Wound Care: Phases of Wound Healing

1. Hemostasis Mn

• Timing: Immediate
• Vasoconstriction – First Step
• Collagen is Exposed & Endothelium Releases Platelet-Activating Factor (PAF)
• Platelets Bind Collagen & Form Platelet Plug
• Coagulation Cascade Reinforces the Platelet Plug

2. Inflammation

• Timing: Days 1-10
• Initiated by Transudate Leakage into Tissues from Injured Blood Vessels
• Causes Swelling, Pain, Erythema & Pain
• Dominant Cell Types:
  • Day 0-2: Neutrophils (PMNs) Mn
  • Day 3-4: Macrophages #1, Then Lymphocytes

3. Proliferation

• Timing: 5 Days – 3 Weeks
• Wound is Rebuilt with New Tissue
• Primary Cell Type: Fibroblasts
  • Deposit Collagen & Replace Fibrin
  • Myofibroblasts – Cause Wound Contraction
• Phases:
  • Neovascularization/Angiogenesis
    • Growth of New Blood Vessels/Capillaries into Injured Tissue
    • Allows Formation of Granulation Tissue
    • Stimulated By: TGF-β, TNF-α, VEGF, PDGF, FGF & Angiogenin
      • Hypoxia is the #1 Stimulator of Angiogenesis
    • Proteolytic Enzymes are Activated by Endothelial Cells & Dissolve the Basement Membrane
    • Endothelial Cells Migrate into the Wound Using Integrins
    • Matrix Metalloproteinases (MMPs) Dissolve Surrounding Tissue to Create a Path
  • Granulation
    • Well-Vascularized Tissue Covers the Wound Bed to Allow Epithelialization
    • Healthy Granulation Tissue – Red/Pink & Granular/Uneven in Texture (“Cobblestone”-Like)
    • Dark Granulation Tissue Indicates Ischemia or Infection
  • Epithelialization
    • Epithelial Cells Cover the Wound Bed
    • Produced by Keratinocytes
• Reopened Wounds Heal Faster the Second Time (Healing Cells Already Present)

4. Remodeling (Maturation)

• Timing: > 3 Weeks
• Collagen is Remodeled from Type III to Type I
  • Net Amount of Collagen is Unchanged
• Collagen is Also Cross-Linked to Increase Strength & Decrease Scar Thickness
• Results in Scar Formation

Tensile Strength

• Dependent on Collagen Deposition & Cross-Linking
• Maximum Collagen Amount at 3 Weeks
  • Mostly Type III – Then Replaced by Type I & Cross-Linking
• Maximum Strength at 6 Weeks
  • Only a Maximum 80% Total Strength of Original Skin