Bleeding Disorders Flashcards
What are the phases of homeostasis in clot formation?
(1) vasocontriction - endothelin release at the site of injury causes reflex vasoconstriction; (2) platelet adhesion - von Willebrant Factor (protein layer that acts like glue when endothelium is breeched) causes platelets to adhere and release cytokines; (3) platelet aggregation - activation of cytokines (ADP and TXA2) cause platelets to aggregate and form a platelet plug at the site of injury; (4) release of t-PA (fibrinolysis) and thrombomodulin (blocks coagulation cascade) prevent the clot from growing too large
What is the intrinsic pathway in the coagulation cascade?
includes Factors XII, XI, IX, and VIII to Factor X (more stable because it produces more fibrin) => affects the Partial Thromboplastin Time (PTT)
What is the extrinsic pathway in the coagulation cascade?
includes tissue factor and Factor VII (unstable because tissue factor is short-lived) => affects Prothrombin Time (PT)
What is the role of clotting factors in clot formation?
stabilize the platelet plug
What are clotting factors?
proteins produced in the liver with the help of Vitamin K
What is fibrin?
insoluble fibers that help to reinforce the platelet plug
Which therapies that reduce clot formation act on platelets?
aspirin and clopidogrel (Plavix)
How does aspirin prevent clot formation?
blocks TXA2 - prevents platelets from aggregating => platelet plug cannot form
How does clopidogrel (Plavix) prevent clot formation?
blocks ADP - prevents platelets from aggregating => platelet plug cannot form
How does Vitamin K deficiency contribute to bleeding?
Vitamin K deficiency causes a decrease in Factor VIII which, in turn, stops the intrinsic clotting cascade (liver will not produce clotting factors without Vitamin K)
How does coumadin (Warfarin) prevent clotting?
acts as an indirect anticoagulant => reduces Vitamin K
How do rivaroxaban (Xarelto) and apixaban (Eliquis) prevent clotting?
act as direct anticoagulant => directly inhibit Factor X (think rivaroXaban and apiXaban = X for Factor X)
How does dabigatran (Pradaxa) prevent clotting?
directly inhibits thrombin production
What is the mechanism of tissue plasminogen factor (t-PA) in preventing clots?
breaks up only fresh clots (acts only on newly released fibrin) - has to be given within 3.5 hours of a thrombotic stroke
What does the presence of D-Dimer indicate?
recency of a clot - reflects active/fresh coagulation