A reduction in fatalities due to extensive burn wounds is achieved by treating with skin grafts. The success of skin graft treatment depends on vascular supply to the graft and sufficient angiogenesis (blood vessel formation) early in the healing process. Healing after skin grafting involves essential cellular processes such as cell proliferation and tissue remodeling, and these processes depend on factors such as cytokines (cell signals) and growth factors. Studies have shown that paracrine factors have positive effects on necessary wound healing processes such as angiogenesis. Unlike endocrine factors (hormones) that circulate to cell targets, paracrine factors are released by cells and diffuse into the surrounding local environment to act on nearby cells.