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24 Cards in this Set
- Front
- Back
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Platelets: general considerations:
Normal values -Same in children as in adults (150-400K) Around ... of platelets at any given time are in the spleen Express ABO antigens Receptors on the platelet surface -GPIb - ... receptor -GPIIb/IIIa - ... receptor |
1/3
vWF Fibrinogen |
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Platelet granule contents:
alpha granules -..., mitogens (PDGF, TGF-b), protease inhibitors ... granules -ADP, calcium, serotonin Lysosomes -Degrading enzymes (role in the ECM/plasma) Peroxisomes -Peroxidase, catalase |
vWF
Dense |
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How platelets work: first contact:
Tissue injury damages the endothelium -... released into the extracellular matrix (ECM) Adherence of platelets to area of injury -Interaction of platelet ... receptors with vWF Anchoring of platelets to area of injury -Interaction of platelet ... receptors with ECM collagen |
Von Willebrand’s factor
GP-Ib GPIIb/IIIa |
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How platelets work: thrombus formation:
Activation of anchored platelets -Spreading out of platelets -Release of granule contents *... promotes platelet aggregation -Synthesis of ... *Further amplifies platelet adhesion/aggregation Aggregation of platelets -Fibrinogen bound to surface GPIIb/IIIa receptors links platelets together -Thrombin generated on the platelet membrane *Transforms ... into ... |
ADP
thromboxane A2 fibrinogen fibrin |
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Regulation of platelet activity:
Prostacyclin (PGI2) -Synthesized in ... cells -... cAMP in the platelet -... platelet adhesion/aggregation Thromboxane A2 -Synthesized in the ... -... cAMP in the platelet -... platelet adhesion/aggregation |
endothelial
Increases Inhibits platelet Decreases Activates |
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Lab evaluation of platelet function:
... -Measure of vascular and platelet phases of hemostasis -Does not discriminate between vascular defects, thrombocytopenia, or platelet dysfunction -Reproducibility issues ... -External aggregating agents to screen for functional defects *ADP, collagen, ristocetin, epinephrine, arachidonic acid -Time and resource-consuming ... -Simplified version of aggregation studies -Suffices to rule out functional defects if normal -More readily available |
Bleeding time
Platelet aggregation studies Platelet function assay |
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Mechanisms of thrombocytopenia:
General mechanisms -Impaired ... *Marrow suppression *Defects in synthesis -Increased ... *Infections *Autoimmune -Abnormal ... *Splenic sequestration *Giant hemangiomas ... -The most common cause of a low platelet count -Usually due to clumping of platelets in the sample -Repeat the CBC/review the smear before extensive workup |
production
destruction distribution Spurious thrombocytopenia |
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“...-type” bleeding
-Petechiae, purpura -Epistaxis, mucous membrane bleeding -Persistent bleeding from superficial cuts, scratches “...-type” bleeding -Deep hematomas, -Superficial ecchymoses (usually large and solitary) -Hemarthroses -Delayed bleeding -Positive family history |
Platelet
Factor |
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Effects of aspirin on platelet function:
Mechanism -Acetylation of platelet cyclo-oxygenase -Cyclo-oxygenase required for generating ... Effect -Decreased ... -Inhibition of platelet ... Duration -As long as the affected platelets survive (about a week) |
thromboxane A2
thromboxane A2 aggregation |
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Drugs inhibiting platelet function:
... – e.g ibuprofen, naproxen, indomethacin -Similar mechanism to aspirin, although less potent. -Shorter duration of effects Antimicrobials -Amantidine, ampicillin, beta-lactams, nafcillin, ticarcillin, penicillin Antidepressants -Amitryptyline, phenothiazines, imiprimine, cyproheptadine Miscellaneous -Propranalol, antihistamines, Benedryl, Lasix, daunorubicin, dipyridamole |
NSAIDS
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Uremia
-Impaired platelet aggregation --> “...-type” bleeding -Treatment: Dialysis, ... |
platelet
DDAVP |
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Bernard-Soulier syndrome:
Defect -Absence of ... (vWF receptor) *Necessary for normal platelet adhesion and normal response to thrombin. -... is also involved in maintaining the cytoskeleton Clinical findings -Easy bruising and severe hemorrhage at times of injury or surgery Laboratory findings -Platelet count is usually mildly ... -... platelets noted on smear Treatment -Transfusion with platelet concentrates at the times of life-threatening hemorrhage -Isoantibodies against GPIb often present |
GPIb
GPIb decreased Giant |
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Glanzmann thrombasthenia:
Defect -Absence of ... (fibrinogen receptor) Clinical findings -... -type bleeding: petechiae, purpura, GI, mucous membranes Laboratory findings -Normal platelet numbers and appearance -Prolonged bleeding time and aggregation noted only with ristocetin Treatment -Transfusion with normal platelets for severe hemorrhage -Platelet transfusion frequently results in alloimmunization against GPIIb/IIIa |
GPIIb/IIIa
Platelet |
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ADP storage pool defect:
Defect -Deficient granule contents/release -Can’t release ... *Deficient aggregation Clinical findings -Heterogenous with mild to moderate symptoms -Only finding may be easy ... Laboratory findings -Normal platelet counts/appearance -Bleeding time is normal to markedly ... Treatment -... transfusions/DDAVP if needed |
ADP
bruising prolonged Platelet |
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Wiskott-Aldrich syndrome:
X-linked ... inheritance Clinical triad ... Platelet abnormalities in Wiskott Aldrich syndrome -Smaller than normal -Granule-deficient -Deficient aggregation -... helps the thrombocytopenia but worsens the immune deficiency Death from bleeding or infection usually occurs in the first decade |
recessive
Recurrent infection, Thrombocytopenia, Eczema Splenectomy |
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Acute idiopathic thrombocytopenic purpura: presentation:
Clinical presentation: well-appearing child/adult -... onset petechiae, purpura, epistaxis -History of preceding ... illness *EBV, CMV have been noted -Platelet count commonly < ... -Spontaneous recovery within 6 months -Intracranial hemorrhage in 0.5-1% |
Sudden
viral 20,000 |
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Mechanisms of platelet destruction in acute ITP:
... to platelet antigens bind to platelets Coated platelets then cleared by the RES (spleen) -... is the main organ of the RES system -Spleen is a major site of autoantibody production Anti-platelet ... most commonly implicated |
Autoantibodies
Spleen IgG |
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Acute ITP: evaluation:
-CBC with peripheral smear, metabolic profile -Obtain ANA in adolescent/adult patients -HIV test if risk factors -... testing not usually helpful Indications for bone marrow examination -Concerning features in history, physical, laboratory -If ... will be used, many still advocate a marrow -If ITP persists for six months, most advocate a marrow *The purpose is to exclude other conditions and establish the presence of ... |
Anti-platelet antibody
steroids megakaryocytes |
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Acute ITP: therapies:
... -Rapid response, takes several hours to give -Works via blockade of the reticuloendothelial system ... -Usually second-line therapy -Multifactorial mechanism *Downregulation of Fc receptors *Decreased autoantibody production, *Increased vascular stability ... -Similar to IVIG, less expensive -Limited to Rh+ patients. ... -Reserved for patients with chronic, severe ITP (risk of hemorrhage) -Not usually considered until after 6 months -Pneumococcal vaccine at least 2 weeks prior to surgery -Prophylactic antibiotics should be given to young patients post-splenectomy -Persistent refractory disease in approximately 20% |
IVIG
Steroids RhoD Splenectomy |
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Chronic ITP:
Clinical presentation -ITP of > ... months’ duration (10-20% of acute ITP will become chronic ITP) -Older children and adults , more common in females Laboratory features -Similar to acute ITP, but higher likelihood of positive ANA, Coombs tests -Chronic ... is occasionally the presenting feature of HIV Therapeutic options - Goal is to decrease the risk of ..., not to normalize the platelet count -Tapered ... are helpful, even to low doses/intervals -... is often considered the next move after steroids -Immunosuppressants in refractory cases *Examples: Cyclosporine, Cytoxan, azathioprine |
6
thrombocytopenia hemorrhage steroids Splenectomy |
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Thrombocytosis:
Primary (in the marrow) thrombocytosis - Rare, but occurs -Essentially a ... disorder, seen in older individuals -Thrombotic/hemorrhagic complications more common -Persistent, not transient -Leukocyte count usually ... (90% of cases) Secondary thrombocytosis – Most of the time -Reactive -Almost never associated with ... complications Conditions when thrombocytosis may be associated with thrombosis -Primary or “essential” thrombocythemia -Sick patients, counts > ... /ml Treatments -... for counts > 1,000,000 -Alkylating agents -Emergent thrombocytopheresis if required |
myeloproliferative
increased thrombotic 1,000,000 Aspirin |
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Causes of thrombocytosis:
Physiologic -Exercise, parturition, epinephrine, trauma, post-op, post-splenectomy Hematologic -“Rebound” after marrow suppression -... deficiency -Vitamin E deficiency Infectious/inflammatory -Infections associated with significant or systemic inflammation -... diseases *Vasculitis, inflammatory bowel disease, rheumatic fever, Kawasaki’s disease Neoplasms |
Iron
Inflammatory |
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Infection-related thrombocytopenia: mechanisms
Viral infections - ... -Megakaryocytic infection -Destruction of circulating platelets by the virus -Association with viral antigen-antibody complexes Bacterial infections - ... -Increased platelet utilization on damaged endothelium -Platelet interaction with circulating immune complexes -Direct interaction between bacterial and the platelets -Effects of bacterial toxins - Direct invasion of platelets (malarial infection) |
myelosuppression
consumption |
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other causes of thrombocytopenia:
Impaired production - Aplastic anemia, leukemia, marrow replacement with tumor ... platelet turnover/sequestration - Hemangiomas (with or without intravascular coagulation) ... - Shift in the distribution of platelets from the circulation to the splenic pulp -Splenic/extrahepatic portal vein obstruction, cirrhosis -Hemorrhage unusual despite decreased platelet counts Nutritional deficiencies - Severe iron, folate, and vitamin B12 deficiencies. Cardiovascular disorders - Likely consumptive (shortened platelet survival) Dilutional thrombocytopenia - Large transfusions without replacing platelets |
Increased
Splenomegaly |
