Platelets in Hemostasis

Platelets contribute to the hemostatic process in two different ways. First, through their adhesive and cohesive functions leading to the formation of a hemostatic plug. Second, they can activate coagulation mechanisms through the exposure of an adequate phospholipidic surface, acting as a catalytic site for the development of coagulation and the consolidation of the hemostatic plug. To promote a correct hemostasis, platelets should ideally retain their adhesive and procoagulant properties.

Platelets possess important secretory functions. During the process of activation, platelets express internal membrane proteins and release adhesive proteins, coagulation and growth factors. Some of the proteins facilitate the cross-talk of platelets with leukocytes and endothelial cells. Thus platelets play and important role in imflamatory and proliferative events and play a critical role for tissue remodeling and wound healing.

The following animation shows, step by step, the physiological process of hemostasis as it occurs in flowing blood:

Physiological Hemostasis

Scanning electron micrographs of different stages of platelet adhesion are shown: Resting platelet (left, x10,000); Attached platelet showing shape change and pseudopodia emission (center, x3,000); Spread platelet (right, x3,000). Click on pictures to enlarge.

(Pictures have been kindly provided by Dr. J. White. For image uses, please see Use of Content at Legal Information.

Bibliography

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Rodgers GM. Overview of platelet physiology and laboratory evaluation of platelet function. Clin Obstet Gynecol 1999; 42:349-59.

Jurk K, Kehrel BE. Platelets: physiology and biochemistry. Semin Thromb Hemost 2005; 31:381-92.