Question

multiple choice question
which lists the correct order of events for the intrinsic pathway of coagulation?

xiii activates xi which activates ix and vii which finally activates factor x.

xii activates vii which activates ix and xi which finally activates factor x.

xii activates xi which activates ix and viii which finally activates factor x.

x activates xi which activates ix and viii which finally activates factor xii.

Explanation:

The intrinsic coagulation pathway starts with factor XII (XII) activation. XII activates XI, then XI activates IX and VIII. The complex of IX, VIII, and calcium (along with phospholipids) activates factor X. Let's analyze each option:

• First option: Starts with XIII, which is incorrect (XIII is involved in fibrin stabilization, not the start of intrinsic pathway).
• Second option: XII activates VII, but VII is part of the extrinsic pathway, so this is wrong.
• Third option: XII activates XI, XI activates IX and VIII, and then factor X is activated. This matches the intrinsic pathway sequence.
• Fourth option: The order is reversed (X activating XI and ending with XII activation) which is incorrect.

Answer:

C. XII activates XI which activates IX and VIII which finally activates factor X. (Assuming the third option is labeled C; if the original options had labels like A, B, C, D, adjust the label as per the actual numbering, but based on the content, the correct sequence is the third option in the list provided, so the answer is the option "XII activates XI which activates IX and VIII which finally activates factor X".)