Ch 16.5 Learning Objectives

16.5.1 What is the difference between hemostasis and coagulation?

Hemostasis - entire process of stopping bleeding

• Vasoconstriction

• Platelet plug formation

• Coagulation

Coagulation - one part of hemostasis

• formation of a stable fibrin clot via the coagulation cascade

16.5.2 What are the steps of Hemostasis?

1. damaged blood vessel releases Endothelin and TX-A2 causing vasoconstriction

2. platelets stick to exposed collagen (sticky=activated),

   1. releases serotonin (5-HT), and TX A2

   2. positive feedback - coagulation forms a temporary plug

16.5.2 what are the steps of Coagulation?

1. coagulation cascade triggered

   1. intrinsic pathway - triggered by exposed collagen → factor XII

   2. Extrinsic pathway - triggered by tissue factor (factor III) → factor VII

   3. Both (common) leads to

      1. Prothrombin → Thrombin

      2. Fibrinogen → Fibrin

   4. Factor XIII stabilizes fibrin → strong clot

   5. Final result is a stable fibrin mesh over platelet plug

16.5.2 What are the steps of fibrinolysis

1. Clot contains plasminogen (inactive)

2. Converted to plasmin by:

   1. Thrombin

   2. Tissue plasminogen activator (tPA)

3. Plasmin breaks down fibrin → clot dissolves

Ensures clots are temporary

16.5.3 what are the clinical approaches to preventing blood clotting

• Fibrinolytics (“clot busters”)

• NSAIDs (Nonsteroidal Anti-Inflammatory Drugs)

• Anticoagulants

16.5.3 what is the mechanism of fibrinolytics?

Convert plasminogen → plasmin → breaks up fibrin

16.5.3 What is the mechanism of NSAIDS?

inhibits cyclooxygenase, and prevents Thromboxane A2 in platelets

16.5.3 What is the mechanism of anticoagulants?

interferes with coagulation cascade:

• Warfarin (Coumadin)

  • Blocks Vitamin K → prevents clotting factor synthesis

• Heparin

  • Inhibits thrombin and Factor X

• EGTA

  • removes calcium from blood