Final answer:
Vascular spasm is caused by damage to the vascular wall, resulting in a sharp contraction of the smooth muscle in the vessel walls due to the release of endothelin's in response to the injury. The option (A) is correct.
Step-by-step explanation:
A vascular spasm is caused by damage to the vascular wall. When the wall of a vessel is damaged, the smooth muscle within the vessel walls contracts sharply. This process involves both circular and, in the case of larger vessels, longitudinal layers of muscle. The contraction of the circular layers decreases blood flow, while the contraction of the longitudinal layers pulls back the vessel into the surrounding tissue.
The contraction, or vascular spasm, is believed to be triggered by substances known as endothelins, which are released by the cells lining the vessel and by pain receptors as a consequence of the injury. Additionally, this spasm can be understood as the initial step in hemostasis, which also includes the formation of a platelet plug and coagulation. Therefore, option (A) is correct.