Question

what is the first event of hemostasis after an injury to a blood vessel?
a vascular spasm
b coagulation
c clot retraction
d platelet plug formation

Explanation:

Hemostasis is the process to stop bleeding. The first event is vascular spasm. When a blood vessel is injured, the smooth muscle in its wall contracts (vascular spasm) to constrict the vessel, reducing blood loss. Then platelet plug formation occurs (platelets adhere to the damaged area and aggregate), followed by coagulation (blood clotting with fibrin threads), and finally clot retraction (the clot becomes more compact).

Answer:

A. Vascular spasm