STRUCTURE AND FUNCTION OF PLATELETS

Blood platelets are discoid cellular fragments without nucleus originating from megakaryocytes. Platelets are able to respond to a great variety of agonists which bind to specific receptors localized on the plasma membrane. This process takes place when blood vessels are cut. Platelets then change their shape, adhere to newly exposed subendothelial tissues, release the content of numerous secretory granules and aggregate together. During this process, a great numbers of biochemical reactions are triggered such as phospholipases activation, synthesis of mediators and protein phosphorylation. These events result from increased cytoplasmic free calcium originating through calcium channels from the extracellular medium and from internal stores. Involvement of blood platelets in cardiovascular diseases may result from an exageration of these mechanisms by risk factors and are also discussed.