The response of tissue to injury goes through several phases which are:
- Inflammatory phase
- Proliferative phase
- Maturation phase
Also called the lag or executive phase, the inflammatory phase is characterized by vascular and cellular responses that occur immediately after tissue injury takes place. The length of time this phase lasts is about 1-4 days. The following events occur during this phase:
- BLOOD CLOT FORMATION. Right after tissue injury takes place, vasoconstriction of vessels occurs and in an attempt to stop or control bleeding, a fibrinoplatelet clot forms. Lasting for about 5 to 10 minutes, this reaction is followed by vasodilation of the venules. Vasoconstriction is stopped as norepinephrine is destroyed by the intracellular enzymes. The result is an increased permeability of the capillary due to the destruction of norepinephrine and the release of histamine.
- WOUND BECOMES EDEMATOUS. Damage of the microcirculation results to the infiltration of blood elements such as antibodies, plasma proteins, electrolytes, complement and water for approximately 2 to 3 days after the tissue injury. This mechanism causes the occurrence of edema, warmth, redness and pain on the affected area.
- PHAGOCYTES ENGULF DEBRIS OF DAMAGED TISSUE AND BLOOD CLOT. The first leukocytes that move into the damaged tissue are the neutrophils. The component of WBC that transforms to macrophages to engulf the debris, monocytes, transports the phagocytized debris from the injured area. Antigen-antibodies also appear and the basal cells present at the edges of the wound undergo mitosis and the resulting daughter cells migrate. Through this activity, the secretion of proteolytic enzymes and its breakdown at the base of the clot is made possible. Thus, the break in the continuity of the cells is progressively bridged and by about 24 to 48 hours the sides of the wound would eventually meet.
Hyperplastic bone marrow activity enhances cell migration progressing to the next phase of wound healing.
The proliferative phase, also called the fibroblastic or connective tissue phase, is the time where fibroblasts are multiplying and a lattice framework is formed for migrating cells. Proliferative phase occurs during the 5th to the 20th day after tissue injury took place. The following events are noted during this phase of wound healing:
- GRANULATION TISSUE FORMS. By this time, epithelial cells form buds at the edges of the wound. These beds are the ones that develop into capillaries. These capillaries serve as the nutritional source for the new granulation tissue.
- COLLAGEN PRODUCTION. The primary component of replaced connective tissue is collagen. It is the fibroblasts that initiate the synthesis of collagen and mucopolysaccharides. Chains of amino acids form into fibers of increasing length and diameter in about 2 to 4 weeks. The formed fibers become a well-structured pattern of packed bundles. Collagen synthesis causes depletion in the number of capillaries.
- INCREASED WOUND TENSILE STRENGTH. Synthesis of collagen and lysis of capillaries results in the increased tensile strength of the wound. About 3% to 5% of the original skin strength is the amount of skin present 2 weeks after the injury. About a month, only 35% to 59% of wound strength has been reached. Never more than 70% to 80% of the strength is regained after wound has occurred. For wound strength to be made possible vitamins, especially Vitamin C, aid in the metabolic process necessary for wound healing.