To form a platelet plug, platelets must adhere to the vessel inner layer. For this to occur, which protein molecule is required?
A) Von Willebrand factor
B) Plasminogen
C) Lipoprotein
D) Thromboxane A2
Ans: A
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Platelet adhesion requires a protein molecule called von Willebrand factor (vWF). This factor is produced by both megakaryocytes and endothelial cells and circulates in the blood as a carrier protein for coagulation factor VIII. The plasma also contains a plasma protein called plasminogen, which gets activated and converted to plasmin, an enzyme capable of digesting the fibrin strands of the clot. The extrinsic pathway of coagulation, which is a much faster process, begins with trauma to the blood vessel or surrounding tissues and with the release of an adhesive lipoprotein called tissue factor (also known as thromboplastin or factor III) from the subendothelial cells. Thromboxane A2 (TXA2) is released during platelet aggregation, the step after adhesion.
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