HOW WOUNDS HEAL
The process of growing new tissue to close a wound occurs in two distinct stages: granulation, a mixture of tiny blood vessels, connective tissue cells (fibroblasts) and collagen that fills in the gap; and epithelialization, the growth of new skin cells across the surface of the wound to close it.
If sutures are used to bring the edges of a wound together, the gap between the two sides is narrow, and both stages happen more or less simultaneously. This is called “first intention” healing of a wound.
If a wound is wide, and too much tissue has been lost, it may be impossible to bring the edges together with sutures. In this case, the wound will be left open to heal. This is called “second intention” healing, and granulation and epithelialization occur at different rates:
• First, as soon as the wound occurs, blood and lymph fluids rush to the scene; blood platelets are stimulated to form long, sticky protein threads that dry into a clot to seal off the wound and protect it from contaminants. White blood cells also arrive to help fight infection. The platelets and other agents also release other factors that stimulate the next stages of healing.
• Next, granulation tissue begins to form over the exposed surfaces within the wound. Because most wounds are narrowest at their deepest part, the gap usually closes from the inside outward.
As healing progresses, the granulation tissue pulls the edges of the wound together. Meanwhile, the wound continuously cleans itself, sloughing off fluids filled with dead cells and other wastes.
• Finally, epithelial cells multiply along the edges of the wound, growing outward from the edge of the skin, to cover and adhere to the bed of granulation tissue. If all goes well, epithelialization and granulation continue until the wound closes and healing is complete.