Cell Injury PDF

Cell Injury: The cell tends to preserve its intracellular milieu within a narrow range of physiologic activities, as the cell encounters physiologic stresses or pathologic stimuli, it can undergo adaptation preserving viability. If the cells adaptive capability is exceeded, cell injury develops. The...

Cell Injury: The cell tends to preserve its intracellular milieu within a narrow range of physiologic activities, as the cell encounters physiologic stresses or pathologic stimuli, it can undergo adaptation preserving viability. If the cells adaptive capability is exceeded, cell injury develops. There are two principal patterns of cell death: 1. Necrosis: Occurs after exposure to noxious conditions, and characterized by cell swelling, protein denaturation and organellar breakdown. 2. Apoptosis: Is a programmed cell death occurring in the normal or physiologic conditions. Causes of Cell Injury: 1. Hypoxia: Impinges on ærobic oxidative respiration. It should be distinguished from ischæmia, which also results in hypoxic cell injury. It occurs in inadequate oxygenation of the blood. 2. Physical agents: Including trauma, extremes of temperatures, radiation, electric shock, and sudden changes in atmospheric pressure. 3. Chemicals and drugs: Any chemical agent may cause cell injury by altering membrane permeability, osmotic homeostasis or the integrity of the enzyme cofactor. 4. Microbiologic agents: ranging from viruses to tapeworms. 5. Immunologic reactions: The immune system of the body may cause cell injury, e.g. anaphylactic reaction. 6. Genetic defects: e.g. Down's syndrome, sickle cell anæmia. 7. Nutritional imbalances: Protein-calorie insufficiency, vitamin deficiencies. Diets rich in animal fat has been strongly implicated in the pathogenesis of atherosclerosis. 8. Aging:. Mechanisms of Cell Injury: Cell response to injurious stimuli depends on the type of injury, its duration and its severity. The consequences of an injurious stimulus is also dependent on the type of cell injured, its current status of health and its adaptability. Four intracellular systems are vulnerable to injury: 1. Cell membrane integrity, with changing cell ionic and osmotic homeostasis. 2. Ærobic respiration. 3. Protein synthesis. 4. The genetic apparatus. Cytosolic free calcium is maintained at extremely low levels by ATP- dependent calcium transporters. Mitochondria and endoplasmic reticulum contain a higher concentration of calcium. Ischæmia or toxins allow an influx of calcium from the extracellular space with a release of mitochondrial calcium, resulting in activation of various enzymes including phospholipases (degrade membranes), proteases (catabolizing structural proteins), ATPases (resulting in ATP depletion) and endonucleases (fragmenting the DNA). The generation of oxygen free radicals are important mediators of cell death. Ischæmic And Hypoxic Injury: Reversible injury: The first effect of hypoxia is on the ærobic respiration (oxidative phosphorylation by mitochondria), consequently resulting in reduced intracellular ATP which in turn results in influx of extracellular calcium and reduction of the plasma membrane sodium pump with accumulation of intracellular sodium and diffusion of potassium out of the cell, with consequent gain in isosmotic water producing acute cellular swelling. This is associated with accumulation of other metabolites like inorganic phosphates, lactic acid and purine nucleotides. Decreased ATP and AMP results in stimulation of phosphofructokinase and an increased rate of anærobic glycolysis. As a result, glycogen is rapidly depleted, with accumulation of lactic acid and inorganic phosphates and reduced intracellular pH, seen under the light microscope as cytoplasmic eosinophilia. Detachment of ribosomes from RER occurs with consequent reduction of protein synthesis. If hypoxia continues, the cytoskeleton disappears resulting in loss of ultrastructural features like microvilli and formation of cell surface blebs. Irreversible Injury: Is seen as 1. Severe vacuolization of mitochondria and accumulation of calcium particles. 2. Extensive damage of plasma membrane. 3. Swelling of lysosomes. 3. Reperfusion of oxygen results in calcium mediated injury. 4. Continued loss of proteins, coenzymes and RNA from the hyperpermeable membranes, with leak of lysosomal enzymes into the cytoplasm, where they are activated by the reduced pH starting degrading the cytoplasmic components. 5. Dead cells may be replaced by whorled masses of phospholipids (myelin figures). Mechanisms of Irreversible Injury: 1. Progressive loss of membrane phospholipids. 2. Cytoskeletal abnormalities: Activation of proteases and increased calcium may result in detachment of the cell membrane.  3. Toxic oxygen radicals: generated after reperfusion of the ischæmic area released by influxed neutrophils. 4. Lipid breakdown products: have detergent effects. Free Radical Mediation of Cell Injury: Are implicated in: 1. Chemical mediated injury. 2. Radiation mediated injury. 3. Oxygen toxicity. 4. Cellular aging. 5. Microbial killing. 6. Inflammatory damage. 7. Tumour killing. Free radicals are chemical species with a single unpaired electron in an outer orbital; they are extremely unstable and readily react with organic and inorganic chemicals. They may be generated within the cell by: 1. Absorption of radiant energy: e.g. hydrolysis of water into OH. and H.. 2. The reduction-oxidation (redox) reactions, occur during normal physiologic conditions. O2 is reduced by the addition of four electrons to generate water, with the generation of small amounts of toxic intermediate species including superoxide radicals (O2.-), hydrogen peroxide (H2O2) and OH.-. Some intracellular enzymes like xanthine oxidase generate superoxide radicals. Copper and iron accept or donate electrons with free radical formation. H2O2 + Fe+2 Fe+3 + OH- + OH. 3. Enzymatic catabolism of oxygenous chemicals e.g. CCl4 CCL3. in the liver with generation of an autocatalytic membrane phospholipids peroxidation. Oxygen free radicals react with three main cell components: 1. Lipid peroxidation of plasma membranes. 2. Deoxyribonucleic acid (DNA): react with thymine. 3. Cross linking of proteins. Chemical Injury: Two main mechanisms of chemical injury is identified: 1. By combining with a critical molecular component or cellular organelle: e.g. mercury binds to sulfhydryl groups of the cell membrane and other proteins causing inhibition of ATP dependent transport. 2. Other chemicals are not toxic by themselves and must be converted to reactive toxic metabolites, usually happens by the P-450 oxidases in the SER. Carbon tetrachloride (CCl4) is converted to the toxic free radical  CCl3. in the liver this will cause autocatalytic membrane peroxidation with rapid breakdown of endoplasmic reticulum in less than 30 min. Within 2 hours, swelling of SER and dissociation of ribosomes from the RER will occur, with resultant reduced lipid export from hepatocytes and fatty liver change. Patterns of Acute Cell Injury: Reversible Cell Injury: Light microscopic changes: 1. Cell swelling: Is difficult to appreciate on light microscope, but small clear vacuoles may be seen within the cytoplasm (hydropic changes or vacuolar degeneration). 2. Cytoplasmic eosinophilia due to cytoplasmic acidosis and loss of ribosomes. 3. Fatty change; seen in hypoxic and chemical injury, in the liver and myocardial cells. Ultrastructural changes (EM): 1. Plasma membrane: Blebing, distortion of microvilli and loosening of intercellular attachments. 2. Mitochondrial changes: Swelling and appearance of phospholipids rich amorphous densities. 3. Dilatation of endoplasmic reticulum, detachment of ribosomes and dissociation of polysomes. 4. Nuclear alterations: Disaggregation of granular elements. Necrosis: Refers to a sequence of morphologic changes that follow cell death in living tissue, and is the gross and the histologic terms of cell death occurring in the setting of irreversible exogenous injury. The morphologic appearances of necrosis is the result of two processes: enzymatic digestion of the cell and denaturation of proteins. The hydrolytic enzymes may be derived from the dead cells themselves (autolysis) or from lysosomes of the infiltrating leukocytes (heterolysis). - Cytoplasmic changes: Eosinophilia and glassy appearance due to loss of glycogen, cytoplasmic vacuolation and calcification. - Nuclear changes: 1. Karyolysis: due to digestion of DNA. 2. Pyknosis: nuclear shrinkage and increased basophilia, seen mainly in apoptosis. 3. Karyorrhexis: The pyknotic nucleus fragments. Types of Necrosis: 1. Coagulative necrosis: Preservation of the structural outlines of the coagulated cell or tissue for days. The injury and acidosis denatures the enzymes that block cellular hydrolysis. The prime example is myocardial infarction appearing as acidophilic coagulated anucleated cells. The necrotic cells are removed by fragmentation and phagocytosis by leukocytes. Coagulative necrosis is characteristic of hypoxic death in all tissues except in the brain. 2. Liquefactive necrosis: Caused by focal bacterial or fungal infection with accumulation of white cells. Hypoxic cell death in the CNS also results in liquefactive necrosis. 3. Gangrenous necrosis: is not a distinctive pattern of necrosis, but is still being used in surgical practice, referring to ischæmic coagulative necrosis with superimposed infection and liquifactive necrosis, called "wet gangrene". 4. Caseous necrosis: Seen in tuberculous infection, derived from the cheesy, white gross appearance of the central necrotic area. Microscopically, it is composed of structureless amorphous granular debris within granulomatous inflammation. 5. Fat necrosis: It describes focal areas of fat destruction following acute pancreatitis, resulting from release of activated pancreatic enzymes with resultant hydrolysis of triglyceride esters within fat cells of the peritoneal cavity. Apoptosis: Is responsible for the programmed cell death in physiologic and pathologic conditions, including: 1. Programmed cell death during embryogenesis. 2. Hormone dependent physiologic involution, such as the endometrium during the menstrual cycle. 3. Cell deletion in proliferating populations, such as intestinal crypt epithelium. 4. Deletion of autoreactive T cells in the thymus. Apoptosis usually involves single cells or clusters of cells appear on H&E stained sections as round masses with intensely eosinophilic cytoplasm. The nuclear chromatin is condensed aggregating peripherally under the nuclear membrane into well delimited masses of various shapes and sizes. The karyorrhexis occurs by the activation of endonucleases. The cell shrinks, form cytoplasmic buds and fragment into apoptotic bodies. Apoptosis does not elicit an inflammatory response. Apoptosis is initiated by: 1. Withdrawal of growth factors or hormones. 2. Engagement of specific receptors (e.g. FAS, and TNF). 3. Injury by radiation, toxins and free radicals. 4. Intrinsic protease activation (e.g. in embryogenesis). All these stimuli will lead to activation of intracellular proteases including calpain I and interleukin 1β converting enzyme (Ice), culminating in endonuclease activation, catabolism of cytoskeleton and formation of apoptotic bodies with identification by phagocytic cell receptors. Intracellular Accumulations: Normal cells may accumulate abnormal substances in various circumstances, either transiently or permanently, being harmful or injurious, and may locate in the cytoplasm or within the nucleus. It may be synthesized by the affected cell or produced elsewhere. Intracellular accumulation can be subdivided into three categories: 1. A normal endogenous substance produced at a normal or increased rate with an inadequate rate of metabolism. E.g. fatty change of the liver. 2. A normal or abnormal endogenous substance which can not be metabolized by genetic enzymatic defect, these diseases are called storage diseases. 3. An abnormal exogenous substance deposit because the cell has neither the enzymatic machinery nor the ability to transport it to other sites. Fatty Change (Steatosis): Is an abnormal accumulation of triglycerides within parenchymal cells. Fatty change is most often seen in the liver, and is reversible, but it may also occur in the heart, skeletal muscle, kidney and other organs. It may be caused by toxins, diabetes mellitus, protein malnutrition, obesity and anoxia. Excess acuumulation of triglycerides may result from defects at any step from fatty acid entry to synthesis of lipoproteins. Hepatotoxins (e.g. alcohol) alter mitochondrial and SER function, CCl4 and protein malnutrition decrease synthesis of apoproteins, anoxia inhibits fatty acid oxidation and starvation increases fatty acid mobilization from peripheral stores. When fatty change is mild, it may have no effect on cellular function, more severe changes may transiently impair cellular function. Grossly the liver enlarges and become progressively yellow. It is first seen by light microscope as small vacuoles in the cytoplasm around the nucleus, these vacuoles coalesce to create clear spaces displacing the nucleus to the periphery. Cholesterol And Cholesterol Esters: Macrophages in contact with lipid debris of necrotic cells may become stuffed with lipid because their phagocytic activities, appearing as foamy cells. In atherosclerosis, the smooth muscle cells and macrophages are filled with lipid vacuoles composed of cholesterol and cholesterol esters. Xanthomas are accumulation of fat within macrophages of subcutaneous connective tissues, appearing as white nodules. Proteins: Are less commonly seen, e.g. in glomerular diseases with proteinuria, accumulating in proximal convoluted tubules. Glycogen: Seen in cases of abnormal metabolism of glucose or glycogen, and appear under the light microscope as vacuoles. Pigments: Are colored substances either exogenous or endogenous. Melanin accumulate in basal cells of the epidermis resulting in freckles or in dermal macrophages. Hæmosiderin is a hæmoglobin-derived granular pigment, golden brown, accumulates in tissues when there is local or systemic excess iron. Pathologic Cacification: It is an abnormal accumulation of calcium salts, with smaller amounts of iron, magnesium and other minerals. When deposition occurs in dead or dying tissues it is called dystrophic calcification, despite normal serum levels of calcium and in the absence of calcium metabolic derangement. It is encountered in areas of necrosis anywhere, seen in atheromas of advanced atherosclerosis on areas of intimal injuries of large arteries. It is also seen in aging and in aortic valves. It appears as intracellular or extracellular basophilic deposits, sometimes heterotopic bone may be formed. Metastatic calcification: may occur in normal tissues whenever there is hypercalcæmia. Causes of hypercalcæmia include: 1. Primary endocrine dysfunction (e.g. hyperparathyroidism). 2. Tumours associated with increased bone catabolism (e.g. multiple myeloma, metastatic cancer and leukæmia). 3. Ingested exogenous substances resulting in vitamin D intoxication or milk alkali syndrome. 4. Sarcoidosis. 5. Advanced renal failure where the resulting phosphate retention leads to secondary hyperparathyroidism. Metastatic calcification may occur widely in tissues principally in the interstitial tissues, kidneys, lungs and gastric mucosa. They usually do not cause significant impairment of organ function, but in extensive nephrocalcinosis, some impairment may occur. Cellular Adaptations of Growth And Differentiation: Physiologic adaptations usually represent responses of cells to normal stimulations by hormones or endogenous chemicals (induction of breast growth and lactation). Pathologic adaptations often share the same underlying mechanisms, but they allow the cells to modulate their environment and hopefully escape injury. Atrophy: Is shrinkage in the size of the cell by loss of cell substance, it may involve the entire organ. Atrophic cells have diminished function but are not dead. Apoptotic death may also be induced by the same signals that cause atrophy. Causes: 1. Decreased work load. 2. Loss of innervation. 3. Diminished blood supply. 4. Inadequate nutrition. 5. Loss of endocrine stimulation. 6. Aging. Cells become smaller in size at which survival is possible with a new equilibrium between cell size and diminished blood supply, nutrition or trophic stimulation. Biochemically, there is decreased synthesis, increased catabolism or both. Hypertrophy: Is an increase in the size of cells by increased synthesis of the structural proteins and organelles with an increase in the size of the organ. It can be physiologic or pathologic, caused by increased functional demand or specific hormonal stimulation (e.g. hypertrophy of smooth muscles of the uterus during pregnancy). Hyperplasia: Is an increase in the number of cells in an organ or tissue. Hypertrophy and hyperplasia are closely related and often develop concurrently in tissues. Hyperplasia can be physiologic or pathologic. Physiologic hyperplasia is divided into: 1. Hormonal hyperplasia. 2. Compensatory hyperplasia, occurs when a portion of tissue is removed or diseased. Most cases of pathologic hyperplasia are due to excessive hormonal or growth factor stimulation. Metaplasia: Is a reversible change in which one adult cell type is replaced by another adult cell type, another cellular adaptation where cells sensitive to a particular stress are replaced by other cell types able to withstand the adverse environment. INFLAMMATON Prof. Dr. Rafal Al-Saigh MBChB, PhD, FIBMS Pathology Specialist Pathologist  Inflammation Host response to foreign invaders and necrotic tissue, but it is itself capable of causing tissue damage OR reaction of tissues to various injurious stimuli a protective response → remove the initial cause of cell injury, necrotic cells and tissues have harmful effects like anaphylactic shock, rheumatoid arthritis and atherosclerosis The main components of inflammation 1. Vascular reaction 2. Cellular response Both are activated by mediators derived from plasma proteins and various cells. The steps of the inflammatory response (1) recognition of the injurious agent, (2) recruitment of leukocytes, (3) removal of the agent, (4) regulation (control) of the response, (5) resolution (repair).  Features of Acute and Chronic Inflammation Feature Acute Chronic Onset Fast: minutes or hours Slow: days Cellular infiltrate Mainly neutrophils Monocytes/ macrophages and lymphocytes Tissue injury, fibrosis Usually mild and self-limited Often severe and progressive Local and systemic signs Prominent Less prominent; may be subtle Acute inflammation short duration (few minutes - few days) 1.Vascular changes leading to increased blood flow (hyperæmia). 2.Microvascular structural changes leading to leakage of plasma proteins (exudation). 3.Emigration of leukocytes (neutrophilic) towards the site of injury. The outcome of acute inflammation is either elimination of the noxious stimulus, followed by decline of the reaction and repair of the damaged tissue, or persistent injury resulting in chronic inflammation. ▪ heat (calor) ▪ redness (rubor) ▪ swelling (tumour) ▪ pain (dolor) ▪ loss of function (functio læsa)  Reaction of Acute Inflammation 1. Vasodilation is induced by chemical mediators such as histamine (described later) and is the cause of erythema and stasis of blood flow. 2. Increased vascular permeability is induced by histamine, kinins, and other mediators that produce gaps between endothelial cells; by direct or leukocyte- induced endothelial injury; and by increased passage of fluids through the endothelium. 3. This increased permeability allows plasma proteins and leukocytes to enter sites of infection or tissue damage; fluid leak through blood vessels results in edema. Leukocyte Recruitment to Sites of Inflammation Leukocytes are recruited from the blood into the extravascular tissue, where infectious pathogens or damaged tissues may be located, and are activated to perform their functions. Leukocyte recruitment is a multi-step process consisting of loose attachment to and rolling on endothelium (mediated by selectins); firm attachment to endothelium (mediated by integrins); and migration through interendothelial spaces. Various cytokines promote expression of selectins and integrin ligands on endothelium (TNF, IL-1), increase the avidity of integrins for their ligands (chemokines), and promote directional migration of leukocytes (also chemokines); many of these cytokines are produced by tissue macrophages and other cells responding to pathogens or damaged tissues. Neutrophils predominate in the early inflammatory infiltrate and are later replaced by macrophages. Leukocyte Effector Mechanisms Leukocytes can eliminate microbes and dead cells by phagocytosis, followed by their destruction in phagolysosomes. Destruction is caused by free radicals (ROS, NO) generated in activated leukocytes and lysosomal enzymes. Enzymes and ROS may be released into the extracellular environment. The mechanisms that function to eliminate microbes and dead cells (the physiologic role of inflammation) are also capable of damaging normal tissues (the pathologic consequences of inflammation). Major Cell-Derived Mediators of Inflammation Vasoactive amines—histamine, serotonin: Their main effects are vasodilation and increased vascular permeability. Arachidonic acid metabolites—prostaglandins and leukotrienes: Several forms exist and are involved in vascular reactions, leukocyte chemotaxis, and other reactions of inflammation; they are antagonized by lipoxins. Cytokines: These proteins, produced by many cell types, usually act at short range; they mediate multiple effects, mainly in leukocyte recruitment and migration; principal ones in acute inflammation are TNF, IL-1, IL-6, and chemokines. ROS: Roles include microbial killing and tissue injury. NO: Effects are vasodilation and microbial killing. Lysosomal enzymes: Roles include microbial killing and tissue injury. Plasma Protein–Derived Mediators of Inflammation Complement proteins: Activation of the complement system by microbes or antibodies leads to the generation of multiple breakdown products, which are responsible for leukocyte chemotaxis, opsonization and phagocytosis of microbes and other particles, and cell killing. Coagulation proteins: Activated factor XII triggers the clotting, kinin, and complement cascades and activates the fibrinolytic system. Kinins: Produced by proteolytic cleavage of precursors, this group mediates vascular reaction and pain. Sequence of Events in Acute Inflammation The vascular changes are characterized by increased blood flow secondary to arteriolar and capillary bed dilation (erythema and warmth). Increased vascular permeability, as a consequence of either widening of interendothelial cell junctions of the venules or direct endothelial cell injury, results in an exudate of protein-rich extravascular fluid (tissue edema). The leukocytes, initially predominantly neutrophils, adhere to the endothelium via adhesion molecules and then leave the microvasculature and migrate to the site of injury under the influence of chemotactic agents. Phagocytosis, killing, and degradation of the offending agent follow. Genetic or acquired defects in leukocyte functions give rise to recurrent infections. The outcome → removal of the exudate with restoration of normal tissue architecture (resolution); transition to chronic inflammation; or extensive destruction of the tissue resulting in scarring. Benificial Effects of Acute Inflammation 1. Dilution of toxins. 2. Exudation of protective antibodies. 3. Fibrin formation which delays bacterial spread. 4. Exudation of plasma mediators (complement, coagulation, fibrinolytic and kinin). 5. Exudation of nutrient materials. 6. Promotion of immunity. Outcomes of Acute Inflammation 1. Complete resolution to histologic and functional normality. 2. Fibrosis: Occurs in A. When inflammation in tissues that do not regenerate. B. After substantial tissue destruction. C. Extensive fibrinous exudates. 3. Abscess formation in pyogenic infection. 4. Progression to chronic inflammation Chronic inflammation longer duration (days or years) ❖ Infiltration by mononuclear cells (monocytes, lymphocytes & macrophages. ❖Tissue destruction. ❖Tissue repair. (vascular proliferation and fibrosis). Causes 1.Persistent infections like tuberculosis, syphilis. 2.Prolonged exposure to potentially toxic agents. 3.Autoimmune disorders. Features of Chronic Inflammation Prolonged host response to persistent stimulus Caused by microbes that resist elimination, immune responses against self and environmental antigens, and some toxic substances (e.g., silica); underlies many important diseases Characterized by persistent inflammation, tissue injury, attempted repair by scarring, and immune response Cellular infiltrate consisting of activated macrophages, lymphocytes, and plasma cells, often with prominent fibrosis. Mediated by cytokines produced by macrophages and lymphocytes (notably T lymphocytes), with a tendency to an amplified and prolonged inflammatory response owing to bidirectional interactions between these cells.  Cells Macrophages derived from monocytes → increasing in size, contents of lysosomes and more active metabolism. lymphocytes, plasma cells eosinophils Activation signals include IFN-γ secreted from T lymphocytes, Macrophages secrete: 1) Acid and neutral proteases. 2) Complement components. 3) Oxygen-free radicals and nitric oxide. 4) Cytokines (IL-1, TNF). Granulomatous Inflammation aggregation of activated macrophages as (epithelioid) appearance. 1.Bacterial infection: e.g. tuberculosis, leprosy, syphilis, cat scratch disease. 2.Parasitic: Bilharziasis. 3.Fungal: Histoplasmosis. 4.Inorganic metals: Silica, berylliosis. 5.Foreign body. Unknown: Sarcoidosis. Systemic Effects of Inflammation Fever: cytokines (TNF, IL-1) stimulate production of prostaglandins in hypothalamus Production of acute-phase proteins: C-reactive protein, stimulated by cytokines (IL-6, others) acting on liver cells Leukocytosis: cytokines (CSFs) stimulate production of leukocytes from precursors in the bone marrow. In severe infections, septic shock: fall in blood pressure, disseminated intravascular coagulation, metabolic abnormalities; induced by high levels of TNF Cell Proliferation, the Cell Cycle, and Stem Cells Regeneration of tissues is driven by proliferation of uninjured (residual) cells and replacement from stem cells. Cell proliferation occurs when quiescent cells enter the cell cycle. The cell cycle is tightly regulated by stimulators and inhibitors and contains intrinsic checkpoint controls to prevent replication of abnormal cells. Tissues are divided into labile, stable, and permanent, according to the proliferative capacity of their cells. Continuously dividing tissues (labile tissues) contain mature cells that are capable of dividing and stem cells that differentiate to replenish lost cells. Stem cells from embryos (ES cells) are pluripotent; adult tissues, particularly the bone marrow, contain adult stem cells capable of generating multiple cell lineages. Induced pluripotent stem cells (iPS cells) are derived by introducing into mature cells genes that are characteristic of ES cells. iPS cells acquire many characteristics of stem cells Extracellular Matrix and Tissue Repair The ECM consists of the interstitial matrix between cells, made up of collagens and several glycoproteins, and basement membranes underlying epithelia and surrounding vessels, made up of nonfibrillar collagen and laminin. The ECM serves several important functions: It provides mechanical support to tissues; this is the role of collagens and elastin. It acts as a substrate for cell growth and the formation of tissue microenvironments. It regulates cell proliferation and differentiation; proteoglycans bind growth factors and display them at high concentration, and fibronectin and laminin stimulate cells through cellular integrin receptors. An intact ECM is required for tissue regeneration, and if the ECM is damaged, repair can be accomplished only by scar formation.  Morphologic Patterns of Acute And Chronic Inflammation 1.Serous Inflammation: Effusions of watery, protein-poor fluid derived from serum or mesothelial cells, lining peritoneal, pleural or pericardial cavities. 2.Fibrinous Inflammation: Occurs in severe injuries, appearing as a meshwork of threads or as an amorphous coagulum. Fibrinous exudates is either removed by macrophages or fibrinolysis or replaced by fibrosis (organization). 3.Suppurative (Purulent) Inflammation: Manifested by the presence of a large amount of purulent exudates (pus), consisting of neutrophils, necrotic cells and fluid, caused by bacteria (pyogenic) like staphylococci. Abscess is a focal collection of pus caused by deep seeding of MO in tissues or by secondary infection of necrotic areas, having large central necrotic region rimmed by preserved neutrophils and surrounded by dilated blood vessels and proliferated fibroblasts. 4.Ulceration: This refers when an epithelial surface becomes eroded by necrosis with associated subepithelial acute and chronic inflammation. Toxic or traumatic, e.g. peptic ulcer. Vascular e.g. foot ulcers of diabetes. Cutaneous Wound Healing and Pathologic Aspects of Repair Cutaneous wounds can heal by primary union (first intention) or secondary union (second intention); secondary healing involves more extensive scarring and wound contraction. Wound healing can be altered by many conditions, particularly infection and diabetes; the type, volume, and location of the injury are also important factors in healing. Excessive production of ECM can cause keloids in the skin. Persistent stimulation of collagen synthesis in chronic inflammatory diseases leads to fibrosis of the tissue.  Neoplasia (Benign and malignant tumour)  Neoplasia Is a new growth or an abnormal outgrowing mass of tissue and uncoordinating with the normal tissue, which may persist after the cessation of the stimuli. General Charachteristics of Neoplasms 1. Unresponsive to the normal growth factors controlling cell division (continue to replicate ). 2. Competing with the normal cells and tissues for their metabolic needs. 3. Have degree of autonomy steadily increasing in size regardless of their local environment and the nutritional status of the host. 4. Require endocrine stimulatory signals for their growth. Epidemiology of Cancer The incidence of cancer varies with age, race, geographic factors, and genetic backgrounds. Cancers are most common at the two extremes of age. The geographic variation results mostly from different environmental exposures. Most cancers are sporadic, but some are familial. Predisposition to hereditary cancers may be autosomal dominant or autosomal recessive. The former usually are linked to inheritance of a germ line mutation of cancer suppressor genes, whereas the latter typically are associated with inherited defects in DNA repair. Familial cancers tend to be bilateral and arise earlier in life than their sporadic counterparts. Some acquired diseases, known as preneoplastic disorders, are known to be associated with an increased risk for development of cancer. Genetic Lesions in Cancer Tumor cells may acquire mutations through several means, including point mutations, and nonrandom chromosomal abnormalities that contribute to malignancy; these include balanced translocations, deletions, and cytogenetic manifestations of gene amplification. Balanced translocations contribute to carcinogenesis by overexpression of oncogenes or generation of novel fusion proteins with altered signaling capacity. Deletions frequently affect tumor suppressor genes, whereas gene amplification increases the expression of oncogenes. Overexpression of miRNAs can contribute to carcinogenesis by reducing the expression of tumor suppressors, while deletion or loss of expression of miRNAs can lead to overexpression of proto-oncogenes. Tumor suppressor genes and DNA repair genes also may be silenced by epigenetic changes, which involve reversible, heritable changes in gene expression that occur not by mutation but by methylation of the promoter. Insensitivity to Growth Inhibitory Signals Tumor suppressor genes encode proteins that inhibit cellular proliferation by regulating the cell cycle. Unlike oncogenes, both copies of the gene must be dysfunctional for tumor development to occur. In cases with familial predisposition for development of tumors, affected persons inherit one defective (nonfunctional) copy of a tumor suppressor gene and lose the second one through somatic mutation. In sporadic cases, both copies are lost through somatic mutations. Neoplasm is “a tumour OR swelling”. Tumours can be subdivided into 1. Benign considered innocent: remaining localized, not spreading to other sites, may produce local effects. 2. Malignant tumours, cancers, which can invade and destroy adjacent structures and spread to distant sites (metastasize). Benign tumours Resemble their normal cells of origin morphologically and functionally Well differentiated cells Mitoses are very scanty in number and are of normal configuration Grow slowly, localized, not infilterate. Acquired preneoplastic disorders 1. Persistent regenerative cell replication, e.g. long standing skin ulcer, and hepatic cirrhosis. 2. Hyperplastic and dysplastic proliferations, e.g. endometrial hyperplasia and dysplastic changes of the bronchus. 3. Chronic atrophic gastritis. 4. Chronic ulcerative colitis. 5. Leukoplakia of the oral cavity. 6. Villous adenomas of the colon.  Nomenclature of Benign tumours - Cell type from tumour arises + suffix “-oma” , e.g. fibroma, chondroma, leiomyoma. - according to cells of origin, e.g.: Adenoma: glandular pattern. Papilloma: epithelial surfaces, producing microscopic or macroscopic finger-like structure. Polyp: Is a mass projects above the mucosal surface to form a macroscopically visible structure. Cystadenomas: Hollow cystic masses (in the ovary). Fibroadenoma of the breast and benign mixed tumour of salivary glands (pleomorphic adenoma): Mixed type Malignant tumours 1. Pleomorphism: variation in size and shape. 2. Hyperchromasia: Increased nuclear pigmentation. 3. High nuclear/ cytoplasmic (N/C) ratio. 4. Giant cells may be formed containing several nuclei. 5. Nuclear pleomorphism, with coarse and clumped chromatin. 6. Numerous mitoses with atypical forms. 7. Loss of polarity: cells fail to form a recognizable pattern of orientation. 8. Dysplasia: loss in the uniformity of individual cells and their architectural orientation (partial or the entire thickness of the epithelium (carcinoma in situ)). - Rapidly growing tumour with progressive infiltration, invasion, destruction and penetration of the surrounding tissue. - Metastasis: secondary implants discontinuous with the primary tumour. Pathways: 1. Seeding within body cavities. 2. Lymphatic spread typical for carcinomas. 3. Hæmatogenous spread for sarcomas, but carcinomas also metastasize by this route. The liver and lungs →most secondary sites. Mechanisms of Local And Distant Spread 1. Invasion of ECM: reach to the basement membrane, then invade the interstitial connective tissue and then penetrate the blood vessels’ basement membrane; As four stages: A. Detachment of tumour cells from each other by loss of surface E-cadherins. B. Attachment of tumour cells to matrix components. C. Degradation of ECM by production and induction of fibroblasts to produce proteases, especially metalloproteinases including gelatinases, collagenases and stromelysins. D. Migration of tumour cells by cell-derived cytokines, cleavage products of matrix components and some growth factors. 2. Vascular dissemination: - Intravasation: by degradation of blood vessels’ basement membrane, forming tumour emboli by aggregation with leukocytes and platelets, hiding tumour cells from the immune system. - Extravasation of free tumour cells involves adhesion to the endothelium followed by transgression through the basement membrane by a similar mechanism to intravasation. Development of Sustained Angiogenesis Vascularization of tumors is essential for their growth and is controlled by the balance between angiogenic and antiangiogenic factors that are produced by tumor and stromal cells. Hypoxia triggers angiogenesis through the actions of HIF-1α on the transcription of the pro-angiogenic factor VEGF. Many factors regulate angiogenesis; for example, p53 induces synthesis of the angiogenesis inhibitor Ability to invade tissues, a hallmark of malignancy, occurs in four steps: loosening of cell–cell contacts, degradation of ECM, attachment to novel ECM components, and migration of tumor cells. Cell–cell contacts are lost by the inactivation of E-adherin through a variety of pathways. Basement membrane and interstitial matrix degradation is mediated by proteolytic enzymes secreted by tumor cells and stromal cells, such as MMPs Proteolytic enzymes also release growth factors sequestered in the ECM and generate chemotactic and angiogenic fragments from cleavage of ECM glycoproteins. The metastatic site of many tumors can be predicted by the location of the primary tumor. Many tumors arrest in the first capillary bed they encounter (lung and liver, most commonly). Some tumors show organ tropism, probably due to activation of adhesion or chemokine receptors whose ligands are expressed by endothelial cells at the metastatic site. Nomenclature of Malignant tumours - Mesenchymal origin→ sarcomas e.g. fibrosarcoma, chondrosarcoma, leiomyosarcoma. - Epithelial origin (endo, meso and ectoderm) →carcinomas, e.g. squamous cell carcinoma, adenocarcinoma. - Two components (mesenchymal and epithelial) e.g. Teratomas → divergent differentiation into all embryonic layers, commonly seen in the ovaries and testicles, being benign or malignant. Characteristics of Benign and Malignant Tumors Benign and malignant tumors can be distinguished from one another based on the degree of differentiation, rate of growth, local invasiveness, and distant spread. Benign tumors resemble the tissue of origin and are well differentiated; malignant tumors are poorly or completely undifferentiated (anaplastic). Benign tumors are slow-growing, whereas malignant tumors generally grow faster. Benign tumors are well circumscribed and have a capsule; malignant tumors are poorly circumscribed and invade the surrounding normal tissues. Benign tumors remain localized to the site of origin, whereas malignant tumors are locally invasive and metastasize to distant sites. Laboratory Diagnosis of Cancer Several sampling approaches exist for the diagnosis of tumors, including excision, biopsy, fine-needle aspiration, and cytologic smears. Immunohistochemistry and flow cytometry studies help in the diagnosis and classification of tumors, because distinct protein expression patterns define different entities. Proteins released by tumors into the serum (tumor markers), such as PSA, can be used to screen populations for cancer and to monitor for recurrence after treatment. Molecular analyses are used to determine diagnosis, prognosis, the detection of minimal residual disease, and the diagnosis of hereditary predisposition to cancer. Molecular profiling of tumors by cDNA arrays and sequencing can determine expression of large segments of the genome and catalog all of the mutations in the tumor genome and thus may be useful in molecular stratification of otherwise identical tumors or those of distinct histogenesis that share a mutation for the purpose of treatment and prognostication. Tumour antigens (tumour markers): 1. Tumour-specific antigens: unique antigens for tumours. - melanoma associated antigen-1 (MAGE-1) - some pancreatic and breast carcinoma (CA-125, CA-119). 2. Tumour-Associated Antigens: shared by normal untransformed cells, -prostate-specific antigens (PSA -alfa-fœtoprotein (AFP) in hepatocellular carcinoma - carcinoembryonic (CEA) antigen in colorectal carcinomas. Grading And Staging Grading: based on cytological differentiation of tumour cells and the number of mitoses within the tumour. Graded I, II, III or IV in order of increasing anaplasia. Staging: is based on: 1. The size of the primary lesion. 2. Extent of spread to regional lymph nodes. 3. Presence or absence of metastases. TNM staging system: T: tumour size, N: Lymph node metastases, M: Distant metastases. The Immune System: The immune response can be divided into two types: 1. Innate immunity (also called natural, or native, immunity) refers to defense mechanisms that are present even before infection and have evolved to specifically recognize microbes and protect multicellular organisms against infections. Its components are epithelial barriers that block entry of environmental microbes, phagocytic cells (mainly neutrophils and macrophages), natural killer (NK) cells, and several plasma proteins, including the proteins of the complement system. 2. Adaptive (acquired or specific) immunity, consists of mechanisms that are stimulated by (adapt to) microbes and are capable of also recognizing nonmicrobial substances, called antigens. There are two main types of adaptive immunity, cell-mediated (or cellular) immunity, which is responsible for defense against intracellular microbes, and humoral immunity, which protects against extracellular microbes and their toxins. Cellular immunity is mediated by T (thymus-derived) lymphocytes, and humoral immunity is mediated by B (bone marrow-derived) lymphocytes and their secreted products, antibodies. Cells of The Immune System: I. T-Lymphocytes: They make up 60-70% of circulating lymphocytes, they are also found in the paracortical area of lymph nodes and periarteriolar sheath of the spleen. Each T-cell contains a specific T cell receptor (TCR). The TCR is composed of α and β polypeptide chains connected by a disulfide bond, each have a variable (antigen-binding) and a constant region. Both α and β complexes are linked to five polypeptide chains referred to as CD3 complex involved in signal transduction. Somatic rearrangement of TCR gene results in TCR diversity. CD4 and CD8 are expressed in two mutually exclusive subsets of T- lymphocytes serve as coreceptors. CD4 is present in about 60% of T cells while CD8 in about 30%. CD4:CD8 ratio is about 2:1. CD4 molecule binds to class II MHC molecule expressed on antigen presenting cells. CD8 binds to class I MHC molecules. There are two subsets of TH cells; The T-helper-1 (TH1) subset synthesizes and secretes IL-2 and interferon-γ (IFN-γ) but not IL-4 or IL-5, whereas TH2 cells produce IL-4, IL-5 and IL-13 but not IL-2 or IFN-γ. The TH1 subset is involved in facilitating delayed hypersensitivity, macrophage activation, and synthesis of opsonizing and complement- fixing antibodies. The TH2 subset aids in the synthesis of other classes of antibodies, and in the activation of eosinophils. CD8+ T cells function mainly as cytotoxic cells to kill other cells but, similar to CD4+ T cells, they can secrete cytokines, primarily of the TH1 type. During antigen recognition, T cells require two signals for complete activation: 1. Engagement of TCR by appropriate MHC-antigen complex with CD4 and CD8 coreceptors. 2. Interaction of CD28 on T cells with CD80 or CD86 on antigen-presenting cells. In the absence of this signal, T cells undergo apoptosis or become unreactive (anergic); a process which prevents autoimmunity.  II. B-Lymphocytes: Constitute 10-20% of circulating lymphocytes. In lymph nodes, they are found in the superficial cortex and in the spleen in the white pulp, forming lymphoid aggregates, which when activated will form germinal centers. After antigen stimulation, B-cells will transform into plasma cells that secrete immunoglobulins (IgG, IgM, IgA) constituting 95% of plasma immunoglobulins, while IgE occurs in traces in the serum, while IgD is only cell-bound to B cells. Monomeric IgM is present on the surface of all B cells forming an antigen receptor of B cells (BCR). Somatic rearrangement of immunoglobulin genes results in unique antigen specificity. Several other molecules are expressed on B cells including CD 19 and CD20. CD21 serves as a complement receptor and also binds to Epstein-Barr virus (EBV). CD40 interacts with CD154 on activated T-lymphocytes. III. Macrophages: Play several roles in immune response: 1. Present antigens to T-cells through class II MHC molecules. 2. Production of cytokines influence the function of T and B cells, endothelial cells and fibroblasts. 3. Secretion of toxic metabolites and proteolytic enzymes which lyse tumour cells. 4. Are important effector cells in cell-mediated immunity of delayed hypersensitivity reaction. IV. Dendritic and Lengerhan's cells: They have dendritic cytoplasmic processes and large amounts of class II MHC molecules. Dendritic cells are found in lymphoid tissue, Langerhan's cells are found in the epidermis. They are efficient in antigen presentation with poor phagocytic activity. Follicular dendritic cells of germinal centers are different, contain antibodies on their cell surfaces, Fc receptors trap antibodies. V. Natural killer cells (NK cells): Make up 10-15% of peripheral blood lymphocytes and do not express TCR nor immunoglobulin. They are larger than small lymphocytes and contain azurophilic granules (large granular lymphocytes). They are a part of the natural immune system killing tumour cells and virally-infected cells without previous sensitization. CD16 and CD56 are used to identify NK cells. CD16 is an Fc receptor for IgG-coated cells in a process called antibody dependant cell mediated cytotoxicity. It expresses two sets of receptors: 1. Activators: recognize ill-defined molecules. 2. Inhibitors; recognize class I MHC. All nucleated normal cells express class I MHC. NK cells also secrete IFN-γ. Main Histocompatibility Complex (MHC): The principal physiologic function of the cell surface histocompatibility molecules is to bind peptide fragments of foreign proteins for presentation to antigen-specific T cells. The genes encoding the MHC molecules are clustered on a small segment of chromosome 6, called human leukocyte antigen (HLA). MHC gene products are classified into three categories, class I and class II genes encode cell surface glycoproteins involved in antigen presentation, class III genes encode components of the complement system. Class I MHC molecules are expressed on all nucleated cells and platelets. They are encoded by three closely linked loci, designated HLA-A, HLA-B, and HLA-C. In general, class I MHC molecules bind and display peptides that are derived from proteins, such as viral antigens, synthesized within the cell, the TCR recognizes the MHC-peptide complex, and the CD8 molecule, acting as a coreceptor. CD8+ cytotoxic T cells can recognize viral (or other) peptides only if presented as a complex with self-class I antigens, and therefore CD8+ T cells are said to be class I MHC-restricted. Class II MHC molecules are coded for in a region called HLA-D, which has three subregions: HLA-DP, HLA-DQ, and HLA-DR. Class II molecules present exogenous antigens (e.g., extracellular microbes, soluble proteins) that are first internalized and processed in the endosomes or lysosomes, Ag-MHC complex can be recognized by CD4+ helper T cells (class II MHC-restricted). Hypersensitivity Reactions: Diseases due to immunologic reactions can happen due to four mechanisms: 1. Type I (immediate) hypersensitivity reaction: is a rapidly developing immunologic reaction occurring within minutes after the combination of an antigen with antibody bound to mast cells in individuals previously sensitized to the antigen. It passes in two phases, immediate phase (5-30 min, subsiding in 60 min), characterized by vasodilatation and exudation due to the release of vasoactive amines, and the late phase which may follow (e.g. bronchial asthma, allergic rhinitis) after 2-4 hours lasting for days, and characterized by influx of leukocytes.  2. Type II Hypersensitivity reaction: is mediated by antibodies directed toward antigens present on cell surfaces or extracellular matrix. The antigens are either intrinsic or extrinsic. Destruction of the foreign or intrinsic antigen happens by three mechanisms: a. Opsonization and complement-and Fc receptor-mediated phagocytosis. b. Antibody-dependent cellular cytotoxicity (ADCC); examples include transfusion reactions, autoimmune hæmolytic anæmia, drug reactions. c. Antibody-mediated cellular dysfunction, examples include myasthenia gravis, Grave's disease. Examples of type II hypersensitivity reaction is glomerulonephritis and organ rejection. 3. Immune complex-mediated (type III) hypersensitivity: Antigen-antibody complexes produce tissue damage mainly by eliciting inflammation at the sites of deposition. Circulating immune complexes deposit in various organs mainly blood vessels producing disease. Examples include; systemic lupus erythematosus, polyarteritis nodosa, poststreptococcal glomerulonephritis, serum sickness. 4. Cell-Mediated (Type IV) Hypersensitivity: is initiated by antigen-activated (sensitized) T lymphocytes. It includes the delayed type hypersensitivity  reactions mediated by CD4+ T cells and representing a major mechanism of defense against a variety of intracellular pathogens, including mycobacteria, fungi, and certain parasites, and is also involved in transplant rejection and tumor immunity, and direct cell cytotoxicity mediated by CD8+ T cells mainly encountered in graft rejection. Autoimmune Diseases Organ-Specific Systemic Hashimoto thyroiditis Systemic lupus erythematosus Autoimmune hemolytic anemia Rheumatoid arthritis Autoimmune atrophic gastritis of pernicious anemia Sjögren syndrome Multiple sclerosis Reiter syndrome Autoimmune orchitis Inflammatory myopathies Goodpasture syndrome Systemic sclerosis (scleroderma) Autoimmune thrombocytopenia Polyarteritis nodosa Insulin-dependent diabetes mellitus Myasthenia gravis Graves disease Primary biliary cirrhosis Autoimmune (chronic active) hepatitis Ulcerative colitis