Platelets Flashcards
What is the process of thrombus formation during vascular injury?
Vasoconstriction and activation of hemostasis
Primary hemostatic plug of platelets
Secondary hemostatic plug of fibrin
When you have an imbalance in hemostatis what are the two main outcomes?
Thrombus
Hemorrhage
Thrombus can be formed due to increased __________ activity or decreased ____________
Procoagulant; fibrinolysis
Hemorrhage can be caused by a decreased in __________________ or __________________, and an increase in _______________
Procoagulant activity, platelet number/function; fibrinolyisis
What is the lifespan of a platelet?
5-10days
How much of the platelet mass in in the spleen?
1/3
What is the sequence of maturation of a platelet?
Stem cell -> megakayroblast -> megakaryocytes -> platelet
How are platelets formed form megakaryocytes ?
Megakaryocytes are located in the bone marrow
Long pro platelet processes extend into sinus lumen
Individual platelets break off
What hormone regulates the production of platelets? Where is it produced?
Thrombopoeitin (TPO)
Liver, kidney, muscle
If the number of platelets decreases, the amount of free TPO _____________
Increases
What are the two main effects of TPO in the bone marrow
Increase number, size and policy of megakaryocytes
Decreased maturation time of megakaryocytes
How long does it take to form a primary hemostatic plug?
3 to 5 mins
What are the stages of formation of the primary hemostatic plug?
Adhere
Activate
Secretion
Aggregation
What factor is involved in the adhesion phase of primary hemostatis
Von willebrand factor
-binds to GPlb on PLT surface
What occurs in the activation of platelets?
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
Is the aggregations of platelets reversible, or irreversible?
Irreversible
Secondary hemostasis involves the deposition of __________
Fibrin
How are platelet clots are retracted via ?
Actinomyosin filaments
-> wound closure and vessel patency
What tests measure the platelet concentration and morphology?
Blood smear
Hematology analyzers
What tests can measure function of planets?
Bleeding time tests
Specific platelet function test
What test can you do to determine platelet production?
Bone marrow aspirate (BMA)
Why should you collect your blood samples in a purple top tube for determining platelet function?
contains EDTA -> Ca chelator -> prevent clotting
What is the minimum concentration of platelets in a blood smear?
7-10 PLT/high power field
Except in horse 4-7
Patients are at risk for spontaneous hemorrhage when the platelet count is < ___________
30,000/ uL
An increased mean platelet volume suggests ____________
Thrombopoiesis
Bleeding time tests can be abnormal when ?
Decreased platelet function
Decreased platelet numbers
What are clinical features of thrombocytopenia?
Mucosal bleeding Petechiation Ecchymosis Spontaneous hemorrhage : <30,000/ul Hemorrhagic aneimia
What are the mechanisms of thrombocytopenia?
Decreased production Destruction Sequestration Loss Consumption
Pseduothrombocytopenia
What can causes decreased production of platelets?
Bone marrow hypoplasia
Neoplasia (primary or metastatic leukemia)
Myelonecrosis or myelofibrosis
(Affecting only megakaryocytes or multiple cell lines)
What can cause destruction of platelets?
Immune mediated thrombocytopenia
Alloimmune thrombocytopenia
Modified live virus vaccination
Piglets have high mortality rates from hemorrhage due to what disease?
Alloimmune thrombocytopenia
Dam produces anti-platelet antibodies from a previous pregnancy
How does a modified live virus vaccination cause platelet destruction ?
Vaccination can induce immune response against the PLT -> platelet aggregation -> clearance
Occur 3-10days post vaccination
How are platelets sequestered ?
In large vascular beds
- splenomegaly, scenic torsion, neoplasia
- hepatomegaly, portal hypertension
- vasodilation in endotoxic shock
T/F: Hemorrhage can cause thrombocytopenia
FALSE
Acute severe hemorrhage may result in mild thrombocytopenia
What are common causes of consumption causing thrombocytopenia?
Disseminated intravascular coagulation (DIC)
Vasculitis (rickettsial or FIP)
What is pseudothrombocytopenia?
False thrombocytopenia because the analyazer doesn’t measure the platelets because they are
- Too big
- Clumped
What are the two major mechanisms of thrombocytoisis?
Increased production
Increased distribution in plasma
A thrombocytoisis can be associated with what diseases?
Chronic inflammatory disease (eg IMHA) Chronic hemorrhage (IDA)
If you have a normal platelet count but the patient has clinical signs of thrombocytopenia, what might you suspect?
Qualitative disorder of platelets
What are acquired causes of qualitative disorders of platelets?
Uremia
Drugs
Fibrin desecration products - inhibit PLT function in disease process
Paraprotiens -plasma cell myeloma cause increased globulins coating PLT surface
What are inherited qualitative disorders of platelets?
Absences of glycoproteins receptors
Absence/reduction in platelet granules
Single transduction defects
Von willebrands disease
T/F: in von Willebrands disease, platelets are usually normal
True
Defect is in the von Willebrands factor that in in endothelial wall
What are the two types of von willebrands disease?
Quantitative deficiency (type 1 and 3)
Qualitative abnormality (type 2)
What breed of dog is predisposed to vonWillebrands disease ?
Doberman
