Hemostasis

Hemostasis

1. Blood vessel ruptures

   • 1).Vascular spasm
     • The smooth muscle layer constricts

2. 2).Platelet plug formation

   • Platelets attach to exposed collagen fibres
     • Release substances that promotes platelet aggregation

3. Coagulation

   • The intrinsic mechanism
     • Initiated by contact with exposed the exposed collagen
       • Activated simultaneously
         • Prothrombin activator is formed
           • Converted into thrombin
             • Forms long threads of fibrin
               • Surrounds the platelets and creates the framework
                 • RBC become trapped in the framework
                   • Platelets contract and clot retracts
                     • Blood vessel repairs
                       • Plasmin destroys fibrin network
                         • Fluidity of the plasma is restored
   • The extrinsic mechanism
     • Damaged tissue releases tissue thromboplastin and activates this mechanism
       • Both mechanisms are activated simultaneously