Blood Coagulation Flashcards
What is thrombosis?
The formation of an unwanted clot within blood vessels or the heart.
What is a thrombus?
A clot that adheres to a vessel wall.
What is an embolus?
A clot that floats within the blood.
Why are thrombi and emboli dangerous?
They may occlude blood vessels.
What are the steps required for clot formation?
Platelet activation and aggregation, formation of thrombin, production of fibrin.
How do platelets respond to vascular trauma?
By adhesion to the injury site, release of intracellular granules, and aggregation of the platelets.
What initiates the coagulation cascade leading to fibrin formation?
Factors released from injured tissue and platelets.
How is thrombin formed?
From prothrombin (factor II) by factor Xa.
What does thrombin catalyze?
The conversion of fibrinogen to fibrin.
What stabilizes the clot?
Cross-linking of fibrin strands.
What do endothelial cells maintain to prevent pathological thrombosis?
A nonthrombogenic lining in blood vessels.
How does the maintenance of transmural negative electrical charge help in preventing thrombosis?
It prevents the adhesion of circulating platelets.
What activates the fibrinolytic pathway?
The release of plasminogen activators.
What degrades coagulation factors in the prevention of thrombosis?
The activation of protein C.
What do Heparin-like proteoglycans do in preventing thrombosis?
Inhibit coagulation.
What is the role of prostacyclin (PGI2) in thrombosis prevention?
It is a potent inhibitor of platelet aggregation.
Name three categories of drugs that affect blood coagulation.
Platelet inhibitors, anticoagulants, thrombolytics.
List the platelet inhibitors.
Aspirin, ticlopidine, clopidogrel, abciximab, dipyridamole, eptifibatide.
Name the anticoagulants.
Heparin, warfarin, bivalirudin, lepirudin, enoxaparin, dalteparin, rivaroxaban.
Name the thrombolytics.
Alteplase, streptokinase, urokinase.
Name the drugs used in the treatment of bleeding.
Aminocaproic acid, protamine sulfate, vitamin K, tranexamic acid, aprotinin.
When should antiplatelet therapy be initiated after an infarction or stroke to obtain significant benefit?
Within 2 hours.
Why are antiplatelet drugs administered as adjuncts to thrombolytic therapy along with anticoagulants like heparin?
To maintain perfusion and limit the size of myocardial infarction.
What do platelet aggregation inhibitors target to interfere with platelet aggregation signals?
Inhibit COX-1, block GPIIb/IIIa, or ADP, or increase cAMP.
What is the goal of therapy with aspirin?
To selectively inhibit the synthesis of platelet thromboxane A2 by irreversibly inhibiting cyclooxygenase enzyme, thereby inhibiting platelet aggregation.
What does a small dose of aspirin inhibit?
Thromboxane synthesis in platelets (TXA2) but not prostacyclin (PGI2) synthesis in endothelium.
What is the dosage range for low-dose aspirin therapy?
81 to 325 mg per day.
What is the mechanism of action of aspirin?
Selective inhibition of COX-1 in low dose.
List the therapeutic uses of aspirin.
Prophylactic treatment of transient cerebral ischemia, reducing the incidence of recurrent myocardial infarction, decreasing mortality in post-myocardial infarction, and preventing coronary thrombosis in patients with unstable angina.
What are the adverse effects of aspirin?
Bleeding and gastrointestinal ulceration.
How do ticlopidine and clopidogrel inhibit platelet activation?
By blocking specific receptors for adenosine diphosphate (ADP) on the platelet membrane and inhibiting glycoprotein (GP IIb/IIIa) receptors.
What are the therapeutic uses of ticlopidine and clopidogrel?
Alternative prophylactic therapy to aspirin in secondary prevention of stroke, myocardial infarction, and unstable angina.
What is the most serious side effect of ticlopidine?
Neutropenia.
What other side effects are associated with ticlopidine?
Thrombocytopenia and aplastic anemia.