When blood vessels are injured, the Cloze (1): JXUwMDI4JXUwMDFjJXUwMDBkJXUwMDE1JXUwMDExJXUwMDA5JXUwMDA5JXUwMDExJXUwMDA3 are exposed to air causing them to Cloze (2): JXUwMDJhJXUwMDEzJXUwMDExJXUwMDA0JXUwMDAxJXUwMDA3JXUwMDE3 . They release thromboplastin

(thrombokinase) which initiates the clotting process. Thromboplastin neutralizes Cloze (3): JXUwMDMwJXUwMDBkJXUwMDE1JXUwMDExJXUwMDEzJXUwMDFiJXUwMDA3 and activates conversion of prothrombin to Cloze (4): JXUwMDJjJXUwMDFjJXUwMDFhJXUwMDFkJXUwMDAyJXUwMDBmJXUwMDBiJXUwMDA3 . Calcium ions are required for this process. Thrombin catalyzes the conversion of Cloze (5): JXUwMDNlJXUwMDBmJXUwMDBiJXUwMDEwJXUwMDFiJXUwMDA3JXUwMDAxJXUwMDA4JXUwMDAyJXUw MDBi (soluble protein) to fibrin(insoluble). Fibrin forms a meshwork of fibers on the cut surface which trap red blood cells forming a Cloze (6): JXUwMDNiJXUwMDBmJXUwMDAzJXUwMDFiJXUwMDVh