The skin contains stem cells that allow it to repair itself in four major steps: hemostasis, inflammation, reepithelialization, and tissue maturation and remodeling.
Following an injury, the skin repairs itself in four major steps: hemostasis, inflammation, reepithelialization, and tissue maturation and remodeling.
- The first step is hemostasis, or blood clotting. In this step, platelets in the blood stick to the injured site. This activates a signaling cascade that causes the platelets to bind to one another and form a clot. This clot blocks damaged blood vessels and prevents additional bleeding.
- The second step is inflammation. In this step, platelets release growth factors that attract white blood cells, or leukocytes, to clear out the wound. White blood cells engulf bacteria, pathogens, dirt, and other debris, including dead and damaged cells.
- During the third step, reepithelialization, new tissues grow. New blood vessels form via a process called angiogenesis. At the same time, cells called fibroblasts gather and proliferate at the wound site. Fibroblasts excrete collagen and fibronectin to form new extracellular matrix. The new, rudimentary tissue that results is called granulation tissue. Once granulation tissue has formed, keratinocytes from the stratum basale undergo physiological changes that cause them to detach from the basement membrane. These cells migrate across the wound bed in a sheet, while new cells proliferate from stem cells on the wound margins. The migration of cells from the edges of the wound stops when the sheets meet in the middle. When this happens, the keratinocytes reverse the physiological changes they underwent in order to migrate, and they begin to divide as they do in normal skin, reestablishing the epithelial layers.
- In the fourth step, tissue maturation and remodeling, the disorganized collagen fibers created during proliferation rearrange into a more mature formation. This increases the strength of the wound. During this stage the scar loses its red appearance as blood vessels that were needed for healing die off.