Epithelialization

Epithelialization is the formation of epithelium over a denuded surface within hours of injury. Epithelialization of an incisional wound involves the migration of cells at the wound edges over a distance of less than 1 mm from one side of the incision to the other. Incisional wounds are epithelialized within 24 to 48 h after injury. This epithelial layer provides a seal between the underlying wound and the environment. Epidermal cells at the wound edges undergo structural changes, allowing them to detach from their connections to other epidermal cells and to their basement membrane.

Intracellular actin microfilaments are formed, allowing the epidermal cells to creep across the wound surface. As the cells migrate, they dissect the wound and separate the overlying eschar from the underlying viable tissue. Epidermal cells secrete collagenases that break down collagen and plasminogen activator, which stimulates the production of plasmin. Plasmin promotes clot dissolution along the path of epithelial cell migration. The extracellular wound matrix over which epithelial cells migrate has received increased emphasis in wound healing research. Migrating epithelial cells interact with a provisional matrix of fibrin cross-linked to fibronectin and collagen. The matrix components may be a source of cell signals to facilitate epithelial cell proliferation and migration. In particular, fibronectin seems to promote keratinocyte adhesion to guide these cells across the wound base. Epithelial cell migration also may be facilitated in wound beds containing critical water content. Wounds with adequate tissue humidity demonstrate a faster and more direct course of epithelialization. Occlusive and semiocclusive dressings applied in the first 48 h after injury may maintain tissue humidity and optimize epithelialization. When epithelialization is complete, the epidermal cell assumes its original form and new desmosomal linkages to other epidermal cells and hemidesmosomal linkages to the basement membrane are restored. Zinc and saline wet dressings, for example, have been shown to promote epithelialization followed by faster healing.

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