Hemostasis

Blood Components: Platelets

Figure 16-10c: Megakaryocytes and platelets

• Coagulate, form plug, prevent blood loss• Formed by fragmentation from megakaryoctyes

Overview of Hemostasis: Clot Formation & Vessel Repair

Figure 16-11: Overview of hemostasis and tissue repair

Hemostasis: Vasoconstriction & Plug Formation

• Vasoconstriction• Platelet activation– Multiple factors– Positive feedback

• Aggregation • Loose plug

Hemostasis: Vasoconstriction & Plug Formation

Figure 16-12: Platelet plug formation

Hemostasis: Coagulation & Clot Stabilization

Figure 16-13: The coagulation cascade

• Prothrombin• Ca++• Fibrinogen• Fibrin• Polymerization

Dissolving the Clot and Anticoagulants

• Bleeding stopped• Vessel repair• Plasmin• Fibrinolysis• Clot dissolved

Dissolving the Clot and Anticoagulants

Figure 16-14: Coagulation and fibrinolysis

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…)

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