Wound Healing

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Phases of Healing - The Repair Crew

📌 Mnemonic: I Prefer Many Red Apples (Inflammation, Proliferation, Maturation/Remodeling)

  • Hemostasis: Platelets, fibrin clot formation.
  • Inflammatory Phase (0-3 days):
    • Cells: Neutrophils (PMNs), Macrophages (M1/M2).
    • Mediators: Cytokines (TNF-α, IL-1, IL-6), PDGF, VEGF.
  • Proliferative Phase (3 days - 3 weeks):
    • Cells: Fibroblasts, myofibroblasts.
    • Events: Collagen Type III, granulation tissue, angiogenesis, epithelialization.
  • Remodeling/Maturation Phase (3 weeks - 1 year+):
    • Events: Collagen Type I (replaces III), ↑ tensile strength, scar formation.
    • Enzymes: MMPs, TIMPs.

Mammalian wound healing phases, cells, and timeline

⭐ Maximum collagen deposition occurs by 3 weeks, but wound strength reaches only ~20-30% of normal tissue; it reaches ~80% by 1 year but never 100%.

Healing Intentions - Stitch in Time

FeaturePrimary IntentionSecondary IntentionTertiary Intention (Delayed Primary)
EdgesClean, approximatedOpen, not approximatedInitially open, later approximated
Tissue LossMinimalSignificantVariable, often present
ProcessDirect closureGranulation, contraction, epithelializationInitial debridement, delayed closure
Infection RiskLowHighModerate (initially high, then reduced)
ScarMinimal, linearLarge, irregular; significant contractionMore than primary, less than secondary
ExamplesSurgical incisionAbscess cavity, burns, pressure soresContaminated traumatic wound, burst abdomen

⭐ Wound contraction is a key feature of secondary intention healing, primarily mediated by myofibroblasts.

📌 Mnemonic: Primary = Perfect; Secondary = Slow & Scarring; Tertiary = Two-stage/ Time-delayed closure

Healing Hurdles - Repair Roadblocks

  • Local Factors:
    • Infection (most common cause of delay)
    • Hypoxia/Ischemia
    • Foreign body
    • Hematoma/Seroma
    • Radiation
    • Edema, Pressure
    • Poor surgical technique
  • Systemic Factors:
    • Age (advanced)
    • Nutrition: Deficiencies (Protein, Vit C, Vit A, Zinc, Copper)
    • Diabetes Mellitus
    • Corticosteroids
    • Smoking
    • Chemotherapy/Immunosuppression
    • Uremia, Jaundice
    • Malignancy
    • Genetic disorders (e.g., Ehlers-Danlos) 📌 Mnemonic (DIDN'T HEAL):
    • Diabetes
    • Infection
    • Drugs (e.g., steroids)
    • Nutrition deficiencies
    • Tissue necrosis
    • Hypoxia
    • Excessive tension
    • Another wound
    • Low temp / Local factors

⭐ Vitamin C is essential for collagen synthesis (hydroxylation of proline and lysine), and Vitamin A can counteract the inhibitory effects of steroids on wound healing.

Scar Stories - Healing Gone Rogue

FeatureHypertrophic ScarKeloid
BoundariesStays within wound marginsExtends beyond wound margins
CollagenMainly Type IIIType I & III
Natural HistoryMay regressRarely regresses; recurs
Skin TypeAllDark skin predilection
  • Acute Complications:
    • Wound Dehiscence: Separation of wound layers.
    • Evisceration: Protrusion of viscera.
  • Chronic Wounds (Impaired healing >3 months):
    • Types: Diabetic foot ulcers, Venous stasis ulcers, Arterial insufficiency ulcers.
    • Pressure Sores (Decubitus): Staged I-IV.

      ⭐ Pressure ulcers are staged I-IV: Stage I (non-blanchable erythema), Stage II (partial-thickness loss), Stage III (full-thickness skin loss), Stage IV (full-thickness tissue loss with exposed bone/tendon/muscle).

  • Marjolin's Ulcer: SCC arising in chronic wounds or old scars (e.g., burn scars).

High‑Yield Points - ⚡ Biggest Takeaways

  • Healing phases: Inflammation (0-3d), Proliferation (3d-3wks), Remodeling (3wks-2yrs).
  • Macrophages are pivotal, bridging inflammation and repair; neutrophils are first responders.
  • Collagen switch: From Type III (early, weak) to Type I (late, strong scar).
  • Scar strength: Reaches ~80% of original tissue strength by 3 months, never 100%.
  • Keloids grow beyond original wound margins; hypertrophic scars remain within.
  • Myofibroblasts mediate wound contraction, reducing defect size.
  • Factors impairing healing: Infection, ischemia, diabetes, steroids, malnutrition.

Practice Questions: Wound Healing

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Delayed wound healing is seen in all except-

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Flashcards: Wound Healing

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_____ is a biological dressing made form collagen fibroblast derivative

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_____ is a biological dressing made form collagen fibroblast derivative

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