Answer :
Final answer:
Warfarin chiefly affects the extrinsic pathway and results in a rise in PT/INR levels by inhibiting the synthesis of vitamin K-dependent clotting factors. This process disrupts the clotting process, therefore extending the time it takes for blood to clot, which is measured by PT and INR tests.
Explanation:
The direct answer to your question is: Warfarin affects the Extrinsic pathway and causes an increase in PT/INR levels, hence, option 3) Extrinsic pathway, increased, is the correct one.
Warfarin works as an anticoagulant by inhibiting the synthesis of vitamin K-dependent clotting factors, which include Factors II, VII, IX, and X, and the anticoagulant proteins C and S. The clotting process involves a cascade of enzymatic reactions, leading to the conversion of fibrinogen to fibrin, which forms the structural basis of a blood clot.
Now, the extrinsic pathway, predominantly affected by Warfarin, is initiated by damage to the surrounding tissues (extravascular cells) causing factor III (thromboplastin) to be released. The PT (Prothrombin Time) test measures the time it takes for clotting to occur in a blood sample given thromboplastin (which initiates the extrinsic pathway). Thus, Warfarin, by inhibiting the aforementioned factors, impairs the clotting process thereby increasing the PT. INR (International Normalized Ratio) is based on PT values to monitor the dosage of warfarin.
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