1. HEMOSTASIS

2. Due to damaged blood vessels Events that stop bleeding

3. Sequence of events 1. Vascular spasm 1. Circular smooth muscle of walls contracts 2. Reduces blood loss during repair

4. 2. Platelet plug formation a. platelet adhesion: platelets stick to blood vessel b. platelet release reaction: platelets release contents – ADP and thromboxane A2 activate other platelets, serotonin and thromboxane A2 vasocontrict c. platelet aggregation: ADP makes other platelets sticky, forms platelet plug

5. 3. Blood clotting def: a series of chemical reactions that results in fibrin threads background: too easy – thrombosis; too long - hemorrhage

6. a. Formation of prothrombinase 1. Extrinsic pathway: (seconds) tissue factor (protein) leaked into blood from surface of hurt cells. TF + calcium activates factor X. Factor X + factor V + calcium to form prothrombinase 2. Intrinsic pathway: (minutes) damaged endothelial cells (lining) exposes collagen fibers. Contact with collagen fibers activates clotting factor XII. Activates factor X. Factor X + factor V + calcium  prothrombinase

7. b. Prothrombinase + Calcium convert prothrombin (protein) to thrombin (an enzyme) c. Thrombin (+ calcium) converts fibrinogen (protein) to fibrin threads.