Figure 1.
Phases of wound healing. A three-phase injury and wound-healing model describes distinct phases of a successful response. (1) Injury; many agents can cause pulmonary injury, including environmental particles, allergens, infectious agents, chemotherapy and radiation. Disruption of epithelial and endothelial cells initiate an anti-fibrinolytic cascade, temporarily plugging the affected tissue. (2) Inflammation; circulating inflammatory cells and fibrocytes are recruited to the injured site through chemokine gradients, supplying fibroblast-activating cytokines and growth factors. Neo-vascularization provides access to damaged areas and a steady stream of inflammatory, anti-inflammatory, and phagocytic cells. (3) Fibroblasts contract and decrease the size of the wound. Inflammatory cells and α-SMA+ myofibroblasts undergo apoptosis, terminating collagen deposition, and are cleared by phagocytic cells. Epithelial and endothelial cells are replaced and tissue architecture is restored.