Wound healing of the integument in the 5-day chick embryo.

A morphological study of wound healing has been performed by light and electron microscopy in 5-day chick embryos. The operation consisted in the excision of a rectangular piece of epidermis and subjacent mesenchyme from the right flank. After 18 hours, 61% of the embryos were completely healed. Wound closure was completed in all embryos within 24 hours. Shortly after the operation, the basal epidermal cells at the wound edge enlarged and lost their regular arrangement. The intercellular spaces disappeared. The peridermal cells became thicker and acquired a rounded and swollen appearance. The lamina densa of the basement membrane showed a folded appearance near its free edge (2 minutes after the excision). The mesodermal face of the plasma membrane of the basal epidermal cells was deprived of lamina densa over a distance of approximately 4 micrometers from the wound edge. The epidermis began to migrate 3 hours after the excision. After 8 hours of wound healing, the lamina densa was progressively reconstituted by deposits of irregular and non uniformly dense material. The bare mesoderm showed a disorganized cellular arrangement with numerous blood cells and many phagocytes. Between 5 and 8 hours, the surface of the mesenchyme became epithelized. After 24 hours, the bare epithelized mesenchyme progressively took the appearance of a normal predermal dense mesenchyme. During the migration of the epidermis from the wound edges, no lamina densa was present between epidermal and dermal cells. Basal epidermal cells established direct contacts and zones of close parallel apposition with dermal cell processes. Between 24 and 30 hours, the lamina lucida and lamina densa were completely reconstructed in their normal appearance.