1. Hemostasis

2. Blood Components: Platelets
• Coagulate, form plug, prevent blood loss
• Formed by fragmentation from megakaryoctyes
Figure 16-10c: Megakaryocytes and platelets

3. Overview of Hemostasis:
Clot Formation & Vessel Repair
Figure 16-11: Overview of hemostasis and tissue repair

4. Hemostasis: Vasoconstriction & Plug
Formation
• Vasoconstriction
• Platelet activation
– Multiple factors
– Positive feedback
• Aggregation
• Loose plug

5. Hemostasis: Vasoconstriction & Plug
Formation
Figure 16-12: Platelet plug formation

6. Hemostasis: Coagulation & Clot
Stabilization
• Prothrombin
• Ca++
• Fibrinogen
• Fibrin
• Polymerization
Figure 16-13: The coagulation cascade

7. Dissolving the Clot and Anticoagulants
• Bleeding stopped
• Vessel repair
• Plasmin
• Fibrinolysis
• Clot dissolved

8. Dissolving the Clot and Anticoagulants
Figure 16-14: Coagulation and fibrinolysis

9. Coagulation and Disease
• Hemophilia
• Cardiovascular Diseases
– Key problem – clots block undamaged blood vessels
– Anticoagulants prevent coagulation
• Keep platelets from adhering
• Prevent fibrin coagulation
– "Clot Busters": Prevent further clotting
• Speed fibrinolysis
• Limit tissue damage (heart, brain…)

10. Summary
• Blood is about 50% plasma, water solvent &
solutes: ions, elements, gasses, proteins, wastes
& nutrients
• White blood cells function in internal defense
• Iron in hemoglobin is key to RBC transport of O2
• Platelet activation initiates clot formation
• Clotting prevents blood loss but is a problem in
cardiovascular disease