A wound is a break in the outer layer of the skin, called the epidermis. Wounds are usually caused by cuts or scrapes. Different kinds of wounds may be treated differently from one another, depending upon how they happened and how serious they are. Other wounds include puncture wounds, lacerations (cuts), pressure sores, anal fissures, extravasations (a drug accidentally going outside of a vein causing tissue damage), skin damage caused by incontinence (lack of bladder control), skin graft healing (split thickness), diabetic ulcers, and surgical skin flap ischemia (lack of blood flow to surgically attached skin).
Healing is a response to the injury that sets into motion a sequence of events. With the exception of bone, all tissues heal with some external scarring. The object of proper care is to minimize the possibility of infection and scarring.
There are basically four phases to the healing process: the inflammatory phase, proliferative phase, remodeling phase, and epithelialization phase.
The inflammatory phase begins with the injury itself. In the inflammatory phase, there is bleeding, immediate narrowing of the blood vessels, clot formation, and release of various chemical substances into the wound that will begin the healing process. Specialized cells (macrophages) clear the wound of debris over the course of several days.
Next is the proliferative phase in which a matrix or latticework of cells forms. On this matrix, new skin cells and blood vessels will form. It is the new small blood vessels (known as capillaries) that give a healing wound its pink or purple-red appearance. These new blood vessels will supply the rebuilding cells with oxygen and nutrients to sustain the growth of the new cells and support the production of proteins (primarily collagen). The collagen acts as the framework upon which the new tissues build. Collagen is the dominant substance in the final scar.
The remodeling phase begins after 2-3 weeks. The framework (collagen) becomes more organized making the tissue stronger. The blood vessel density becomes less, and the wound begins to lose its pinkish color. Over the course of six months, the area increases in strength, eventually reaching 70% of the strength of uninjured skin.
Epithelialization is the process of laying down new skin, or epithelial, cells. The skin forms a protective barrier between the outer environment and the body. Its primary purpose is to protect against excessive water loss and bacteria. Reconstruction of this layer begins within a few hours of the injury and is complete within 24-48 hours in a clean, sutured (stitched) wound. Open wounds may take 7-10 days because the inflammatory process is prolonged, which contributes to scarring. Scarring occurs when the injury extends beyond the deep layer of the skin (into the dermis, which is the second layer of skin).
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