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56 Cards in this Set

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What is the marrow precursor cell for platelets? What stimulates platelet growth?
Megakaryocytes. Platelet growth is stimulated by Thrombopoeitin
What effect might a large spleen have on circulating platelets? No spleen?
1/3 of circulating platelets are sequestered in the spleen. Splenomegaly is cause of low circulating platelets. Asplenic patients will have higher than average circulating platelet counts.
What's the lifespan of a circulating platelet?
9-10 days.
What are the two internal membrane systems of platelets?
1) Open Canalicular System - route for degranulation
2) Dense Tubular System - stores calcium required for platelet activation
What do Platelet Dense Granules contain?
ADPP
What do platelet Alpha Granules contain?
vWF, Fibrinogen
What are four proteins involved in platelet adhesion?
1) vWF
2) Fibronecin
3) Laminin
4) Thrombospondin
What is the main receptor for vFW?
Glycoprotein 1b
What are two INHIBITORS of protein adhesion?
1) Prostacyclin
2) NO
(Both released by intact endothelium.)
Name four platelet activation AGONISTS:
1) Collagen
2) Thrombin
3) Calcium
4) Thromboxane A2
5) ADP
6) Epinepherine
Why does aspirin have an anti-clotting effect?
Aspirin inhibits cyclooxygenase. Platelets need CO to produce Thromboxane A2, a clotting agonist.
What are the THREE STEPS in platelet activations?
1) Platelet calcium mobilization and granule secretion
2) Cyclooxygenase formation of Thromboxane A2
3) Platelet contraction
How do platelets AGGREGATE after activation?
Exposure of glycoprotein IIb-IIIa receptor complexes are exposed, binding fibrinogen. Fibrinogen networks bridge between platelets.
How do platelets enhance COAGULATION?
Activated platelets form surface complexes (collectively called Platelet Factor 3), which enhance the activation of Factors IX, X and Thrombin
Are platelets involved in anti-coagulation?
Yes - they carry Protein S, an anticoagulant.
Name four causes of thrombocytopenia caused by marrow suppression or decreased platelet production.
1) Radiation
2) Leukemia
3) Aplastic anemia
4) Folate/B12
What are the marrow and platelet characteristics of a thrombocytopenia from increased platelet destruction?
1) Normal to increased Megakaryocytes
2) "Young" circulating platelets, peripheral blast
3) (Hepatosplenomegaly)
What is the most common immune thrombocytopenia?
Idiopathic Thrombocytopenic Purpura
What causes ITP?
Auto-antibodies recognize and bind circulating platelet. They are then destroyed by the SPLEEN, liver and marrow (reticuloendothelial system)
What is the natural history of ITP?
PEDS: spontaneous resolution in 90% of cases
ADULTS: chronic. most common in young women, esp. surrounding pregnancy
How is ITP diagnosed?
Thrombocytopenia with normal to elevated # of megakaryocytes in the marrow, after exclusion of other causes (i.e. DIC). Response to corticosteroid therapy is supportive of the diagnosis.
How is ITP treated?
1) Corticosteroids
2) Splenectomy
3) Refractory: other immunosuppressives, IgG
Other than ITP, name additional disease triggers associated with auto-immune destruction of platelets.
1) HIV
2) Hepatitis C
3) SLE
4) Lymphoma, CLL
What is the classic drug-induced thrombocytopenia?
Quinine and quinine derivatives. Drug-antibody complexes deposit on the platelet surface.
What is the most important part of treatment for a drug-induced thrombocytopenia?
Removal of the offending drug. Immunosuppressives have little effect in these cases.
Use of what common anticoagulant can result in a low platelet count?
Heparin Induced Thrombocytopenia may be caused by even trace amounts heparin in the system.
What is the pathophysiology of heparin-induced thrombocytopenia?
Heparin use can induce formation of anti-platelet antibodies.
What serious complication can develop from heparin-induced thrombocytopenia?
Thrombosis due to formation of platelet plugs. Prolonged treatment with a direct thrombin inhibitor is required.
What are the two major ways in which thrombocytopenia may develop in HIV-infected patients?
1) Decreased Platelet Production - virus directly affects marrow production of platelets
2) Chronic ITP
What are the two main thrombotic microangiopathies?
1) TTP - thrombotic thrombocytopenic purpura
2) HUS - hemolytic uremic syndrome
What is the fundamental pathology in TTP?
Inhibitory autoantibodies against ADAMTS13 prevent cleavage of multimer vWF strands, leading to platelet agglutination.
Does TTP affect the RBCs?
Yes. The microangiopathy leads to RBC sheer stress,
Name the classic pentad of TTP:
1) Thrombocytopenia
2) Neurologic problems
3) Microangiopathic hemolytic anemia
4) Renal abnormalities
5) Fever
What are the two main classes of TTP?
1) Idiopathic
2) Secondary, caused by cancer, pregnancy, HIV, etc.
What is the mainstay of treatment for TTP?
1) *PLASMA TRANSFUSION*
2) Plasmapheresis
3) Splenectomy (refractory disease)
What microangiopathy is associated with a bacterial toxin?
Hemolytic Uremic Syndrome is commonly triggered by Shigatoxin-producing bacteria (E. coli O157:H7)
What's the treatment for HUS?
Supportive care. HUS is self-resolving.
What blood pathway is NOT activated with microangiopathies?
Coagulation pathways are not activated with TTP, HUS or vasculitis-associated platelet consumption.
Is thrombocytopenia in pregnancy always concerning?
No. Approx. 5-10% of women with a normal pregnancy may develop incidental thrombocytopenia, with no evidence of an autoantibody. (ITP commonly presents with pregnancy as well.)
Name four common causes for Thrombocytopenia due to SEQUESTRATION.
Congestive: portal hypertension, CHF
Infiltrative: myeloproliferative
Infections: TB, sarcoid
Hyperplastic: hemolytic anemias
What are the two main causes for thrombocytosis?
1) Increased Production
2) Decreased Sequestration
Thrombocytosis due to Increased Production may be split into two groups:
1) Primary (Essential Thr)
2) Reactive (Low Iron)
Essential Thrombocytosis is...
a myeloproliferative disease where the major manifestation is increased platelet count.
What are the bone marrow characteristics of ET?
Increased # of megakaryocytes, fibrosis.
What other cell lines may be affected in ET?
Many patients have neutrophilia, and a small increase in hematocrit.
What are the four myeloproliferative disorders?
1) Essential thrombocytosis
2) Chronic myelogenous leukemia
3) Polycythemia vera
4) Myelofibrosis
What enzyme mutation has been associated with ET?
JAK2 kinase mutations have been associated with ET.
What platelet morphology may be found in ET?
Platelets may be extremely large in ET, and they may clump on the smear.
What drug helps to lower platelet counts in ET w/out an increased risk of malignancy?
Anagrelide helps to lower the platelet count in ET, without long-term risk of malignancy.
What were the two Platelet Adhesion Defects mentioned in class?
1) Bernard Soulier
2) Thrombasthenia
What are the characteristics of Bernard Soulier?
* Platelet adhesion problem
* Problem with Glycoprotein 1 complex
* Normal vWF and Factor VIII levels
What are "exhausted platelets?"
Activation of the platelet membrane and release of storage pool depletes platelet of functional capacity.
What are some of the causes for "exhausted platelets?"
Heart-lung bypass, valvular heart disease, DIC, burns
What class of disorders might lead to platelets with an increased volume? (MPV?)
Myelodysplastic syndromes or with increased platelet production.
What does an abnormal "bleeding time" signify?
An abnormally long bleeding time indicates a problem with platelet plug formation. This may be caused by thrombocytopenia, or a disorder with platelet function.
What assay is NORMAL in congenital disorders of coagulation (i.e. the hemophilias?) In which coag. problem is it prolonged?
The bleeding time is NORMAL in congenital coag factor deficiencies. Bleeding time is LONG in vWF diseases, as vWF is required for platelet plug formation.