Final answer:
The clotting cascade is initiated by either the intrinsic pathway, which is triggered by internal damage or contact with certain substances within the bloodstream, or the extrinsic pathway, which starts with external tissue trauma. Both pathways lead to the common pathway, resulting in the formation of a stable blood clot.
Step-by-step explanation:
The clotting cascade can be initiated by either the intrinsic pathway or the extrinsic pathway. Both of these pathways lead to the common pathway, where the final events in the formation of a blood clot occur.
The extrinsic pathway is usually triggered by trauma that causes damage to the tissues outside of the blood vessels, leading to the release of tissue factor or factor III. This pathway is quicker and more direct, as it requires fewer steps to activate the final coagulation pathway.
The intrinsic pathway, on the other hand, is more complex and can be initiated by damage to the blood vessel walls or contact with negatively charged molecules. This pathway involves several clotting factors that are present within the bloodstream and is completed within a few minutes.
Once either pathway has been activated, they converge on the common pathway. In the common pathway, factor X is activated and leads to the conversion of prothrombin into thrombin. Thrombin then converts fibrinogen into fibrin, which forms the stable blood clot, with factor XIII stabilizing the clot.