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 Vol. 29 No. 4, April 2008
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Right arrow Disorders of Blood/Neoplasms

(Pediatrics in Review. 2008;29:121-130.)
© 2008 American Academy of Pediatrics

Bleeding Disorders


Anjali A. Sharathkumar, MD*
Steven W. Pipe, MD*
 * Department of Pediatrics and Communicable Diseases, University of Michigan, Ann Arbor, Mich

The first 300 words of the full text of this article appear below.


   Objectives
 
After completing this article, readers should be able to:

  1. Discuss the physiology of hemostasis.
  2. Describe the clinical features suggestive of an underlying bleeding disorder.
  3. Develop a diagnostic algorithm for evaluating patients who are suspected of having bleeding disorders.
  4. Recognize the inheritance and clinical management of the commonly encountered bleeding disorders.


   Overview of Hemostasis
 
Hemostasis refers to the process whereby bleeding is halted in a closed circulatory system. Understanding the physiology of hemostasis allows the clinician to identify children who have both inherited and acquired abnormalities of hemostasis, guide laboratory investigations, and facilitate effective therapeutic interventions.

In response to an injury (Fig. 1), local vasoconstriction reduces blood flow to limit or prevent bleeding. Primary hemostasis describes the subsequent interaction between platelets, von Willebrand factor (vWF), and the vessel wall to form a platelet plug at the site of vascular injury. vWF, a large multimeric plasma glycoprotein that is synthesized and stored in endothelial cells and megakaryocytes, is released at the site of vascular injury. Circulating vWF also binds and stabilizes factor VIII (FVIII). Exposed subendothelial elements, such as collagen, serve as a binding site for vWF, which, in turn, mediates platelet adherence to the area of injury. Platelet receptors, vWF, and fibrinogen mediate platelet-platelet interactions, leading to aggregation, activation, secretion of platelet granules, and additional platelet aggregation. The platelet plug that ensues contributes to bleeding cessation but is unstable. Thus, for stability, the platelet plug must be reinforced by the formation of an organized fibrin clot through the activation of the blood coagulation system or secondary hemostasis.


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  		Figure 1. The coagulation system. F=factor, vWF=von Willebrand factor, TFPI=tissue factor pathway inhibitor. Coagulation inhibitors are indicated in red.

Blood coagulation involves a cascade of activation reactions. At each stage, a precursor protein (eg, FX) is converted to an active protease (eg, FXa) in the presence of calcium . . . [Full Text of this Article]






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