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PROTECTING, SENSING, REPAIRING |
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Sunburned forearm |
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WOUND AND HEALING
Burns, scratches, grazes and cuts are wounds which injure the skin and induce a complex repair mechanism known as healing.
A burn is an injury, affecting either the epidermis or the dermis. The sources for these injuries are numerous : flame, liquid, hot surfaces or harmful sun rays. Burns are categorized by degrees, defined according to the depth of the injury :
First degree burns are superficial injuries that involve only the epidermis and produce skin redness. A "sunburn" is an example of a first degree burn. Second degree burns, involve both epidermis and dermis, and are characterized by the presence of blisters.
Third degree burns are by far the most serious of all burns. The deep dermis is affected, where blood vessels and nerve endings are usually destroyed.
In the most serious cases, skin gafts are necessary to induce the healing process which cannot occur on its own.
The process of healing of superficially burned skin is well documented: Blisters form as a result of liquid influx from the dermis as cells are lifted and separated from the epidermal layer. As the skin heals, the liquid resorbs and dead cells are replaced by new cells, a process that last for a few weeks.
In the case of deeper wounds (such as cuts), where there is injury to the dermis, associated with bleeding, a more complex phenomenon takes place.
The first step is formation of a blood clot, which protects the underlaying tissue. Fibroblasts actively divide and regenerate scar and connective tissue which will eventually replace the blood clot, allowing the edges of the wound to migrate closer. Simultenaously, cells in the basal layer of the epidermis undergo increase in activity: keratinocytes divide and differentiate to build a new horny layer. When the gap is closed, the proliferation of fibroblasts and keratinocytes stops. This last phase may take weeks, months even years, resulting in the formation of a scar.
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