In the sequence of hemostasis following arterial injury, which order correctly lists the major steps from first to last?

• A. Vascular spasm; formation of platelet plug; blood coagulation; clot retraction
• B. Formation of platelet plug; vascular spasm; blood coagulation; clot retraction
• C. Vascular spasm; blood coagulation; formation of platelet plug; clot retraction
• D. Vascular spasm; formation of platelet plug; clot retraction; blood coagulation

Answer: (A)

The main idea is the chronological progression of hemostasis after arterial injury: first a rapid narrowing of the vessel, then a platelet-based plug forms, followed by a fibrin-based coagulation that stabilizes the clot, and finally the clot retracts to bring the wound edges together.

Right after injury, the vessel constricts to limit blood loss. This vascular spasm sets the stage for rapid control of bleeding. Next, platelets adhere to exposed subendothelial surfaces and aggregate to form a temporary platelet plug—this is primary hemostasis. Only after this plug is established does the coagulation cascade kick in, producing fibrin to create a stable, cross-linked clot that reinforces the plug—this is secondary hemostasis. Once the clot is formed, platelets pull on the fibrin strands, causing clot retraction which tightens and stabilizes the clot.

This sequence aligns with the option that lists vascular spasm, formation of the platelet plug, blood coagulation, and clot retraction in that order. The other sequences disrupt the order by placing coagulation before platelet plug formation or clot retraction before the clot is actually formed (or not placing vascular spasm first), which would not reflect the physiological sequence of events.