Hemostasis Flashcards
What are the 3 phases of platelet activation?
Adhesion-platelets adhere to exposed collagen receptor (glycoprotein VI); GPIb-IX-V complex (which is the receptor for vWF) is activated by stress and ristocetin
Secretion-release of TXa2 from granules and dense bodies; results in recruitment of more platelets to the vessel wall
Aggregation-adherence of platelets to each other/mediated by GPIIb/IIIa receptor on the pot, which binds o fibrinogen in the presence of ionized calcium
What is the lifespan of a platelet?
7-10 days
_________factor is unstable in plasma and so it circulates in a complex with _______.
Factor VIII
VWF
How long does it take a Megakaryocyte to produce platelets?
1 week
Platelet activation in primary hemostasis is stimulated by which factors:
vWF
collagen
Epinephrine
ADP
Thrombin
thromboxane A2 (TXA2)
What are the three steps of the cell based model of coagulation/
Initiation-occurs on a TF bearing cell/vascular endothelial cells are disrupted; interaction of FVII and TF
Amplification-platelets and co-factors are activated; FV, FVIII and FIX activated by thrombin on the platelet’s surface
Propagation-large amounts of thrombin are generated on the plt surface; production of temporary plu at the site of the injury & stops the interruption to the blood supply
What is the main enzyme in the fibrinolytic system?
Plasmin-serine protease that digests fibrin, FV, FVIII and fibrinogen;
What are the vitamin K dependent factors?
II, VII, IX, X, Protein C and Protein S
What is a mixing study?
Test performed on a sample with a prolonged PT or PTT to determine if it is caused by a factor deficiency or an inhibitor
In a mixing study equal parts of patient plasma and pooled normal plasma are mixed and the prolonged screening test (PT or PTT) is repeated. If the results are corrected, the missing factor has been replaced by the pooled normal plasma and the patient should be worked up for a __________deficiency.
Factor
If not corrected, there is something in the patient’s plasma inhibiting a correction and an workup for an inhibitor should be performed.
PT based factors include:
FVII, FX, FV, FII
PTT based factors include:
FXII, FXI, FIX, FVIII
Which factor is not measured in the coagulation cascade?
FXIII
Fibrin stabilizing factor
Normal PT and PTT
Which factor deficiency is screened using the clot solubility test (5M urea)?
FXIII
What is the lifespan of a platelet in the peripheral blood?
7-10 days
What is the extrinsic tenase (activates X to Xa) complex?
TF:VIIa+Ca2+ + PF3
What is the intrinsic tenase complex?
Intrinsic pathway initiated by negatively charged phospholipids
FIXa + FVIIIa + Ca2+ + PF3
What is the prothrombinase complex?
FX + FV + PF3 + Ca2+
Converts prothrombin (FII) to Thrombin (FIIa)
What is the role of FXIII!
FXIIIa cross-links the fibrin monomers into an insoluble fibrin polymer (clot)
What is a role of Thrombin?
1-converts fibrinogen to fibrin monomers
Fibrinogen concentration is_________proportional to the thrombin clotting time of diluted plasma.
Inversely
-Patient’s plasma is diluted and excess thrombin is added
What does Thrombin time measure?
the conversion of fibrinogen to fibrin
What is the Reptilase Time?
-Modification of thrombin time using snake venom (Bothrops atrocity)
-detects fibrin degradation products (FDPs)
-not affected by presence of heparin (like the clotting time)
What is a mixing study?
-performed on prolonged PT or PTT to determine if caused by a factor deficiency or an inhibitor
-equal parts of pt plasma and pooled normal plasma are mixed and the prolonged screening test is repeated
-if results are corrected——factor deficiency
-results are not corrected—possible inhibitor?
