What is the sequence of clot formation following an injury?

• A. Prothrombin to thrombin to fibrin
• B. Thromboplastin to fibrinogen to thrombin
• C. Fibrin to fibrinogen to thrombin
• D. Thrombin to fibrinogen to thromboplastin

Answer: (A)

The sequence of clot formation initiated following an injury begins with the conversion of prothrombin, a plasma protein, to thrombin due to the action of thromboplastin, also known as tissue factor. This transformation is a crucial step in the coagulation cascade. Once thrombin is formed, it then catalyzes the conversion of fibrinogen, a soluble plasma protein, into fibrin, which is the actively involved component that forms the mesh structure of a clot.

This process highlights the essential role of thrombin as a key enzyme in the coagulation process, facilitating the stabilization of the clot through the formation of fibrin strands. The fibrin forms a fibrous mesh that ultimately traps blood cells, leading to the formation of a stable clot that can effectively stop bleeding.

In contrast, other options do not accurately reflect the biological sequence involved in clot formation. For example, thromboplastin is not transformed into thrombin but rather acts to initiate the conversion of prothrombin to thrombin. Similarly, fibrinogen is not converted to thrombin; instead, it is the reactant that thrombin converts to fibrin. Understanding this sequential transformation underscores the complex interplay of procoagulant factors that are critical in hemostasis.