what is the location of the intrinsic pathway and extrinsic pathway?

Extrinsic Pathway - Is initiated with material outside of or "extrinsic" to the blood. This material, Tissue Thromboplastin (Factor III), is released by damaged tissue cells. Factor III permits the clotting process to take a chemical shortcut. As a result, the extrinsic pathway is a very rapid process, i.e., within 12 to 15 seconds. However, the production of Thrombin is low and the resulting clot is small. This pathway is most effective as a "quick patch" process.

1. Damaged tissue releases Tissue Thromboplastin (Factor III).

2. Tissue Thromboplastin activates Factor VII (Calcium dependent step).

3. Factor VII activates Factor X - Prothrombin Activator (Calcium dependent step).

Intrinsic Pathway - Is initiated by the blood coming in contact with exposed collagen in the blood vessel wall, i.e., material within the blood or blood vessel wall. This process is considerably slower (5 to 10 minutes) but results in the formation of larger amounts of thrombin. This allows the formation of larger clots.

1. Factor XII is activated by making contact with exposed collagen underlying the endothelium in the blood vessel wall.

2. Factor XII activates Factor XI.

3. Factors XII and XI (contact activation product) jointly activate Factor IX.

4. Factor IX activates Factor VIII.

5. Factor VIII together with Calcium ions and Factor III from platelets (Platelet Thromboplastin) activate Factor X - Prothrombin Activator. Since Factor III is released from activated platelets, the completion of the Intrinsic Pathway depends on there being an adequate number of platelets in circulation.