This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
Following injury to blood vessels , immediate haemostasis is achieved by which of the following 
Select and explain. 
A. Fibrin deposition, B. Vasoconstriction, C. Platelets adhesion, D. Thrombosis
B: Vasoconstriction
Answer: B: Vasoconstriction 
Explanation: ref Robbins 8/e p115 Vascular spasm (Vasoconstriction) -Vasoconstriction is produced by vascular smooth muscle cells, and is the blood vessel's first response to injury. ... When a blood vessel is damaged, there is an immediate reflex, initiated by local sympathetic pain receptors, which helps promote vasoconstriction