Question

multiple choice question
the extrinsic mechanism of coagulation is initiated by which of the following?

myeloblasts released prematurely from the bone marrow

factors released by damaged blood vessels (thromboplastin)

prostacyclin coating the endothelium

clotting factors in the plasma

Explanation:

To determine the initiator of the extrinsic coagulation mechanism, we analyze each option:

1. Myeloblasts (immature white blood cells) are not involved in coagulation initiation, so this is incorrect.
2. The extrinsic pathway is triggered by tissue factor (thromboplastin) released from damaged blood vessels (or tissues), matching this option.
3. Prostacyclin is an anticoagulant (prevents clotting) by inhibiting platelet aggregation, so it does not initiate coagulation.
4. The intrinsic pathway uses clotting factors in plasma, while the extrinsic is tissue - factor - driven, so this is for the intrinsic pathway.

Answer:

Factors released by damaged blood vessels (thromboplastin)