Platelets - R. Gianani - SRS

Question 1

What is this?

Answer 1

Megakaryocyte

Question 2

What is this?

Answer 2

Platelet

Question 3

Describe the physical appearance of a platelet

Answer 3

Small, disc shaped anucleate cells with tiny visible rim of cytoplasm surrounding a granular center.

Question 4

What types of granules do platelets contain?

Answer 4

Alpha granules

Delta granules

Question 5

What do alpha granules contain?

2 functional categories with three components each

Answer 5

Coagulation factors

1. fibrinogen
2. Factor V
3. vWF

Wound healing factors

1. fibronectin
2. platelet factor 4
3. PDGF

Question 6

What does the membrane of alpha granules contain?

Answer 6

P-selectin

Question 7

What do delta granules contain?

Answer 7

ADP

ATP

Ionized calcium

Serotonine

Epinephrine

(ESAAC)

Question 8

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?

Answer 8

Formation of secondary hemostatic plug and wound helaing (re-endothelization)

Question 9

What are the phases of platelet activation?

Answer 9

1. adhesion
2. activation
3. aggregation

Question 10

What receptors are involved in the adhesion step of the platelet reaction?

Answer 10

GpIb and vWF on exposed collagen

Question 11

What are the two components of the activation step of the platelet reaction?

Answer 11

1. Change of shape
2. Secretion

Question 12

What does the change of shape during platelet activation lead to?

Answer 12

1. Increased surface area and Increased affinity of GpIIb/IIIa and fibrinogen.
2. Translocation of calcium binding negatively charged phospholipids to the surface of the cells.

Question 13

What is involved in the aggregation phase of the platelet reaction?

Answer 13

Binding of GpIIB to fibrinogen. Initial reversible phase followed by thrombin induced further platelet activation aggregation and irreversible platelet contraction.

Question 14

What are four broad mechanisms of thrombocytopenia?

Answer 14

1. decreased production
2. decreased survival
3. sequestration
4. dilution

Question 15

What are some examples of disease states that decrease platelet production?

Answer 15

1. Selective impairment of platelet production
2. Drug-induced: alcohol, thiazides, cytotoxic drugs
3. Infections: measles, human immunodeficiency virus (HIV)
4. Nutritional deficiencies
5. B12, folate deficiency (megaloblastic leukemia)
6. Bone marrow failure
7. Aplastic anemia
8. Bone marrow replacement
9. Leukemia, disseminated cancer, granulomatous disease
10. Ineffective thrombopoiesis .
11. Myelodysplastic syndromes

Question 16

What are three broad categories of conditions that decrease platelet survival?

Answer 16

Primary autoimmune

Secondary autoimmune

Nonimmunologic destruction

Question 17

What are two examples of primary autoimmune platelet destruction?

Answer 17

1. Chronic immune thrombocytopenia
2. acute immune thrombocytopenic purpura

Question 18

What are four examples of secondary autoimmune platelet destruction?

Answer 18

1. Systemic lupus erythematosus, B-cell lymphoid neoplasms
2. Alloimmune: posttransfusion and neonatal
3. Drug-associated: quinidine, heparin, sulfa compounds
4. Infections

Question 19

What are some infections that cause secondary autoimmune platelet destruction? 3

Answer 19

1. HIV
2. infectious mononucleosis (transient, mild)
3. dengue fever

Question 20

What are three nonimmunologic examples of platelet destruction?

Answer 20

1. Disseminated intravascular coagulation
2. Thrombotic microangiopathies
3. Giant hemangiomas

Question 21

What is the cause of platelet sequestration?

Answer 21

hypersplenism

Question 22

What is the cause of dilution of platelets?

Answer 22

Transfusion

Question 23

When enumerating platelets, you can see falsely low platelet counts - pseudothrombocytopenia.

What are some examples of causes of pseudothrombocytopenia?

Answer 23

1. Platelet agglutinins
2. paraproteinemias
3. giant platelets
4. lipemia
5. EDTA induced platelet clumping

Question 24

You can also see falsely high platelet counts. What are three causes of this?

Answer 24

Microspherocytes

WBC/RBC fragments

Pappenheimer bodies

Question 25

What are the two main causes of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome?

Answer 25

* Deficiency of ADAMTS13 - either acquired or inherited * Infection - primarily E. coli 0157:H7

Question 26

What causes typical HUS?

Answer 26

E. Coli 0157:H7 via Shiga-like toxin

Question 27

What is the distinction between TTP and HUS?

Answer 27

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,

Question 28

What are atypical causes of TTP/HUS?

Answer 28

Alternative pathway inhibitor deficiencies (complement factor H, mebrane cofactor protein (CD46), or factor I.

Question 29

What are some miscellaneous associations with TTP/HUS?

Answer 29

1. Drugs (cyclosporine, chemotherapeutic agents) 2. Radiation, bone marrow transplantation 3. Other infections (HIV, pneumococcal sepsis) 4. Conditions associated with autoimmunity (systemic lupus erythematosus, HIV infection, lymphoid neoplasms)