What is the difference between intrinsic and extrinsic pathways of coagulation?

The intrinsic and extrinsic pathways of coagulation are critical components of the hemostatic process, working together to form a clot in response to vascular injury.

The intrinsic pathway is initiated by damage to the blood vessels, which exposes collagen and other sub-endothelial structures, activating platelets and set off a cascade of clotting factors that leads to the formation of a fibrin clot. It involves factors already present in the bloodstream and these factors work through a series of enzymatic reactions leading to thrombin formation.

The extrinsic pathway, on the other hand, is triggered by the exposure of tissue factor (TF), typically released from perivascular tissues surrounding damaged vessels. This pathway functions as a rapid response to vascular injury, allowing for the immediate activation of the coagulation cascade and ultimately resulting in thrombin generation.

Understanding that the intrinsic pathway is primarily initiated by vascular damage while the extrinsic pathway is directly associated with tissue factor helps clarify why the selected answer is accurate. The distinctions between these pathways are crucial when considering clinical conditions where coagulation may be disrupted, and they emphasize the complex nature of hemostasis.