The PrinciPles Of WOund healing

1. What events occur during each of the primary phases of wound healing? Wound healing has three principal phases: inflammatory, proliferative, and remodeling. The inflammatory phase begins at the time of injury and lasts for 24 to 48 hours. This phase begins with hemostasis and leads to inflammation. Platelets form the initial thrombus release growth factors that induce the chemotaxis and proliferation of neutrophils and macrophages, which cooperate to remove necrotic tissue, debris, and bacteria from the wound. Macrophages then become the prominent cell of this phase and release various growth factors and cytokines that change the relatively acellular wound into a highly cellular environment. Next, fibroblasts proliferate to become the dominant cell of the proliferative phase. They produce collagen, which provides structure to the wound and replaces the fibronectin–fibrin matrix. Angiogenesis of new capillaries occurs to sustain the fibroblast proliferation. Keratinocytes also epithelialize the wound. The remodeling phase begins at about 2 to 3 weeks and can last up to 2 years. At this time, collagen synthesis and degradation reach equilibrium. Fibroblasts organize and cross-link the collagen, wound strength gradually increases, wound contraction occurs, and the wound loses its pink or purple color as capillary and fibroblast density decrease. All stages may vary in length because of infection, malnutrition, or other exogenous factors.