Hemostasis and coagulation Flashcards
What is hemostasis?
Prevention of blood loss
What are the general steps of hemostasis?
Vascular constriction
Formation of platelet/primary plug
Formation of blood clot/secondary plug
Clot retraction and dissolution
Growth of fibrous tissue into the blood clot
What causes vasoconstriction in response to trauma?
Local myogenic spasm/contraction
Release of vasoconstrictors from platelets
What are the histological features of platelets?
Very small
No nucleus
What stimulates platelet production?
Thrombopoietin
What inhibits platelet activation?
Prostacyclin produced by endothelial cells
What is a potent inducer of platelet activation?
TXA2/thromboxane
What are the steps of platelet plug formation?
Adhesion
Activation
Aggregation
What mediates platelet adhesion?
Platelet receptors/glycoproteins bind to vWF on endothelial cells
What molecules released or produced from activated platelets help with platelet aggregation?
ADP
Serotonin
Thrombaxin
How does aspirin work?
It inhibits clycooxygenase and decreases the release of thrombaxin
What platelet receptors bind to vWF?
Gp 1b/1a
What platelet receptors bind to fibrinogen?
Gp IIb/IIa
What forms bridges between platelets?
Fibrinogen
What normally occurs to activate procoagulants?
Injury to endothelial cells
Failure of endothelial cells to produce anticoagulant factors
Activation of platelets
When does a clot start developing after trauma?
Within 15 to 20 seconds
What does a clot begin to retract?
After 20 to 60 minutes
What clotting factors require vitamin K?
Factor II, VII, IX, X
What anticoagulants require vitamin K?
Protein C
Protein S
What activates protein C?
Thrombomodulin
How does Warfarin work?
Inhibits VKOR from reactivating vit K
What activates the intrinsic pathway of coagulation?
When blood comes into contact with a negatively charged surface
What activates the extrinsic pathway of coagulation?
When blood comes into contact with material from damaged cells
Tissue factor activation
What is the function of thrombin?
Catalyzes the proteolysis of fibrinogen to fibrin
Activates factor XIII
Catalyzes the formation of new thrombin
Catalyzes the formation of Va and VIIIa
What is the function of factor XIII?
Mediates formation of stable fibrin
What can be indicated by failure of clot retraction?
Low platelets
What activates and accelerates contraction during clot retraction?
Thrombin
Calcium ions
What molecules in platelets lead to strong contraction during clot retraction?
Thrombosthenin
Actin
Myosin
What increases the levels of circulating t-PA?
Bradykinin
Catecholamines
What are the paracrine factors?
Prostacyclin
NO
What is the function of prostacyclin?
Vasodilation
Inhibits platelet activation
What is the general time frame to change a clot into fibrous tissue?
1 to 2 weeks
What is the cessation of bleeding dependent on when testing bleeding time?
Adequate number of platelets
Ability of platelets to adhere to vWF and fibrinogen
Ability of the platelets to aggregate
What is pathway is assessed by PT?
Extrinsic pathway
What factors are assessed by PT?
Factors VII, X, II, V, and fibrinogen
What pathway is assessed by PTT?
Intrinsic pathway
What factors are assessed by PTT?
Factors XII, XI, IX, VIII, X, V, II, and fibrinogen
