HEALING AND REPAIR

REPAIR It is the regeneration of vascular , fibrous connective tissue . it is characterised by the proliferation and maturation of this tissue to : 1) Replace the loss of more specialised tissue . 2)Replace inflammatory exudate and haemorrhage . 3)Replace thrombus within blood vessels .

Repair begins very early in the process of inflammation and involves two processes : 1. regeneration of injured tissue by the same cell type . 2. replacement by connective tissue ( fibroplasia ) .

Regeneration Is the replacement of lost cells by those of the same type .

PROLIFERATIVE POTENTIAL OF DIFFERENT CELL TYPES 1) Continuously dividing ( labile ) cells . 2) Quiescent (stable) cells . 3) Nondividing (permanent) cells .

PROLIFERATIVE POTENTIAL OF DIFFERENT CELL TYPES 1) Continuously dividing ( labile ) cells : proliferate throughout life , replacing cells that are continuously dying . stratified squamous cell : skin , oral cavity , vagina. Cuboidal cells : salivary glands , pancreas , biliary tract . Transitional epithelium : urinary tract . Hematopoietic cells of the bone marrow .

2) Quiescent (stable) cells : It has a low level of replication , when there is injury or stimulus it start to divid and replicate The ability of the liver to regenerate after hepatectomy or following , toxic, viral , or chemical injury . smooth muscles .

3) Nondividing (permanent) cells : the cell cycle at some point in intrauterine development and cannot undergo further mitotic division in postnatal life . Include nerve cells and cardiac myocytes .

REPAIR BY CONNECTIVE TISSUE Severe or persistent tissue injury and inflammation with severe tissue damage , the nonregenerated parenchymal cells begin being replaced within 24 hours by proliferating fibroblasts and vascular endothelial cells . By 3 to 5 days , the healing process will be established by granulation tissue . Granulation tissue then progressively accumulates in connective tissue matrix and eventually results in fibrosis ( scarring) .

Formation of new blood vessels (angiogenesis) . Fibrosis . There are three components to this process : Formation of new blood vessels (angiogenesis) . Fibrosis . Maturation and organization of the scar (remodeling ) .

GRANULATION TISSUE It is the pink , soft , granular gross appearance , such as that seen beneath the scab of a skin wound Histologic appearance is characterized by prolifertion of fibroblasts , and new thin-walled delicate capillaries , in a loose extracellular matrix .

angiogenesis New vessels originate by budding from preexisting vessels , a process called Angiogenesis or neovascularization . It has four general steps : 1) Proteolytic degradation of the parent vessel basement membrane , allowing formation of a capillary sprout . 2) Migration of the endothelial cells toward the angiogenic stimulus . 3) Proliferation of the endothelial cells behind the leading front of migrating cells . 4) Maturation of endothelial cells with organization into capillary tubes.

Fibrosis (fibroplasia) It occurs on the granulation tissue framework of new vessels and loose ECM that develop early at the repair site . It has two steps : 1) emigration and proliferation of fibroblasts in the site of injury . 2) deposition of ECM by these cells .

Healing ulcer

SCAR REMODELING The process of remodeling is regulated a group of enzymes , which is secreated from the inflammatory cells .

WOUND HEALING 2) Parenchymal cell regeneration . It involves processes that have been well-described previously : 1) Induction of an acute inflammatory response by the initial injury . 2) Parenchymal cell regeneration . 3) Migration and proliferation of both parenchymal and Connective tissue cells . 4) Synthesis of ECM proteins . 5) Remodeling of parenchymal elements to restore tissue function . 6) Remodeling of connective tissue to achieve wound strength .