Acute Wound Healing

Authors: Hasan Gökcer Tekin MD., Christian Kaare Paaskesen Med.Stud., Dorte Barrit, Diploma of Health, Specialist nurse in wound care, and Magnus Avnstorp, MD

Phase 1:

Hemostasis/Coagulation (Day 1): Injury inflicts the wound and bleeding from vessels occurs. Initial vasoconstriction happens for 10 minutes to reduce blood flow, followed by histamine release and vasodilatation. Damaged collagen fibers and endothelial cells activate the coagulation cascade. Platelets bind to damaged collagen and form a stable fibrin blood clot by further aggregation. This forms a reservoir of cytokines and chemokines, which initiates the next phase.  

Phase 2:

Inflammation (Day 2-4): Red and tender wound-surroundings as capillaries are opened to carry white blood cells to the wound. Neutrophils destroy bacteria and remove debris. Macrophages clear debris and secrete growth factors and proteins to facilitate repairing. Fibroblasts arrive to the wound preparing for repairing. Cytokines such as platelet-derived growth factor (PDGF), interleukines and transforming growth factor (TGF)-β are elevated in the inflammatory phase.

Phase 3:

Proliferation and Epithelialisation (Day 4-21): Granulation tissue is formed (Red, shiny, consisting of connective tissue and capillaries). The wound edges contracts while the blood clot/scap is removed. The wound is finally covered with epithelial cells from the margin and bottom. Epithelial stem cell proliferate is driven by a variety of epidermal growth factors.

Phase 4:

Remodeling/Maturation (Day 21 to 2 years): Collagen fibers re-organise from old collagen 1 to newer and stronger collagen 3 by matrix metalloproteinase (MMPs). New tissue slowly strengthen and achieve flexibility. Maximum wound strenght is 80% of pre-injury strenght.