Wound Healing: Phases and Factors

Wound healing is a complex, overlapping cascade of four phases. Phase 1 — Hemostasis (immediate): vascular injury triggers vasoconstriction, platelet aggregation, and fibrin clot formation creating a temporary wound seal. Platelets release growth factors (PDGF, TGF-beta) that initiate the inflammatory phase. Phase 2 — Inflammation (days 1-6): neutrophils arrive within hours to phagocytize bacteria and debris; macrophages arrive by day 2-3 and are the MOST IMPORTANT cells in wound healing (they coordinate the entire healing process by secreting cytokines, growth factors, and transitioning the wound from inflammation to proliferation). Cardinal signs of inflammation: rubor (redness), calor (heat), tumor (swelling), dolor (pain), and functio laesa (loss of function). Phase 3 — Proliferation (days 4-21): fibroblasts synthesize collagen and form granulation tissue (red, beefy, vascular tissue); epithelial cells migrate across the wound surface (epithelialization); angiogenesis creates new blood vessels; wound contraction reduces wound size. Phase 4 — Remodeling/Maturation (day 21 to 2 years): type III collagen is replaced by stronger type I collagen; scar tissue reorganizes along lines of stress; maximum tensile strength reaches only 80% of original tissue strength. Wounds heal...