What are platelets? How do they help with blood clotting?
Platelets, cell fragments shed from megakaryocytes in red bone marrow, are involved in the clotting of blood. When platelets hit damaged tissue, they release thromboplastin which, in the presence of ions, converts the plasma protein prothrombin into thrombin. Thrombin, then, converts the plasma protein fibrinogen into fibrin. Fibrin forms a network of shrinking fibers through which serum (plasma without fibrinogen) is forced. The serum, then, forms a hard clot on the fibrin fiber network.
