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Hematology

Christine Du

INTRODUCTION

Test Taking Tip

Hematology requires lots of memorization. Important topics to look over include bleeding disorders and the various anticoagulants. These are basic questions you don’t want to miss.

THE COAGULATION PATHWAY

Sequence of the intrinsic pathway of coagulation:

  • Prekallikrein + HMW kininogen + factor XII + exposed collagen → activates factor XI → activates factor IX, combines with factor VIII → activates factor X, combines with factor V → converts prothrombin (factor II) into thrombin. Thrombin converts fibrinogen into fibrin.

FIGURE 2-1

Schematic of the coagulation system. HMW, high molecular weight. (Reproduced with permission from Brunicardi FC, Andersen DK, Billiar TR, et al: Schwartz’s Principles of Surgery, 9th ed. New York, NY: McGraw Hill; 2010.)

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Sequence of the extrinsic pathway of coagulation:

  • Factor VII + tissue factor → activates factor X, combines with factor V → converts prothrombin into thrombin. Thrombin converts fibrinogen into fibrin.

Which factor is the convergence point and common to both the extrinsic and intrinsic pathways of coagulation?

  • Factor X

What does the prothrombin complex consist of?

  • Factor V, X, platelet factor 3, and prothrombin catalyze the formation of thrombin

What function does thrombin have?

  • Activates factors V and VIII, activates platelets, and converts fibrinogen into fibrin and fibrin split products

Which factor has the shortest half-life?

  • Factor VII

What factor can be used to differentiate a consumptive coagulopathy from hepatocellular disease?

  • Factor VIII:C; consumptive coagulopathy will have reduced levels of all factors, and hepatocellular disease will have reduced levels of all factors except factor VIII

Which factors are known as the labile factors (activity lost in stored blood)?

  • Factors V and VIII

What function does factor XIII have?

  • Cross-links fibrin

What does protein C do?

  • Degrades fibrinogen and factors V and VIII (vitamin K dependent)

What does protein S do?

  • Acts as protein C cofactor (vitamin K dependent)

What does Von Willebrand factor (vWF) do?

  • Links collagen to the GpIb receptor on platelets

What is the function of antithrombin III?

  • Binds heparin, inhibits factors IX, X, XI, and thrombin

Where does tissue plasminogen activator come from, and what does it do?

  • Released from endothelium, and it converts plasminogen into plasmin

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