wound healing.pdf

General surgery ‫د صباح الهيتي‬ Wound Healing The healing wound is cellular and biochemical responses directed toward restoring tissue integrity and functional capacity following injury. Injured organisms...

General surgery ‫د صباح الهيتي‬ Wound Healing The healing wound is cellular and biochemical responses directed toward restoring tissue integrity and functional capacity following injury. Injured organisms survive only if they can repair themselves quickly and effectively. The healing response depends primarily on the type of tissue involved and the nature of the tissue disruption. When restitution occurs by means of tissue that is structurally and functionally indistinguishable from native tissue, regeneration has taken place. However, if tissue integrity is reestablished primarily through the formation of fibrotic scar tissue tissue, Then repair has occurred. With the exception of bone and liver, tissue disruption invariably results in repair rather than regeneration Wound healing involves three overlapping phases : 1- Inflammation, 2- Proliferation 3- Remodelling. This produce scar which represent trace of healing wound. Inflammatory phase 1. Begins at the time of injury; lasts 2 to 3 days. 2. Begins with vasoconstriction to achieve hemostasis (epinephrine and thromboxane). 3. Platelet plug forms and clotting cascade is activated, resulting in fibrin deposition. 4. Platelets release platelet-derived growth factor (PDGF) and transforming growth factor β (TGF-β) from their alpha granules, attracting inflammatory cells, particularly macrophages. 5. After hemostasis is achieved, vasodilation occurs and vascular permeability increases (due to histamine, platelet-activating factor, bradykinin, prostaglandin I2, prostaglandin E2, and nitric oxide), aiding the infiltration of inflammatory cells into the wound. 6. Neutrophils peak at 24 hours and help with débridement. 7. Monocytes enter the wound, becoming macrophages, and peak within 2 to 3 days. 8. Limited numbers of lymphocytes arrive later, but their significance is unknown. Proliferative phase 1. Begins around day 3, as fibroblasts arrive; lasts through week 3. 2. Fibroblasts: Attracted and activated by PDGF and TGF-β; arrive day 3, reach peak numbers by day 7. 3. Collagen synthesis (mainly type III), angiogenesis, and epithelialization occur. 4. Total collagen content increases for 3 weeks, until collagen production and breakdown become equal and the remodeling phase begins. Remodeling phase 1. Increased collagen production and breakdown continue for 6 months to 1 year. 2. Type I collagen replaces type III until it reaches a 4:1 ratio of type I to type III (that of normal skin and mature scar tissue). 1 General surgery ‫د صباح الهيتي‬ 3. Wound strength increases as collagen reorganizes along lines of tension and is cross-linked. 4. Vascularity decreases. 5. Fibroblast and myofibroblasts cause wound contraction during the remodeling phase. 6- Wounds have 50% of their final strength at 6 weeks, but never reaches normal (only 80% normal). Fetal wound healing A. Skin (but not all fetal tissue) heals by regeneration without scarring. This is limited to the first two trimesters. B. Many aspects of fetal tissue and the fetal environment may contribute to scarless healing. 1. The fetal environment (amniotic fluid) is sterile. 2. Amniotic fluid contains growth factors and extracellular matrix molecules. 3. The inflammatory phase is minimal, and macrophages may or may not be the main organizing cells in the healing process in the fetus. 4. The growth factor and cytokine milieu is different in the fetus, although the significance of any particular difference is unclear TYPES OF WOUND HEALING A. Primary Healing Wounds are closed by reapproximation using suture or by some other mechanical means within hours of their creation. This is indicated in newly created wounds (