Wound healing

Posted by e-Medical PPT
Wound healing is an intricate process in which the skin (or another organ-tissue) repairs itself after injury.In normal skin, the epidermis and dermis exists in a steady-state equilibrium, forming a protective barrier against the external environment. Once the protective barrier is broken, physiologic process of wound healing is immediately set in motion. The classic model of wound healing is divided into three or four sequential, yet overlapping,phases:hemostasis, inflammatory,proliferative and remodeling.Upon injury to the skin, a set of complex biochemical events takes place in a closely orchestrated cascade to repair the damage.Within minutes post-injury, platelets  aggregate at the injury site to form a fibrin clot. This clot acts to control active bleeding.
In the inflammatory phase, bacteria and debris are phagocytosed and removed, and factors are released that cause the migration and division of cells involved in the proliferative phase.
The proliferative phase is characterized by angiogenesis, collagen deposition, granulation tissue formation, epithelialization, and wound contraction.In angiogenesis, new blood vessels are formed by vascular endothelial cells.In fibroplasia and granulation tissue formation, fibroblasts grow and form a new, provisional extracellular matrix (ECM) by excreting collagen and fibronectin.Concurrently, re-epithelialization of the epidermis occurs, in which epithelial cells proliferate and 'crawl' atop the wound bed, providing cover for the new tissue.
In contraction, the wound is made smaller by the action of myofibroblasts, which establish a grip on the wound edges and contract themselves using a mechanism similar to that in smooth muscle cells. When the cells' roles are close to complete, unneeded cells undergo apoptosis.
In the maturation and remodeling phase, collagen is remodeled and realigned along tension lines and cells that are no longer needed are removed by apoptosis.

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