Department of Anatomic PathologyFaculty of MedicineBrawijaya University

Regeneration and HealingDefinition : Regeneration HealingControl of Normal Cell Proliferation and Tissue Growth Cell cycleTissue Proliferative ActivityGrowth FactorExtracellular Matrix (ECM) and Cell-Matrix InteractionsRepair by Healing, Scar Formation, and Fibrosis Healing : Scar FormationCutaneous Wound Healing Primary Union Secondary UnionWound StrengthLocal and Systemic Factors That Influence Wound Healing

Regeneration1. Definition : Growth of cells and tissues to replace lost

structures

2. Occurs if the ECM framework is not damaged / intact

( framework provide for cell migration and maintain the

correct cell polarity for re-assembly of multilayer structures )

3. Regenerated cells : - Original cells - Stem cells Note : Stem cells : - Embryonic stem cells - Adult stem cells * Hematopoietic stem cells / HSCs * Tissue stem cells - Asymmetric replication

Healing1.Definition : A tissue response * to a wound (commonly in the skin), * to inflammatory processes in internal

organs, or * to cell necrosis in organs incapable of regeneration

2. Occurs if the ECM framework is damaged

3. Healing consists regeneration and scar formation

may restore original structures but involves

collagen deposition and scar formation.

Figure 3-1 Tissue response to injury. Repair after injury can occur by regeneration, which restores normal tissue, or by healing, which leads to scar formation and fibrosis.

Control of Normal Cell Proliferation and Tissue Growth* Repair : Regeneration / growth of cells / tissue* In adult tissues, the size of cell populations is determined by the rates of cell proliferation, differentiation, and death by apoptosis. * Cell Cycle :

TISSUE-PROLIFERATIVE ACTIVITY The cells of the body :1. Labile (Continuously dividing) tissue Cell proliferate throughout life : surface epithelia, oral

cavity, vagina, cervix, the secretory ducts of the glands, epithel gastrointestinal tract, uterus, urinary, bone

marrow, and hematopoietic tissue. mature cells are derived from stem cells2. Stable (Quiescent) tissue Normally have a low level of replication (G0 G1 cell

cycle) : parenchymal cells of liver, kidneys, pankreas,

mesenchymal cells such as fibroblast, smooth muscles, vascular endothelial cells and resting lymphocytes and other leukocytes.3. Permanent (Non dividing) tissue Contain cell that have left the cell cycle and cannot

undergo mitotic division in postnatal life : neurons, skeletal and cardiac muscle cell

Growth Factor Epidermal Growth Factor (EGF) and Transforming Growth Factor-α (TGF-α) -EGF : * Mitogenic for a variety of epithelial cells, hepatocytes, and fibroblasts. * Produced by keratinocytes, macrophages, and other inflammatory cells in wound healing

Hepatocyte Growth Factor (HGF) * Mitogenic effects in hepatocytes, cells of the biliary epithelium in the liver, and epithelial cells of the lungs, mammary gland, skin, and others* Produced by fibroblasts, endothelial cells, and liver non- parenchymal cells.

Vascular Endothelial Growth Factor (VEGF) Platelet-Derived Growth Factor (PDGF) * Produced by activated platelets, activated macrophages, endothelial cells, smooth muscle cells, and many tumor cells. * Causes migration and proliferation of fibroblasts, smooth muscle cells, and monocytes

Fibroblast Growth Factor (FGF) * Have a large number of functions : New blood vessel formation (angiogenesis), wound repair, skeletal muscle development, development of bone marrow stroma

Extracellular Matrix (ECM) and Cell-Matrix InteractionsThe ECM is secreted locally and assembles into a network in the spaces surrounding cells. The ECM serves many functions: * matrix proteins sequester water that provides turgor to soft tissues * minerals give rigidity to skeletal tissues. * reservoir for growth factors controlling cell proliferation. * provides a substratum for cells to adhere, migrate and proliferate *directly modulating cell form and function

Macromolecules which are constitute the ECM: (1)fibrous structural proteins, such as the collagens and elastins(2)adhesive glycoproteins(3)proteoglycans and hyaluronic acid

1,2 and 3 : assemble into two general organizations: a. Interstitial matrix It consists of fibrillar and nonfibrillar collagen, elastin, fibronectin, proteoglycans, hyaluronate b. basement membrane (BM) Produced by epithelial and mesenchymal cells They consist of a network of amorphous nonfibrillar collagen (mostly type IV), laminin, heparan sulfate, proteoglycan, and other glycoproteins.

Repair by Healing, Scar Formation, and FibrosisHealing : involving a number of processes: Induction of an inflammatory process in response to the initial injury, with removal of damaged and dead tissue Proliferation and migration of parenchymal and connective tissue cells Formation of new blood vessels (angiogenesis) and granulation tissue Synthesis of ECM proteins and collagen deposition Tissue remodeling Wound contraction Acquisition of wound strength

Scar formationGrowth factors and cytokines released at the site of injury induce fibroblast proliferation and migration into the granulation tissue framework of new blood vessels and loose ECM that initially forms at the repair site.

Three processes that participate in the formation of a scar: (1) emigration and proliferation of fibroblasts in the site of injury, (2) deposition of ECM, and (3) tissue remodeling.

Cutaneous wound healingCutaneous wound healing : divided into three phases: (1) inflammation (early and late); (2) granulation tissue formation and reepithelialization; (3) wound contraction, ECM deposition, and remodeling These phases overlap, and their separation is somewhat arbitrary.

HEALING BY FIRST INTENTION ( primary union ) WOUNDS WITH OPPOSED EDGES

In a clean, uninfected surgical incision

•Within 24 hours, neutrophils at the margins of the incision, moving toward the fibrin clot. •In 24 to 48 hours, epithelial cells move from the wound edges along the cut margins of the dermis fuse in the midline beneath the surface scab producing a continuous but thin epithelial layer that closes the wound. •By day 3, neutrophils replaced by macrophages. - Granulation tissue invades the incision space. - Collagen fibers present in the margins of the incision, at first : vertically oriented and do not bridge the incision. - Epithelial cell proliferation thickens the epidermal layer.

By day 5, the incisional space is filled with granulation tissue. Collagen fibrils : more abundant and begin to bridge the incision. The epidermis normal thickness, surface keratinization. During the second week : accumulation of collagen, proliferation of fibroblasts, leukocytic infiltrate, edema, increased vascularity ↓ blanching, accumulation of collagen ↑ within the incisional scar, regression of vascular channels. By the end of the first month, the scar is made up of a cellular connective tissue , inflammatory infiltrate (-), covered by intact epidermis, the dermal appendages are permanently lost. Tensile strength of the wound increases thereafter, but it may take months for the wounded area to obtain its maximal strength.

HEALING BY SECOND INTENTION ( secondary union ) WOUNDS WITH SEPARATED EDGES

* In surface wounds that create large defects * Regeneration of parenchymal cells cannot completely restore the original architecture abundant granulation tissue

Figure 3-21 Steps in wound healing by first intention (left) and second intention (right). Note large amounts of granulation tissue and wound contraction in healing by

second intention.

WOUND STRENGTHAt the end of the first week, wound strength ±10% increases rapidly over the next 4 weeks. This rate of increase then slows at ± the third month after the original incision reaches a plateau at about 70% to 80% of the tensile strength persist for life.

LOCAL AND SYSTEMIC FACTORS THAT INFLUENCE WOUND HEALING Systemic factors :Nutrition : Protein deficiency, vit C deficiency inhibit collagen synthesisMetabolic status : Diabetes mellitus (microangiopathy)Circulatory status : arteriosclerosis / venous abnormalities (e.g. varicose veins) Inadequate blood supplyHormones : glucocorticoids inhibit collagen synthesis.

Local factors :Infection : persistent tissue injury and inflammation. Mechanical factors : early motion of wounds delay healing, by compressing blood vessels and separating the edges of the wound. Foreign bodies : fragments of steel, glass, boneLocation : wounds in richly vascularized areas e.g.faceheal faster than those in poorly vascularized ones e.g. foot. Size : small incisional injuries heal faster and < scar formation than large excisional woundsType of wound : wounds caused by blunt trauma heal slower

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