Wound Healing

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The third phase of wound healing is granulation phase, which takes place to repair the damaged cells by regenerating new cells. This phase consists of different subphases, which can last up to 4 weeks in the clean and uncontaminated wound. These sub phases do not happen in discrete time frames but constitute an overall and ongoing process. The sub phases are "fibroplasia, matrix deposition, angiogenesis and re-epithelialization" (Cho & Lo, 1998). The first sub phase of granulation process is fibroplasia. In days 5-7, fibroblasts have migrated into the wound, laying down new collagen of the subtypes I and III. In normal wound healing, early type III collagen predominates but is later replaced by type I collagen. Tropocollagen, which is the precursor of all collagen types, is then transformed within the cell's rough endoplasmic reticulum, where proline and lysine are hydroxylated. After tropocollagen transformation, disulfide bonds are established, allowing 3 tropocollagen strands to form a triple left-handed triple helix, termed procollagen. As the procollagen is secreted into the extracellular space, peptidases in the cell wall cleave terminal peptide chains, creating true collagen fibrils, which mark the hallmark of fibroplasia. After fibroplasia, matrix deposition takes place. In matrix deposition, the wound is first suffused with GAGs and fibronectin produced by fibroblasts. These GAGs include heparan sulfate, hyaluronic acid, chondroitin sulfate, keratan sulfate, and proteoglycans. Then, proteoglycans bond covalently to a protein core and this contributes to matrix deposition. Later, angiogenesis takes place. Angiogenesis is the product of parent vessel offshoots which is known as new vasculature. The formation of new vasculature requires extracellular matrix and basement membrane degradation followed by migration, mitosis, and maturation of endothelial cells. Basic FGF and vascular endothelial growth factor are also involved in the modulating...
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