Wound contraction is mediated by -
Ans. is 'a' i.e., MyofibroblastsWound contraction is a feature of healing by secondary intention. This is the feature that most clearly differentiates primary from secondary healing.Contraction has been ascribed to the presence of myofibroblasis - altered fibroblasts that have the ultrastructual characteristics of smooth muscle cells.In above explanation, I have explained healing in general. Here I am giving brief description of wound healing. Skin wound healingSkin wounds are classically described to heal by primary or secondary intention.A. Healing by primary intentionIt occurs in wounds with opposed edges, e.g., surgical incision.The healing process follows a series of sequantial steps : ?Immediate after incisionIncisional space filled with blood containing fibrin and blood cells.Dehydration of the surface clot forms scab that covers the wound.Within 24 hoursNeutrophils appear at the margins of wound.In 24-48 hoursEpithelial cells move from the wound edges along the cut margin of dermis, depositing basement membrane components as they move.They fuse in the midline beneath the surface scab, producing a continuous but thin epithelium layer that closes the wound.By day 3Neutrophils are largely replaced by macrophages.Granulation tissue progressively invades the incision space.Collegen fibers now present in the margin but do not bridge the incision.ci By day SIncisional space is largely filled with granulation tissue.Neovascularization is maximum.Collegen fibrils become more abundant and begin to bridge the incision.The epidermis recovers its normal thickness.Et During second weekLeukocytes and edema have disappeared.There is continued accumulation of collegen and proliferation of fibroblast.o By the end of first monthScar is made up of a cellular connective tissue devoid of inflammatory infiltrate covered now by intact epidermis.B. Healing by secondary intentionIt occurs in wounds with seperated edges in which there is more extensive loss of cells and tissue.Regeneration of parenchymal cells cannot completely restore the original architecture, and hence abundant granulation tissue grows.Healing by secondary intention differ from primary intention in several respects : ?1. Inflammatory reaction is more intense.2. Much larger amounts of granulation tissue are formed.3. Wound contraction occurs --> Feature that most clearly differentiate secondary from primary healing.Permanent wound contraction requires the action of myolifibroblasts - Fibroblasts that have the ultrastructural characteristic of smooth muscle cells.
Myofibroblasts
Epithelial cells
Collagen
Elastin