Extrinsic Clotting Factors vs. Intrinsic Clotting Factor

Attribute	Extrinsic Clotting Factors	Intrinsic Clotting Factor
Origin	Released by damaged tissues	Present in the blood
Activation	Activated by tissue factor	Activated by contact with foreign surfaces
Factors involved	Factor III (tissue factor), Factor VII	Factors XII, XI, IX, VIII
Pathway	Extrinsic pathway	Intrinsic pathway

Introduction

Clotting factors play a crucial role in the process of blood clotting, also known as coagulation. There are two main pathways involved in blood clotting: the extrinsic pathway and the intrinsic pathway. Both pathways involve a series of clotting factors that work together to form a blood clot and stop bleeding. In this article, we will compare the attributes of extrinsic clotting factors and intrinsic clotting factors.

Extrinsic Clotting Factors

The extrinsic pathway is activated by external trauma that causes blood to escape from the vascular system. This pathway is initiated by the release of tissue factor (TF) from damaged tissues. Tissue factor then forms a complex with factor VII, which activates factor X. Factor X then combines with factor V to form the prothrombinase complex, which converts prothrombin to thrombin. Thrombin is a key enzyme in the clotting process, as it converts fibrinogen to fibrin, which forms a mesh that traps blood cells and platelets to form a clot.

• Initiated by external trauma
• Activated by tissue factor (TF)
• Requires factor VII, X, and V
• Key enzyme is thrombin
• Forms fibrin mesh to trap blood cells and platelets

Intrinsic Clotting Factors

The intrinsic pathway is activated by internal trauma, such as damage to blood vessels. This pathway is initiated by the activation of factor XII, also known as Hageman factor. Factor XII activates factor XI, which then activates factor IX. Factor IX, in combination with factor VIII and factor X, forms the tenase complex, which converts factor X to its active form. This leads to the formation of the prothrombinase complex and the subsequent conversion of prothrombin to thrombin, as seen in the extrinsic pathway.

• Activated by internal trauma
• Initiated by factor XII (Hageman factor)
• Requires factor XI, IX, VIII, and X
• Forms tenase complex to activate factor X
• Leads to conversion of prothrombin to thrombin

Comparison

Both extrinsic and intrinsic clotting factors play essential roles in the blood clotting process, but there are some key differences between the two pathways. The extrinsic pathway is faster and more direct, as it is activated by external trauma and involves fewer clotting factors. In contrast, the intrinsic pathway is slower and more complex, as it is activated by internal trauma and requires more clotting factors to form the tenase complex.

Another difference between the two pathways is their regulation. The extrinsic pathway is regulated by tissue factor pathway inhibitor (TFPI), which inhibits the activity of factor VIIa and the formation of the prothrombinase complex. On the other hand, the intrinsic pathway is regulated by antithrombin III, which inhibits the activity of thrombin and other clotting factors involved in the pathway.

Despite these differences, both pathways ultimately lead to the formation of a stable blood clot that stops bleeding and promotes wound healing. The balance between the extrinsic and intrinsic pathways is crucial for maintaining hemostasis, the process of preventing excessive bleeding while allowing for normal blood flow throughout the body.

Conclusion

In conclusion, the extrinsic and intrinsic clotting factors are essential components of the blood clotting process. While the extrinsic pathway is activated by external trauma and involves fewer clotting factors, the intrinsic pathway is activated by internal trauma and requires more factors to form the tenase complex. Understanding the differences between these pathways is crucial for medical professionals in diagnosing and treating bleeding disorders and other conditions related to blood clotting.