American Society of Hematology

Hemostatic Plug (Platelets)

Medical Importance

Optimal numbers and function of platelets are the key to cessation of bleeding from small vascular injuries. Disorders of platelet number or function can lead to bleeding from the skin, mucous membranes, brain or other sites. Tests are commonly used in clinical practice to examine each phase of platelet plug formation.  Defects in platelet numbers or function can be corrected or improved by transfusion of normal platelets, von Willebrand factor (cryoprecipitate or vWF concentrates) or certain drugs (DDAVP).

Objectives

  1. Be able to diagram the structure of a mature platelet and show the location of: dense granules, alpha granules, glycoprotein Ib, glycoprotein IIb/IIIa, and phospholipids.

  2. Be able to list three functions of platelets.

  3. Be able to construct a simple diagram that depicts the process of platelet adhesion. Include in the drawing subendothelial collagen, von Willebrand factor, and glycoprotein Ib. Explain why platelet adhesion to blood vessels does not occur under normal circumstances. 

  4. Similarly, be able to construct a simple diagram that shows the process of platelet aggregation; include the release reaction (ADP), thromboxane synthesis, ADP and thromboxane receptors, glycoprotein IIb/IIIa, and fibrinogen.

  5. List three mechanisms that could lead to thrombocytopenia.

  6. Be able to identify three methods of treating ITP and the mechanism by which they increase the platelet counts.
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