wound healing

wound healing

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wound healing phases mechanisms

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wound healing impaired chronic wound management

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wound healing phases diagram

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Wound healing is a complex, dynamic biological process involving overlapping phases of cellular and molecular activity. In adults, it typically results in fibrosis and scar formation rather than true tissue regeneration (Bailey & Love's Surgery, p. 45).

The Four Phases

Phase	Timing	Key Events
Hemostasis	Immediate (0–few hours)	Vasoconstriction, platelet aggregation, clot formation, fibrin scaffold
Inflammation	Days 1–4	Neutrophil influx (debris/bacteria clearance), macrophage recruitment (growth factor release)
Proliferation	Days 4–21	Fibroblast activity, collagen deposition, angiogenesis, epithelial migration, granulation tissue
Remodeling	Weeks to years	Collagen crosslinking and reorganization, scar maturation, wound contraction

Phase Details

1. Hemostasis

Damaged vessels constrict; platelets adhere and aggregate at the injury site
Coagulation cascade activated → fibrin clot forms
Clot acts as a scaffold and releases growth factors (PDGF, TGF-β) that recruit inflammatory cells

2. Inflammation

Neutrophils (first 24–48 hrs): phagocytose bacteria and debris; release proteases
Macrophages (day 2 onward): key orchestrators — release VEGF, TGF-β, IL-1, TNF-α; bridge inflammation to proliferation
Classic signs: rubor, calor, dolor, tumor

3. Proliferation

Fibroblasts migrate in and synthesize collagen (initially type III, later type I) and extracellular matrix
Angiogenesis: new capillaries restore oxygen supply
Epithelialization: keratinocytes migrate from wound edges under the scab
Granulation tissue: pink/red vascular connective tissue fills the wound bed

4. Remodeling

Type III collagen replaced by stronger type I collagen
Maximum tensile strength (~80% of original) reached at ~3 months
Myofibroblasts drive wound contraction
Hypertrophic scars or keloids may form if remodeling is dysregulated

Types of Healing

Type	Description	Example
Primary intention	Clean wound edges apposed (sutured/stapled)	Surgical incision
Secondary intention	Wound left open to granulate and contract	Abscess cavity
Tertiary intention	Delayed primary closure after initial open management	Contaminated wounds

Chronic Wounds

Chronic wounds fail to progress through normal healing stages in a timely manner (Bailey & Love's Surgery, p. 55). Key features:

Prolonged inflammatory phase — persistent neutrophil activity damages healthy tissue
Persistent infection — biofilm formation common
Elevated proteases — degrade growth factors and matrix
Common examples: diabetic foot ulcers, venous leg ulcers, pressure injuries, arterial ulcers

Management principles:

Treat the underlying cause (glycemic control, compression therapy, revascularization)
Wound bed preparation (TIME framework):
- Tissue debridement (surgical, autolytic, enzymatic)
- Infection/inflammation control
- Moisture balance (appropriate dressings)
- Edge advancement (assess for non-healing epithelia)
Advanced therapies: negative pressure wound therapy (NPWT), growth factors, skin substitutes, hyperbaric oxygen

Factors Impairing Wound Healing

Local Factors	Systemic Factors
Infection/biofilm	Diabetes mellitus
Poor blood supply (ischemia)	Malnutrition (esp. vitamin C, zinc, protein)
Foreign body	Corticosteroids / immunosuppression
Radiation damage	Obesity
Repeated trauma	Advanced age
Desiccation	Renal/hepatic failure

Fetal vs. Adult Healing

Fetal wounds (early gestation) heal without scar formation — this involves elevated hyaluronic acid, different TGF-β isoform ratios, and a more anti-inflammatory microenvironment. Understanding these differences drives regenerative medicine research aimed at scarless wound repair in adults (Bailey & Love's Surgery, p. 45).

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