Which event can lead to blood clot formation at an injury site?

• A. red blood cells release hemoglobin.
• B. white blood cells release antibodies.
• C. bone marrow cells decrease platelet production.
• D. ruptured platelets release thromboplastin.

Answer: (D)

When an injury occurs, a key step in stopping the bleed is the release of thromboplastin (tissue factor) from damaged platelets at the site. Thromboplastin kicks off the coagulation cascade, activating clotting factors that convert fibrinogen to fibrin and form a stable fibrin mesh that traps blood cells to create a clot. The other events don’t promote clotting: hemoglobin release from red blood cells isn’t a clotting signal, antibodies from white blood cells are part of the immune response, and decreased platelet production would hinder clotting rather than promote it.