Re-epithelization: The epithelial cells migrate across the new tissue to form an insulator between the wound and the environment and the granulation tissue formation giving rise to the initiation of re-epithelialization phase. Remnants of skin appendages (sweat and sebaceous glands, dermal appendages for example) advance in a a coherent sheet across the wound site and proliferate at its periphery and stopping movement when they met in the middle. (38, 44, 45,480) Migration of keratinocytes may start with-out proliferation. Migration can begin as early as a few hours after injury, while epithelial cells require viable tissue to migrate across, granulation tissue must fully fill the deep wound before initiation of re-epithelization process, the time of onset of migration is variable and may occur about 24 hours after wounding. Cells on the wound margins proliferate about 48 to 72 hours post-wounding in order to provide more cells for migration. (28, 47, 48)
If the basal membrane is intact, epithelial cells are replaced within 3 days by division and upward migration of cells in the basal layer in the same fashion that occurs in normal skin. However, if the basement membrane is breached at the wound site and ruined, re-epithelization must occur from the wound margins and from skin that enter the dermis and are lined with viable keratinocytes. If the wound is very deep, skin appendages may also be ruined and migration can only occur from wound edges. (28, 48)
Wound Contraction: If contraction continues for too long, it can lead to (dis-figuarment) and ( loss of function) but still essential in wound healing and repair . Contraction starts approximately seven days after wounding, when fibroblasts start differentiation into modified (myofibroblasts). (33,55) In epidermal –dermal (full thickness) wounds, contraction peaks at five to fourteen days post wounding and can last for several weeks to months, (33,47) and continues even full re-epithelialization. A wound can contacts 0.5 to 1mms per day with a size of a wound 50% to 70% of its original size at the end depending on how much loose tissue available in the wound, at first contraction committed with fibroblasts later differentiation into more functional myofibroblasts (contain actin) which responsible for the final wound contraction.(32,33,38,43,57)
Re-modeling and wound maturation
When collagen degradation and production reaches equilibrium, then the phase of maturation begin. Collagen type one is he predominant type during maturation and develop crosslinking and re-arrangement to get the full wound tension and resilience. (17, 20, 32) Onset of maturation is variable from 3 days to three weeks and may last for years and the scar tissue is inactive tissue so unnecessary blood vessels will be removed by the process of apoptosis, a wound tesile strength reaches 20% at about 3 weeks and needs 12 weeks to be 80% of the original. (20, 59)


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