Question

All of the following are true about blood coagulation EXCEPT:

• A. Factor X is a part of both the intrinsic and the extrinsic pathway
• B. The extrinsic pathway is activated by contact with plasma and negatively charged surfaces
• C. Calcium is very important for coagulation
• D. The intrinsic pathway can be activated in vitro

Hint:

Contact with a negatively charged surface starts the intrinsic, not the extrinsic, pathway.

Answer 1

The Correct Option is B

This is a find-the-wrong-statement item, so the goal is to spot the single line that misassigns a property. Coagulation runs along two starting arms that merge into a shared final arm. The shared arm begins at Factor X, which means Factor X genuinely belongs to both the intrinsic and the extrinsic routes, so that claim holds. Calcium ions are needed for the assembly of clotting complexes on phospholipid surfaces, so that claim also holds. When blood is placed in a glass tube the negatively charged glass activates the contact factors and drives clotting through the intrinsic arm, so the statement that the intrinsic pathway works in vitro is correct as well. The flaw lies in the description of the extrinsic pathway: that arm is set off by tissue factor exposed at the site of injury along with Factor VII, whereas activation by contact with a negatively charged surface and plasma contact proteins is precisely the trigger for the intrinsic arm. Because the option swaps the intrinsic trigger onto the extrinsic pathway, it is the false statement. \[\boxed{\text{Extrinsic pathway activated by contact with negatively charged surfaces (FALSE)}}\]