Phases of wound healing

The wound healing process comprises several phases that take days to years to achieve almost initial skin integrity. A wound usually heals by one of primary, secondary, or delayed secondary intention.

Phases of wound healing

In the event of a tissue injury, the body initiates a cascade of overlapping cellular and extracellular activities that immediately start post-injury and lasts several months. This process comprises four distinct yet overlapping phases.

Haemostasis:

• Starts immediately following injury.
• Activation of the coagulation cascade and temporary constriction of blood vessels directly supplying the injured area.
• The platelets trapped in the blood clots kick starts a series of inflammatory response.

Inflammation:

• Activation of the complement cascade within 1-2 days of the injury.
• Wound infiltration by polymorphonuclear leukocytes. (PML)
• PML occupies the wound sites, phagocytose bacteria, and other foreign particles, kill them off and goes dormant.
• During this period, epithelial cells from both edges start depositing the basement membrane as they migrate towards each other.
• Macrophages activation in 48-72hrs and act as the regulatory cells for repair by producing growth factors responsible for the proliferation.

Proliferation:

• Starts about day three and last 2-4 weeks.
• Characterized by fibroblast migration and deposition of the extracellular matrix.
• Fibrin matrix is subsequently replaced by newly formed granulation tissue.
• Epithelization continues

Remodelling and scar maturation:

• May continue for several months.
• Continuous breakdown of collagen and remodelling of the extracellular matrix.
• Decrease in underlying contractile connective tissue brings the wound edges closer.
• Collagen bundles increase in diameter as well as increasing the tensile strength of the wound.
• Vascularity decreases and surface scar appear paler.

Learning Bite

Following scar maturation, the skin collagen fibre only regains a maximum of 80% of its pre-injury strength and integrity. ²