Razi Journal of Medical Sciences

Platelets as cellular elements are the constituants of blood tissue and their main function is to participate in hemostatic processes.

The glycocalyx which intimately surrounds the platelets contains a number of glycoproteins which are responsible for blood group specificity (ABO), tissue compatibility (human leukocyte antigen = HLA) , and platelet antigenicity. Platelets contain granules which are involved in many sorts of activities like maintaining the integrity of vascular endothelial cells.

This process is mostly mediated by platelet derived growth factor (PDGF) Adhesion of platelets to each other and thrombus formation are mediated by different factors such as platelet activation and release of ADP which facilitate formation of glycoprotein and phospholipoprotein complexes in the membrane of neighboring platelets.

TXA₂ released from arachidonic acid originally from membrane otiosphotipides also plays a role in thrombus formation. Thrombus then binds to collagene fibers of subendothelium through VWF or fibronectins and prevents bleeding by forming platelets plugs.

Platelets release factors such as I, V, VII to facilitate coagulation, and for this reason, are called thrombocytes. They also release heparin neutralizing proteins (PF4, TG) that help from clots at the injured sites.

Finally, they participate in clot retraction through contractile proteines, specifically thrombostenin.