Understanding Coagulation Cascade and Hemostasis

Apr 25, 2025

Lecture Notes: Coagulation Cascade and Hemostasis

Introduction

  • Topic: Coagulation Cascade
  • Importance: Understanding coagulation factors and their roles in hemostasis.
  • Source: Coagulation factors originate from the liver and are beta globulins.

Hemostasis Overview

  • Purpose: Prevention of blood loss by stopping bleeding.
  • Steps:
    1. Vasoconstriction: Narrowing of blood vessels.
    2. Temporary Platelet Plug: Primary hemostasis via platelets.
    3. Coagulation: Secondary hemostasis involving coagulation factors.
    4. Clot Dissolution: Fibrinolysis to restore blood flow.
    5. Regeneration: Tissue repair and regeneration.

Primary Hemostasis

  • Balance: Between smooth endothelium (promotes blood flow) and thrombocytes (favor thrombosis).
  • Process:
    • Injury → Vasoconstriction → Platelet plug (if sufficient) or requires secondary hemostasis.
    • Platelet Activation: Involves GP 1B, von Willebrand factor, and platelet granules (ADP, thromboxane A2).

Secondary Hemostasis

  • Coagulation Cascade:
    • Intrinsic Pathway: Involves Factors 12, 11, 9, and 8.
    • Extrinsic Pathway: Involves Factor 7.
    • Common Pathway: Begins with Factor 10, leading to thrombin formation.
    • Thrombin: Converts fibrinogen to fibrin (Factor 1).
    • Fibrin Stabilization: Requires Factor 13.

Intrinsic vs. Extrinsic Pathways

  • Intrinsic Pathway:
    • Activated by subendothelial collagen.
    • Self-sufficient; longer cascade; more steps = more efficient.
  • Extrinsic Pathway:
    • Activated by tissue factor.
    • Requires external trigger; shorter cascade; faster but less efficient.

Coagulation Cascade Details

  • Injury leads to:
    • Extrinsic Activation: Tissue factor → Factor 7 → Factor 10.
    • Intrinsic Activation: Factors 12 → 11 → 9 → 8 → 10.
    • Common Pathway: Factor 10 and 5, calcium, and phospholipids form prothrombinase complex converting prothrombin to thrombin.

Importance of Factor 10

  • Central role in the coagulation cascade.
  • Requires "checks and balances" with other factors like 5, calcium, and phospholipids.

Fun Facts and Mnemonics

  • Mnemonic: For remembering pathways: Intrinsic pathway has more letters, thus longer and more steps.
  • Uses of PT and PTT tests to measure coagulation efficiency (PT for extrinsic, PTT for intrinsic).

Conclusion

  • Blood coagulates in vitro via the intrinsic pathway.
  • Further study: Fibrinolysis and tissue plasminogen activator in upcoming sessions.
  • Encouragement to subscribe and support the learning channel.

This concludes the notes on the coagulation cascade and hemostasis, providing a comprehensive overview of the pathways and their physiological significance.

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