Being a barrier organ, the skin is particularly exposed to damaging effects of our environment. After injury of this barrier the tissue damage needs to be repaired as quickly as possible and the skin’s protective function must be restored. Normal wound healing is of high priority for the organism. Formation of scab is necessary to avoid excessive losses of water and heat through the wound as well as dehydration of the wound. This also provides protection from exogenous influences, infections and mechanical irritation. Under normal circumstances, wound healing takes place smoothly and the barrier function is quickly restored.
Phases of wound healing
Immediately after injury of the skin repair mechanism are starting in order to restore the skin’s barrier function as quickly as possible. The entire wound healing process comprises a number of individual phases. A common characteristic is the activation, co-operation, and secretion of different cell types. The inflammation (proliferative) phase is also a cleansing phase. When the wound is healing, the cleaning process predominates.
Phases of wound healing
During the latent phase, processes involving the removal of cell debris prevail. Defense against infections and the healing process are starting slowly. In this phase the risk of infection is high.
In the subsequent proliferation phase, successful defense against wound infection is most likely due to the formation of new blood vessels in the connective tissue. During that time, all defense mechanisms are mobilized. All overall, this wound healing phase offers the best requirements for a quick, smooth wound repair.
About one week after injury, the reparative phase of the healing process begins and the wound closure is starting.
Physiology of wound healing
Wound repair and defense against wound infection require a properly working endogenous defense system. Macrophages are the key cells of the immune system. This Greek word means ‘big eaters’, as they engulf and incorporate pathogens before digesting them. Macrophages are present in all tissues and in the lymph fluid.
Macrophage ingesting bacteria
On closer inspection of the wound healing, the individual phases of wound healing can be distinguished by their characteristic features. After injury, blood coagulation is activated primarily, and macrophages and granulocytes immigrate. Macrophages cleanse the wound while granulocytes fight against bacteria that have entered the wound. This cleansing/inflammation phase is normally followed by the proliferation phase. New connective tissue is synthesized, vessels emerge into the wound area, and the tissue defect is slowly refilling. Keratinocytes (cells in the epidermis) migrate across the temporary connective tissue and close the defect. Wound closure is followed for some time by rebuilding processes in the connective tissue, which is summarized as cicatrisation phase.
Wound healing disorders and problem wounds
Wound healing disorders are a considerable medical problem. If normal wound healing mechanisms are inhibited by different primary diseases, even a minor injury can result in a poorly healing wound. For an efficient therapy the primary disease needs to be identified and treated, and the pathologically disturbed healing process has to be normalized in a specific way. In rare cases the wound healing process may fail to appear, resulting in a problem wound needing a long treatment period. In fact, there are many diseases that impede normal wound healing. Therefore, patient’s primary diseases should always be taken into account in the differential diagnosis of wound healing disorders. Examples of problem wounds include: