NURS 6501: Final Exam: Please contact Assignment Samurai for help with NURS 6501: Final Exam or any other assignment. Email: assignmentsamurai@gmail.com   In the process of hemostasis following vessel injury, which factor is critical for initiating the coagulation cascade leading to fibrin formation? Group of answer choices

• Thrombopoietin
• von Willebrand factor
• Factor VIII
• Tissue factor

  The correct answer is: Tissue factor   Explanation: In hemostasis, the extrinsic pathway is triggered first after vessel injury, and tissue factor (Factor III) is the key initiator:

1. Tissue factor (exposed on subendothelial cells) binds Factor VII, forming the TF-VIIa complex.
2. This activates Factor X → Xa, leading to thrombin (IIa) generation and fibrin formation.

Why Not the Others?

• von Willebrand factor (vWF): Mediates platelet adhesion (primary hemostasis), not coagulation cascade initiation.
• Factor VIII: A cofactor for Factor IX in the intrinsic pathway, but not the initiator.
• Thrombopoietin: Stimulates platelet production in bone marrow; unrelated to acute clotting.

Key Concept:

• The extrinsic pathway (TF-driven) is the physiologically relevant trigger in vivo.
• The intrinsic pathway (activated by contact with collagen/negatively charged surfaces) is less critical for normal clotting.

Thus, tissue factor is the critical initiator.