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RUSVM Clinical Pathology > Platelets > Flashcards

Platelets Flashcards

1
Q

What is the process of thrombus formation during vascular injury?

A

Vasoconstriction and activation of hemostasis

Primary hemostatic plug of platelets

Secondary hemostatic plug of fibrin

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2
Q

When you have an imbalance in hemostatis what are the two main outcomes?

A

Thrombus

Hemorrhage

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3
Q

Thrombus can be formed due to increased __________ activity or decreased ____________

A

Procoagulant; fibrinolysis

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4
Q

Hemorrhage can be caused by a decreased in __________________ or __________________, and an increase in _______________

A

Procoagulant activity, platelet number/function; fibrinolyisis

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5
Q

What is the lifespan of a platelet?

A

5-10days

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6
Q

How much of the platelet mass in in the spleen?

A

1/3

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7
Q

What is the sequence of maturation of a platelet?

A

Stem cell -> megakayroblast -> megakaryocytes -> platelet

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8
Q

How are platelets formed form megakaryocytes ?

A

Megakaryocytes are located in the bone marrow

Long pro platelet processes extend into sinus lumen

Individual platelets break off

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9
Q

What hormone regulates the production of platelets? Where is it produced?

A

Thrombopoeitin (TPO)

Liver, kidney, muscle

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10
Q

If the number of platelets decreases, the amount of free TPO _____________

A

Increases

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11
Q

What are the two main effects of TPO in the bone marrow

A

Increase number, size and policy of megakaryocytes

Decreased maturation time of megakaryocytes

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12
Q

How long does it take to form a primary hemostatic plug?

A

3 to 5 mins

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13
Q

What are the stages of formation of the primary hemostatic plug?

A

Adhere
Activate
Secretion
Aggregation

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14
Q

What factor is involved in the adhesion phase of primary hemostatis

A

Von willebrand factor

-binds to GPlb on PLT surface

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15
Q

What occurs in the activation of platelets?

A

Shape change in response to thrombin
-shift from smooth disc to sphere with filopodia

Flips membrane phosphatidylserine
-negative charge on the outer membrane surface

Secretion of granule products -> factor V and VIII, thromboxane A2, an Ca

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16
Q

Is the aggregations of platelets reversible, or irreversible?

A

Irreversible

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17
Q

Secondary hemostasis involves the deposition of __________

A

Fibrin

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18
Q

How are platelet clots are retracted via ?

A

Actinomyosin filaments

-> wound closure and vessel patency

19
Q

What tests measure the platelet concentration and morphology?

A

Blood smear

Hematology analyzers

20
Q

What tests can measure function of planets?

A

Bleeding time tests

Specific platelet function test

21
Q

What test can you do to determine platelet production?

A

Bone marrow aspirate (BMA)

22
Q

Why should you collect your blood samples in a purple top tube for determining platelet function?

A

contains EDTA -> Ca chelator -> prevent clotting

23
Q

What is the minimum concentration of platelets in a blood smear?

A

7-10 PLT/high power field

Except in horse 4-7

24
Q

Patients are at risk for spontaneous hemorrhage when the platelet count is < ___________

A

30,000/ uL

25
Q

An increased mean platelet volume suggests ____________

A

Thrombopoiesis

26
Q

Bleeding time tests can be abnormal when ?

A

Decreased platelet function

Decreased platelet numbers

27
Q

What are clinical features of thrombocytopenia?

A 
Mucosal bleeding 
Petechiation  
Ecchymosis
Spontaneous hemorrhage : <30,000/ul 
Hemorrhagic aneimia
28
Q

What are the mechanisms of thrombocytopenia?

A 
Decreased production 
Destruction 
Sequestration 
Loss 
Consumption

Pseduothrombocytopenia

29
Q

What can causes decreased production of platelets?

A

Bone marrow hypoplasia
Neoplasia (primary or metastatic leukemia)

Myelonecrosis or myelofibrosis
(Affecting only megakaryocytes or multiple cell lines)

30
Q

What can cause destruction of platelets?

A

Immune mediated thrombocytopenia

Alloimmune thrombocytopenia

Modified live virus vaccination

31
Q

Piglets have high mortality rates from hemorrhage due to what disease?

A

Alloimmune thrombocytopenia

Dam produces anti-platelet antibodies from a previous pregnancy

32
Q

How does a modified live virus vaccination cause platelet destruction ?

A

Vaccination can induce immune response against the PLT -> platelet aggregation -> clearance

Occur 3-10days post vaccination

33
Q

How are platelets sequestered ?

A

In large vascular beds

  • splenomegaly, scenic torsion, neoplasia
  • hepatomegaly, portal hypertension
  • vasodilation in endotoxic shock
34
Q

T/F: Hemorrhage can cause thrombocytopenia

A

FALSE

Acute severe hemorrhage may result in mild thrombocytopenia

35
Q

What are common causes of consumption causing thrombocytopenia?

A

Disseminated intravascular coagulation (DIC)

Vasculitis (rickettsial or FIP)

36
Q

What is pseudothrombocytopenia?

A

False thrombocytopenia because the analyazer doesn’t measure the platelets because they are

  1. Too big
  2. Clumped
37
Q

What are the two major mechanisms of thrombocytoisis?

A

Increased production

Increased distribution in plasma

38
Q

A thrombocytoisis can be associated with what diseases?

A 
Chronic inflammatory disease (eg IMHA)
Chronic hemorrhage (IDA)
39
Q

If you have a normal platelet count but the patient has clinical signs of thrombocytopenia, what might you suspect?

A

Qualitative disorder of platelets

40
Q

What are acquired causes of qualitative disorders of platelets?

A

Uremia
Drugs
Fibrin desecration products - inhibit PLT function in disease process
Paraprotiens -plasma cell myeloma cause increased globulins coating PLT surface

41
Q

What are inherited qualitative disorders of platelets?

A

Absences of glycoproteins receptors
Absence/reduction in platelet granules
Single transduction defects
Von willebrands disease

42
Q

T/F: in von Willebrands disease, platelets are usually normal

A

True

Defect is in the von Willebrands factor that in in endothelial wall

43
Q

What are the two types of von willebrands disease?

A

Quantitative deficiency (type 1 and 3)

Qualitative abnormality (type 2)

44
Q

What breed of dog is predisposed to vonWillebrands disease ?

A

Doberman

RUSVM Clinical Pathology (18 decks)

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