Platelets - R. Gianani - SRS Flashcards
What is this?
Megakaryocyte
What is this?
Platelet
Describe the physical appearance of a platelet
Small, disc shaped anucleate cells with tiny visible rim of cytoplasm surrounding a granular center.
What types of granules do platelets contain?
Alpha granules
Delta granules
What do alpha granules contain?
2 functional categories with three components each
Coagulation factors
- fibrinogen
- Factor V
- vWF
Wound healing factors
- fibronectin
- platelet factor 4
- PDGF
What does the membrane of alpha granules contain?
P-selectin
What do delta granules contain?
ADP
ATP
Ionized calcium
Serotonine
Epinephrine
(ESAAC)
Following blood vessel injury a number of physiological events take place aiming at restoring vessel integrity. Both platelets and soluble molecules. take part in these events. What does the repair of the vessel culminate in?
Formation of secondary hemostatic plug and wound helaing (re-endothelization)
What are the phases of platelet activation?
- adhesion
- activation
- aggregation
What receptors are involved in the adhesion step of the platelet reaction?
GpIb and vWF on exposed collagen
What are the two components of the activation step of the platelet reaction?
- Change of shape
- Secretion
What does the change of shape during platelet activation lead to?
- Increased surface area and Increased affinity of GpIIb/IIIa and fibrinogen.
- Translocation of calcium binding negatively charged phospholipids to the surface of the cells.
What is involved in the aggregation phase of the platelet reaction?
Binding of GpIIB to fibrinogen. Initial reversible phase followed by thrombin induced further platelet activation aggregation and irreversible platelet contraction.
What are four broad mechanisms of thrombocytopenia?
- decreased production
- decreased survival
- sequestration
- dilution
What are some examples of disease states that decrease platelet production?
- Selective impairment of platelet production
- Drug-induced: alcohol, thiazides, cytotoxic drugs
- Infections: measles, human immunodeficiency virus (HIV)
- Nutritional deficiencies
- B12, folate deficiency (megaloblastic leukemia)
- Bone marrow failure
- Aplastic anemia
- Bone marrow replacement
- Leukemia, disseminated cancer, granulomatous disease
- Ineffective thrombopoiesis .
- Myelodysplastic syndromes
What are three broad categories of conditions that decrease platelet survival?
Primary autoimmune
Secondary autoimmune
Nonimmunologic destruction
What are two examples of primary autoimmune platelet destruction?
- Chronic immune thrombocytopenia
- acute immune thrombocytopenic purpura
What are four examples of secondary autoimmune platelet destruction?
- Systemic lupus erythematosus, B-cell lymphoid neoplasms
- Alloimmune: posttransfusion and neonatal
- Drug-associated: quinidine, heparin, sulfa compounds
- Infections
What are some infections that cause secondary autoimmune platelet destruction? 3
- HIV
- infectious mononucleosis (transient, mild)
- dengue fever
What are three nonimmunologic examples of platelet destruction?
- Disseminated intravascular coagulation
- Thrombotic microangiopathies
- Giant hemangiomas
What is the cause of platelet sequestration?
hypersplenism
What is the cause of dilution of platelets?
Transfusion
When enumerating platelets, you can see falsely low platelet counts - pseudothrombocytopenia.
What are some examples of causes of pseudothrombocytopenia?
- Platelet agglutinins
- paraproteinemias
- giant platelets
- lipemia
- EDTA induced platelet clumping
You can also see falsely high platelet counts. What are three causes of this?
Microspherocytes
WBC/RBC fragments
Pappenheimer bodies
What are the two main causes of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome?
- Deficiency of ADAMTS13 - either acquired or inherited
- Infection - primarily E. coli 0157:H7
What causes typical HUS?
E. Coli 0157:H7 via Shiga-like toxin
What is the distinction between TTP and HUS?
Disorders in adults are typically described as TTP and are relatively less likely to involve renal failure. Also, neurological complications are more likely in TTP.
Disorders in children are typically described as HUS, and are relatively more likely to involve renal failure. Neurological problems less common in HUS.
**Per MERK manual**
Also,
What are atypical causes of TTP/HUS?
Alternative pathway inhibitor deficiencies
(complement factor H, mebrane cofactor protein (CD46), or factor I.
What are some miscellaneous associations with TTP/HUS?
- Drugs (cyclosporine, chemotherapeutic agents)
- Radiation, bone marrow transplantation
- Other infections (HIV, pneumococcal sepsis)
- Conditions associated with autoimmunity (systemic lupus erythematosus, HIV infection, lymphoid neoplasms)
