IHL I - Platelet Function Flashcards
what two events occur during endothelial injury?
endothelin release and contact with ECM
endothelin
causes vasoconstriction
result of endothelial injury
vWF
synthesized by endothelial cells
-forms a matrix on the basolateral surface that is exposed during damage
sources of vWF
endothelial cells (basolateral surface)
megakaryocytes produce vWF in circulating blood
-complexed to factor VIII
platelet alpha granules
what is vWF bound to in circulation
factor VIII
-increases the half life of factor 8
A3 domain
binds to the collagen of the ECM
domain of vWF
A1 domain
portion of vWF
binds to the platelet receptor (GPIb) on filopodia
GPIb
receptor on platelets for vWF
sequence of primary hemostasis
adhesion, activation, aggregation
Gp IIb/IIIa
binds platelets to eachother
via fibrinogen
fibrinogen
allows platelets to bond to one another
-bind to Gp IIb/IIIa receptors
von willebrand disease
cannot produce vWF
-platelets cannot bind to injury site
factor VIII also has a decreased life time***
-inhibition of coagulation cascade
glanzmann thrombasthenia
inability to form the GpIIb/IIIa receptors
cannot bind platelets together
what to look for on labs for coagulation?
platelet count (quantitative) and activity (qualitative)
what happens when platelet plug is formed?
the clot contracts down to the wall
forms a platform for secondary hemostasis
-needs to be smooth (don’t want thrombi breaking off)
abciximab
used in patient to prevent micro thrombi
block GpIIb/IIIa receptor
-induces glanzmann thrombasthenia
what is the mechanism of aspirin?
blocks cyclooxygenase activity
TxA2 prostaglandin reduction
factor XIII
tissue factor
starts phosholipid platform that causes the coagulation to occur
serum
blood is allowed to clot then centrifuged
plasma
anticoagulant present that prevents clotting
blood is centrifuged and fluid supernatant collected
anticoagulation to prepare plasma?
chelator of Ca2+
ex/ sodium citrate
guantitative test?
platelet count (automated analyzer)
qualitative test?
aggregation studies
looks at activity of platelets
bleeding time?
excellent test for overall deficits in vWF
time for standardized skin incision to bleeding
less than 8 minutes (less than 5 optimal)
**tests for von willebrand disease and disorders of primary hemostatis
**ineffective in detecting disorders of secondary hemostasis
normal range of platelets?
150-450 x 10”9 /L
mean platelet volume
indicated through automated analyzer that tells size of platelet
**young platelets are larger
increase in platelet production results in an increase in MPV
lab tests in glanzmann thrombasthenia
platelet count normal
aggregation studies has no response to epinephrine, ADP, collagen, arachidonic acid, or thrombin
tests for secondary hemostasis problems?
prothrombin time (PT) and activated partial thromboplastin time (aPTT)
prothrombin time
tests in the extrinsic pathway
and to monitor anticoagulant patients
aPTT
used in the intrinsic pathway monitor
can also be used to monitor heparin
