During homeostasis, platelet affects the coagulation by: (PGI May-2011)
|A||Platelet adhesion to exposed endothelium|
|C||Activation of prothrombinase complex|
|E||All of the above|
I. Vasoconstriction - due to release of vasoconstrictor substance. e.g. TXA2, serotonin. Q
II. Adherence: the glycoproteins coat of the cell membrane of platelet cause adherence to the exposed linjured endothelium; but repulses to normal endothelium.
III. Platelet plug for closing small vascular holes.
IV. Conversion of prothrombin to thrombin: the activation of prothrombin occurs on the surface of activated platelets and requires the assembly of a prothrombinase complex, consisting of platelet anionic phospholipids Ca, factor Va, factor Xa and prothrombin.
V. Stabilization of fibrin :Fibrin stabilizing factors released from platelets cause stabilization of fibrin (fibrin monomers polymerization and cross-linking of fibrin fibers). But, thrombin causes conversion of fibrinogen to fibrin.
VI. Fibrous organization of the blood clot. The growth factors secreted by platelet involved in fibrous organization.
VII. Clot retraction
VIII. Contraction of platelet by contractile proteins actin, myosin and thrombosthenin.