.wikipedia.org/wiki/Hermansky-Pudlak_Syndromehttp://en.wikipedia.org/wiki/Hermansky-Pudlak_Syndromehttp://en.wikipedia.org/wiki/Gray_platelet_syndromehttp://en.wikipedia.org/wiki/Gray_platelet_syndromehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Wiskott%E2%80%93Aldrich_syndromehttp://en.wikipedia.org/wiki/Wiskott%E2%80%93Aldrich_syndromehttp://en.wikipedia.org/wiki/Wiskott%E2%80%93Aldrich_syndromehttp://en.wikipedia.org/wiki/Wiskott%E2%80%93Aldrich_syndromehttp://en.wikipedia.org/wiki/Atherosclerosishttp://en.wikipedia.org/wiki/Atherosclerosishttp://en.wikipedia.org/wiki/Coronary_artery_diseasehttp://en.wikipedia.org/wiki/Coronary_artery_diseasehttp://en.wikipedia.org/wiki/Myocardial_infarctionhttp://en.wikipedia.org/wiki/Myocardial_infarctionhttp://en.wikipedia.org/wiki/Myocardial_infarctionhttp://en.wikipedia.org/wiki/Cerebrovascular_diseasehttp://en.wikipedia.org/wiki/Cerebrovascular_diseasehttp://en.wikipedia.org/wiki/Strokehttp://en.wikipedia.org/wiki/Strokehttp://en.wikipedia.org/wiki/Strokehttp://en.wikipedia.org/wiki/Peripheral_artery_occlusive_diseasehttp://en.wikipedia.org/wiki/Peripheral_artery_occlusive_diseasehttp://en.wikipedia.org/wiki/Peripheral_artery_occlusive_diseasehttp://en.wikipedia.org/wiki/Strokehttp://en.wikipedia.org/wiki/Cerebrovascular_diseasehttp://en.wikipedia.org/wiki/Myocardial_infarctionhttp://en.wikipedia.org/wiki/Coronary_artery_diseasehttp://en.wikipedia.org/wiki/Atherosclerosishttp://en.wikipedia.org/wiki/Wiskott%E2%80%93Aldrich_syndromehttp://en.wikipedia.org/wiki/Cyclooxygenasehttp://en.wikipedia.org/wiki/Gray_platelet_syndromehttp://en.wikipedia.org/wiki/Hermansky-Pudlak_Syndromehttp://en.wikipedia.org/wiki/Glanzmann_thrombastheniahttp://en.wikipedia.org/wiki/Bernard-Soulier_syndromehttp://en.wikipedia.org/wiki/Myeloproliferative_diseasehttp://en.wikipedia.org/wiki/Essential_thrombocytosishttp://en.wikipedia.org/wiki/Thrombocytosishttp://en.wikipedia.org/wiki/Denguehttp://en.wikipedia.org/wiki/Chemotherapyhttp://en.wikipedia.org/wiki/Hemolytic-uremic_syndromehttp://en.wikipedia.org/wiki/HELLP_syndromehttp://en.wikipedia.org/wiki/Fetomaternal_alloimmune_thrombocytopenia -
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Cancer[21] Malaria[22] Asthma[23][24] Samters Triad (Aspirin Exacerbated Respiratory Disease/AERD)[25][26]
Laboratory findings in various platelet and coagulation disorders (V-T)
ConditionProthrombin
time
Partial
thromboplastin time
Bleeding
timePlatelet count
Vitamin K deficiencyorwarfarin ProlongedNormal or mildly
prolongedUnaffected Unaffected
Disseminated intravascular
coagulation Prolonged Prolonged Prolonged Decreased
Von Willebrand disease Unaffected Prolonged Prolonged Unaffected
Hemophilia Unaffected Prolonged Unaffected Unaffected
Aspirin Unaffected Unaffected Prolonged Unaffected
Thrombocytopenia Unaffected Unaffected Prolonged Decreased
Liver failure, early Prolonged Unaffected Unaffected Unaffected
Liver failure, end-stage Prolonged Prolonged Prolonged Decreased
Uremia Unaffected Unaffected Prolonged Unaffected
Congenital afibrinogenemia Prolonged Prolonged Prolonged Unaffected
Factor Vdeficiency Prolonged Prolonged Unaffected Unaffected
Factor X deficiency as seen in
amyloid purpura Prolonged Prolonged Unaffected Unaffected
Glanzmann's thrombasthenia Unaffected Unaffected Prolonged Unaffected
Bernard-Soulier syndrome Unaffected Unaffected ProlongedDecreased or
unaffected
http://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Malariahttp://en.wikipedia.org/wiki/Malariahttp://en.wikipedia.org/wiki/Malariahttp://en.wikipedia.org/wiki/Asthmahttp://en.wikipedia.org/wiki/Asthmahttp://en.wikipedia.org/wiki/Platelet#cite_note-24http://en.wikipedia.org/wiki/Platelet#cite_note-24http://en.wikipedia.org/wiki/Aspirin-induced_asthmahttp://en.wikipedia.org/wiki/Aspirin-induced_asthmahttp://en.wikipedia.org/wiki/Platelet#cite_note-26http://en.wikipedia.org/wiki/Platelet#cite_note-26http://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Platelet_counthttp://en.wikipedia.org/wiki/Vitamin_K_deficiencyhttp://en.wikipedia.org/wiki/Vitamin_K_deficiencyhttp://en.wikipedia.org/wiki/Warfarinhttp://en.wikipedia.org/wiki/Warfarinhttp://en.wikipedia.org/wiki/Warfarinhttp://en.wikipedia.org/wiki/Disseminated_intravascular_coagulationhttp://en.wikipedia.org/wiki/Disseminated_intravascular_coagulationhttp://en.wikipedia.org/wiki/Von_Willebrand_diseasehttp://en.wikipedia.org/wiki/Hemophiliahttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Liver_failurehttp://en.wikipedia.org/wiki/Liver_failurehttp://en.wikipedia.org/wiki/Uremiahttp://en.wikipedia.org/wiki/Congenital_afibrinogenemiahttp://en.wikipedia.org/wiki/Congenital_afibrinogenemiahttp://en.wikipedia.org/wiki/Factor_Vhttp://en.wikipedia.org/wiki/Factor_Vhttp://en.wikipedia.org/wiki/Factor_Xhttp://en.wikipedia.org/wiki/Factor_Xhttp://en.wikipedia.org/wiki/Amyloid_purpurahttp://en.wikipedia.org/wiki/Amyloid_purpurahttp://en.wikipedia.org/wiki/Glanzmann%27s_thrombastheniahttp://en.wikipedia.org/wiki/Glanzmann%27s_thrombastheniahttp://en.wikipedia.org/wiki/Bernard-Soulier_syndromehttp://en.wikipedia.org/wiki/Bernard-Soulier_syndromehttp://en.wikipedia.org/wiki/Glanzmann%27s_thrombastheniahttp://en.wikipedia.org/wiki/Amyloid_purpurahttp://en.wikipedia.org/wiki/Factor_Xhttp://en.wikipedia.org/wiki/Factor_Vhttp://en.wikipedia.org/wiki/Congenital_afibrinogenemiahttp://en.wikipedia.org/wiki/Uremiahttp://en.wikipedia.org/wiki/Liver_failurehttp://en.wikipedia.org/wiki/Thrombocytopeniahttp://en.wikipedia.org/wiki/Aspirinhttp://en.wikipedia.org/wiki/Hemophiliahttp://en.wikipedia.org/wiki/Von_Willebrand_diseasehttp://en.wikipedia.org/wiki/Disseminated_intravascular_coagulationhttp://en.wikipedia.org/wiki/Disseminated_intravascular_coagulationhttp://en.wikipedia.org/wiki/Warfarinhttp://en.wikipedia.org/wiki/Vitamin_K_deficiencyhttp://en.wikipedia.org/wiki/Platelet_counthttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Platelet#cite_note-26http://en.wikipedia.org/wiki/Aspirin-induced_asthmahttp://en.wikipedia.org/wiki/Aspirin-induced_asthmahttp://en.wikipedia.org/wiki/Platelet#cite_note-24http://en.wikipedia.org/wiki/Asthmahttp://en.wikipedia.org/wiki/Asthmahttp://en.wikipedia.org/wiki/Malariahttp://en.wikipedia.org/wiki/Malariahttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancer -
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Laboratory findings in various platelet and coagulation disorders (V-T)
ConditionProthrombin
time
Partial
thromboplastin time
Bleeding
timePlatelet count
Factor XII deficiency Unaffected Prolonged Unaffected Unaffected
C1INH deficiency Unaffected Shortened Unaffected Unaffected
Discovery :
Although red blood cells had been known sincevan Leeuwenhoek(16321723), the German anatomist
Max Schultze(18251874) was the first to describe platelets.[27][28] He described "spherules" that were
much smaller than red blood cells and that occasionally clumped and were found in collections of
fibrous material.
Giulio Bizzozero (18461901), building on Schultze's findings, used "living circulation" to study bloodcells of amphibians microscopicallyin vivo. He is especially noted for discovering that platelets clump at
the site of blood vessel injury, a process that precedes the formation of ablood clot. This observation
confirmed the role of platelets incoagulation.[29]
In transfusion medicine :
Platelet concentrate.
Platelets are either isolated from collected units ofwhole bloodand pooled to make a therapeutic dose
or collected byapheresis, sometimes concurrently withplasmaorred blood cells. The industry standard
is for platelets to be tested forbacteriabefore transfusion to avoid septic reactions, which can be fatal.
http://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Platelet_counthttp://en.wikipedia.org/wiki/Factor_XII#Role_in_diseasehttp://en.wikipedia.org/wiki/Hereditary_Angioedemahttp://en.wikipedia.org/wiki/Anton_van_Leeuwenhoekhttp://en.wikipedia.org/wiki/Anton_van_Leeuwenhoekhttp://en.wikipedia.org/wiki/Anton_van_Leeuwenhoekhttp://en.wikipedia.org/wiki/Max_Johann_Sigismund_Schultzehttp://en.wikipedia.org/wiki/Max_Johann_Sigismund_Schultzehttp://en.wikipedia.org/wiki/Platelet#cite_note-Brewer-27http://en.wikipedia.org/wiki/Platelet#cite_note-Brewer-27http://en.wikipedia.org/wiki/Platelet#cite_note-Brewer-27http://en.wikipedia.org/wiki/Fibrinhttp://en.wikipedia.org/wiki/Fibrinhttp://en.wikipedia.org/wiki/Giulio_Bizzozerohttp://en.wikipedia.org/wiki/Giulio_Bizzozerohttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/Thrombushttp://en.wikipedia.org/wiki/Thrombushttp://en.wikipedia.org/wiki/Thrombushttp://en.wikipedia.org/wiki/Coagulationhttp://en.wikipedia.org/wiki/Coagulationhttp://en.wikipedia.org/wiki/Platelet#cite_note-Bizzozero-29http://en.wikipedia.org/wiki/Platelet#cite_note-Bizzozero-29http://en.wikipedia.org/wiki/Platelet#cite_note-Bizzozero-29http://en.wikipedia.org/wiki/Whole_bloodhttp://en.wikipedia.org/wiki/Whole_bloodhttp://en.wikipedia.org/wiki/Whole_bloodhttp://en.wikipedia.org/wiki/Apheresishttp://en.wikipedia.org/wiki/Apheresishttp://en.wikipedia.org/wiki/Apheresishttp://en.wikipedia.org/wiki/Blood_plasmahttp://en.wikipedia.org/wiki/Blood_plasmahttp://en.wikipedia.org/wiki/Blood_plasmahttp://en.wikipedia.org/wiki/Red_blood_cellshttp://en.wikipedia.org/wiki/Red_blood_cellshttp://en.wikipedia.org/wiki/Red_blood_cellshttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/File:Platelet_blood_bag.jpghttp://en.wikipedia.org/wiki/File:Platelet_blood_bag.jpghttp://en.wikipedia.org/wiki/File:Platelet_blood_bag.jpghttp://en.wikipedia.org/wiki/File:Platelet_blood_bag.jpghttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Red_blood_cellshttp://en.wikipedia.org/wiki/Blood_plasmahttp://en.wikipedia.org/wiki/Apheresishttp://en.wikipedia.org/wiki/Whole_bloodhttp://en.wikipedia.org/wiki/Platelet#cite_note-Bizzozero-29http://en.wikipedia.org/wiki/Coagulationhttp://en.wikipedia.org/wiki/Thrombushttp://en.wikipedia.org/wiki/In_vivohttp://en.wikipedia.org/wiki/Giulio_Bizzozerohttp://en.wikipedia.org/wiki/Fibrinhttp://en.wikipedia.org/wiki/Platelet#cite_note-Brewer-27http://en.wikipedia.org/wiki/Platelet#cite_note-Brewer-27http://en.wikipedia.org/wiki/Max_Johann_Sigismund_Schultzehttp://en.wikipedia.org/wiki/Anton_van_Leeuwenhoekhttp://en.wikipedia.org/wiki/Hereditary_Angioedemahttp://en.wikipedia.org/wiki/Factor_XII#Role_in_diseasehttp://en.wikipedia.org/wiki/Platelet_counthttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Bleeding_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Partial_thromboplastin_timehttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Prothrombin_timehttp://en.wikipedia.org/wiki/Template_talk:Bleeding_worksheethttp://en.wikipedia.org/wiki/Template:Bleeding_worksheet -
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Recently the AABB Industry Standards for Blood Banks and Transfusion Services (5.1.5.1) has allowed for
use of pathogen reduction technology as an alternative to bacterial screenings in platelets.[30]
Pooled whole-blood platelets, sometimes called random platelets, are made primarily by two
methods.[31]In the US, a unit of whole blood is placed into a largecentrifugein what is referred to as a
soft spin. At these settings, the platelets remain suspended in the plasma. The platelet-rich plasma(PRP) is removed from the RBCs, then centrifuged at a faster setting to harvest the platelets from the
plasma. In other regions of the world, the unit of whole blood is centrifuged using settings that cause
the platelets to become suspended in the buffy coat layer, which includes the platelets and the white
blood cells. The buffy coat is isolated in a sterile bag, suspended in a small amount of red blood cells
and plasma, then centrifuged again to separate the platelets and plasma from the red and white blood
cells. Regardless of the initial method of preparation, multiple donations may be combined into one
container using a sterile connection device to manufacture a single product with the desired therapeutic
dose.
Apheresis platelets are collected using a mechanical device that draws blood from the donor and
centrifuges the collected blood to separate out the platelets and other components to be collected. The
remaining blood is returned to the donor. The advantage to this method is that a single donation
provides at least one therapeutic dose, as opposed to the multiple donations for whole-blood platelets.
This means that a recipient is not exposed to as many different donors and has less risk of transfusion-
transmitted disease and other complications. Sometimes a person such as acancerpatient who requires
routine transfusions of platelets will receive repeated donations from a specific donor to further
minimize the risk. Pathogen reduction of platelets using for example,riboflavin and UV light treatments
can also be carried out to reduce the infectious load of pathogens contained in donated blood products,
thereby reducing the risk of transmission of transfusion transmitted diseases.[32][33]
Platelets are not cross-matched unless they contain a significant amount ofred blood cells(RBCs), which
results in a reddish-orange color to the product. This is usually associated with whole-blood platelets, as
apheresis methods are more efficient than soft spin centrifugation at isolating the specific
components of blood. An effort is usually made to issue type specific platelets, but this is not as critical
as it is with RBCs.
Platelets collected by either method have a very short shelf life, typically five days. This results in
frequent problems with short supply, as testing the donations often requires up to a full day. Since there
are no effective preservative solutions for platelets, they lose potency quickly and are best when fresh.
Platelets are stored under constant agitation at 2024 C. Storage at room temperature provides anenvironment where any bacteria that are introduced to the blood component during the collection
process may proliferate and subsequently causebacteremia in the patient. Regulations are in place in
the United States that require products to be tested for the presence of bacterial contamination before
transfusion.[34]
Platelets, either apheresis or random-donor platelets, can be processed through a volume reduction
process. In this process, the platelets are spun in a centrifuge and the excess plasma is removed, leaving
http://en.wikipedia.org/wiki/Platelet#cite_note-30http://en.wikipedia.org/wiki/Platelet#cite_note-30http://en.wikipedia.org/wiki/Platelet#cite_note-30http://en.wikipedia.org/wiki/Platelet#cite_note-31http://en.wikipedia.org/wiki/Platelet#cite_note-31http://en.wikipedia.org/wiki/Platelet#cite_note-31http://en.wikipedia.org/wiki/Centrifugehttp://en.wikipedia.org/wiki/Centrifugehttp://en.wikipedia.org/wiki/Centrifugehttp://en.wikipedia.org/wiki/Platelet-rich_plasmahttp://en.wikipedia.org/wiki/Platelet-rich_plasmahttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Pathogen_reduction_using_riboflavin_and_UV_lighthttp://en.wikipedia.org/wiki/Pathogen_reduction_using_riboflavin_and_UV_lighthttp://en.wikipedia.org/wiki/Pathogen_reduction_using_riboflavin_and_UV_lighthttp://en.wikipedia.org/wiki/Platelet#cite_note-32http://en.wikipedia.org/wiki/Platelet#cite_note-32http://en.wikipedia.org/wiki/Platelet#cite_note-32http://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Bacteremiahttp://en.wikipedia.org/wiki/Bacteremiahttp://en.wikipedia.org/wiki/Bacteremiahttp://en.wikipedia.org/wiki/Platelet#cite_note-34http://en.wikipedia.org/wiki/Platelet#cite_note-34http://en.wikipedia.org/wiki/Platelet#cite_note-34http://en.wikipedia.org/wiki/Platelet#cite_note-34http://en.wikipedia.org/wiki/Bacteremiahttp://en.wikipedia.org/wiki/Red_blood_cellhttp://en.wikipedia.org/wiki/Platelet#cite_note-32http://en.wikipedia.org/wiki/Platelet#cite_note-32http://en.wikipedia.org/wiki/Pathogen_reduction_using_riboflavin_and_UV_lighthttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Platelet-rich_plasmahttp://en.wikipedia.org/wiki/Centrifugehttp://en.wikipedia.org/wiki/Platelet#cite_note-31http://en.wikipedia.org/wiki/Platelet#cite_note-30 -
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10 to 100 mL of platelet concentrate. Volume-reduced platelets are normally transfused only to
neonatal and pediatric patients when a large volume of plasma could overload the child's small
circulatory system. The lower volume of plasma also reduces the chances of an adverse transfusion
reaction to plasma proteins.[35]Volume reduced platelets have a shelf life of only four hours.[36]
Other species:
Nucleated thrombocytes of nonmammalian vertebrates differ from the mammalian thrombocytes not
only in having a nucleus and resembling B lymphocytes, but also these nucleated thrombocytes do not
aggregate in response to ADP, serotonin and adrenaline (although they do aggregate with thrombin).
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