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