The Function of Platelets

Abstract

The main function of platelets, the maintenance of hemostasis, depends on three of their properties, the endothelial supporting function of platelets, the ability to form hemostatic plugs and to release lipoprotein material (platelet factor 3). When the number of circulating platelets is reduced the capillary endothelium becomes weakened as platelets are not available to enter the endothelial cytoplasm to support it and the capillary wall ruptures when exposed to minor trauma. The bleeding through the ruptured vessel wall is arrested by formation of a clump of platelets forming a hemostatic plug. Damage to the vessel wall initiates both the coagulation mechanisms and degradation of adenosine triphosphate. The products of each of these reactions, namely, thrombin and adenosine diphosphate bring about aggregation of platelets to form the hemostatic plug. These are the platelet functions performed following a transfusion of platelets into a thrombocytopenic recipient. The platelets remaining in the circulation and which are counted in platelet survival studies are those in excess of the immediate need of the recipient.

Circulation and hemostatic function of autologous fresh, liquid‐preserved, and cryopreserved baboon platelets transfused to correct an aspirin‐induced thrombocytopathy

“…The function of fresh and lyophilized platelets in thrombocytopenic dogs has been evaluated by the detection of RBCs in the lymphatic circulation 14,15 . The function of platelets has been reported to maintain endothelial integrity, which is difficult to assess, 17 and the platelet count has been correlated to the bleeding time 18,19 …”

Nonsurgical bleeding diathesis in anemic thrombocytopenic patients: role of temperature, red blood cells, platelets, and plasma‐clotting proteins

“…Restoration of hemostasis at the BT site depends on two vasoconstrictor substances that are released to reduce blood flow: thromboxane, produced by PLTs at the BT site, and endothelin released from endothelial cells 124,125 . PLTs are necessary to maintain endothelial cell integrity 154‐161 . Activation of clotting proteins, PLTs, and RBCs at the BT site produces thrombin to convert fibrinogen to fibrin.…”

Effects of Platelet Transfusions: Plug Formation and Maintenance of Vascular Integrity

“…The possibility that small numbers of platelets may suffice to plug hypothetical minute holes in the blood vessel wall through which red cells escape into the lymph spaces is possible, but unlikely, since discontinuity of endothelial structures in bleeding thrombocytopenic animals is not generally observed ( 17,18) and diapedesis of red cells across blood vessels has been shown to occur in the presence of normal platelet counts (19), as well as in thrombocytopenic animals. Increased diapedesis of red cells in irradiated 75 thrombocytopenic animals has been at-'tributed to eiidothelial damage other than formation of discrete holes (20); and has also been shown to be reduced or eliminated by the injection of platelet factor 3 (8,9 ) , or soybean phosphatides (2 1 ) , neither of which is capable of forming hemostatic plugs.…”

“…The hemostatic functions of platelets include promotion of blood clotting (1)(2)(3), clot retraction (4, S), vascular support (6)(7)(8), and platelet plug lormation (9). Although much information of a qualitative nature is presently available concerning the relationship of platelets to these various functions, there is a dearth of quantitative knowledge concerning platelet requirements to correct the sequelae of thrombocytopenia.…”