injuries poisoning
Lacerations
Physiology of Lacerations
Healing of lacerations begins immediately after injury with coagulation and introduction of white blood cells; neutrophils and macrophages remove debris (including devitalized tissue) and bacteria. Macrophages also encourage fibroblast replication and neovascularization. Fibroblasts deposit collagen, typically beginning within 48 hours and reaching a maximum in about 7 days. Collagen deposition is essentially complete in 1 month, but collagen fiber strength builds more slowly as fibers undergo crosslinking. Wound tensile strength is only about 20% of ultimate by 3 weeks, 60% by 4 months, and maximum at 1 year; strength never becomes equivalent to the undamaged state. Epithelial cells from the wound edge migrate across the wound shortly after injury. In a surgically repaired wound (healing by primary intention), they form an effective protective barrier to water and bacteria in 12 to 24 hours and resemble normal epidermis within 5 days. In a wound that is not repaired (ie, heals by secondary intention), epithelialization is prolonged proportionally to the defect size. There are static forces on the skin because of its natural elasticity and the underlying muscles (see figure). Because scar tissue is not as strong as adjacent undamaged skin, these forces tend to widen scars, sometimes resulting in a cosmetically unacceptable appearance after apparently adequate wound closure. Scar widening is particularly likely when the forces are perpendicular to the wound edge. This tendency (and resultant wound stress) is readily observed in the fresh wound; gaping edges indicate perpendicular tension, and relatively well approximated edges indicate parallel forces. Direction of force is along each line. Cuts perpendicular to these lines are thus under greatest tension and most likely to widen. Scars tend to be red and prominent for about 8 weeks. As collagen remodeling occurs, the scar becomes thinner and loses its erythema. In some patients, however, the scar hypertrophies, becoming unsightly and raised. Keloids are exuberant scars that extend beyond the limits of the original wound and are more likely in patients with darker skin. The most common factors that interfere with wound healing involve tissue ischemia, infection, or both (see table); tissue ischemia predisposes to infection. Lower extremities are usually at greatest risk of infection and poor healing due to impaired circulation. The scalp and face are at lowest risk. Certain drugs and disorders can also interfere with wound healing. Human and Mammal Bites are usually heavily contaminated. 