Following injury to a blood vessel, immediate haemostasis is achieved by –
**Core Concept**
Immediate haemostasis after injury to a blood vessel is a complex process involving the coordinated action of various cellular and molecular mechanisms. The primary goals of haemostasis are to stop bleeding, prevent excessive blood loss, and initiate the healing process. This process involves the activation of platelets, coagulation cascade, and the formation of a platelet plug.
**Why the Correct Answer is Right**
The correct answer is vasoconstriction, which is the initial response to vascular injury. Vasoconstriction is mediated by the release of serotonin from platelets, endothelin from endothelial cells, and thromboxane A2 from platelet activation. This rapid narrowing of the blood vessel lumen reduces blood flow to the injured area, thereby minimizing blood loss.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because platelet plug formation is a secondary response to vascular injury, following initial vasoconstriction.
**Option B:** This option is incorrect because coagulation cascade activation is a slower process that occurs after platelet plug formation and vasoconstriction.
**Option D:** This option is incorrect because fibrinolysis is the process of breaking down fibrin clots, which occurs after haemostasis has been achieved.
**Clinical Pearl / High-Yield Fact**
It is essential to understand the sequence of events in haemostasis, as failure to achieve immediate haemostasis can lead to excessive blood loss and potentially life-threatening complications.
**Correct Answer: C. Vasoconstriction**