Inflammation and Healing PowerPoint Presentation

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Inflammation Outcomes: Healing, Sepsis

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Summary of acute inflammation Stimulated by physical injury, infection, foreign body Resident macrophages and/or damaged endothelium, mast cells—IL-1, TNF, endothelin, histamine Vascular response: vasodilation, endothelial contraction, exudation of plasma Neutrophils: marginate (selectin-glycoprotein), adhere (integrin-CAM), extravasate (CD31), migrate (IL-8, chemotactic stimuli) Phagocytosis: recognition, engulfment, killing Phagocytosis receptors bind mannose, oxidized lipids, lipopolysaccharides, lipoteichoic acids, opsonins Killing is O2-dependent (respiratory burst, NADPH oxidase generated H2O2; myeloperoxidase generated HOCl; iNOS generated NO) or independent (lysozyme, lactoferrin, defensins) Responding leukocytes cause pain and loss-of-function via prostaglandins, enzymes Complete resolution; fibrosis, organization or scarring; abcess formation; progression to chronic inflammation

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Outcomes of Acute Inflammation Resolution of tissue structure and function with elimination of stimulus Tissue destruction and persistent inflammation Abscess pus-filled cavity (neutrophils, monocytes and liquefied cellular debris) walled off by fibrous tissue and inaccessible to circulation tissue destruction caused by lysosomal and other degradative enzymes Ulcer loss of epithelial surface acute inflammation in epithelial surfaces Fistula abnormal communication between organs or an organ and a surface Scar Causes distortion of structure and sometimes altered function Chronic inflammation Marked by replacement of neutrophils and monocytes with lymphocytes, plasma cells and macrophages Accompanied by proliferation of fibroblasts and new vessels with scarring

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Causes of chronic inflammation Persistent infections Organisms usually of low toxicity that invoke delayed hypersensitivity reaction M. tuberculosis and T. pallidum causes granulomatous reaction Prolonged exposure to potentially toxic agents Exogenous agents include silica which causes silicosis Endogenous causes include atherosclerosis caused by toxic plasma lipid components Autoimmunity Auto-antigens provoke self-perpetuating immune responses that cause chronic inflammatory diseases like RA, MS Responses against common environmental substances cause chronic allergic diseases, such as bronchial asthma

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Granulomatous inflammation Focus of chronic inflammation encountered in a limited number of conditions Cellular attempt to contain a foreign body or an offending agent that is difficult to eradicate (i.e. Tb) Microscopic aggregation of macrophages that are transformed into epithelioid cells, surrounded by a collar of lymphocytes and occasionally plasma cells Epithelioid cells have a pale pink granular cytoplasm with indistinct cell boundaries, often merging as giant cells Foreign body epitheloids have dispersed nuclei Infectious body epitheloids have marginal or horse-shoe nuclei Enlarged granuloma with central necrosis is an abcess Enlarged granuloma on a surface is an ulcer

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Patterns of Inflammation Serous Inflammation Marked by outpouring of thin fluid From blood serum, e.g. burn blisters Effusion from mesothelial cells lining the pleural, peritoneal and pericardial cavity Fibrinous Inflammation A feature of pericardial and peritoneal inflammation Vascular permeability allows larger molecules like fibrin to pass or procoagulant stimulus exists in the interstitium (e.g. cancer cells) Suppurative Inflammation Characterized by production of large amount of pus composed of neutrophils, necrotic cells and edema fluid Involves pyogenic bacteria e.g. Streptococci and Staphylococcus aureus Abscesses are focal localized collections of purulent inflammatory tissue caused by suppuration. Ulcers Local defect or excavation of the surface of an organ or tissue by sloughing of inflammatory necrotic tissue Acute stage - intense polymorphonuclear infiltration and vascular dilation in margin Chronic stage - margin and base develop fibroblastic proliferation, scarring and accumulation of lymphocytes, plasma cells and macrophages

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Systemic inflammatory response Acute Phase Response Fever Acute-phase protein secretion from liver Leukocytosis Tachycardia, increased blood pressure Shivering, chills Anorexia, somnolence, malaise Septic shock

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Acute Phase Proteins Secretion of Acute Phase proteins by the liver C-reactive Protein (CRP) Serum Amyloid A (SAA) Serum Amyloid P (SAP) Complement Fibrinogen Prothrombin Ferritin Ceruloplasmin α1-antitrypsin α2-macroglobulin Acute phase proteins bind: Microbial constituents, acting as opsonins to fix complement Chromatin, aiding early clearing of necrotic cells

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Autonomic redirection of blood flow from cutaneous to vascular bed increased pulse and blood pressure decreased sweating Behavioral Rigors (Shivering) Chills Anorexia Somnolence Malaise Autonomic and Behavioral Responses

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Sepsis Systemic Inflammatory Response Syndrome involves two or more of the following temperature >38.3ºC or <36ºC heart rate >90 beats/min; <32 mm Hg respiratory rate >20 breaths/min, PaCO2 or need for mechanical ventilation WBC count >12,000/uL or <4,000/uL or >10% immature forms (bands) Sepsis is defined as SIRS associated with suspected or confirmed infection--positive blood cultures are not necessary Severe sepsis is sepsis complicated by a predefined organ dysfunction Septic shock is cardiovascular collapse (hypotension) related to severe sepsis despite adequate fluid resuscitation

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Septic stimuli Gram-negative bacteria LPS, endotoxin Binds to LPS binding protein (LBP) Binds to CD14 opsonin receptor TLR-4 binds LPS and LPS-LBP Stimulates release of TNF, IL-1, IL-6 Gram-positive bacteria Exotoxins, superantigens Bind Vb regions of TCRs and/or to MHC-II TLR-2 binds cell wall components Stimulates release of IFN-g, TNF, IL-1, IL-6

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Progression of sepsis Cytokine release and amplification Vasular response and neutrophil migration Coagulation cascade Short arm, extrinsic pathway, activated by expression of Tissue Factor VIIa Xa thrombin fibrin high plasma levels of plasminogen-activator inhibitor type-1 (PAI-1) suppress plasmin and fibrinolysis disseminated intravascular coagulation in 30-50% cases Counter-inflammatory response Apoptosis of Th and B-cells Systemic acute phase response increased cortisol production and release of catecholamines upregulation of adhesion molecules release of prostanoids and platelet-activating factor (PAF) Organ failure

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Multiple organ failure Neutrophils damage tissue directly by releasing lysosomal enzymes and superoxide-derived free radicals TNF-α induces nitric oxide synthase nitric oxide causes further vascular instability contributes to direct myocardial depression Widespread vasodilation Decreased production of vasopressin (ADH) and glucocorticoids Circulatory collapse and tissue hypoxia

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Findings of shock at autopsy Congestion of lung may also have fibrinous casts lining alveolar spaces Petechial or ecchymotic hemorrhages on serosal and endothelial surfaces Necrosis proximal tubular epithelium in kidneys entrilobular hepatocytes

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Restoration of Structure and Function Occurs if connective tissue structure relatively intact Surviving parenchymal cells must have the capacity to regenerate Labile Cells Actively divide throughout life cells of the epidermis and gastrointestinal mucosa cells lining surface of the genitourinary tract hematopoietic cells of the bone marrow Stable Cells Undergo few divisions normally, but can be activated from G0 cells when needed hepatocytes renal tubular cells parenchymal cells of glands mesenchymal cells (smooth muscle, cartilage, connective tissue, endothelium, osteoblasts)

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Regeneration Proliferation of cells and tissues to replace lost structures Whole organs and complex tissues rarely regenerate after injury Compensatory growth rather than true regeneration Liver hypoplasia and kidney hypertrophy Continuously renewing tissues regenerate after injury if tissue stem cells are not destroyed

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Stem Cells Characterized by self-renewal properties and capacity to generate differentiated cell lineages obligatory asymmetric replication one daughter cell retains its self-renewing capacity the other enters a differentiation pathway stochastic differentiation stem cell divisions generate either two self-renewing stem cells or two cells that differentiate Stimulation for either outcome is conjecture—seemingly random embryonic stem cells (ES cells) are pluripotent adult (somatic) stem cells are restricted by niche skin, gut lining, cornea, hematopoietic tissue

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ES cells and KO/transgenic mice KO mice have specific gene deletion or inactivation Transform cultured ES cells Transformants injected into blastocysts Blastocyst transplanted to surrogate dam Mouse develops in utero Transgenic mice have specific human gene insertion or replacement Transformed ES cells injected into blastocysts Continued development in surrogate dam

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Somatic cell cloning Reproductive Transfer of adult nucleus into enucleated oocyte restores pluripotency Transfer of resulting embryo to surrogate dam Production of cloned individual Therapeutic Transfer of adult nucleus into enucleated oocyte restores pluripotency Induced to differentiate into various cell types in vitro Injected into damaged organ

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Induced Pluripotent Stem Cells Mouse ES cell pluripotency depends on the expression of Oct3/4, Sox2, c-myc, Klf4, Nanog Human fibroblasts from adults and newborns have been reprogrammed Oct3/4, Sox2, c-myc and Kfl4 Oct3/4, Sox2, Nanog, and Lin28 Generated cells from endodermal, mesodermal, and ectodermal origin c-myc and Kfl4 are oncogenes

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Stem Cells in Homeostasis and Healing Bone marrow Hematopoietic Stem Cells generate all of the blood cell lineages Marrow Stromal Cells generate precursors of tissue to which migrated Liver Oval cells are bipotential progenitors of hepatocytes and biliary cells Brain Neural precursor cells generate neurons, astrocytes, and oligodendrocytes in the subventricular zone and the dentate gyrus of the hippocampus Skin Hair follicle bulge, interfollicular areas of the surface epidermis, and sebaceous glands Intestinal epithelium crypts are monoclonal structures derived from single stem cells villus contains cells from multiple crypts Skeletal and cardiac muscle satellite cells beneath the myocyte basal lamina generate differentiated myocytes after injury Cornea limbal stem cells maintain corneal transparency

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Proliferative capacity of tissues Labile tissues Continuously dividing tissues containing stem cells Stable tissues Parenchymal cells of solid organs in G0 Endothelial cells, fibroblasts, smooth muscle Limited regeneration after wounding Permanent tissues Absolutely nonproliferative Cardiac muscle, neurons

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Growth factors Polypeptides that promote survival and proliferation by signal transduction Increase in cell size true growth factors Increase in cell number mitogens Protection from apoptosis survival factors

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Signaling mechanisms Receptors with intrinsic tyrosine kinase activity Dimeric transmembrane molecules Ligand binding induces stable dimerization and phosphorylation 7tm GPCRs Seven transmembrane proteins Ligand binding induces association with GTP-binding protein, which swaps GDP for GTP Gi or Gs protein inactivates or stimulates another effector Gs activates membrane adenylyl cyclase; GTPGDP cAMP activates PKA, etc. Receptors without intrinsic enzymatic activity Monomeric transmembrane molecules Ligand binding stimulates interaction with JAKs

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Growth Factor-mediated Proliferation Platelet Derived Growth Factor (PDGF) promotes the chemotactic migration of fibroblasts and smooth muscles chemotactic for monocytes competence factor that promotes the proliferative response of fibroblasts and smooth muscles upon concurrent stimulation with progression factors Epidermal Growth Factor (EGF) promotes growth for fibroblasts, endothelial and epithelial cells is a progession factor - promotes cell-cycle progression. Fibroblast Growth Factor (FGF) promote synthesis of fibronectin and other extracellular matrix proteins chemotactic for fibroblast and endothelial cells promotes angiogenesis links extracellular matrix components (collagen, proteoglycans) and macromulocules (fibrin, heparin) to cell-surface integrins. Transforming Growth Factors (TGFs) TGF-α - similar to EGF TGF-β - mitosis inhibitor that aids in modulating the repair process. May be responsible for hypertrophy by preventing cell division. Chemotactic for macropahges and fibroblasts Macrophage-derived cytokines (IL-1 and TNF) promote proliferation of fibroblasts, smooth muscle and endothelial cells

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Repair Process Removal of Debris begins early and initiated by liquefaction and removal of dead cells and other debris Formation of Granulation Tissues connective tissue consisting of capillaries and fibroblasts that fills the tissue defect created by removal of debris Scarring fibroblasts produce collagen until granulation tissue becomes less vascular and less cellular progessive contraction of the wound occurs, resulting in deformity of original structure

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Factors that Impede Repair Retention of debris or foreign body Impaired circulation Persistent infection Metabolic disorders diabetes Dietary deficiency ascorbic acid protein

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Healing and granulation Fibroplasia is a response to Damaged connective tissue Parenchymal damage exceeds regenerative capacity Hyperplasia of connective tissue Neovascularization Granulation coordinated proliferation of fibroblasts with a rich bed of capillaries intensely hyperemic with a roughened or granular, glistening surface healthy granulation tissue resists secondary infections

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Healing by First Intention Clean, surgical incision or other clean narrow cut Focal disruption of epithelial basement membrane with little cell damage Regeneration dominates fibrosis Scabbing with fibrin-clotted blood Neutrophils migrate to edges Epidermis becomes mitotic and deposits ECM Macrophages replace neutrophils Vascularization and collagen deposition fills gap Contraction of collagen minimizes epidermal regeneration

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Healing by Second Intention Larger area of tissue injury such as abcess, ulcer, infarction that destroys ECM Large clot or scab with fibrin and fibronectin fills gap Larger volume of necrotic debris must be removed by more neutrophils and macrophages Opportunity for collateral damage by phagocytes Scar tissue formed from vascular cells, fibroblasts, and myofibroblasts Contraction of myofibroblasts distorts tissue More prone to infection

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Keloid—excessive cutaneous fibrosis

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Granulation at tracheotomy