Immediately after an incision is made with a scalpel, what is the FIRST physiological event to occur?

Correct answer: A. Vasoconstriction of the transected vessels

• A. CORRECT. The instant a vessel is cut, reflex vasoconstriction narrows its lumen within seconds. It is mediated by direct injury to vascular smooth muscle, local neural reflexes, and vasoconstrictors including endothelin, thromboxane A₂ and serotonin released from activated platelets. This transient constriction — lasting seconds to minutes — limits blood loss and allows the platelet plug and then the fibrin clot to form. Only afterward does the vessel dilate, producing the redness and swelling of inflammation.
• B. Vasodilation with increased permeability is the SECOND vascular event, following the initial constriction. It is what delivers plasma proteins and leukocytes to the site and produces the classic cardinal signs of inflammation.
• C. Neutrophil margination and migration begin within minutes to hours and peak at 24–48 hours. They constitute the cellular phase of inflammation, which follows the vascular phase.
• D. Fibroblast proliferation and collagen synthesis belong to the proliferative phase, beginning around day 3 and peaking at 1–2 weeks. This is the latest event listed.

Note: The correct sequence: vasoconstriction (seconds) → platelet plug → coagulation cascade and fibrin clot → vasodilation with increased permeability → neutrophils (peak 24–48 h) → macrophages (peak day 3) → fibroblasts and angiogenesis (day 3 onward) → remodelling (weeks to months, up to 80% of original strength).