Porth's Essentials of Pathophysiology, 4e

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Cell and Tissue Function

U N I T 1

Wound healing involves the restoration of the integrity of injured tissue.The healing of skin wounds, which are commonly used to illustrate the general principles of wound healing, is generally divided into three phases: (1) the inflammatory phase, (2) the proliferative phase, and (3) the wound contraction and remodeling phase. Each of these phases is mediated through cytokines and growth factors. U N D E R S T A N D I N G Wound Healing

Clot

Inflammatory Phase. The inflammatory phase begins at the time of injury with the formation of a blood clot and the migration of phagocytic white blood cells into the wound site. The first cells to arrive, the neutrophils, ingest and remove bacteria and cellular debris. After 24 hours, the neutrophils are joined by macrophages, which continue to ingest cellular debris and play an essential role in the production of growth factors for the proliferative phase. 1

Fibrin

Epidermis

Dermis

Fat

Neutrophil

Granulation tissue

Proliferative Phase. The pri- mary processes during this phase focus on the building of new tissue to fill the wound space. The key cell during this phase is the fibroblast, a connective tissue cell that synthesizes and secretes the collagen, proteo- glycans, and glycoproteins needed for wound healing. Fibroblasts also produce a family of growth factors that induce angiogenesis (growth of new blood vessels) and endothelial cell proliferation and migration. The final component of the proliferative phase is epithelialization, during which epithelial cells at the wound edges proliferate to form a new surface layer that is similar to that which was destroyed by the injury. 2

Epithelial cells

Fibroblast

Blood vessel

Macrophage