Wound healing

From ArticleWorld

Wound healing is a natural repair process whereby the body repairs and regenerates skin and soft tissue, forming an unbroken area of skin that often becomes scarred. There are many different phases of wound healing necessary for proper reconstruction of damaged tissue.

Inflammatory phase

The first phase is called the inflammatory phase. This happens so that cells which phagocytize debris, bacteria and devitalized tissue can get to the site and begin cleaning up the wound. In addition, clotting must occur to stop the flow of blood as much as possible.

Clotting occurs when blood comes into contact with collagen and triggers platelets to secrete inflammation factors. Platelets are also made to stick together and help form a blood clot. Blood vessels also go into spasm which further reduces blood flow. Spasm in the blood vessels keeps the cells necessary for inflammation to remain in the area.

Following spasm, the blood vessels dilate due to the presence of histamine and the area swells due to increased leakage of the blood vessels. Neutrophils are able to enter through the leaky blood vessels and reach the site of injury to cleanse the wound. Macrophages also “chew up” and digest bacteria and devitalized tissue. While the inflammatory phase is necessary, if allowed to go on too long, excessive tissue damage is possible.

Proliferative phase

This phase occurs approximately 2-3 days after the wound occurs. This can happen at the same time as the inflammatory phase. It involves the bringing together of fibroblasts that begin cellular reconstruction. This phase includes the formation of new blood vessels to supply the area. Stem cells form the endothelial lining of capillaries and other new blood vessels. They are attracted to the site by macrophages and platelets that release angiogenic factors. This results in a well-perfused area.

Fibroblasts in the wound begin accumulating at day 2 and can be inside a wound for up to four weeks post-injury. Fibroblasts lay down collagen layers in a matrix. Then they deposit ground substance in the bed of the wound, followed by new collagen. If a wound is gaping, granulation tissue must fill the void. It consists of new blood vessels, provisional extracellular matrix inflammatory cells, fibroblasts, inflammatory cells and endothelial cells.

When the wound is filled in, it can begin to epithelialize and cover the surface of granulation tissue. Keratinocytes migrate across the wound and fill in from the edges of the wound. These cells are responsible for re-epithelializing the wound. The cells climb over each other and flatten to form early skin formation. They migrate under any scab that was formed.

The wound begins contracting after about a week. If allowed to happen too long, disfigurement occurs. The wound loses water and the fibroblasts differentiate into myofibroblasts. They act like smooth muscle cells and can contract a wound to 40-80% of its original size.

Maturation phase

In maturation, the level of collagen roughly equals the rate of degradation so that mature, stronger collagen is laid down. The disorganized collagen organizes along tension lines and the strength of the wound increases. The extra capillaries needed in wound healing are degraded and the scar fades.