Which of the following is not a phase of hemostasis? A platelet plug formation. B vascular spasm. C fibrinolysis. D coagulation. A include thrombus formation, a clot in a broken blood vessel.
The correct answer and explanation is:
The correct answer is C. fibrinolysis.
Hemostasis is the process that prevents and stops bleeding or hemorrhage. It occurs in three main phases: vascular spasm, platelet plug formation, and coagulation. Each phase plays a crucial role in stopping blood loss after a blood vessel is injured.
- Vascular spasm: The first response to a vessel injury is a vascular spasm, or constriction, which reduces blood flow and limits blood loss. This is an immediate and temporary reaction as the smooth muscles in the blood vessel walls contract.
- Platelet plug formation: Platelets are activated when they come into contact with exposed collagen in the damaged blood vessel. They adhere to the site of injury, becoming sticky and aggregating together to form a temporary plug. This platelet plug helps seal the breach in the blood vessel.
- Coagulation: This is the final phase of hemostasis, where a stable blood clot is formed. Coagulation involves a complex cascade of enzymatic reactions, leading to the conversion of fibrinogen (a plasma protein) into fibrin threads. These threads form a mesh that stabilizes the platelet plug, solidifying the clot and stopping the bleeding.
Fibrinolysis, on the other hand, is not a phase of hemostasis but a process that occurs after the clot has fulfilled its role. It is the breakdown of the fibrin clot once the vessel has healed. Plasminogen, which is incorporated into the clot, is activated to plasmin, an enzyme that digests fibrin and dissolves the clot. This ensures that the clot is removed once the vessel is no longer at risk of bleeding, allowing for normal blood flow to resume.
In summary, while the three phases of hemostasis focus on stopping bleeding, fibrinolysis serves as a later mechanism to resolve the clot after its purpose has been achieved.