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MEDICAL ANIMATION TRANSCRIPT: An injury to the skin, such as a cut, scrape, or puncture wound kills nearby cells and damages underlying structures and triggers the complex process of repairing the skin. Wound healing is a three-step process. The inflammatory phase begins immediately upon injury. Blood vessels constrict to reduce blood loss. Then, platelets arrive to plug the leak. The platelet plug initiates the clotting mechanism by facilitating the reactions of plasma proteins called clotting factors, which interact to form a fibrin clot. After the clot forms, the blood vessels vasodilate and become more porous to allow white blood cells to leave the blood vessel and populate at the site of injury. During this process called phagocytosis, white blood cells eat debris and kill bacteria, reducing the risk of infection. The proliferative phase begins two days to three weeks after injury. The first step in the proliferative stage is granulation. Connective tissue cells, called fibroblasts, lay a matrix of collagen that reinforces the wound and provides structure for other cells. Collagen then contracts to pull together the margins of the wound. Angiogenesis, or the growth of new blood vessels, begins almost simultaneously and supplies oxygen to the repairing cells. Epithelialization is the restoration of the protective skin barrier. Epithelial cells migrate from the margins of the wound, protected by the scab, until they meet. Eventually, the scab falls off. The remodeling phase begins several weeks after the injury and can continue for years. During this phase, a new, more organized collagen matrix forms in the wound bed and capillaries disappear, leaving an avascular scar. One possible complication of wound healing is keloid formation. A keloid results from an overgrowth of granulation tissue extending beyond the borders of the original wound. Composed of mostly collagen, keloids are slow-growing. They do not regress spontaneously, and tend to reoccur after excision. A common initial treatment for keloids includes multiple injections of corticosteroids to help reduce the size of the scar. ♪ [music] ♪