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Unformatted text preview: Platelets Platelets are small disk-shaped blood fragments produced in the bone marrow. They lack nuclei and are much smaller than erythrocytes. Also known technically as thrombocytes , they serve as the starting material for blood clotting. The platelets adhere to damaged blood vessel walls, and thromboplastin is liberated from the injured tissue. Thromboplastin, in turn, activates other clotting factors in the blood. Along with calcium ions and other factors, thromboplastin converts the blood protein prothrombin into thrombin. Thrombin then catalyzes the conversion of its blood protein fibrinogen into a protein called fibrin , which forms a patchwork mesh at the injury site. As blood cells are trapped in the mesh, a blood clot forms. Lymphatic system The lymphatic system is an extension of the circulatory system consisting of a fluid known as lymph,...
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- Fall '07