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platelet adhesion - okt3
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09-25-2007, 05:45 PM
During the passage of an intravenous catheter, numerous endothelial cells are dislodged from the lining of the popliteal vein. What substance allows platelet adhesion to the exposed collagen fibers?
A. Factor VIII B. Factor IX C. Fibronectin D. Tissue factor E. Von Willebrand factor
09-25-2007, 05:47 PM
The correct answer is E. Von Willebrand factor (vWF) is a self-polymerizing clotting protein present in the serum and the subendothelial basal lamina, which has binding sites for collagen, platelets, and fibrin. At a site of injury, vWF forms the bridge between the exposed collagen fibers and platelets in circulation, stimulating platelet degranulation and initiating the cellular component of the clotting cascade. An equally important role for vWF is binding platelets to the newly formed fibrin strands in a blood clot.
Factor VIII (choice A) and Factor IX (choice B) are clotting proteins of the intrinsic pathway. Factor VIII acts in concert with activated Factor IX (IXa) to cleave Factor X to Xa. Xa is the prothrombin activator central to both the intrinsic and extrinsic pathways. Fibronectin (choice C) is a serum protein that acts as an opsonin for phagocytic cells in clots. Fibronectin binds non-specifically to bacteria and other materials in the newly forming clots, and draws the cell membrane of phagocytes into contact with these substances. Tissue factor (choice D) is a protein released from injured tissues that works in concert with Factor VII to initiate the extrinsic pathway of coagulation. Like Factors VIII and IX, tissue factor and Factor VII cleave Factor X to Xa. |
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