Hemostasis Flashcards
what is another name for platelets, and what are they derived from?
thrombocytes, they are derived from megakaryocytes
what is the regulation of the production of platelets controlled by?
TPO
what is TPO produced by?
kidney and liver
what is the role of TPO?
it increases the differentiation and maturation rate of hematopoietic stem cells resulting in more megakaryocytes and platelets
what does thrombopoietin (TPO) bind to?
c-MPL receptor
where is the c-MPL receptor found?
on megakaryocytes and other hematopoietic cells
how is TPO secretion controlled?
by itself and platelets themselves
what effect will a high number of platelets have on TPO?
the TPO will more likely bind to the c-MPL, so there will be less free TPO
what effect will a low number of platelets have on TPO?
the TPO will not bind to c-MPL as readily, so there will be more free TPO
What are the four basic steps of hemostasis?
vascular spasm, formation of platelet plug, formation of blood clot, repair of damage
what is the purpose of vascular spasm/ vasospasm?
it disrupts blood flow to keep blood above the spasm and avoid further blood loss
what are the platelet factors that contribute to vasospasm?
serotonin and thromboxane A2
what is adhesion of platelets to each other and endothelial cells initiated by?
the activation of platelet receptors GP Ib/Ia
what does the GP Ib/Ia bind to on the endothelial cells?
VWF
what is the first step of formation of the platelet plug?
adhesion
what is the second step of formation of the platelet plug?
activation
what happens once the platelet receptors are activated?
they release ATP, ADP, serotonin, and Ca2+ from their dense granules; they release growth factors, VWF, factor V, and fibrinogen from their alpha-granules; they generate thromboxane A2
what happens once ADP, serotonin, and thromboxane is released from the dense granules?
they activate additional platelets which promotes aggregation
what does the ADP bind to?
P2Y12 receptors on platelets
what does binding of the ADP on the P2Y12 receptors cause?
a conformation change in the GP IIb/IIIa
what does a conformation change in the GP IIb/IIIa cause?
the binding of fibrinogen
what happens when fibrinogen can bind?
it bridges other platelets and participates in forming the platelet plug
what is aspirin?
a cyclooxygenase inhibitor
what is the action of aspirin?
it inhibits clotting by reducing release of thromboxane A2
what is Clopidogrel (Plavix)?
an antiplatelet agent
what is the action of clopidogrel (plavix)?
it inhibits P2Y12 receptors- so it blocks further platelet activation and aggregation
what is the first thing to occur during blood clot formation?
there will be activation of pro thrombin activator, which will then activate thrombin
thrombin will then work on fibrinogen to make what?
fibrin monomers
what do the fibrin monomers eventually become?
stable fibrin
what is the main purpose of the blood clot formation step in hemostasis?
it starts to contract everything
if a patient doesn’t have VWF, what will be the issue?
an issue with adhesion
if a patient doesn’t have GPIIb-GPIIIa, what will be the issue?
they will struggle with the aggregation process
