Wound Healing and Repair

Wound Healing

• Regeneration: replacement of lost or damaged tissue by that of a similar type, derived from the proliferation of surrounding undamaged cells.
• Repair: replacement of lost or damaged tissue by granulation tissue, which later matures into fibrous scar tissue.

Healing Routes

• Helpful route: healing
• Not helpful route: fibrosis/scar formation

Primary and Secondary Intention Healing

• Primary intention: wound is narrow, wound edges are in close apposition, re-epithelialisation dominates healing.
• Secondary intention: wound is more extensive, wound edges are widely separated, granulation tissue covers the wound and the wound area is reduced by contraction.

Stages of Healing

• 1. Haemostasis (1 hour): platelet plug formation, fibrin clot formation
• 2. Inflammation (48 hours): macrophage infiltration, debridement
• 3. Granulation tissue formation (2-5 days): endothelial cell and fibroblast proliferation, new blood vessels migrate from wound edges, collagen extra-cellular matrix
• 4. Maturation of connective tissue (5+ days): decreased cellularity, decreased vascularity, remodelling of collagen matrix, collagen cross-linking
• 5. Re-epithelialisation (1-3 days): proliferation of basal epithelial cells, migration of basal epithelial cells across wound bed, epithelial cells differentiate and stratified squamous structures reform

Haemostasis

• Consists of: platelet plug formation, fibrin clot formation
• Inhibited by: aspirin, warfarin, factor VIII deficiency

Inflammation

• Caused by: macrophage infiltration

Granulation Tissue

• Forms through: endothelial cell and fibroblast proliferation, new blood vessels migrate into damaged area, fibroblasts lay down collagen extra-cellular matrix
• Consists of: fibroblasts, blood vessels, inflammatory cells

Maturation of Connective Tissue

• Results in: decreased cellularity, decreased vascularity, remodelling of collagen matrix, collagen cross-linking

Re-epithelialisation

• Occurs through: proliferation of basal epithelial cells, migration of basal epithelial cells across wound bed, epithelial cells differentiate and stratified squamous structures reform

Factors Affecting Wound Healing

• 3 systemic factors: ageing, nutritional status, iatrogenic, pre-existing medical conditions
• 7 local factors: blood supply, infection, persistent irritation, poor wound stability, poor apposition of wound edges, direction of incision, ionising radiation
• 3 factors important in controlling wound healing: cell-cell interactions, cell-matrix interactions, autocrine/paracrine interactions

Macrophages

• 3 traditional functions: phagocytosis, protease synthesis, regulation of immune cell function
• 4 additional functions: fibroblast recruitment, extra-cellular matrix synthesis, platelet recruitment, growth of blood vessels

Complications of Wound Healing

• 5 complications: wound dehiscence, contractures, keloid/hypertrophic scar formation, weak scars, pigmentation

Keloids and Hypertrophic Scarring

• Keloid: sharply elevated, progressively enlarging scar characterised by excessive collagen formation in the dermis
• 2 differences between keloids and hypertrophic scarring: keloids may spread beyond the margins of the original wound, hypertrophic scars do not; keloids are mainly found in Afro-Caribbean populations, hypertrophic scarring affects varied population groups
• 1 similarity: seen on the face but does not affect the oral mucosa

Embryonic and Oral Mucosal Wound Healing

• Embryonic wound healing: peculiar due to absence of scarring, possibly due to immaturity of immune system
• Oral mucosal wound healing: peculiar due to less scarring than skin, no keloids/hypertrophic scarring, immune response seems different

This quiz covers the concepts of regeneration and repair in wound healing, including the differences between primary and secondary intention healing. Test your knowledge of the helpful and not-so-helpful routes of repair and the characteristics of granulation tissue and fibrous scar tissue.