Which blood component is primarily responsible for clotting?

• A. white blood cells
• B. red blood cells
• C. platelets
• D. plasma

Answer: (C)

Clotting starts with platelets, the small cell fragments that rush to a damaged vessel and stick to the exposed site. They adhere, become activated, and release signals that recruit more platelets to form a quick platelet plug, which is the first fast seal of a break in the vessel. Plasma then provides the clotting factors that lay down a fibrin mesh to strengthen and stabilize that plug, but the initial and primary action in forming the clot comes from platelets. Red blood cells and white blood cells aren’t responsible for forming clots, while plasma supplies the chemicals needed for the full coagulation cascade.