Injury to the epidermis alone results in regeneration without scar, whereas wounds that penetrate the dermis result in repair by fibrosis (Yannas, 2001). The degree of dermal fibrosis depends on the type of tissue and the extent of the wound. The original tissue architecture is most closely restored in wounds made by shallow surgical incisions, where there is no loss of tissue and the wound edges either do not pull apart or are sutured together. These wounds heal primarily by simple fibro-blast proliferation with minimal scar formation because there is little wound space that needs to be filled in. Deep incisions in which the wound edges pull apart, as well as excisional wounds and burns that destroy substantial amounts of tissue, repair by the formation of extensive scar tissue.
An interesting and important fact is that both regeneration and scarring occur simultaneously in excisional wounds. While the dermal connective tissue heals by fibrosis, the epidermis and the vasculature regenerate, though the epidermis may lack structures such as hair follicles and sebaceous glands. Regeneration of the basic epidermal structure and the vasculature are constant features associated with repair by regeneration or scarring and reflect selective pressure for re-forming a barrier to the external environment and nourishment and oxygenation of underlying tissue. Why epidermal and endothelial cells respond to the wound environment by regenerating and dermal fibroblasts do not is a question of considerable interest.
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