Plateletplug

1 The extrinsic pathway of clotting isstimulated by thromboplastin,released by damaged tissue.

2 The intrinsic pathway of clottingstarts when inactive factor XII,which is in the blood, is activated bycoming into contact with a damagedblood vessel.

3 Activation of the extrinsic or intrinsicpathway results in the production ofactivated factor X.

4 Activated factor X, factor V,phospholipids, and Ca 2+ formprothrombinase.

5 Prothrombinase convertsprothrombin to thrombin.

6 Thrombin converts fibrinogen tofibrin (the clot).

7 Thrombin activates clotting factors,promoting clot formation andstabilizing the fibrin clot.

PROCESS FIGURE 19.11 Clot Formation

In a sequence of chemical reactions, activated clotting factors ( white ovals ) activate inactive clotting factors ( blue ovals ). Clot formation begins through eitherthe extrinsic or the intrinsic pathway. The common pathway starts with factor X and results in a fibrin clot.

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