Emergency Medical Technician (EMT) Intermediate Practice Exam

What occurs during the initial phase of hemostasis?

1. Formation of a fibrin mesh

2. Platelet aggregation and local vasoconstriction

3. Vascular dilation

4. Activation of intrinsic pathway

The correct answer is: Platelet aggregation and local vasoconstriction

During the initial phase of hemostasis, the primary processes involve platelet aggregation and local vasoconstriction. When a blood vessel is injured, the immediate response is vasoconstriction, which helps to reduce blood flow to the affected area. This response is crucial in minimizing blood loss immediately following an injury. As the blood vessels constrict, platelets in the vicinity of the injury begin to adhere to the exposed collagen fibers in the damaged endothelium. This leads to the activation of the platelets, which release various chemical mediators that attract more platelets to the site of injury and promote aggregation. This aggregation forms a temporary "platelet plug" that serves as an essential first barrier to blood loss until further clotting mechanisms can take place. The other options represent processes that occur in later stages of hemostasis or do not accurately describe the initial phase. For example, the formation of a fibrin mesh occurs after the initial platelet plug is established and is part of the later coagulation cascade. Vascular dilation generally occurs later in the healing process rather than during the immediate response to injury, while the activation of the intrinsic pathway typically refers to the coagulation cascade that follows after the initial hemostatic response. Thus, the choice of