What contribution from the intrinsic and the extrinsic pathways is necessary for the common pathway to begin?

Verified step by step guidance

1. Understand that the coagulation cascade is divided into three pathways: intrinsic, extrinsic, and common pathways, each involving a series of clotting factors that lead to blood clot formation.
2. Recognize that the intrinsic pathway is activated by damage inside the blood vessel and involves factors XII, XI, IX, and VIII, ultimately leading to the activation of factor X.
3. Know that the extrinsic pathway is triggered by external trauma causing blood to escape the vessel, involving tissue factor (factor III) and factor VII, which also leads to the activation of factor X.
4. Identify that the common pathway begins once factor X is activated (to factor Xa), which then combines with factor V, calcium ions, and phospholipids to convert prothrombin (factor II) into thrombin.
5. Conclude that both intrinsic and extrinsic pathways contribute to the activation of factor X, and this activation is the necessary step for the common pathway to begin.

Key Concepts

Intrinsic Pathway

The intrinsic pathway is one of the two initial routes that trigger blood coagulation. It is activated by damage inside the blood vessel and involves clotting factors present within the blood. This pathway leads to the activation of factor IX, which is essential for progressing toward the common pathway.

Extrinsic Pathway

The extrinsic pathway is initiated by external trauma that causes blood to escape the vascular system. It begins with the release of tissue factor (factor III), which activates factor VII. This pathway rapidly generates activated factor X, contributing to the start of the common pathway.

Common Pathway

The common pathway is the final sequence in the coagulation cascade where both intrinsic and extrinsic pathways converge. Activation of factor X leads to the conversion of prothrombin to thrombin, which then transforms fibrinogen into fibrin, forming a stable blood clot. Both pathways must activate factor X to initiate this process.