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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.)

A schematic diagram shows a coagulation system. The coagulation system has an extrinsic and an intrinsic pathway. In the extrinsic pathway, upon vascular injury, tissue factor and factor 7 are released that triggers the release of tissue factor-factor 7a and converts factor 9 to factor 9a with the addition of calcium ions and factor 11a. The tissue factor-factor 7a converts factor 10 to factor 10a with the addition of calcium ions and factor 9a. Prothrombin (factor 2) is converted to Thrombin (factor 2a) by the addition of factor 10a along with factor 5a, calcium ions, and phospholipid. In the intrinsic pathway, factor 12 yields factor 12a upon the surface and leads to inflammation, complement activation, and fibrinolysis. Prekallikrein, HMW kininogen, and surface yield Kallikrein which leads to the production of the surface. Factor 12a also aids in the conversion of factor 11 to factor 11a; factor 8 to factor 8a which requires phospholipids; factor 5 to 5a, calcium ions, and phospholipid. Factor 12a combined with thrombin (factor 11a) aids in the conversion of Fibrinogen to Fibrin, factor 13a, and X-linked fibrin; factor 13 is converted into Fibrin, factor 13a, and X-linked fibrin in the presence of fibrin and calcium ion.
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A schematic diagram shows a coagulation system. The coagulation system has an extrinsic and an intrinsic pathway. In the extrinsic pathway, upon vascular injury, tissue factor and factor 7 are released that triggers the release of tissue factor-factor 7a and converts factor 9 to factor 9a with the addition of calcium ions and factor 11a. The tissue factor-factor 7a converts factor 10 to factor 10a with the addition of calcium ions and factor 9a. Prothrombin (factor 2) is converted to Thrombin (factor 2a) by the addition of factor 10a along with factor 5a, calcium ions, and phospholipid. In the intrinsic pathway, factor 12 yields factor 12a upon the surface and leads to inflammation, complement activation, and fibrinolysis. Prekallikrein, HMW kininogen, and surface yield Kallikrein which leads to the production of the surface. Factor 12a also aids in the conversion of factor 11 to factor 11a; factor 8 to factor 8a which requires phospholipids; factor 5 to 5a, calcium ions, and phospholipid. Factor 12a combined with thrombin (factor 11a) aids in the conversion of Fibrinogen to Fibrin, factor 13a, and X-linked fibrin; factor 13 is converted into Fibrin, factor 13a, and X-linked fibrin in the presence of fibrin and calcium ion.

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

What ...

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