The blood flow to the injured area increases, bringing nutritive substances to the damaged tissue. Macrophages also stimulate fibroblasts to secrete collagen, a type of protein that strengthens the tissues. New blood vessels are formed to continue the supply of nutrients to the wound. Although the mechanism is not well understood, the wound then begins to contract and tissue forms from the wound's edge. Within one to two days, the epithelial cell layer begins to form.
Oxygen affects the production of collagen, epithelial cell growth, and the growth of blood vessels.
A decrease in the volume of circulating blood and the concentration of red blood cells can compromise the amount of oxygen available for wound healing. Interventions to improve oxygenation and enhance wound healing include replacing reduced blood volume, monitoring fluids, watching for signs of infection, and monitoring the overall healing progress.