Tissue Repair 2024 PDF

Dr. Ibrahim Hachim  Tissue Repair Critical to the survival of an organism is the ability to repair the damage caused by toxic insults and inflammation. Tissue repair (also referred to as healing): Is the restoration of tissue architect...

Dr. Ibrahim Hachim  Tissue Repair Critical to the survival of an organism is the ability to repair the damage caused by toxic insults and inflammation. Tissue repair (also referred to as healing): Is the restoration of tissue architecture and function after an injury Repair : mainly used for parenchymal and connective tissue. Healing : mainly for surface epithelium. The inflammatory response to microbes and injured tissues not only serves to eliminate these dangers , but also sets into motion the process of repair. Healing is an Outcome for: ❑ Acute Inflammation ❑ Chronic Inflammation ❑ Ischemic Necrosis ❑ Skin Wounds  Repair or healing of damages tissue occur by two types of reactions: Regeneration Scar formation Replacement of the lost In which the damaged parenchymal cells by tissue is replaced by surviving parenchymal connective tissue with scar cells of the same type. formation (fibrosis). Consequently, the injured tissue is restored to its normal (pre-injury) state Some tissues can For tissues that are If damage persists, completelybe reconstituted incapable of inflammation becomes chronic, after injury, such as repair regeneration, repair is and tissue damage and repair of bone after a fracture or accomplished by may occur concurrently. the regeneration of the connective tissue Connective tissue deposition in surface epithelium a deposition, producing these conditions is usually cutaneousinwound. a scar referred to as fibrosis. The regeneration of injured cells and tissues involves cell proliferation, which is driven by growth factors and is critically dependent on the integrity of the extracellular matrix, and by the development of mature cells from stem cells Repair by tissue regeneration or healing depend on cell type.  Permanent tissues: Their injury is thus followed by scar formation. Regeneration fails to occur when: The connective tissue framework of a tissue formed of stable cells has been destroyed. There is extensive necrosis, so no viable cells are available for regeneration.  Repair By Scarring If repair cannot be accomplished by regeneration alone, it occurs by replacement of the injured cells with connective tissue, leading to the formation of a scar, or by a combination of regeneration of some residual cells and scar formation. When resolution and regeneration are not possible, necrotic cells are replaced with collagen; this is termed organization, or repair by scar formation. In many instances, a combination of healing Mechanism of fibrosis Scar formation: Tissue injury is severe or chronic and results in damage to parenchymal cells and epithelia as well as to the connective tissue framework. If nondividing cells are injured. Steps in Scar Formation Within minutes after injury, a hemostatic plug is formed, which stops bleeding Repair begins early in inflammation. Macrophages are the central cellular players in the repair process At site of inflammation, fibroblasts and vascular endothelial cells begin proliferating granulation tissue : isa specialized type of tissue (hallmark of healing) called: Macroscopically, it is the slightly grainy brown layer at the base of a skin wound  Three main phases of cutaneous wound healing. Three main phases of cutaneous wound healing:- ▪ Inflammation ▪ Cell proliferation : up to 10 days, several types, cell including epithelial cells, endothelial and other vascular cells, and fibroblasts ▪ ECM deposition and remodeling Classifications of wounds  Classification of Healing by Primary Intention wounds closure : ▪ Surgical incision ▪ Edges easily joined together ▪ Small amount of granulation tissue ▪ Little fibrosis ▪ Wound strength 70-80% of normal by 3 months  Classification of Healing by Secondary Intention : ▪ Large wound,wounds may be infectedclosure ▪ Edges not brought close together ▪ Large amount of granulation tissue ▪ Scar formation and contracture  Wound strength At the end of the first week , when sutures are removed from a surgical wound , wound strength is about 10% of unwounded skin. Wound strength increases rapidly over the next 4 weeks. Slows down at approximately the 3rd month after the original wound to reach a plateau at about 70-80% of the strength of unwounded skin. The recovery of wound strength results from: ❑ the excess of collagen synthesis over collagen degradation during the first 2 months of healing ❑ Later from structural modifications of collagen fibers as cross linking and increased collagen  Difference between primary intention and secondary intention The basic process of healing is the same in all wounds. In contrast to healing by primary intention, wounds healing by secondary intention :- o Require more time to close because the edges are far apart o Show a more prominent inflammatory reaction in and around the wound o Contain more copious granulation tissue inside the tissue defect o Wound contraction (5 to 10%) (myofibroblasts) Complications  Exuberant granulation ▪ Is another deviation in wound healing characterized by the formation of excessive amounts of granulation tissue. ▪ Protrudes above the level of the surrounding skin ▪ Blocks reepithelialization (this process has been called proud flesh). ▪ Must be removed by cautery or surgical excision to permit restoration of epithelial continuity. Desmoids, or aggressive fibromatoses Incisional scars or traumatic injuries may be followed by exuberant proliferation of fibroblasts and other connective tissue elements that may, in fact, recur after excision. Lie at the gray zone of benign and malignant low-grade tumors Wound contraction Contracture is an important part of the normal healing process. An exaggeration of this process gives rise to contracture and results in deformities of the wound and the surrounding tissues. Distortion due to thickening and shortening of collagen bundles. Contractures are particularly prone to develop on the palms, the soles, and the anterior aspect of the thorax. Contractures Commonly seen after are serious burns and can compromise the movement of joints