Wound Healing

Question 1

What are the phases of wound healing?

Answer 1

1 - Haemostasis and inflammation
2 - Proliferation/fibroplasia
3 - Maturation

Question 2

What is haemostasis?

Answer 2

Self-regulating process by which biological systems maintain stability while adjusting to changing external conditions
Occurs immediately after injury

Question 3

Describe the steps of haemostasis

Answer 3

1. Tissue damage
2. Blood leakage from vessels
3. Activation of clotting cascade (due to damage of endothelium of blood vessels)
   ○ Intrinsic and extrinsic pathways
4. Platelet aggregation
5. Release of cytokines from platelets
   ○ Triggers the rest of the clotting cascade and inflammatory phase
6. Stabilisation of platelet plug by fibrin formation
   ○ Platelet plug is not strong enough on its own
   § Doesn’t provide strength to wound
   § Just prevents blood loss
   § ‘first aid’ after injury
7. Transient vasoconstriction during haemostasis
   Restricts blood flow to area to reduce blood loss

Question 4

What happens during the inflammation phase and when does it occur?

Answer 4

Overlap with haemostasis
Occurs in the first 72 hours after injury
Vasodilation following transient vasoconstriction
Cytokines in the fibrin clot attract white blood cells
Initially neutrophils, then macrophages
Destruction of cells by phagocytosis
Helps to “clean up” bacteria and devitalised tissue

Question 5

What happens during the proliferation phase and when does it occur?

Answer 5

Some overlap with inflammatory phase
Formation of granulation tissue
○ Red and shiny - ‘strawberry jam’
Formed of:
○ Macrophages
○ Fibroblasts
○ New blood vessels
Gives red appearance
Fibroblasts proliferate and produce:
○ New extracellular matrix
○ Elastin
○ Collagen
Formation of new epithelial tissue
○ Myofibroblasts cause wound contraction
○ Contact inhibition
When epithelial cells come into contact - inhibits further call division
Allows for smooth layer of epithelial tissue

Question 6

What happens during the maturation phase>

Answer 6

• Remodelling
  
  • Wound starts to get some strength
  • Type III (immature) collagen is replaced by type I (mature)
  • Cross-linking of collagen
  • Change in components of extracellular matrix
  • Increases tensile strength
    ○ Resistance of a material to breaking under tension
  • Takes weeks to months
    Depending on size and location of wound

Question 7

What is the normal time scale for wound healing

Answer 7

• 2 weeks
  ○ 20% of pre-wound strength
  
  • 5 weeks
    ○ 50%
  • 10 weeks
    ○ 80%

Question 8

What factors affect wound healing?

Answer 8

Patient Factors
Wound Factors
Concurrent Factors

Question 9

What are patient factors?

Answer 9

Age
○ Older animals heal slower
Rates of cell division and tissue remodelling is slower
Co-morbidities
○ E.g. HAC, Diabetes - slow down wound healing
Nutrition status
○ E.g. Hypoproteinaemia
○ Post-op nutrition is important
○ Wound healing is high energy demand - patients need a good plane of nutrition (high protein and calories)

Question 10

What are wound factors?

Answer 10

• Infection
  ○ Decontaminate wound
  ○ Flush wound
  
  • Location
    ○ Tension
    ○ Movement
    ○ Local blood supply
    ○ Can think about where we make surgical incisions

Question 11

What are concurrent treatment factors?

Answer 11

Corticosteroids delay all stages of wound healing
Hyperadrenocorticism
Radiation
Causes tissue fibrosis and vascular scarring
Overgrowth, hardening, and/or scarring of various tissues
Due to excess deposition of extracellular matrix components including collagen