Wound Healing

• Give a generalised overview of the process of wound healing.

  
• What is regeneration?

  Replacement of lost or damaged tissue by that of a similar type derived from the proliferation of the surrounding undamaged cells
• What is repair?

  Replacement of lost or damaged tissue by granulation tissue which later matures into fibrous scar tissue

  
• What is healing by primary & secondary intention?

  Healing by primary intention: the wound edges are in close apposition (so re-epithelialisation dominates healing)

  
  

  Healing by secondary intention: the wound is more extensive and the wound edges are widely separated

  (granulation tissue covers wound & wound area is reduced by contraction).

  
  

  You then get re-epithelialisation from wound edges but also from residual appendages (hair follicles etc.)
• What's the first thing that happens when you injure yourself?

  Platelet plug formation

  Fibrin clot formation
• What are some examples of factors which inhibit the formation of the platelet plug and fibrin clot?

  Aspirin, Warfarin, factor VIII deficiency (also inhibits wound healing)
• What follows the process of haemostasis in wound healing?

  Inflammation

  Macrophage infiltration

  Debridement
• What happens exclusively in the connective tissue following haemostasis & debridement? (Granulation tissue formation)

  
• What is granulation tissue?

  A loose cellular connective tissue with many plump, synthetic fibroblasts; dilated irregular blood vessels; and inflammatory cells
• What happens in the connective tissue after granulation tissue formation?

  maturation occurs:

  
  

  -Decreased cellularity

  -Decreased vascularity

  -Remodelling of collagen matrix

  -Collagen cross linking

  
  

  INVOLVES MMP's1 and other proteases

  
• What changes in the epithelium are happening alongside all these events in the connective tissue?

  Re-epithelialisation:

  
  

  Proliferation of basal epithelial cells adjacent to the wound

  
  

  Migration of basal epithelial cells across wound bed under fibrin scab to restore epithelial continuity

  
  

  Epithelial cells differentiate and stratified squamous structures reform

  
• Summarise the healing of a small skin wound.

  
• Is the control of wound healing a simple process?

  No it's a complex process involving convergence of signals from many sources

  
• What dramatically impaired wound healing in guinea pigs?

  Mononuclear (macrophage precursor) depletion
• What are the traditional functions of macrophages?

  -Phagocytosis

  -Protease synthesis

  -Regulation of immune cell function
• What is the significance of macrophages in wound healing?

  They produce growth factors like: FGF a/b, TGF-b, PDGF, VEGF, other bioactive molecules etc.
• What systemic factors could interfere with wound healing?

  Age

  
  

  Nutritional status (e.g vitamin deficiency, protein deficiency)

  
  

  Iatrogenic (people on steroids)

  
  

  Pre-existing medical conditions (e.g diabetes)
• What local factors could affect wound healing?

  Blood supply (poor blood supply can lead to infection)

  Infection

  Persistent irritation

  Poor wound stability

  Poor apposition of wound edges

  Skin wounds: direction of incision- Langers lines

  Ionising radiation
• What are some possible complications of wound healing?

  Wound dehiscence (breakdown of wound)

  Contractures

  Keloid/hypertrophic scar formation

  Weak scars (incisional hernia)

  Pigmentation

  Neoplastic changes (Marjolin's ulcer)
• What is a keloid and hypertrophic scarring?

  
• What do keloids/hypertrophic scarring look like?

  
• How do embryonic wounds heal?

  Heal without scarring
• How is scaring on the oral mucosa?

  There is still scaring but it is less than the skin