Following injury to a blood vessel, immediate haemostasis is achieved by
**Question:** Following injury to a blood vessel, immediate haemostasis is achieved by
A. Platelet plug formation
B. Coagulation cascade activation
C. Vasoconstriction
D. Vasospasm
**Correct Answer:** B. Coagulation cascade activation
**Core Concept:** Haemostasis is the process by which an injury to a blood vessel is sealed to prevent excessive bleeding. It involves a delicate balance between coagulation (clotting) and fibrinolysis (clot breakdown). There are two primary pathways of haemostasis:
1. **Venous and arterial pathways**: These pathways are activated when blood vessel injury occurs, leading to the formation of a stable platelet plug and subsequent clotting.
2. **Tissue factor pathway**: This pathway is activated when injury is severe, involving tissue factor, which triggers coagulation cascade activation.
**Why the Correct Answer is Right:**
Immediate haemostasis is achieved through activation of the coagulation cascade. This cascade is a series of enzymatic reactions that lead to the conversion of soluble fibrinogen into insoluble fibrin, forming a stable clot that seals the blood vessel injury. The coagulation cascade is initiated by the tissue factor pathway in the case of severe injury or venous and arterial pathways in case of minor injuries.
**Why Each Wrong Option is Incorrect:**
A. Platelet plug formation (A) is crucial but occurs after clotting factors activation, not the primary mechanism for immediate haemostasis.
C. Vasoconstriction (C) is a physiological response to reduce blood flow to the injured area, but it does not directly contribute to immediate haemostasis.
D. Vasospasm (D) is a vasoconstrictor response that occurs in response to cold temperatures or hypoxia, not directly related to haemostasis after injury.
**Clinical Pearl:** Understanding the different pathways of haemostasis can help guide appropriate treatment in clinical scenarios, such as administering anticoagulants or antiplatelet medications. Adequate knowledge of these pathways can prevent potential complications or errors in patient care.