Question

1. A. Why and how are the intrinsic and extrinsic pathways activated? B. How is fibrin made to help aid in coagulation?

Answer 1

Both intrinsic and extrinsic pathway of blood coagulation are activated to form stable fibrin (final product of coagulation Cascade). This will helps to coagulation of blood and prevent bleeding.

How both pathways are activated

Intrinsic pathway is activated, when endothelium is exposed, trauma in the blood vessels ( inside) and by platelets

Extrinsic pathway is activated extrnal trauma.

B. Fibrin, the final product of coagulation cascade is formed by intrinsic, extrinsic, and common pathways.

There are 13 different types of clotting factors (Proteins)a available in our blood namely,

Factor I - Fibrinogen

Factor II - Prothrombin

Factor III - Thromboplastin

Factor IV - Calcium

Factor V - Labile factor

Factor VI - Absent

Factor VII - Stable factor

Factor VIII - Antihemophilic factor

Factor IX - Christmas factor

Factor X - Stuart Power factor

Factor XI - Plasma thromboplastin

Factor XII - Hegman factor

Factor XIII - Fibrin stabilising factor

Intrinsic pathway

When there is a endothelial damage, there is exposure of endothelial collegen. Intrinsic pathway starts when this exposed collegen activates factor XII. Activated factor XII is XIIa. Then this XIIa actives factor XI to factor XIa. This factor XIa activates factor IX to factor IXa. The intrinsic pathway enter the common pathway by the activation of factor X to factor Factor Xa by the action of factor IXa, calcium and factor VIII.

Extrinsic Pathway

It is very short pathway endothelial cells of damaged blood vessels releases tissue factor. This tissue factor activates factor VII to factor VIIa and this go and actives factor X to factor Xa.

Common pathway

Both intrinsic and extrinsic Pathway come together once factor X is activated.

Activated factor X activates Prothrombin activator with the help of calcium, activated factor V ( Va). Prothrombin activator cleaves Prothrombin ( factor II) to thrombin. This thrombin catalyses conversation of Fibrinogen to fibrin with the help of calcium and clotting factor XIIIa.