This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Which of the following statements is true concerning the vascular response to injury? 
Select and explain. 
A. Vasoconstriction is an early event in the response to injury, B. Vasodilatation is a detrimental response to injury with normal body processes working to avoid this process, C. Vascular permeability is maintained to prevent fuher cellular injury, D. Histamine, prostaglandin E2 (PGE2) and prostacyclin (PGI2) are impoant mediators of local vasoconstriction
A: Vasoconstriction is an early event in the response to injury
Answer: A: Vasoconstriction is an early event in the response to injury 
Explanation: After wounding, there is transient vasoconstriction mediated by catecholamines, thromboxane, and prostaglandin F2 (PGF2a). This period of vasoconstriction lasts for only five to ten minutes. Once a clot has been formed and active bleeding has stopped, vasodilatation occurs in an around the wound. Vasodilatation increases local blood flow to the wounded area, supplying the cells and substrate necessary for fuher wound repair. The vascular endothelial cells also deform, increasing vascular permeability. The vasodilatation and increased endothelial permeability is mediated by histamine, PGE2, and prostacyclin as well as growth factor VEGF (vascular endothelial cell growth factor). These vasodilatory substances are released by injured endothelial cells and mast cells and enhance the egress of cells and substrate into the wound and tissue.