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.
Adapted from the physiology of blood components in wound healing8

Learning Bite

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

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