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.
Image from a light microscope (40x) from a peripheral blood smear surrounded by red blood cells.
^ Red Blood Cells What are red cells?
  • three types of blood donation 10 January 2010 8:40 UTC www.donateblood.com.au [Source type: FILTERED WITH BAYES]

^ A platelet surrounded by red blood cells.
  • Platelet - Medpedia 10 January 2010 8:40 UTC wiki.medpedia.com [Source type: Academic]

^ Red blood cells 4.

One platelet can be seen in the upper left side of the image (purple) and is significantly smaller in size than the red blood cells (stained pink) and the two neutrophils (stained purple).
Platelets, or thrombocytes (from Greek θρόμβος — «clot» and κύτος — «cell»), are small, irregularly-shaped anuclear cells (i.e. cells that do not have a nucleus containing DNA), 2-3 µm in diameter[1], which are derived from fragmentation of precursor megakaryocytes.  The average lifespan of a platelet is between 8 and 12 days. .Platelets play a fundamental role in hemostasis and are a natural source of growth factors.^ Platelets play a fundamental role in hemostasis and are a natural source of growth factors.
  • Platelet - Kosmix : Reference, Videos, Images, News, Shopping and more... 10 January 2010 8:40 UTC health.kosmix.com [Source type: Academic]

^ Recombinant platelet-derived growth factor (i.e.
  • Platelet-Derived Growth Factors 10 January 2010 8:40 UTC mcgs.bcbsfl.com [Source type: Academic]

^ These platelet-derived growth factors : .
  • Platelet Gel 10 January 2010 8:40 UTC tameriinc.com [Source type: Academic]

.They circulate in the blood of mammals and are involved in hemostasis, leading to the formation of blood clots.^ Blood clot formation .
  • Congenital platelet function defects - Overview 10 January 2010 8:40 UTC www.umm.edu [Source type: Academic]
  • DC Health - Acquired platelet function defect. Acquired platelet function... 10 January 2010 8:40 UTC www.whcenter.org [Source type: Academic]
  • OLOL Baton Rouge - Congenital platelet function defects. Congenital platelet... 10 January 2010 8:40 UTC www.ololrmc.com [Source type: Academic]
  • DC Health - Congenital platelet function defects. Congenital platelet function... 10 January 2010 8:40 UTC www.whcenter.org [Source type: Academic]
  • Acquired platelet function defect 10 January 2010 8:40 UTC www.healthscout.com [Source type: Academic]
  • DHMC | Health Encyclopedia | Acquired platelet function defect 10 January 2010 8:40 UTC www.dhmc.org [Source type: Academic]
  • DHMC | Health Encyclopedia | Congenital platelet function defects 10 January 2010 8:40 UTC www.dhmc.org [Source type: Academic]
  • Acquired platelet function defect Information at myOptumHealth 10 January 2010 8:40 UTC www.myoptumhealth.com [Source type: FILTERED WITH BAYES]

^ Too much clotting of the blood can lead to formation of blood clots that can cause stroke.
  • Low Platelets | TheMedGuru 18 September 2009 12:36 UTC www.themedguru.com [Source type: General]

^ Hemostasis includes clotting of the blood.
  • Introduction: Bleeding and Clotting Disorders: Merck Manual Home Edition 18 September 2009 12:36 UTC www.merck.com [Source type: FILTERED WITH BAYES]

.If the number of platelets is too low, excessive bleeding can occur.^ Bleeding may occur if platelet levels are too low or if platelet function is abnormal.
  • Platelet Abnormalities: Patient Information: Arizona Telemedicine Program 10 January 2010 8:40 UTC www.telemedicine.arizona.edu [Source type: Academic]
  • Inherited Platelet Abnormalities: Patient Information: Arizona Telemedicine Program 10 January 2010 8:40 UTC www.telemedicine.arizona.edu [Source type: Academic]

^ Low platelets can occur with pregnancy complications.
  • Platelet count 10 January 2010 8:40 UTC www.rnceus.com [Source type: Academic]

^ When the platelet count is extremely low, bleeding can occur in almost any organ.
  • High Platelet Count - Web - WebCrawler 25 September 2009 7:31 UTC www.webcrawler.com [Source type: FILTERED WITH BAYES]

.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 a stroke, heart attack, pulmonary embolism or 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 (thrombasthenia), or an increase in the number of (thrombocytosis).^ Bleeding may occur if platelet levels are too low or if platelet function is abnormal.
  • Platelet Abnormalities: Patient Information: Arizona Telemedicine Program 10 January 2010 8:40 UTC www.telemedicine.arizona.edu [Source type: Academic]
  • Inherited Platelet Abnormalities: Patient Information: Arizona Telemedicine Program 10 January 2010 8:40 UTC www.telemedicine.arizona.edu [Source type: Academic]

^ Platelets play a crucial part in the blood clotting process by forming a platelet plug.
  • About ITP - About Platelets - Platelet Disorder Support Association (PDSA) 18 September 2009 12:36 UTC www.pdsa.org [Source type: FILTERED WITH BAYES]

^ Clots in blood vessels of the heart and brain can cause heart attacks and strokes.
  • HOPKINS STUDY SHOWS LOW-DOSE ASPIRIN SUPPRESSES CLUMPING OF BLOOD PLATELETS IN BOTH SEXES 18 September 2009 12:36 UTC www.hopkinsmedicine.org [Source type: Academic]

.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.^ Thrombotic thrombocytopenic purpura (TTP) has also been reported and may be fatal if untreated.

^ Thrombotic Thrombocytopenic Purpura Platelet lifetime avg.
  • Geometry.Net - Health_Conditions: Platelet Disorders 10 January 2010 8:40 UTC www.geometry.net [Source type: Academic]

^ Any platelet disorder affects blood clotting.
  • DC Health - Acquired platelet function defect. Acquired platelet function... 10 January 2010 8:40 UTC www.whcenter.org [Source type: Academic]
  • Acquired platelet function defect 10 January 2010 8:40 UTC www.healthscout.com [Source type: Academic]
  • Acquired platelet function defect Information at myOptumHealth 10 January 2010 8:40 UTC www.myoptumhealth.com [Source type: FILTERED WITH BAYES]

.Platelets release a multitude of growth factors including Platelet-derived growth factor (PDGF), a potent chemotactic agent, and TGF beta, which stimulates the deposition of extracellular matrix.  Both of these growth factors have been shown to play a significant role in the repair and regeneration of connective tissues.  Other healing-associated growth factors produced by platelets include basic fibroblast growth factor, insulin-like growth factor 1, platelet-derived epidermal growth factor, and vascular endothelial growth factor.  Local application of these factors in increased concentrations through Platelet-rich plasma (PRP) has been used as an adjunct to wound healing for several decades[3][4][5][6][7][8][9].^ Faster healing: The supersaturation of the wound with PRP, and thus growth factors, produces an increase of tissue synthesis and thus faster tissue regeneration.

^ Platelet-Rich Plasma, or PRP, is blood plasma with concentrated platelets.
  • RMM Orthopaedics: What is Platelet-Rich Plasma? 10 January 2010 8:40 UTC www.rmmorthopaedics.com [Source type: FILTERED WITH BAYES]

^ Science of platelet rich plasma (PRP) - Technology .
  • Science of platelet rich plasma (PRP) - Technology 10 January 2010 8:40 UTC www.cytomedix.com [Source type: Academic]

Contents

Kinetics

Blood cell lineage
  • Platelets are produced in blood cell formation (thrombopoiesis) in bone marrow, by budding off from megakaryocytes.
  • The physiological range for platelets is 150-400 x 109 per litre.
  • Around 1 x 1011 platelets are produced each day by an average healthy adult.
  • The lifespan of circulating platelets is 7 to 10 days.
  • Megakaryocyte and platelet production is regulated by thrombopoietin, a hormone usually produced by the liver and kidneys.
  • Each megakaryocyte produces between 5,000 and 10,000 platelets.
  • Old platelets are destroyed by phagocytosis in the spleen and by Kupffer cells in the liver.
  • A reserve of platelets are stored in the spleen and are released when needed by sympathetically-induced splenic contraction.

Thrombus formation

.The function of platelets is the maintenance of haemostasis.  This is achieved primarily by the formation of thrombi, when damage to the endothelium of blood vessels occurs.^ Adhesion Platelet adhesion occurs when there is an injury to a blood vessel.
  • IHTC 10 January 2010 8:40 UTC www.ihtc.org [Source type: Academic]

^ Platelets function by adhering to the walls of injured blood vessels.
  • Platelet count 10 January 2010 8:40 UTC www.rnceus.com [Source type: Academic]

^ Platelet function disorders can be inherited, but they may also occur as a symptom of acquired diseases or as a side effect of certain drugs, including aspirin.
  • Platelet function disorders, Information about Platelet function disorders 10 January 2010 8:40 UTC www.faqs.org [Source type: Academic]

.On the converse, thrombus formation must be inhibited at times when there is no damage to the endothelium.^ "There was no correlation between bleeding time and either fall in hemoglobin level (r = 0.04) or chest tube drainage (r = 0.004).
  • PFA-100 | Florida Hospital Center for Thrombosis Research 10 January 2010 8:40 UTC www.fhthrombosis.com [Source type: Academic]

^ Platelets from diabetic subjects produce less NO and prostacyclin, which normally inhibit platelet-endothelium interactions and promote endothelium-mediated vasodilation.

^ In no instance was there evidence that the bleeding time significantly altered a priori estimates (based on prevalence) of the risk of bleeding".
  • PFA-100 | Florida Hospital Center for Thrombosis Research 10 January 2010 8:40 UTC www.fhthrombosis.com [Source type: Academic]

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 to collagen in the basement 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.^ This disease is called pseudo von Willebrand disease or platelet-type von Willebrand disease.
  • Platelet Disorders: eMedicine Hematology 10 January 2010 8:40 UTC emedicine.medscape.com [Source type: Academic]

^ Note: Von Willebrand factor (VWF), released by endothelial cells, is involved in platelet adhesion and later in platelet aggregation.

^ Blood components called platelets that help with blood clotting are stored in donor plasma.
  • FDA OK's platelet storage solution - UPI.com 10 January 2010 8:40 UTC www.upi.com [Source type: News]

.When the endothelial layer is injured, collagen, vWF and tissue factor from the subendothelium is exposed to the bloodstream.^ This platelet glycoprotein complex serves as a binding site for von Willebrand factor (vWF) which then acts as a bridge between sub-endothelial extracellular matrix collagen fibrils exposed at the site of injury and platelets.

^ The initiating factor is the release of tissue factor caused by various mechanisms, including extensive endothelial injury and the monocyte response to endotoxin or various cytokines.

^ Note: Von Willebrand factor (VWF), released by endothelial cells, is involved in platelet adhesion and later in platelet aggregation.

.When the platelets contact collagen or vWF, they are activated.  They are also activated by thrombin (formed with the help of tissue factor).^ When platelets become activated they change.
  • About ITP - About Platelets - Platelet Disorder Support Association (PDSA) 18 September 2009 12:36 UTC www.pdsa.org [Source type: FILTERED WITH BAYES]

^ This attack activates the platelets and they start to form blood clots.
  • Thrombocytopenia, Causes 25 September 2009 7:31 UTC www.nhlbi.nih.gov [Source type: FILTERED WITH BAYES]

^ Platelet-activating factor receptor .
  • IUPHAR DATABASE | Platelet-activating factor receptor | REFERENCES 10 January 2010 8:40 UTC www.iuphar-db.org [Source type: Academic]

.They can also be activated by a negatively-charged surface, such as glass.^ The hypothesis is that once a critical mass of functional platelets is present, they can activate and recruit further platelets by pathways not inhibited by aspirin, e.g., by thrombin generated on their surface.
  • CBBS: Are concerns about recent aspirin ingestion by whole blood donors justified? 18 September 2009 12:36 UTC www.cbbsweb.org [Source type: FILTERED WITH BAYES]

^ Once activated, they release a number of different coagulation factors and platelet activating factors, they also provide a catalytic phospholipid surface for the tenase and prothrombinase complexes.
  • Platelets - Pipeline Drugs -- Clinical Trials 10 January 2010 8:40 UTC www.biotech100.com [Source type: Academic]

^ Platelet activation further results in the scramblase mediated transport of negatively charged phospholipids to the platelet surface.
  • Platelet - encyclopedia article - Citizendium 10 January 2010 8:40 UTC en.citizendium.org [Source type: Academic]

.Platelet activation further results in the scramblase-mediated transport of negatively-charged phospholipids to the platelet surface.  These phospholipids provide a catalytic surface (with the charge provided by phosphatidylserine and phosphatidylethanolamine) for the tenase and prothrombinase complexes.^ Once activated, they release a number of different coagulation factors and platelet activating factors, they also provide a catalytic phospholipid surface for the tenase and prothrombinase complexes.
  • Platelets - Pipeline Drugs -- Clinical Trials 10 January 2010 8:40 UTC www.biotech100.com [Source type: Academic]

^ These phospholipids provide a catalytic surface (with the charge provided by phosphatidylserine and phosphatidylethanolamine ) for the tenase and prothrombinase protein coagulation cascade complexes.
  • Platelet - encyclopedia article - Citizendium 10 January 2010 8:40 UTC en.citizendium.org [Source type: Academic]

^ Platelet activation further results in the scramblase mediated transport of negatively charged phospholipids to the platelet surface.
  • Platelet - encyclopedia article - Citizendium 10 January 2010 8:40 UTC en.citizendium.org [Source type: Academic]

.Calcium ions are essential for binding of these coagulation factors.^ Von Willebrands factor is essential for platelet binding, therefore, a defect in vWF causes impaired platelet adhesion and aggregation.
  • Platelet Information and Courses from MediaLab, Inc. 10 January 2010 8:40 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

Shape change

.Activated platelets change in shape to become more spherical, and pseudopods form on their surface.  Thus they assume a stellate shape.^ When platelets become activated they change.
  • About ITP - About Platelets - Platelet Disorder Support Association (PDSA) 18 September 2009 12:36 UTC www.pdsa.org [Source type: FILTERED WITH BAYES]

^ This attack activates the platelets and they start to form blood clots.
  • Thrombocytopenia, Causes 25 September 2009 7:31 UTC www.nhlbi.nih.gov [Source type: FILTERED WITH BAYES]

^ Platelet aggregation is not initiated by platelet shape change.
  • Publications on platelet quality, function and measurement | LightIntegra Technology 10 January 2010 8:40 UTC www.lightintegra.com [Source type: Academic]

Granule secretion

Platelets contain alpha and dense granules.  Activated platelets excrete the contents of these granules into their canalicular systems and into surrounding blood.  There are three types of granules:

Thromboxane A2 synthesis

.Platelet activation initiates the arachidonic acid pathway to produce TXA2.  TXA2 is involved in activating other platelets and its formation is inhibited by COX inihibitors, such as aspirin.^ Inhibiting platelet activation, recruitment, and aggregation .
  • New Targets for Platelet Inhibition - Thrombosis Adviser 10 January 2010 8:40 UTC www.thrombosisadviser.com [Source type: Academic]

^ Biochemistry of platelet activation and inhibition .

^ Next, the platelets bind to each other (activation).
  • About ITP - About Platelets - Platelet Disorder Support Association (PDSA) 18 September 2009 12:36 UTC www.pdsa.org [Source type: FILTERED WITH BAYES]

Adhesion and aggregation

.Platelets aggregate, or clump together, using fibrinogen and 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 von Willebrand factor (vWF).  Other receptors include GPIb-V-IX complex (vWF) and GPVI (collagen).^ The role of platelet receptors for collagen, von Willebrand factor, thrombin and adenosine diphosphate is briefly reviewed.

^ Other substances released include :- (a) fibrinogen - which will be used to stabilise the clot.

^ The IgG antibody is directed against the glycoprotein IIb/IIIa complex on the platelet membrane.
  • Platelet Information and Courses from MediaLab, Inc. 10 January 2010 8:40 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

.Activated platelets will adhere, via glycoprotein (GP) Ia, to the collagen that is exposed by endothelial damage.  Aggregation and adhesion act together to form the platelet plug.  Myosin and actin filaments in platelets are stimulated to contract during aggregation, further reinforcing the plug.^ Inhibiting platelet activation, recruitment, and aggregation .
  • New Targets for Platelet Inhibition - Thrombosis Adviser 10 January 2010 8:40 UTC www.thrombosisadviser.com [Source type: Academic]

^ If a blood vessel is damaged, platelets will become 'glued' together at the site of the damage to form a platelet plug.
  • The National Blood Service - Platelet Donation 18 September 2009 12:36 UTC www.blood.co.uk [Source type: FILTERED WITH BAYES]

^ Stimulation of P2Y 1 receptors initiates platelet activation and aggregation.
  • New Targets for Platelet Inhibition - Thrombosis Adviser 10 January 2010 8:40 UTC www.thrombosisadviser.com [Source type: Academic]

.Platelet aggregation is stimulated by ADP, thromboxane, and α2 receptor-activation, but inhibited by other inflammatory products like PGI2 and PGD2.  Platelet aggregation is enhanced by exogenous administration of anabolic steroids.^ Inhibiting platelet activation, recruitment, and aggregation .
  • New Targets for Platelet Inhibition - Thrombosis Adviser 10 January 2010 8:40 UTC www.thrombosisadviser.com [Source type: Academic]

^ Stimulation of P2Y 1 receptors initiates platelet activation and aggregation.
  • New Targets for Platelet Inhibition - Thrombosis Adviser 10 January 2010 8:40 UTC www.thrombosisadviser.com [Source type: Academic]

^ Platelets activation is stimulated by many routes, through many different receptors.
  • New Targets for Platelet Inhibition - Thrombosis Adviser 10 January 2010 8:40 UTC www.thrombosisadviser.com [Source type: Academic]

Wound repair

.The blood clot is only a temporary solution to stop bleeding; vessel repair is therefore needed.^ Platelets: Platelets are the cells that form blood clots that stop bleeding.
  • Tennessee Oncology Treatment - Thrombocytopenia (Low Platelet Counts) 10 January 2010 8:40 UTC www.tnoncology.com [Source type: Academic]
  • Thrombocytopenia (Low Platelet Counts) | CancerConsultants 10 January 2010 8:40 UTC www.cancerconsultants.com [Source type: Academic]

^ Hemostasis is the body's way of stopping injured blood vessels from bleeding.
  • Introduction: Bleeding and Clotting Disorders: Merck Manual Home Edition 18 September 2009 12:36 UTC www.merck.com [Source type: FILTERED WITH BAYES]

^ Platelets are a component of blood that is needed for clotting.
  • Questions About Donating Platelets - New York Blood Center 10 January 2010 8:40 UTC www.plateletadvantage.com [Source type: General]

.The aggregated platelets help this process by secreting chemicals that promote the invasion of fibroblasts from surrounding connective tissue into the wounded area to form a scar.^ In most cases, fibroblastic scar tissue is formed.
  • Clinical use of platelet-rich plasma in orthopaedics 10 January 2010 8:40 UTC www.aaos.org [Source type: Academic]

^ Click on the images of aggregating platelets and blot clots forming at a wound.
  • Sandwalk: Blood Clotting: Platelets 18 September 2009 12:36 UTC sandwalk.blogspot.com [Source type: FILTERED WITH BAYES]

^ However, when platelets are stimulated by the proteins (and other chemicals) that are released by tissue injuries , they aggregate together to form plugs that can fill breaks in blood vessels and stop bleeding.
  • Platelet - encyclopedia article - Citizendium 10 January 2010 8:40 UTC en.citizendium.org [Source type: Academic]

.The obstructing clot is slowly dissolved by the fibrinolytic enzyme, plasmin, and the platelets are cleared by phagocytosis.^ However, if the number of platelets is too high, blood clots can form ( thrombosis), which may obstruct blood vessels and result in a stroke and/or a heart attack.
  • Platelet - Kosmix : Reference, Videos, Images, News, Shopping and more... 10 January 2010 8:40 UTC health.kosmix.com [Source type: Academic]

^ If a person already has a blood clot, a thrombolytic (fibrinolytic) drug can be given to help dissolve the clot.
  • Introduction: Bleeding and Clotting Disorders: Merck Manual Home Edition 18 September 2009 12:36 UTC www.merck.com [Source type: FILTERED WITH BAYES]

^ Flavay® inhibits platelet aggregation by inhibiting the enzymes thromboxane A2, 5-lipoxygenase and other clotting compounds.
  • Blood Platelets - Solutions and Information;Blood platelets,blood platelet,low blood platelet,low blood platelet count,blood count platelet,blood count high platelet,blood high platelet,flavay,masquelier's and information on blood platelets 25 September 2009 7:31 UTC www.naturalessentials.com [Source type: Academic]

Other functions

Cytokine signaling

.In addition to being the chief cellular effector of hemostasis, platelets are rapidly deployed to sites of injury or infection, and potentially modulate inflammatory processes by interacting with leukocytes and by secreting cytokines, chemokines, and other inflammatory mediators[11] [12] [13] [14].  Platelets also secrete platelet-derived growth factor (PDGF).^ The a granules store coagulation factors, platelet-derived growth factor (PDGF) and platelet factor 4.
  • Management of Platelet Disorders 10 January 2010 8:40 UTC peir.path.uab.edu [Source type: Academic]

^ Search other sites for Platelet Dysfunction .

^ Platelet derived growth factor Platelet-derived growth factor receptor Thrombopoietin Proteins .
  • Platelet - Kosmix : Reference, Videos, Images, News, Shopping and more... 10 January 2010 8:40 UTC health.kosmix.com [Source type: Academic]

Role in disease

High and low counts

.A normal platelet count in a healthy individual is between 150,000 and 450,000 per μl (microlitre) of blood (150–450 x 109/L)[15].  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.^ The greatest risk is when platelet count falls very low — below 10,000 platelets per microliter.
  • Thrombocytopenia (low platelet count) 10 January 2010 8:40 UTC www.cnn.com [Source type: General]
  • Thrombocytopenia (low platelet count) - Valley Health System 10 January 2010 8:40 UTC www.valleyhealth.com [Source type: FILTERED WITH BAYES]
  • georgiahealthinfo.gov 10 January 2010 8:40 UTC georgiahealthinfo.gov [Source type: General]
  • Thrombocytopenia (low platelet count): Causes - MayoClinic.com 25 September 2009 7:31 UTC www.mayoclinic.com [Source type: General]

^ Q: What is a normal platelet count?
  • FAQ in Adults 10 January 2010 8:40 UTC www.itppeople.com [Source type: FILTERED WITH BAYES]

^ A normal platelet count in a healthy individual is between ...
  • High Platelet Count - Web - WebCrawler 25 September 2009 7:31 UTC www.webcrawler.com [Source type: FILTERED WITH BAYES]

.Both thrombocytopenia and thrombocytosis may present with coagulation problems.  In general, low platelet counts increase bleeding risks; however there are exceptions.^ Bleeding may occur if platelet levels are too low or if platelet function is abnormal.
  • Platelet Abnormalities: Patient Information: Arizona Telemedicine Program 10 January 2010 8:40 UTC www.telemedicine.arizona.edu [Source type: Academic]

^ There may be an inherited problem which means that the platelets are not working properly.
  • Idiopathic Thrombocytopenic Purpura (ITP) - Information sheets - Children & families - GOSH and ICH 25 September 2009 7:31 UTC www.ich.ucl.ac.uk [Source type: FILTERED WITH BAYES]

^ A combination of the above factors also may cause a low platelet count.
  • Thrombocytopenia, Causes 25 September 2009 7:31 UTC www.nhlbi.nih.gov [Source type: FILTERED WITH BAYES]

.For example, immune heparin-induced thrombocytopenia and thrombocytosis (high counts) may lead to thrombosis, although this is mainly when the elevated count is due to myeloproliferative disorder.^ Temporal aspects of heparin-induced thrombocytopenia.
  • WikiGenes - Platelet Count 25 September 2009 7:31 UTC www.wikigenes.org [Source type: Academic]

^ A high platelet count is known as thrombocytosis.
  • Questions about High Platelet Count - Ask.com 10 January 2010 8:40 UTC www.ask.com [Source type: General]

^ Platelet Disorder (Immune mediated thrombocytopenia) .
  • Thrombocytopenia 25 September 2009 7:31 UTC www.vetinfo.com [Source type: FILTERED WITH BAYES]

Low platelet counts are, in general, not corrected by transfusion unless the patient is bleeding or the count has fallen below 5 x 109/L.  Transfusion is contraindicated in thrombotic thrombocytopenic purpura (TTP), as it fuels the coagulopathy.  In patients undergoing surgery, a level below 50 x 109/L is associated with abnormal surgical bleeding, and regional anaesthetic procedures such as epidurals are avoided for levels below 80-100.
.Normal platelet counts are not a guarantee of adequate function.  In some states, the platelets, while being adequate in number, are dysfunctional.  For instance, aspirin irreversibly disrupts platelet function by inhibiting cyclooxygenase-1 (COX1), and hence normal hemostasis.  The resulting platelets have no DNA and are unable to produce new cyclooxygenase.  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, another NSAID, does not have such a long duration effect, with platelet function usually returning within 24 hours[16], and taking ibuprofen before aspirin will prevent the irreversible effects of aspirin[17]Uremia, a consequence of renal failure, leads to platelet dysfunction that may be ameliorated by the administration of desmopressin.^ Low platelet counts can usually be traced to one of the following: .
  • Low Platelet Count Often Related to Underlying Disorder 25 September 2009 7:31 UTC www.mayoclinic.org [Source type: FILTERED WITH BAYES]

^ Q: What is a normal platelet count?
  • FAQ in Adults 10 January 2010 8:40 UTC www.itppeople.com [Source type: FILTERED WITH BAYES]

^ Is 99k platelet count normal?
  • WikiAnswers - What does a low platelet count mean 10 January 2010 8:40 UTC wiki.answers.com [Source type: FILTERED WITH BAYES]

Medications

Oral agents, often used to alter/suppress platelet function:
Intravenous agents, often used to alter/suppress platelet function:

Diseases

Disorders leading to a reduced platelet count:
Alloimmune disorders
Disorders leading to platelet dysfunction or reduced count:
.
  • HELLP syndrome
  • Hemolytic-uremic syndrome
  • Chemotherapy
  • Dengue
  • Alpha–Delta platelet storage pool deficiency (αδSPD) is a rare inherited bleeding disorder.^ Platelet storage pool disorder is a mild defect that causes bruising.
    • Congenital platelet function defects, Henry Ford Hospital, Detroit, MI 10 January 2010 8:40 UTC www.henryford.com [Source type: Academic]

    ^ Inherited disorders of platelet function.
    • Journal of Clinical Investigation -- Platelet genomics and proteomics in human health and disease 10 January 2010 8:40 UTC www.jci.org [Source type: Academic]

    ^ Gray-platelet syndrome (alpha storage pool disease) .
    • Functional Platelet Disorders - ARUP Consult, Your Online Lab Test Resource 10 January 2010 8:40 UTC www.arupconsult.com [Source type: Academic]
    • Functional Platelet Disorders 10 January 2010 8:40 UTC m.arupconsult.com [Source type: Academic]

    [18]
Disorders featuring an elevated count:
Disorders of platelet adhesion or aggregation:
Disorders of platelet metabolism
  • Decreased cyclooxygenase activity, induced or congenital
  • Storage pool defects, acquired or congenital
Disorders that indirectly compromise platelet function:
Disorders in which platelets play a key role:

Discovery

.Brewer[20] traced the history of the discovery of the platelet.  Although red blood cells had been known since van Leeuwenhoek (1632-1723), it was the German anatomist Max Schultze (1825-1874) who first offered a description of the platelet in his newly-founded journal Archiv für mikroscopische Anatomie[21].  He describes "spherules" to be much smaller than red blood cells that are occasionally clumped and may participate in collections of fibrous material.  He recommends further study of the findings.^ Like red blood cells , platelets have no cell nucleus .
  • Platelet - encyclopedia article - Citizendium 10 January 2010 8:40 UTC en.citizendium.org [Source type: Academic]

^ Platelets are cells in the blood that help blood to clot.
  • Platelet Count | LIVESTRONG.COM 10 January 2010 8:40 UTC www.livestrong.com [Source type: General]

^ They include: Red blood cellsWhite blood cells Platelets .
  • Platelet Information and Courses from MediaLab, Inc. 10 January 2010 8:40 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

.Giulio Bizzozero (1846-1901), building on Schultze's findings, used "living circulation" to study blood cells of amphibians microscopically in vivo.  He is especially noted for discovering that platelets clump at the site of blood vessel injury, a process that precedes the formation of a blood clot.  This observation confirmed the role of platelets in coagulation[22].^ Platelets are small blood cells that help stop bleeding after injury to a blood vessel by forming a clot, or plug, in the vessel.
  • Platelet Function in Patients Treated With SSRI and Non-SSRI Antidepressants - Full Text View - ClinicalTrials.gov 10 January 2010 8:40 UTC clinicaltrials.gov [Source type: Academic]

^ Platelets: Platelets are the cells that form blood clots that stop bleeding.
  • Thrombocytopenia (Low Platelet Counts) | CancerConsultants 10 January 2010 8:40 UTC www.cancerconsultants.com [Source type: Academic]

^ Platelets are essential to normal blood clotting.
  • Questions About Donating Platelets - New York Blood Center 10 January 2010 8:40 UTC www.plateletadvantage.com [Source type: General]

In transfusion medicine

.Platelets are either isolated from collected units of whole blood and pooled to make a therapeutic dose or collected by apheresis, sometimes concurrently with plasma or red blood cells.  The industry standard is for platelets to be tested for bacteria before transfusion to avoid septic reactions, which can be fatal.^ Red Blood Cells are perhaps the most recognizable component of whole blood.

^ Like red blood cells , platelets have no cell nucleus .
  • Platelet - encyclopedia article - Citizendium 10 January 2010 8:40 UTC en.citizendium.org [Source type: Academic]

^ Platelets are cells in the blood that help blood to clot.
  • Platelet Count | LIVESTRONG.COM 10 January 2010 8:40 UTC www.livestrong.com [Source type: General]

.Pooled whole-blood platelets, sometimes called "random" platelets, are made by taking a unit of whole blood that has not been cooled and placing it into a large centrifuge in what is referred to as a "soft spin."  This splits the blood into three layers: the plasma, a "buffy coat" layer, which includes the platelets, and the red blood cells.  These are expressed into different bags for storage.^ Red Blood Cells are perhaps the most recognizable component of whole blood.

^ The blood then literally ‘takes a spin’ in a centrifuge to separate your platelets from other blood components.
  • Questions About Donating Platelets - New York Blood Center 10 January 2010 8:40 UTC www.plateletadvantage.com [Source type: General]

^ Platelet-rich plasma (PRP) was obtained by centrifugation of whole blood at 500 g for 6 minutes.
  • Blood -- The contribution of glycoprotein VI to stable platelet adhesion and thrombus... 10 January 2010 8:40 UTC bloodjournal.hematologylibrary.org [Source type: Academic]

.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 a cancer patient that requires routine transfusions of platelets will receive repeated donations from a specific donor to further minimize the risk.^ Usually platelets from 4 donations of the same blood group are combined to provide one adult dose.
  • The National Blood Service - Platelet Donation 18 September 2009 12:36 UTC www.blood.co.uk [Source type: FILTERED WITH BAYES]

^ The number of platelets in your blood can be affected by many diseases.
  • Platelet Count | LIVESTRONG.COM 10 January 2010 8:40 UTC www.livestrong.com [Source type: General]
  • Platelet count - Health Information 10 January 2010 8:40 UTC www.qualityhealth.com [Source type: FILTERED WITH BAYES]
  • Platelet count 10 January 2010 8:40 UTC www.drexelmed.edu [Source type: Academic]
  • Platelet Count - Tests, Test Results & Diagnosis - NY Times Health Information 25 September 2009 7:31 UTC health.nytimes.com [Source type: News]
  • Medical Tests | Platelet Count 25 September 2009 7:31 UTC www.ucsfhealth.org [Source type: Academic]

^ Infections transmitted by platelet transfusions are similar to those associated with other blood components.
  • The National Institutes of Health (NIH) Consensus Development Program: Platelet Transfusion Therapy 10 January 2010 8:40 UTC consensus.nih.gov [Source type: Academic]

.Platelets are not cross-matched unless they contain a significant amount of red 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.^ Red Blood Cells are perhaps the most recognizable component of whole blood.

^ The blood then literally ‘takes a spin’ in a centrifuge to separate your platelets from other blood components.
  • Questions About Donating Platelets - New York Blood Center 10 January 2010 8:40 UTC www.plateletadvantage.com [Source type: General]

^ (MCHC)The platelet count is also usually included in the CBC.See also:Red blood cell...
  • Platelet Count | LIVESTRONG.COM 10 January 2010 8:40 UTC www.livestrong.com [Source type: General]

.Platelets collected by either method have a very short shelf life, typically five or seven days depending on the system used.  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 can then be counted using the automated method.
  • Platelet Information and Courses from MediaLab, Inc. 10 January 2010 8:40 UTC www.medialabinc.net [Source type: FILTERED WITH BAYES]

^ There have been no problems associated with this phenomenon – either for me or for my daughters.
  • Thrombocytopaenia during Pregnancy - Low Platelet Levels. From the UK Midwifery Archives 10 January 2010 8:40 UTC www.radmid.demon.co.uk [Source type: Original source]

^ Platelets have a shelf life of just 5 days.
  • Questions About Donating Platelets - New York Blood Center 10 January 2010 8:40 UTC www.plateletadvantage.com [Source type: General]

.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 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.^ Platelet Concentration System accelerates patient recovery.
  • Platelet Concentration System accelerates patient recovery., Smith Nephew Dyonics, 10 January 2010 8:40 UTC news.thomasnet.com [Source type: News]

^ Reduction of the volume of stored platelet concentrates for use in neonatal patients.
  • The Functional Integrity of Platelets in Volume-Reduced Platelet Concentrates -- Schoenfeld et al. 100 (1): 78 -- Anesthesia & Analgesia 10 January 2010 8:40 UTC www.anesthesia-analgesia.org [Source type: Academic]

^ Patients undergoing ECMO are usually transfused to maintain a platelet count > 100 x 10 9 /L. .
  • Blood Transfusion : Platelet transfusion 10 January 2010 8:40 UTC www.rch.org.au [Source type: Academic]

[23]  .Volume reduced platelets have a shelf life of only four hours.^ Platelets have a shelf life of just 5 days.
  • Questions About Donating Platelets - New York Blood Center 10 January 2010 8:40 UTC www.plateletadvantage.com [Source type: General]

^ This is a time-sensitive test – this test is only available for local clients due to 4-hour sample stability Do not order this test if platelets are decreased ( <100,000/μL) .
  • Functional Platelet Disorders - ARUP Consult, Your Online Lab Test Resource 10 January 2010 8:40 UTC www.arupconsult.com [Source type: Academic]

^ But the cold conditions were unfavorable for platelet survival, so the product had a shelf life of only 24 hours.
  • Future Synthetic Blood Products 10 January 2010 8:40 UTC biomed.brown.edu [Source type: Academic]

[24]

See also

References

  1. ^ Campbell, Neil A. (2008). Biology (8th ed.). London: Pearson Education. p. 912. ISBN 978-0-321-53616-7. "Platelets are pinched-off cytoplasmic fragments of specialized bone marrow cells. They are about 2-3µm in diameter and have no nuclei. Platelets serve both structural and molecular functions in blood clotting." 
  2. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. 
  3. ^ O’Connell S, Impeduglia T, Hessler K, Wang XJ, Carroll R, Dardik H. Autologous platelet-rich fibrin matrix as cell therapy in the healing of chronic lower-extremity ulcers. Wound Rep Reg 2008; 16:749-756.
  4. ^ Sánchez M, Anitua E, Azofra J, Andía I, Padilla S, Mujika I. Comparison of surgically repaired Achilles tendon tears using platelet-rich fibrin matrices. The American Journal of Sports Medicine 2007; 35 (2): 245-51.
  5. ^ Knighton DR, Ciresi KF, Fiegel VD, Austin LL, Butler ELL. Classification and treatment of chronic nonhealing wounds: successful treatment with autologous platelet-derived wound healing factors (PDWHF). Ann surg 1986; 204:322-30.
  6. ^ Knighton DR, Ciresi K, Fiegel VD, Schumerth S, Butler E, Cerra F. Stimulation of repair in chronic, non healing, cutaneous ulcers using platelet-derived wound healing formula. Surg Gynecol Obstet 1990; 170:56-60.
  7. ^ Celotti F, Colciago A, Negri-Cesi P, Pravettoni A, Zaninetti R, Sacchi MC. Effect of platelet-rich plasma on migration and proliferation of SaOS-2 osteoblasts: role of platelet-derived growth factor and transforming growth factor-β. Wound Rep Regen 2006; 14:195-202.
  8. ^ McAleer JP, Sharma S, Kaplan EM, Perisch G. Use of autologous platelet concentrate in a nonhealing lower extremity wound. Adv Skin Wound Care 2006; 19:354-63.
  9. ^ Driver VR, Hanft J, Fylling CP, Beriou JM. Arospective, randomized, controlled trial of autologous platelet-rich plasma gel for the treatment of diabetic foot ulcers. Ostomy Wound Manage 2006;52:68-87.
  10. ^ Movat H.Zet al. (1965). "Platelet Phagocytosis and Aggregation". Journal of Cell Biology 27: 531–543. doi:10.1083/jcb.27.3.531. PMID 4957257. 
  11. ^ Weyrich A.S. et al. (2004). "Platelets: signaling cells inside the immune continuum.". Trends Immunol 25: 489–495. 
  12. ^ Wagner D.D. et al. (2003). "Platelets in inflammation and thrombosis.". Thromb Vasc Biol 23: 2131–2137. 
  13. ^ Diacovo T.G. et al. (1996). "Platelet-mediated lymphocyte delivery to high endothelial venules.". Science 273: 252–255. 
  14. ^ Iannacone M. et al. (2005). "Platelets mediate cytotoxic T lymphocyte-induced liver damage". Nat Med 11: 1167–1169. 
  15. ^ Kumar & Clark (2005). "8". Clinical Medicine (Sixth ed.). Elsevier Saunders. pp. 469. ISBN 0702027634. 
  16. ^ "Platelet Function after Taking Ibuprofen for 1 Week". http://www.annals.org/cgi/content/full/142/7/I-54. Retrieved 2008-08-26. 
  17. ^ "Ibuprofen protects platelet cyclooxygenase from irreversible inhibition by aspirin". http://atvb.ahajournals.org/cgi/content/abstract/3/4/383. Retrieved 2008-08-26. 
  18. ^ Alpha-delta platelet storage pool deficiency in three generations - Platelets
  19. ^ McCarty OJT. et al. (2000). "Immobilized platelets support human colon carcinoma cell tethering, rolling, and firm adhesion under dynamic flow conditions". Blood 96: 1789–1197. 
  20. ^ Brewer DB. Max Schultze (1865), G. Bizzozero (1882) and the discovery of the platelet. Br J Haematol 2006;133:251-8. PMID 16643426.
  21. ^ Schultze M. Ein heizbarer Objecttisch und seine Verwendung bei Untersuchungen des Blutes. Arch Mikrosc Anat 1865;1:1-42.
  22. ^ Bizzozero J. Über einen neuen Forrnbestandteil des Blutes und dessen Rolle bei der Thrombose und Blutgerinnung. Arch Pathol Anat Phys Klin Med 1882;90:261-332.
  23. ^ Schoenfeld H, Spies C, Jakob C (2006). "Volume-reduced platelet concentrates". Curr. Hematol. Rep. 5 (1): 82–8. PMID 16537051. 
  24. ^ CBBS: Washed and volume-reduced Plateletpheresis units

External links

  • The Platelet Forum A site where researchers can discuss their work and multimedia relating to platelets.

Simple English

[[File:|thumb|A 250 ml bag of newly collected platelets.]] A platelet is a cell fragment that circulates in the blood. Platelets are involved in haemostasis through the making of blood clots. A low platelet count (number of platelets in the blood) can cause a person to bleed without their blood clotting (making scabs). A high platelet count can increase the risk of thrombosis (blood clots inside blood vessels), which stops blood from flowing properly.

Anatomy

Platelets do not have a cell nucleus. They are disc-shaped, and are 1.5 to 3 micrometers in diameter. The body does not have a lot of platelets, so they can all be used up quickly. They contain RNA, a canalicular system, and several different types of granules; lysosomes (containing acid hydrolases), dense bodies (containing ADP, ATP serotonin and calcium) and alpha granules (containing fibrinogen, factor V, vitronectin, thrombospondin and von Willebrand factor), the contents of which are released when the platelet is activated.


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