Wound healing

Phases of wound healing:

• Inflammatory (preparative)
• Reparative
• Consolidative

Inflammatory phase:

1. Bleeding followed by clotting and then clot lysis
2. Inflammatory cytokine release with:
• Cell swelling
• Increased capillary permeability
• Intercellular oedema
• Migration of leucocytes into the damaged area
3. Phagocytosis (by macrophages) of dead cells and other debris

The inflammatory phase lasts ~3 days

Reparative phase:

1. Formation of new capillary loops in the damaged area. These provide a blood supply for subsequent events
2. Fibroblasts appear. These are capable of producing strands of collagen.
3. Deposition of extracellular collagen – at first provisional and apparently untidy but gradually becoming orientated along any lines of stress applied to the wound
4. This mass of granulation tissue begins to contract (probably through the effects of specialised myofibroblasts). A distinction is drawn between this active process of contraction of the whole wound mass and the later shrinkage of mature collagen, which may lead to distortion of a healed area – known by the general term contracture

Consolidative phase:

• Collagen synthesis = degradation (both accelerated)
• Ratio of collagen reverts back to normal
• Increased cross-linkage of collagen
• Increased tensile strength (maximum 80%)
• Vascularity of the wound gradually decreases

Collagen:

• Are >14 types
• Ratio of type I: type III
• 4:1 in normal skin
• 2:1 in granulation tissue

Local factors inhibiting wound healing:

• Infection
• Ischaemia
• Foreign bodies
• Tumour

Systemic factors inhibiting wound healing:

• Malnutrition
• Vitamin A and C deficiency
• Diabetes
• Jaundice
• Renal failure
• Steroid or cytotoxic treatment
• Radiotherapy
• Age