Which of the following is true regarding the extrinsic pathway of blood clotting?

• A. The extrinsic pathway is independent of procoagulants.
• B. The extrinsic pathway does not involve calcium ions.
• C. The extrinsic pathway is slower than the intrinsic pathway of blood clotting.
• D. The extrinsic pathway is triggered by tissue factor.

Answer: (D)

Verified step by step guidance

1. Understand the context: Blood clotting involves a series of complex processes that prevent excessive bleeding when a blood vessel is injured. There are two main pathways: the intrinsic and extrinsic pathways, both leading to the formation of a blood clot.
2. Identify the role of the extrinsic pathway: The extrinsic pathway is initiated by external trauma that causes blood to escape from the vascular system. It is known for being a rapid response to injury.
3. Recognize the key components: The extrinsic pathway is triggered by the release of tissue factor (TF), also known as factor III, from damaged tissues. This is a crucial step that distinguishes it from the intrinsic pathway.
4. Clarify the involvement of calcium ions: Calcium ions (Ca²⁺) are essential for various steps in the blood clotting process, including the extrinsic pathway. They act as cofactors in the activation of several clotting factors.
5. Compare the speed of pathways: The extrinsic pathway is generally faster than the intrinsic pathway because it involves fewer steps and is directly activated by tissue factor, leading to a quicker formation of the clot.