Stages of Wound Healing

1. Immediate response to tissue injury

— Vasoconstriction and tissue contraction occur.

— Platelets aggregate and a clotting cascade is activated.

— Once hemostasis is complete, the release of vasoactive amines causes capillary dilation, and an exudate forms.

2. Inflammatory phase 

— Granulocytes and lymphocytes accumulate to control the growth of bacteria and prevent infection.

— Immunoglobulins contribute to the control of infection.

— Macrophages phagocytize debris, encourage collagen deposition, and stimulate neovascularization.

3. Epithelialization

— Within 12 hours of injury, cells of the stratum germinative are activated, and within 24 hours, initial epithelialization may be complete.

4. Neovascularization

— New blood vessels form and bring nutrients and oxygen to the healing wound.

— Neovascularization begins on day 3 and peaks on day 7.

— By day 21, the process is complete and the new blood vessels withdraw as the tissue matures.

5. Collagen synthesis

— Fibrocytes initially lay down a disorganized pattern of collagen.

— Over months to years, the matrix is remodeled to form an organized meshwork of collagen.

6. Wound contraction

— Myofibroblasts are responsible for wound contraction, in which the initial scar contracts to a smaller size.