General pathology
Terms:
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Pathology: study of diseases & suffering
 Study of the structural, biochemical, and functional changes in cells
 Bridge between the basic sciences and clinical medicine
 Uses molecular, microbiologic, immunologic, and morphologic techniques
 Trying to reach a diagnosis and explanation
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Types of pathology:
 General pathology
 Reactions of cells and tissues to abnormal stimuli (cell injury)
 Inflammation and repair & hemodynamic disorders
 Genetic disorders & immune system diseases
 Infectious disease & environmental diseases
 Systemic pathology: alterations in organs and tissues in diseased status
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Etiology: the underlying cause
 Factors responsible for initiation and progression of the disease
 Could be
a- Intrinsic (genetic): inherited mutations
b- Acquired: infectious, nutritional or chemical environmental factors
 The common diseases (hypertension, diabetes, and cancer) are caused by
a combination of inherited susceptibility and environmental triggers
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Pathogenesis:
 Mechanisms of development & progression of the disease
 Sequence of events from initial stimulus to ultimate expression of disease
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Classification of pathology:
1- Anatomical/ surgical pathology:
 Gross examination and microscopic examination to reach a diagnosis
 Morphology of tissues and cells at microscopic and macroscopic levels
 Includes:
a- Histopathology: examination of stained tissues under microscope
b- Cytopathology: examination of cells under microscope (cervical
smear, sputum & gastric washing)
c- Forensic pathology (autopsy): post-mortem examination of corpses
d- Dermatopathology: study of skin diseases
e- Neuropathology
f- Oral pathology
 Diagnosis in anatomical pathology
1- Biopsy:
a- Excisional (the whole tissue)
b- Incisional (part of the tissue)
2- Smear: screening tool to detect precancerous lesions (pap smear:
cervical cancer)
a- Exfoliative cytology (surface): cells shed from body surface (quick
and simple but not accurate)
b- Fine needle aspiration FNAC: deep collection of cells from lesions
by needle (goiter and breast lumps)
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Clinical pathology:
Hematology
Microbiology
Immunology
 Serology
 Biochemistry
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The specimen label must contain:
a- Patient name, medical record number, age and sex.
b- Date and time of collection.
c- Requesting physician's name.
d- Special requests for the pathologist including special stains.
e- Names of other physicians who should receive copies of the report.
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Processing of specimen
 Fixation: we use formalin to fix the tissue and preserve it
 Dehydration: washing tissue cassettes in graded ethanol wash (50-100%)
 Clearing: soaking in Citrasolv bath to make tissues miscible to paraffin
 Infiltration: by soaking the tissue with paraffin
 Embedding: allowing infiltrated tissues to harden in a paraffin block
 Sectioning: forming a block that is cut with a microtome into slices 7-8 μm
 Staining: with H & E stain (Hematoxylin and Eosin)
 Hematoxylin:
 Basic dye that carries positive charge
 Stains acidic anionic (negative) components
 The blue color always indicates for nucleus
 Structures stained with it are called basophilic
 Eosin
 Acidic dye that carries negative charge
 Stains basic cationic (positive) components
 The pink color always indicates for cytoplasm
 Structures stained with it are called eosinophilic
 Paraffin block can be stored for 30 years and slices (slides) for 10 years.
Cellular responses and adaptations to stress:
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Normal cell
 Needs special environment to function properly. (Homeostasis)
 Adjusts their structure and function to accommodate:
a- Changing demands
b- Extracellular stresses
 Tries to adapt to surrounding stimuli or changes, so it can survive.
 An ↑, ↓ or change in stress on an organ can result in cellular responses.
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Things that might change around the cell:
 PH
 Temperature
 Electrolytes level
 Glucose
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Cellular Responses:
 Adaptation:
a- Hypertrophy
b- Hyperplasia
c- Atrophy
d- Metaplasia
 Injury:
a- Reversible
b- Irreversible (cell death/necrosis)
 Apoptosis.
 Intracellular accumulation & calcification.
 Cellular aging.
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Whether a stress induces adaptation or causes injury depends on:
 Nature of the stress.
 Severity of the stress.
 The involved cell itself (capability to tolerate).
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Adaptation:
 A new steady state which the cells enter
 In response to stress or extracellular events
 Trying to preserve viability and function
 Reversible changes in
 Size
 Number
 Phenotype
 Metabolic activity
 Function
 Adaptation can be both physiologic and/or pathologic (disease)
 Adaptive responses are:
a- Hypertrophy:
 An increase in cell size
 Resulting in increase in the size of the organ
 In non-dividing (permanent) cells
a- Cardiac myocytes
b- Skeletal muscles
c- Nerve cells
 Mechanism: ↑ production of structural proteins & organelles
 There is a limit for hypertrophy
 Caused by:
 Increased functional demand (workload)
 Stimulation by hormones or growth factors
 Coexists with hyperplasia in dividing cells (skin or GI tract cells)
 Example: Heart: left ventricle hypertrophy in hypertension
b- Hyperplasia:
 Increased number of cells
 Resulting in increased mass of the organ or tissue
 Takes place in cells capable of dividing
 If continues it might lead to dysplasia (abnormal cells)
 Caused by hormones and growth factors
 Can be a fertile soil for development of malignancy
 Hyperplasia and hypertrophy generally occur together
 Permanent tissues undergo hypertrophy only
 Physiologic (hormone related or compensatory)
 Uterine enlargement during pregnancy
 Female breast in puberty & lactation
 Compensatory hyperplasia in partial liver resection
 Pathologic (hormone)
 Hyperplasia of the endometrium
 Prostate hyperplasia
 Wound healing (effects of growth factors)
 Infection by papillomavirus (skin warts)
 Pathologic can progress to dysplasia and eventually, cancer
 A notable exception is benign prostatic hyperplasia (BPH),
which does not increase the risk for prostate cancer.
c- Atrophy:
 Reduced size & function of cell, tissue or organ
 As a result of loss of cell substance (size and number)
 The cell is still ALIVE and can at some point go back to normal
 Physiologic:
 Embryonic development
 Involuting gravid uterus
 Pathologic:
 Decreased workload (Disuse atrophy)
 Loss of innervation (Denervation atrophy)
 Diminished blood supply
 Inadequate nutrition
 Loss of endocrine stimulation
 Aging
 Testicular atrophy in undescended testis
 Frontal lobe atrophy in Alzheimer's disease
 Mechanisms:
 Decreased protein synthesis
 Increased protein degradation
 Reduced metabolic activity
 Mainly induced by Ubiquitin-proteasome pathway:
 Protein binds organelles  signals (kill me) 
decrease # of organelles.
 Autophagy (self-eating) to find sources of protein.
(starvation).
d- Metaplasia:
 Reversible change.
 One differentiated (mature) cell type is replaced by another.
 New epithelium is better in dealing with the current stress or
irritation BUT it will lose many functions.
 Some functions might be lost.
 Malignant transformation if the cause of metaplasia persists.
 A notable exception is apocrine metaplasia of breast, which
carries no increased risk for cancer (physiological).
 Mechanism
 Re-programming of stem cells or undifferentiated
mesenchymal cells in connective tissue.
 Signals generated by cytokines, growth factors and
extracellular matrix promote expression of genes
toward a new differentiation.
 Examples
 Pathologic:
 Squamous metaplasia: Replacement of ciliated
columnar epithelium by stratified squamous epithelium
in the respiratory tract of a smoker that might lead to
invasive carcinoma.
 Gastric or intestinal metaplasia: Replacement of nonkeratinized squamous epithelium of esophagus by nonciliated mucin-producing columnar epithelium in reflux
esophagitis that causes Barret's disease that progresses
to adenocarcinoma after 15-20 years.
 Physiologic
 Myositis ossificans: in which connective tissue within
muscle changes to bone during healing after trauma
 Apocrine metaplasia of breast: carries no increased risk
for cancer
e- Dysplasia:
 Disordered, precancerous epithelial cellular growth
 Not considered a true adaptive response
 Dysplasia is reversible, in theory, with alleviation of stress
 If stress persists, progresses to carcinoma (irreversible)
 Characterized by
a- Loss of uniformity of cell size and shape (pleomorphism)
b- Loss of tissue orientation
c- Nuclear changes
 Most often refers to proliferation of precancerous cells
 Cervical intraepithelial neoplasia (CIN)
a- Represents dysplasia
b- A precursor to cervical cancer
 Often arises from:
a- Longstanding hyperplasia (endometrial hyperplasia)
b- Longstanding metaplasia (Barrett's esophagus)
f- Aplasia:
 Not considered an adaptive response
 Failure of cell production during embryogenesis
 Example: unilateral renal agenesis
g- Hypoplasia:
 Not considered an adaptive response
 A decrease in cell production during embryogenesis
 Resulting in a relatively small organ
 Example: streak ovary in Turner
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Cell injury and death
 Cellular injury occurs when a stress exceeds the cell’s ability to adapt
 Cellular injury occurs if cells
 Are no longer able to adapt the stress
 Exposed to damaging agents from the start
 The likelihood of injury depends on
 The type of stress
 Stress severity
 The type of the affected cell
 Neurons are highly susceptible to ischemic injury
 Skeletal muscle is relatively more resistant
 Types
 Reversible
 Cell membrane and chromatin are intact
 99% of cases are pathologic
 Cell can regenerate itself after removal of stress
 The hallmark of reversible injury is cellular swelling
o Cytosol swelling results in
Loss of microvilli
Membrane blebbing
o Swelling of rough endoplasmic reticulum results in
Dissociation of ribosomes
Decreased protein synthesis
 Irreversible (death)
 Cell membrane and chromatin are permanently damaged
 100% of cases are pathologic
 Cell can't regenerate itself
 Also known as necrosis
 The hallmark of irreversible injury is membrane damage
o Plasma membrane damage results in
Cytosolic enzymes leaking into the serum
Additional calcium entering into the cell
o Lysosome membrane damage
Hydrolytic enzymes leaking into the cytosol
Enzymes are activated by the high calcium
 Stress (if severe, prolonged or damaging) leads to Injury
 Stress  Reversible Injury  Irreversible
 Changes can be detected by
a- Histochemical techniques
b- Ultrastructural techniques
c- Microscopy
d- Grossly
 Causes of cell injury
 Hypoxia
 Oxygen Deprivation (deficiency of O2)
 O2 = final electron acceptor (electron transport chain)
 ↓ oxygen impairs oxidative phosphorylation = ↓ ATP
 Low ATP disrupts key cellular functions including
 Na-K pump: sodium and water buildup
 Aerobic glycolysis, resulting in
 Switch to anaerobic glycolysis
 Lactic acid buildup results in low pH
 Low pH denatures proteins
 The most common cause of cell injury
 Causes:
 Ischemia (the most common cause) due to
 ↓ arterial perfusion (atherosclerosis)
 ↓ venous drainage (Budd-Chiari)
 Shock- generalized hypotension
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Inadequate oxygenation (Hypoxemia) due to
 Cardiorespiratory failure
 High altitude
 Hypoventilation
 Diffusion defect
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Decreased oxygen carrying capacity:
 Anemia
 Carbon monoxide poisoning
 Blood loss
 Met-hemoglobinemia
 Physical agents:
 Mechanical trauma
 Extremes of temperature
 Changes in atmospheric pressure
 Radiation & electric shock
 Chemical agents and drugs:
 Glucose or salt
 Oxygen & therapeutic drugs
 Arsenic compounds
 Cyanide & Mercuric salts
 Insecticides & herbicides
 Asbestos
 Alcohol & smoking
 Infectious agents:
 Viruses
 Bacteria
 Fungi
 Parasites
 Immunologic reactions to:
 External stimuli (allergy)
 Endogenous self-antigens (autoimmune)
 Genetic derangement:
 Chromosomal anomalies
 Gene alteration
 Simple amino acid alteration
 Nutritional imbalance:
 Protein calorie deficiencies
 Vitamin deficiencies
 Psychiatric disorders (Anorexia nervosa)
 Excess food & type of food
 Aging: ↓replicative and repair abilities.
 Morphologic alterations in cell injury
 Reversible injury
 Generalized swelling of the cell:
 The first manifestation
 Failure of energy-dependent ion pumps(Na-K)
 Disturbances in ionic and fluid homeostasis
 Fatty changes in hepatocytes and mycoradium
 AKA: hydropic change or vacuolar degeneration
 Plasma membrane alterations:
 Blebs
 Blunting or loss of villi
 Loosening of intercellular attachments
 Mitochondrial changes:
 Swelling
 Appearance of small amorphous densities
 ER dilatation & detachment of polysomes (ribosomes)
 Possibility of myelin figure formation in the cytoplasm
 Nuclear alterations: nuclear chromatin clumping
 Irreversible injury (necrosis)
 Result from:
 Denaturation of intracellular proteins
 Enzymatic digestion of cells
 Structural changes need time to develop.
 Loss of membrane integrity.
 Inflammatory response.
 Increased eosinophilia in H&E stain.
 Vacuolation due to digestion of cytoplasmic organelles.
 Plasma and organelle membrane discontinuities.
 Myelin figures:
 Aggregates of damaged cell membranes
 Phagocytosed or degraded into FA & calcify
 Dilatation of mitochondria.
 Nuclear changes: breakdown of DNA
 Karyolysis: loss of DNA, fade of basophilia.
 Pyknosis: nuclear shrinkage and ↑ basophilia.
 Karyorhexis: fragmentation of pyknotic nucleus.
 Disappearance of the nucleus.
Patterns of necrosis
1- Coagulative necrosis
 Preservation of the architecture of dead tissue for at least some days.
 Denaturation of structural proteins and enzymes.
 Eosinophilic anucleated cells.
 Cells are removed by inflammatory leukocytes.
 Ischemia in any organ except the brain may lead to coagulative necrosis.
 Infarction: localised area of coagulative necrosis.
2- Liquefactive necrosis
 Digestion of dead cells resulting into a liquid viscous mass.
 In focal bacterial or fungal infections.
 In hypoxic death in central nervous system.
 Creamy yellow due to accumulation of dead leukocytes (pus).
3- Gangrenous necrosis
 Not a distinctive pattern.
 Used clinically in describing lower limb coagulative necrosis.
 Secondary to ischemia.
 Once infected by bacteria it becomes wet gangrene (liquefaction).
 Steps of gangrenous necrosis:
a- Loss of blood supply to a limb
b- Coagulative necrosis (dry gangrene)
cdef-
Superimposed bacterial infection
Degradative enzymes and leukocytes
Liquefactive necrosis
Wet gangrene
4- Caseous necrosis
 White cheese-like friable necrosis.
 Tuberculosis.
 Collection of lysed cells with amorphous granular eosinophilic debris.
 Surrounded by histiocytes (macrophages), known as granuloma.
5- Fat necrosis
 Usually used in clinical terms and it is not a specific type.
 Necrosis (destruction) of fat.
 Example: pancreatic enzymes (lipases) release in acute pancreatitis.
 The fatty acids result from the breakdown of fat.
 Fatty acids combine with Ca⁺²  white chalky areas (Saponification).
6- Fibrinoid necrosis
 Immune reactions involving blood vessels.
 Complexes of antigens and antibodies deposited in the walls of arteries.
 Immune complexes deposit along with fibrin.
 Result in a bright pink material on H&E.
 Example: vasculitis.
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Fate of necrotic tissue
1- Phagocytosis.
2- Replacement by scar.
3- Regeneration.
4- Calcification.
Apoptosis
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Pathway of cell death induced by a “suicide” program.
Cells activate enzymes that degrade DNA and proteins.
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Apoptotic cells break into fragments called “apoptotic bodies”
a- Contain portions of the cytoplasm and nucleus
b- Become targets for phagocytosis
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There would be NO inflammatory reaction.
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Physiological or pathological:
a- Physiologic situations:
 Embryogenesis.
 Involution of hormone-dependent tissues upon withdrawal.
b- Pathologic situations:
 DNA damage
 Accumulation of misfolded proteins (ER stress)
 Certain infections (viral ones)
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Morphology
 Cell shrinkage: dense cytoplasm, tightly packed organelles.
 Chromatin condensation: peripherally under nuclear membrane.
 Formation of cytoplasmic blebs and apoptotic bodies.
 Phagocytosis of apoptotic cells or bodies by macrophages.
 On H&E: intensely eosinophilic or shrunken basophilic.
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Notes:
 Apoptosis results from the activation of enzymes called caspases.
 Caspases depends on Bcl proteins family (20 members)
 Pro-apoptotic proteins:
 Induced by GF↓, DNA damage & protein misfolding
 Bak & Bax
 Anti-apoptotic proteins:
 Stimulated by GF & survival signals
 Bcl-2 (the most important), Bcl-x & Mcl-1
 Two distinct pathways converge:
 The mitochondrial pathway
 The death receptor pathway
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Biochemical features
 Activation of Caspases:
 Initiators (caspase 9 & 8)
 Executioners (caspase 3 & 6)
 DNA and protein breakdown
 DNA breaks down into large 50 to 300 kilobase pieces
 Ca⁺² & Mg⁺² dependent endonucleases cut DNA 180-200kb
 Membrane alterations and recognition
 Changes making cells recognisable by phagocytes
 Movement of phosphatidylserine from inner leaflet to outer
leaflet to bind receptors on phagocytes
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Mechanisms of apoptosis
1- Initiation phase
A- The Mitochondrial (Intrinsic) pathway of apoptosis
 Major mechanism
 Cellular damage causes
Stimulation of pro-apototic proteins
Inhibition of anti-apototic proteins
 Other mitochondrial proteins (Smac/DIABLO)
Enter the cytoplasm
Blocking the inhibitors of apoptosis (Bcl-2 and Bcl-xl)
 Release of mitochondrial cytochrome c into the cytosol
 Cytochrome c binds to Apaf-1: forming apoptosome
 Apoptosome binds to caspase-9 (the critical initiator caspase)
B- The Death Receptor (Extrinsic) pathway
 Responsible for
 Elimination of self-reactive lymphocytes
 Damage by cytotoxic T lymphocytes
 Initiated by plasma membrane death receptors (TNF receptor).
 TNF-1 with Fas (CD95) expressed on the surface of many cells.
 Its ligand FasL is expressed on activated T-cells.
 Fas-FasL binding
Activate caspases and drive the cell to apoptosis
Without passing through the mitochondria.
2- The execution phase
 Final step after the initiation phase.
 Caspases 3 & 6.
 Activation of DNase.
 Degradation of structural components of nuclear matrix.
 Fragmentation of nuclei & phagocytosis.
Apoptosis
Affects single cell
No inflammatory response
Cell shrinkage
Membrane blebbing with maintained integrity
Chromatin condensation
Non-random DNA fragmentation
↑ mitochondrial membrane permeability
Release of pro-apoptotic proteins
Formation of apoptotic bodies
Apoptotic bodies are ingested by macrophages
and adjacent cells
Necrosis
Affects group of adjacent cells
Significant inflammatory response
Cell swelling
Loss of membrane integrity
Random DNA fragmentation
Organelle swelling
Lysosomal leakage
Lysed cells are ingested by macrophages
Mechanisms of cell injury
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The cellular response to injurious stimuli depends on
 The nature of the injury
 Duration of the injury
 Severity of the injury
The consequences of injurious stimuli depend on the
 Type of injured cell
 Status of injured cell
 Genetic makeup of injured cell
 Adaptability of the injured cell
Cell injury results from different biochemical mechanisms acting on
 Mitochondria
 Calcium homeostasis
 Plasma membranes
 DNA
Any injurious stimulus may trigger multiple interconnected mechanism
Biochemical mechanisms of cell injury
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Depletion of ATP:
 Usually in hypoxic and chemical injuries.
 Sources of ATP:
 Oxidative phosphorylation of ADP in the mitochondria
 Gycolytic pathway using glucose
 The major causes of ATP depletion are
 Reduced supply of oxygen and nutrients
 Mitochondrial damage
 The actions of some toxins (Cyanide)
 Tissues with a greater glycolytic capacity (liver) are able to survive loss of
oxygen and decreased oxidative phosphorylation better than tissues with
limited capacity for glycolysis (brain)
 Consequences of ATP depletion
 ↓ Activity of Na-K pump
 ↑ influx of Ca, Na & water
 ER swelling
 Cellular swelling
 Loss of microvilli
 Formation of blebs
 Anaerobic glycolysis
 ↓ glycogen
 ↑ lactic acid
 ↓ PH: clumping of nuclear chromatin
 Detachment of ribosomes
 ↓ protein synthesis
 ↑ lipid deposition
 Low oxygen situation results in
 Misfolding of proteins  unfolded protein response
 May lead to cell death (activation of pathologic apoptosis)
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Mitochondrial damage:
 Supplies ATP (energy) to the cell.
 Damaged by
 Calcium influx
 Reactive oxygen species
 Radiation
 Oxygen deprivation
 Toxins
 Mutations in mitochondrial genes
 Lipid peroxidation
 Consequences of mitochondrial damage:
 Formation of mitochondrial permeability transition pore
 Loss of membrane potential
 Failure of phosphorylation
 ATP depletion
 Formation of reactive oxygen species
 Necrosis
 Release of cytochrome c into cytosol activate apoptosis (death).
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Influx of calcium and loss of calcium homeostasis
 Depleting extracellular Ca protects the cell from injury and delays it.
 Cytosolic Ca conc. is very low and is present in mitochondria & ER.
 Injury will lead to increase cytosolic Ca.
 Consequences of Ca increase:
 Opening of mitochondrial permeability transition pore
 Activation of a number of enzymes
 Phospholipases: causes membrane damage
 Proteases: damage of cytoskeletal proteins
 Endonucleases: nuclear damage
 ATPases: depletion of ATP
 Induction of apoptosis by
 Direct activation of caspases
 Increasing mitochondrial permeability
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Accumulation of oxygen derived free radicals
 It is important in
 Chemical and radiation injuries
 Ischemia-reperfusion injury
 Cellular aging
 Microbial killing by phagocytosis
 Free radicals:
 Species with single unpaired electron in the outer orbital
 Unstable atoms
 React with inorganic and organic chemicals
 Initiate autocatalytic reactions
 Creation of more radicals (propagation)
 Reactive oxygen species (ROS)
 Oxygen derived free radicals
 Produced normally in small amounts
 Produced by leukocytes and macrophages in inflammation
 Removed by defence mechanisms
 Once the ROS amount increases  oxidative stress.
 Oxidative stress:
 Cell injury
 Cancer
 Aging
 Some degenerative diseases like Alzheimer
 Generation of free radicals
 Reduction oxidation reactions:
 Normal mitochondrial respiration
 By-products are:
 superoxide anion (O2.-)
 hydrogen peroxide (H2O2)
 hydroxyl ions (OH.)
 Absorption of radiant energy
 UV light and X-rays
 Hydrolyse water into OH & H free radicals
 Production by leukocytes
 Plasma membrane multiprotein using NADPH oxidase
 Intracellular xanthine oxidase  superoxide anion
 Not ROS but similar: CCL4  CCL3
 Enzymatic metabolism of exogenous chemicals or drugs.
 Transition metals.
 Iron and copper.
 Fenton reaction (H2O2 + Fe²⁺  Fe³⁺+OH•+OH⁻)
 Ferric iron should be reduced to ferrous iron to participate
in Fenton reaction.
 Reaction is enhanced by superoxide anion
 Sources of iron and superoxides may participate in
oxidative cell damage.
 Nitric oxide (NO).
 Endothelial cells, macrophages, neurons and other cells
 Can act as a free radical
 Can also be converted to
 Highly reactive peroxynitrite anion
 NO2
 NO3
 Removal of free radicals
 Decay spontaneously.
 Antioxidants: Vitamin E and A, ascorbic acid and glutathione
 Binding proteins.
 Enzymes:
 Catalase: H2O2  O2 and H2O
 Superoxide dismutase: superoxide anion H2O2
 Glutathione peroxidase: H2O2  H2O or OH. H2O
 Pathological effects of free radicals
 Lipid peroxidation in membranes:
 Oxidative damage of the double bonds in the
polyunsaturated fatty acids
 Formation of peroxides which are unstable and lead to
membrane damage
 Oxidative modification of proteins:
 Damage the active sites on enzymes
 Change the structures of proteins
 Enhance proteosomal degradation of unfolded proteins.
 Lesions in DNA:
 Single and double strand breaks in DNA.
 Oxidative DNA damage has been implicated in cell aging
and in malignant transformation of cells.
 Radicals are involved in both necrosis and apoptosis.
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Defects in membrane permeability
 Membrane damage is a constant feature in all forms of cell injury except
apoptosis.
 Causes include
 Ischemia that causes
 ATP depletion
 Calcium mediated activation of phospholipases
 Direct damage by
 Bacterial toxins
 Viral proteins
 Lytic complement components
 Physical and chemical agents
 Mechanisms of membrane damage
 Reactive oxygen species: lipid peroxidation
 Decreased phospholipids synthesis:
 Due to defective mitochondrial function or hypoxia
 Affects all cellular membranes including mitochondria
 Increased phospholipids breakdown:
 Activation of endogenous phospholipases
 Due to Ca⁺²
 Resulting in accumulation of lipid breakdown products.
 Lipid Breakdown products: include
 Un-esterified free fatty acids
 Acyl carnitine
 Lysophospholipids
 Have a detergent effect on membranes
 Causing changes in permeability
 Causing and electrophysiologic alterations
 Cytoskeletal abnormalities:
 Activation of proteases by high Ca⁺²
 Causes damage to the elements of cytoskeleton
 Most important sites of membrane damage:
 Mitochondrial membrane
 Plasma membrane
 Lysosomal membrane: causes release of degrading enzymes
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
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RNases
DNases
Proteases
 Leakage of intracellular proteins into blood through damaged membranes
provides a means of detecting tissue damage
 CK & troponin in MI
 ALT, AST &ALK (ALP) in liver.
Ischemic and hypoxic injury
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Most common type of injury in clinical medicine.
Hypoxia: anaerobic glycolysis
Ischemia: delivery of substrates is also compromised.
Ischemia is more rapidly damaging than hypoxia in the absence of ischemia.
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Mechanisms of ischemic injury:
Reversible:
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





Loss of oxidative phosphorylation and decreased generation of ATP.
Na/K and Ca⁺² pumps failure.
Progressive loss of glycogen and decreased protein synthesis.
Loss of function though the cell is not yet dead.
Cytoskeleton abnormalities; blebs and loss of villi.
Formation of myelin figures and swollen organelles.
To this point changes are reversible.
Irreversible







Severe swelling to the mitochondria
Extensive damage to the plasma membranes
Myelin figures formation and swelling of lysosomes.
Large densities develop in the mitochondria.
Massive influx of Ca⁺²
Death is mainly by necrosis but apoptosis also takes place.
Dead cells may become replaced by large masses of myelin figures:
 phagocytosed
 degraded more into fatty acids
 may become calcified.
Ischemia-reperfusion injury
-
Restoration of blood flow to ischemic tissues can promote recovery if they
are reversibly injured.
In certain situations, reperfusion paradoxically exacerbates injury
Mechanisms:
 Re-oxygenation:
 increased regeneration of reactive oxygen and nitrogen species
 Ca⁺² influx
 Inflammation response:
 Mediated by cytokines which recruits more leukocytes
 Anti-cytokines might aid in ↓ unwanted effects of inflammation.
 Activation of the complement system:
 Some IgM antibodies are deposited in ischemic tissues
 Once the blood is restored complement proteins bind IgM
 Activation of complement and so more injury
Chemical injury
-
Major problem in drugs.
Liver as a major site of drug metabolism is a target for drug toxicity.
-
Mechanisms:
 Directly by combining with critical molecular component:
 Mercuric chloride poisoning
 Bind to the sulfhydryl groups of cell membrane proteins
 Causing increased permeability
 More in GIT and kidney.
 Cyanide
 Poisons mitochondrial cytochrome oxidase
 Inhibits oxidative phosphorylation
 Most chemicals
 Not biologically active
 Need to be converted into active forms (toxic metabolites)
 Usually takes place in liver (cytochrome P-450 oxidases)
 Free radical formation and lipid peroxidation.
 CCl4 is converted to CCl3
 Lipid peroxidation
 Decrease export of lipids (Fatty change)
 Acetaminophen (paracetamol): converted to toxic products in liver
leading to injury
Intracellular Accumulation
-
Accumulation of abnormal amounts of various substances
Manifestation of metabolic derangements
Types
1- Normal cellular components
2- Abnormal substances (exogenous & endogenous)
-
Transient or permanent
Harmless or toxic
Cytoplasmic, within organelles or nuclear
Can be reversible or progressive leading to death
-
Mechanisms
 Inadequate removal of normal endogenous substance
 Due to defects in packaging and transport
 Example: fatty liver changes
 Accumulation of abnormal endogenous substance
 Due to defects in folding, packaging, transport or secretion
 Examples:
 Antitrypsin deficiency
 CNS degenerative diseases (Alzheimer's disease)
 Normal endogenous substance accumulation
 Due to defects in metabolism (degrading) enzymes
 Example: glycogen storage disease
 Abnormal exogenous substance accumulation
 Due to absence of degrading or transporting mechanisms
 Example: accumulation of carbon & silica in lungs
Lipids
-
All major classes of lipids can accumulate in cells.
Free fatty acids enter the liver and undergo
 Catabolism
 Oxidation to ketone bodies
 Converted to phospholipids
 Converted to cholesterol esters
 Esterification
 Esterified with α-glycerophosphate into triglycerides
 Triglycerides will combine with apoproteins to form lipoproteins
 Lipoproteins leave the hepatocytes
-
Steatosis (Fatty change):
 Triglycerides in parenchymal cells.
 Mainly liver but, heart, muscle and kidney also.
 Microscopic appearance
 Microsteatosis
 Macrosteatosis
-
Causes:
 Toxins (alcohol)
 Protein malnutrition
 DM
 Obesity
 Anoxia.
-
Alcohol increases synthesis and decreases breakdown of lipids.
Protein malnutrition and CCL4 reduce synthesis of apoproteins.
Hypoxia inhibits fatty acid oxidation.
Starvation increases fatty acid mobilization from peripheral stores.
Cholesterol & cholesterol esters
-
Consequences.
 Atherosclerosis:
 Accumulation in walls of blood vessels
 Luminal narrowing of blood vessels
 Reduction of blood supply
 Detachment and thrombus formation
 Infarction of the organ supplied by blood vessel
 Xanthomas
 Accumulation is subcutaneous tissues
 Hereditary or sporadic
 Cholesterolosis
 Accumulation in lamina propria of gallbladder
 Causes cholecystitis
Proteins
-
Less common than lipids.
Appears as rounded eosinophilic droplets, vacuoles or aggregates.
Examples:
 Accumulation of protein in renal tubules
 Seen in glomerulonephritis
 Appears as pink hyaline droplet
 Excessive production of proteins
 Igs in plasma cells
 Called Russell bodies
 Seen in plasmacytosis and chronic inflammation
 Defective intracellular transport and secretion of critical proteins.
 Antitrypsin deficiency
 Alcoholic hyaline (Mallory body)
 Accumulation of cytoskeleton proteins
 Intermediate filaments: keratin, neurofilaments, desmin
 Found in the liver
 Neurofibrillary tangle
 In Alzheimer's disease
 Seen in the brain tissue
Glycogen
-
Accumulated due to lack of enzymes for metabolism
Seen in:
 Glycogen storage diseases
 DM
 Glycogen accumulates in
 Renal tubules
 Hepatocytes
 β islets of Langerhans
 Heart muscle cells
Pigments
-
Exogenous:
 The most common exogenous pigment is carbon (coal dust)
 Causes anthracosis: blackening of Lungs & lymph nodes
 In coal miners coal dust induces fibrosis
 Causes a disease: coal worker's pneumoconiosis
 Tattooing:
 Localized exogenous pigmentation of skin
 Pigment is phagocytosed by macrophages and remains for life
-
Endogenous:
 Lipofuscin
 Wear and tear pigment







Brown-yellow pigment
Seen in old age groups
Consists of: lipids, phospholipids & proteins
Neither harmful nor toxic
Indicates presence of old free radical injury
Produced by peroxidation of polyunsaturated fatty acids
Seen mainly in cardiac myocytes
 Melanin
 Synthesized by melanocytes in skin
 Accumulates due to excessive melanocytes
 Brown-black in color
 Example: freckles and melasma
 Hemosiderin
 Hemoglobin-derived pigment
 Accumulation of iron
 Golden yellow-brown
 Differentiated microscopically from lipofuscin
 By Prussian-blue stain
 Gives iron blue color
 Doesn't stain lipofuscin
 Hemosideriosis:
 Excessive deposition of hemosiderin
 Mainly seen in hepatocytes (liver)
 Due to frequent blood transfusion
Pathologic calcification
-
Abnormal deposition of calcium salts in tissues.
Types:
 Dystrophic:
 In dying and necrotic tissues.
 Normal calcium levels.
 H&E basophilic granular material (intra- or extracellular).
 Heterotopic bone may develop.
 Psammoma bodies.
 Metastatic:
 In normal viable tissues.
 Mainly affects the interstitial tissues of:
 Gastric mucosa
 Kidneys
 Lungs
 Systemic arteries
 Pulmonary veins
 High calcium levels.
 Causes:
 Hyperparathyroidism
 Destruction of bone
 Vitamin D related disorders
 Renal failure
-
Pathogenesis:
1- Initiation (nucleation) and propagation
2- Formation of crystalline calcium phosphate.
3- Calcium is concentrated in membrane bound vesicles.
4- Calcium concentrated due to its affinity to membrane phospholipids.
5- Phosphates accumulate due to phosphatases.
Cellular aging
-
Progressive decline in the proliferative capacity and life span of cells
The effects of continuous exposure to exogenous factors that cause accumulation of
cellular and molecular damage.
Mechanisms:
 DNA damage.
 Accumulation of damaged DNA.
 Some aging syndromes are associated with defects in DNA repair
mechanisms.
 Decreased cellular replication.
 Replicative senescence.
 Telomere shortening and cell cycle arrest.
 Enzyme telomerase maintains the length of these telomeres.
 Defective protein homeostasis.
 Accumulation of metabolic damage.
 Reactive oxygen species
Ways to counteract aging




Calorie restriction
Decreased insulin like GF (IGF) signalling
Reduced activation of kinases (TOR)
Promotion of Sir 2 counteracts aging
Inflammation
-
A dynamic process of chemical and cytological reactions
A response of vascularized tissues to infections and tissue damage
Brings defense cells & molecules from the circulation to the infected sites
A protective response that is essential for survival
-
Historical notes
 Concept of inflammation started 3000 BC in Egyptian civilization(papyrus)
 Roman celsus: first person who put the 4 cardinal signs of inflammation
 German Virchow: in 19th century put the 5th sign of inflammation
 In 1793, Scottish hunter: said that inflammation isn’t a disease
 In 1880, Russian Metchnikoff described the process of phagocytosis
 20th century, Thomas Lewis describes histamine (inflammatory mediator)
-
Inflammation results in:
 Accumulation of leukocytes
 Accumulation of fluid in extravascular tissue
 Systemic effects
-
Inflammation aims
1- Elimination of the cause of cell injury
2- Elimination of the necrotic cells and tissue
3- Paves the way for repair
4- May lead to harmful results
-
Without inflammation
 Infections would go unchecked
 Wounds would never heal
 Injured tissues might remain permanent festering sores
-
Excessive inflammatory reaction become the cause of disease:
 Misdirected (autoimmune)
 Immunological/hypersensitivity (allergies)
 Prolonged (microbes resist eradication)
-
Anti-inflammatory drugs would control the harmful sequelae of inflammation
rather than interfering with its beneficial effects
-
Defective inflammation is also responsible for serious illness as seen in cancer
and immunocompromised patients
-
Five Classic Signs of Acute Inflammation
1- Heat (Calor)
2- Redness (Rubor)
3- Swelling (Tumor)
4- Pain (Dolor)
5- Loss of function (Functio Laesa)
-
Nomenclature (-itis Appendix
 Dermis
 Gallbladder
 Duodenum
 Meninges
-
Causes of inflammation
 Microbial infections: bacteria, viruses, fungi, parasites
 Immunologic: hypersensitivity, autoimmune reactions
 Physical agents: trauma, heat, cold, ionizing radiation
 Chemical agents: acids, alkali, bacterial toxins, metals
 Foreign material: sutures, dirt
 Tissue necrosis: ischemic necrosis
after name of tissue)
Appendicitis
Dermatitis
Cholecystitis
Duodenitis
Meningitis
Participants (The Players)
-
White blood cells and platelets
 Neutrophils
 Monocytes
 Lymphocytes
 Eosinophils
 Basophils
-
Plasma proteins
 Coagulation / fibrinolytic system
 Kinin system
 Complement system
-
Endothelial cells and smooth muscles of vessels
-
Extracellular matrix and stromal cells
 Mast cells, fibroblasts, macrophages & lymphocytes
 Structural fibrous proteins, adhesive glycoproteins, proteoglycans,
basement membrane
Types of Inflammation
-
-
Acute Inflammation
 Initial and rapid response
 If fails to clear stimulus, it will progress to chronic inflammation.
Chronic Inflammation
 May follow acute inflammation
 May arise de novo
Feature
Onset
Cellular infiltrate
Acute
Fast: minutes to hours
Mainly neutrophils
Tissue injury / fibrosis
Local and systemic signs
Mild & self-limited
Prominent
Fluid & plasma protein
exudation
Chronic
Slow: days
Monocytes /macrophages
Lymphocytes
Severe & progressive
Less
Vascular proliferation &
fibrosis
Diseases caused by inflammatory reactions
Disorder
Cells and molecules involved
Acute
Acute respiratory distress syndrome Neutrophils
Asthma
Eosinophils & IgE antibodies
Glomerulonephritis
Antibodies & complement
Neutrophils & monocytes
Septic shock
Cytokines
Chronic
Arthritis
Lymphocytes, macrophages &
antibodies
Asthma
Eosinophils & IgE antibodies
Atherosclerosis
Macrophages & lymphocytes
Pulmonary fibrosis
Macrophages & fibroblasts
-
The inflammatory reaction develops through a series of sequential steps:
1- The offending agent, which is located in extravascular tissues, is
recognized by host cells and molecules.
2- Leukocytes and plasma proteins are recruited from the circulation to the
site where the offending agent is located.
3- The leukocytes and proteins are activated and work together to destroy
and eliminate the offending substance.
4- The reaction is controlled and terminated.
5- The damaged tissue is repaired.
Acute Inflammation
-
Early response of vascularized tissue to injury
Aim of acute inflammation:
 Recruitment of neutrophils (1st 3 days), and monocytes (after 3 days) to
clear the cause of injury and remove necrotic cells.
 Deliver plasma proteins: antibodies, complement, others.
-
The Two Components of Acute Inflammation
1- Vascular changes
 Vasodilatation
 Increased vascular permeability
 Stasis
2- Cellular events
 Emigration of cells from microcirculation
 Accumulation at sites of injury
 Activation to eliminate the offending agent
-
The process is orchestrated by release of chemical mediators
-
Vascular Changes
 Vasodilation
 It may be preceded by transient vasoconstriction
 Induced by the action of histamine, on vascular smooth muscle
 Involves arterioles first
 Then leads to the opening of new capillary beds
 Increased blood flow  heat and redness (erythema)
 Increased permeability of the microvasculature
 Outpouring of protein-rich fluid (exudate)
 Into the extravascular tissues
 Mechanisms
1- Endothelial cell Retraction
 Reversible
 Opening of inter-endothelial spaces
 Immediate transient response
 Short life (15-30 minutes)
 Induced by:
 Histamine
 Bradykinin
 Leukotriens
 Neuropeptide substance P
 Mostly in postcapillary venules
2- Direct endothelial injury
 In Severe injury (Burns or microbial toxins)
 Endothelial cell necrosis and detachment
 Immediate sustained response
 All microvessels can be affected
3- Increased transport of fluid and proteins (transcytosis) through
the endothelial cells stimulated by VEGF
4- Delayed prolonged response
 Begins after delay (2-12 hours), lasts for hours or days
 Caused by thermal injury, UV radiation, bacterial toxins
5- Leukocyte-dependent endothelial injury
6- Leakage from newly formed blood vessels
 Stasis of blood flow
 Engorgement of small vessels with slowly moving red cells
 Seen histologically as vascular congestion
 Seen externally as localized redness (erythema)
 Neutrophils accumulate along the vascular endothelium
 Endothelial cells
 Activated by mediators produced at sites of infection
 Express increased levels of adhesion molecules
 Leukocytes then adhere to the endothelium
 Migrate through vascular wall into the interstitial tissue
Fluid in the Tissues or Cavities
-
Edema is an excess of fluid in the interstitial tissue or serous cavity
It can be either Exudate or Transudate
Pus is a purulent exudate rich in neutrophils, debris of cells, and microbes
TRANSUDATE
Hydrostatic pressure imbalance across
vascular endothelium
Fluid of low protein content
(ultrafiltrate of blood plasma)
Specific gravity <1.012
EXUDATE
Alteration in normal permeabiltiy of
small blood vessels in area of injury
Fluid of high protein content (>3g/dl) &
increased cellular debris
Specific gravity >1.020
Role of Lymphatic System in Inflammation
-
-
The system of lymphatics and lymph nodes filters and polices the
extravascular fluids.
In inflammation, lymph flow is increased to help drain edema fluid that
accumulates because of increased vascular permeability.
Leukocytes and cell debris, as well as microbes, may find their way into
lymph.
Lymphatic vessels, like blood vessels, proliferate during inflammatory
reactions to handle the increased amount of fluid.
The local inflammatory reaction may fail in containing the injurious agent
Secondary lines of defense:
 Lymphatic system:
 Lymphatic vessels drain offending agent, edema fluid & cellular
debris, and may become inflamed (LYMPHANGITIS).
 Draining Lymph nodes may become inflamed (LYMPHADENITIS).
 Lymph nodes may become tender&swollen (LYMPHADENOPATHY)
 Secondary lines of defense may contain infection, or may be
overwhelmed resulting in BACTEREMIA.
 MPS (macrophage-phagocytic system) (also known as RES –reticular
endothelial system-): Phagocytic cells of spleen, liver & BM
Leukocyte Recruitment to Sites of Inflammation
-
-
Leukocytes that are recruited to sites of inflammation perform the key
function of eliminating the offending agents
The most important leukocytes in typical inflammatory reactions are the ones
capable of phagocytosis, namely, neutrophils and macrophages.
The two cell types share many features, such as phagocytosis, ability to
migrate through blood vessels into tissues, and chemotaxis.
These leukocytes ingest and destroy bacteria and other microbes, as well as
necrotic tissue and foreign substances
Macrophages also produce growth factors that aid in repair
When strongly activated, they may induce tissue damage and prolong
inflammation “collateral damage”
Origin
Neutrophil
HSC in BM
Life span
1-2 days
Response
Rapid, short-lived, mostly
degranulation and enzymatic
activity
Rapidly induced by assembly
of phagocyte oxidase
Low levels or none
ROS
NO
Degranulation Major response; induced by
cytoskeletal rearrangement
Cytokine
Low levels or none
production
NET
formation
Secretion of
lysosomal
enzymes
-
Rapidly induced, by extrusion
of nuclear contents
Prominent
Macrophage
HSC in BM
Tissue-resident
Stem cells in yolk sac & fetal liver
Inflammatory: days-weeks
Tissue-resident: years
More prolonged, slower, often
dependent on new gene
transcription
Less prominent
Induced following transcriptional
activation of iNOS
Not prominent
Major functional activity, requires
transcriptional activation of
cytokine genes
No
Less
HSC: Hematopoietic stem cells
iNOS: inducible nitric oxide synthase
NET: neutrophil extracellular traps
2019 Nobel prize in physiology or medicine was awarded to William G., Kaelin
Jr, Peter J. & Gregg L. for discovery of how cells sense and adapt to oxygen
availability
Cellular Events
1- Leukocyte Adhesion to Endothelium:
 Stasis
 Margination
 Rolling
 Adhesion of leukocytes to endothelium
2- Leukocyte Migration through Endothelium: transmigration (diapedesis)
3- Chemotaxis of Leukocytes: migration in the interstitium toward stimulus
4- Phagocytosis and degranulation and clearance of the offending Agent
5- Leukocyte activation and release of products
Leukocyte Adhesion to Endothelium
-
The attachment of leukocytes to endothelial cells is mediated by adhesion
molecules whose expression is enhanced by cytokines
Cytokines are secreted by cells in tissues in response to microbes and injury
Selectins and integrins
 Involved in leukocyte adhesion and migration
 Expressed on leukocytes and endothelial cells
 Selectins: initial weak interactions between leukocytes and endothelium
 Integrins: firm adhesion of leukocytes to endothelium
Selectins
-
Receptors on the surfaces of endothelial cells and leukocytes
Bind selected sugars (sialylated oligosaccharides)
Not expressed on resting endothelial cells (within 30 minutes of stimulation)
Low affinity binding with a fast-off-rate
Single chain transmembrane glycoprotein
Binding to ligand needs Ca
Distribution:
 E-selectin (CD62E): endothelial cells
 P-selectin (CD62P): Platelets & endothelial cells
 L-selectin (CD62L): Leukocytes
Integrins
-
-
Heterodimeric cell surface proteins (α & β chains)
Binds to ligands present in:
 Extracellular matrix
 Complement system
 Surface of other cell
Cytoplasmic domains bind with cytoskeleton
The Process of Extravasation of Leukocytes
1- Rolling/weak adhesion (tethering): by selectins and
their CHO ligands
 L-selectin on WBC & Sialyl-Lewis X or GlyCAM on endothelium
 Sialyl-Lewis X on WBC & E- or P-selectin on endothelium
2- Firm adhesion by integrins & their ligands
 LFA-1 on WBC & ICAM-1,2 on endothelium
 MAC-1 on WBC & ICAM-1,2 on endothelium
 VLA-4 on WBC & VCAM-1 on endothelium
 Note: chemokines play a role in firm adhesion by activating integrins
3- Diapedesis (Transmigration)
 PECAM-1 (CD31) on WBC & PECAM-1 (CD31) on endothelium
4- Chemotaxis
 Migration of cells along a chemical gradient
 Leukocytes are directed by chemoattractant gradients
 To migrate across the endothelium & ECM into the tissue
 Chemotactic factors:
 Soluble bacteial products: N-formyl-methionine termini
 Complement system products: C5a
 Lipooxygenase pathway: LT-B4
 Cytokines: IL-8
 Effects of Chemotactic Factors on Endothelium
 Increase avidity of integrins
 Induction of endothelial adhesion molecules
 Effects of Chemotactic Factors on Leukocytes
 Stimulate locomotion
 Degranulation of lysosomal enzymes
 Production of arachidonic acid metabolites
 Modulation of the numbers and affinity of leukocyte
adhesion molecules
Selectins
Family
Molecule
L-selectin (CD62L)
E-selectin (CD62E)
Distribution
PMN
Monocytes
Lymphocytes
B cells
Endothelium
P-selectin (CD62P)
Endothelium
Integrins
LFA-1 (CD11aCD18)
PMN
Monocytes
T cells
MAC-1 (CD11bCD18) Monocytes
DC
VLA-4
α4β7
Monocytes
T cells
Monocytes
T cells
Ligand
GlyCAM-1 (Sialyl-Lewis X)
MAdCAM-1
CD34
Expressed on endothelium
Sialyl-Lewis X (CLA) on PMN,
Monocytes & T cells
Sialyl-Lewis X (CLA) on PMN,
Monocytes & T cells
ICAM-1 (CD54)
ICAM-2 (CD102)
Both on endothelium
ICAM-1 (CD54)
ICAM-2 (CD102)
Both on endothelium
VCAM-1 (CD106)
On endothelium
VCAM-1 (CD106)
MAdCAM-1
On endothelium in gut
-
Nature of Cell Infiltrate
 Bacterial infections: dominated by neutrophils for several days
 Viral infections: lymphocytes may be the first cells to arrive
 Hypersensitivity reactions: dominated by activated lymphocytes,
macrophages, and plasma cells (reflecting the immune response)
 Allergic reactions, eosinophils may be a prominent cell type
Phagocytosis and Clearance of the Offending Agent
-
Phagocytosis is the process of ingestion and digestion of solid substances
(other cells, bacteria, necrotic tissue or foreign material)
Steps of phagocytosis:
1- Recognition & binding to cellular receptors (Opsonins: IgG ,C3b, collectin)
2- Engulfment
3- Fusion of phagocytic vacuoles with lysosomes
4- Killing or degradation of ingested material
The two most important recognition receptors are:
-
-
Toll-like receptors are microbial sensors
Inflammasome is a multiprotein cytoplasmic complex that recognizes
products of dead cells such as uric acid  activation of caspases-1 
secretion of the biologically active IL-1.
Other receptors:
 Mannose receptors: bind to mannose residues on microbes cell walls.
 Scavenger receptors: oxidized LDL, and microbes.
 Opsonin receptors (high affinity): IgG, C3b, collectins.
 Cytokine receptors.
Intracellular Destruction of Microbes and Debris
-
Oxygen Burst Products/ Reactive Oxygen Species(ROS)
 2O2 + NADPH (NADPH oxidase)  2O2- + NADP+ + H+ (superoxide anion)
 O2- + 2H+ (Dismutase)  H2O2 (hydrogen peroxide)
 H2O2 + Cl- (Myeloperoxidase)  HOCl- (hypochlorite)
 The H2O2-MPO-halide: most efficient bactericidal system in neutrophils
 At low levels: increase chemokines, cytokines & adhesion molecules
 At high levels:
 Endothelial damage & thrombosis
 Protease activation & inhibition of antiproteases
 Direct damage to other cells
 Protective mechanisms
 Transferrin
 Superoxide
 Ceruloplasmin
dismutase
 Catalase
 Glutathione
-
Nitric Oxide:
 Soluble gas produced from arginine
 By the action of nitric oxide synthase (NOS)
 Participates in microbial killing.
 Three different types of NOS:
 Endothelial (eNOS)
 Neuronal (nNOS)
 Inducible (iNOS)
 eNOS and nNOS are constitutively expressed at low levels, and the NO
they generate acts to maintain vascular tone and as a neurotransmitter,
respectively
 iNOS, is involved in microbial killing, is expressed when macrophages are
activated by cytokines (IFN-γ) or microbial products, and induces the
production of NO
-
Neutrophilic Extracellular Traps (NETs)
 Are extracellular fibrillar networks.
 Contains a frame work of nuclear chromatin with granule protein.
 Provides a high concentration of antimicrobial substances.
 In this process the nuclei of the neutrophils are lost.
-
Granule Enzymes and Other Proteins
Neutrophils and monocytes contain granules packed with enzymes and antimicrobial proteins that degrade microbes and dead tissues and may
contribute to tissue damage.
Granule Enzymes and Other Proteins
1- Specific (or secondary) granules: lysozyme, collagenase, gelatinase,
lactoferrin, plasminogen activator, histaminase, and alkaline phosphatase.
2- Larger azurophil (or primary) granules: MPO, bactericidal factors (such as
defensins), acid hydrolases, and a variety of neutral proteases (elastase,
cathepsin G, nonspecific collagenases, proteinase 3)
Lysosomal constituents
-
Released in
 After cell death
 Leakage upon formation of phagocytic vacuoles
 Frustrated phagocytosis (fixed on flat surfaces)
 After phagocytosis of membranolytic substance, e.g. urate..
 Acid proteases: needs low PH as in phagolysomes.
-
Neutral protease effects
 Elastases, collagenases, and cathepsin
 Cleave C3 and C5 producing C3a & C5a
 Generate bradykinin like peptides
-
Minimizing the damaging effects of proteases by antiproteases:
 Alpha 2 macroglobulin
 Alpha 1 antitrypsin
Genetic defects in leukocyte function
Disease
Leukocytes adhesion deficiecny 1
Defect
CD18 unit of integrin
Leukocytes adhesion deficiecny 2
Sialyl-Lewis X
Neutrophil-specific granule deficiency
Absent specific granules
Chronic Granulomatous Disease, Xlinked
Membrane component of NADPH
oxidase
Chronic Granulomatous Disease,
autosomal recessive
Cytoplasmic component of NADPH
oxidase
Myeloperoxidase (MPO) deficiency
Absent MPO-H2O2 system
Chediak-Higashi disease
Organelle trafficking
Acquired defects in leukocyte function
-
Chemotaxis defects
a- Burns
b- Diabetes
c- Sepsis
-
Adhesion
a- Hemodialysis
b- Diabetes
-
Phagocytosis and microbiocidal activity
a- Leukemia
b- Sepsis
c- Diabetes
d- Malnutrition
Chemical mediators of inflammation
-
Substances that initiate and regulate inflammatory reactions
Used to design anti-inflammatory agents such as aspirin and acetaminophen
Mediators may be
 Produced locally by cells at the site of inflammation
 Derived from circulating precursors that are activated at inflammation site
Sources of chemical mediators
-
-
Cell derived
 Formed elements normally sequestered in granules: Vasoactive amines
 Newly synthesized in response to stimulation: PGs, LT, O2 species, NO,
cytokines, PAF
Circulating plasma proteins
 Coagulation / fibrinolytic factors
 Complement System
 Kinins
General characteristics of chemical mediators
-
Bind to specific cellular receptors, or have enzymatic activity
May stimulate target cells to release secondary mediators
Secondary mediators might have similar or opposing functions
May have limited targets, or wide spread activities
If unchecked and uncontrolled, cause harm
Short lived function
 Short half-life (arachidonic acid metabolites)
 Inactivated by enzymes (kininase on bradykinin)
 Eliminated (antioxidants on O2 species)
 Inhibited (complement inhibitory proteins)
Notes regarding the chemical mediators
-
The major cell types that produce mediators of acute inflammation are tissue
macrophages, dendritic cells, and mast cells
Platelets, neutrophils, endothelial cells, and most epithelia also can be induced
to elaborate some of the mediators
Cell-derived mediators: most important for reaction against microbes in tissues
Plasma-derived mediators (complement proteins)
 Produced mainly by the liver
 Present in the circulation as inactive precursors
 Must be activated by a series of proteolytic cleavages
 Effective against circulating microbes, but also can be recruited into tissues
Vasoactive amines (Histamine & Serotonin)
-
So named because they have important actions on blood vessels
Stored in granules in mast cells (histamine), and platelets (serotonin)
Arteriolar dilatation and ↑ permeability of venules (immediate phase reaction)
Induce endothelial cell contraction in venules
Binds to H1 receptors on microvascular endothelial cells
Inactivated by histaminase
The antihistamine drugs
 Commonly used to treat some inflammatory reactions, such as allergies
 H1 receptor antagonists that bind to and block the receptor
-
Release of histamine
 Physical injury (trauma, cold, heat)
 Binding of IgE to Fc receptors
 Anaphylatoxins (C3a, C5a) binding
 Histamine releasing protein derived from PMNs
 Neuropeptides (substance P)
 Cytokines (IL-1, IL-8)
-
Release of serotonin
 Platelets aggregation
 PAF
Arachidonic Acid Metabolites
-
-
-
Arachidonic acid (AA)
 20-carbon polyunsaturated fatty acid
 Derived from
 Dietary sources
 Conversion from the essential fatty acid linoleic acid
Most arachidonic acid is esterified & incorporated into membrane phospholipids
Mechanical, chemical and physical stimuli or other mediators (C5a) trigger the
release of arachidonic acid from membranes by activating cellular
phospholipases, mainly phospholipase A2
Once freed from the membrane, AA is rapidly converted to bioactive mediators
These mediators, also called eicosanoids (Greek eicosa = 20)
Products of the Cycloxygenase pathway of AA metabolism
-
-
-
-
TXA2
 Vasoconstriction
 Stimulates platelets aggregation & thrombosis
PGI2 (Prostacyclin)
 Vasodilatation
 Inhibits platelets aggregation
PGD2, PGE2, PGF2a (Prostaglandins)
 Vasodilatation
 Edema formation
 Pain (PGE2)
PGs are also involved in the pathogenesis of pain and fever
PGE2 makes the skin hypersensitive to painful stimuli, and causes fever
Products of the Lipoxygenase pathway of AA metabolism
-
-
5-Lipoxygenase pathway
 5-HETE and LTB4 (derived from LTA4): Chemotactic agents
 LTC4, LTD4 and LTE4
 Vasoconstriction
 Bronchospasm
 Increased vascular permeability
12- Lipoxygenase pathway
 Lipoxins (LXA4 & LXB4)
 Vasodilatation
 Inhibit neutrophil chemotaxis and adhesion
 Stimulate monocyte adhesion
Pharmacologic Inhibitors of Prostaglandins and Leukotrienes
1- Cyclooxygenase inhibitors (aspirin and other (NSAIDs), such as ibuprofen)
 They inhibit both COX-1 and COX-2 and thus block all prostaglandin synthesis
 Efficient in treating pain and fever
 Selective COX-2 inhibitors
 Newer class of these drugs that
 200- to 300-fold more potent in blocking COX-2 than COX-1
 COX-1: production of PGs that are involved in inflammation & protecting
gastric epithelium from acid-induced injury (Gastric Protective)
 COX-2: PGs that are involved only in inflammation (risk of thrombosis)
2- Lipoxygenase inhibitors
 5-lipoxygenase is not affected by NSAIDs
 Many new inhibitors of this enzyme pathway have been developed.
 Pharmacologic agents that inhibit leukotriene production (zileuton) are
useful in the treatment of asthma
3- Corticosteroids
 Broad-spectrum anti-inflammatory agents
 Reduce the transcription of genes encoding COX-2, phospholipase A2,
pro-inflammatory cytokines (IL-1 and TNF), and iNOS
4- Leukotriene receptor antagonists
 Block leukotriene receptors and prevent the actions of the leukotrienes
 These drugs (Montelukast) are useful in the treatment of asthma
Platelet-activating Factor (PAF)
-
-
Generated from membranes phospholipids by Phospholipase A2
Discovered as a factor that caused platelet aggregation
It is now known to have multiple inflammatory effects
 Aggregates and degranulates platelets
 Potent vasodilator and bronchoconstrictor
 At low concentrations it induces vasodilation and ↑ vascular permeability
Effects on leukocytes
 Increase adhesion to endothelial cells
 Chemotactic
 Degranulation
 Oxygen burst
Cytokines
-
Hormone-like polypeptides (secretion is transient)
Principally secreted by activated lymphocytes, macrophages & dendritic cells
Also produced endothelial, epithelial, and connective tissue cells
Mediate and regulate immune and inflammatory reactions
Growth factors that act on epithelial & mesenchymal cells are not cytokines
Produced by cells, involved in cell to cell communication
Pleiotropic effects: immunologic, hematopoietic & pro-inflammatory activities
Effects: autocrine (same cell), paracrine (adjacent cells), endocrine (distant cells)
Classes of cytokines
-
Regulators of lymphocyte function
 IL-2 stimulates proliferation
 TGF-β inhibits lymphocytes growth
-
Primary responders to injury (innate immunity)
 IL-1 & TNF
-
Activators of cell mediated immunity
 INF-g & IL-12
-
Chemotactics
 IL-8
-
Hematopoietic growth factors
 IL-3 & GM-CSF
TNF & IL-1
-
Produced mainly by macrophages
Secretion stimulated by: bacterial products, immune complexes, endotoxins,
physical injury, other cytokines.
Effects on endothelial cell, leukocytes, fibroblasts, and acute phase reactions.
TNF antagonists have been remarkably effective in the treatment of chronic
inflammatory diseases, particularly
a- Rheumatoid arthritis
b- Psoriasis
c- Inflammatory bowel disease
Chemokines
-
A group of related chemotactic polypeptides
All of which have 4 cysteine residues.
Chemokines are a family of small (8–10 kD) proteins
Act primarily as chemoattractants for specific types of leukocytes
About 40 different chemokines and 20 different receptors for chemokines
Regulate adhesion, chemotaxis and activation of leukocytes
Important for proper targeting of leukocytes to infection site
Mediate their activities by binding to seven-transmembrane GPCR
-
They have two main functions:
 Acute inflammation (inflammatory chemokines)
 Maintenance of tissue architecture (homeostatic chemokines): produced
constitutively by stromal cells in tissues
-
The largest family consists of CC chemokines, so named because the first 2 of the
4 cysteine residues are adjacent to each other
-
Examples of CC chemokines:
 CCL2: Monocyte chemoattractant protein 1 (MCP-1)
 CCL3 & CCL4: Macrophage inflammatory protein 1 (MIP-1a & 1b)
 CCL5: RANTES (regulated and normal T-cell expressed and secreted)
 CCL11: Eotaxin
-
Examples of CXC chemokines:
 CXCL8: IL-8, neutrophil chemotactic
-
Difficult to develop chemokine antagonists that suppress inflammation
(functional redundancy of these proteins).
Nitric Oxide
-
Soluble gas produced from arginine by the action of nitric oxide synthase (NOS)
Participates in microbial killing.
Three different types of NOS:
 Endothelial (eNOS)
 Neuronal (nNOS)
 Inducible (iNOS)
-
Role in inflammation:
 Vasodilator (smooth muscle relaxant)
 Antagonist of platelets adhesion, aggregation and stimulation
 Reduces leukocytes adhesion and recruitment
 Microbiocidal in activated macrophages
-
eNOS and nNOS are constitutively expressed at low levels, and the NO they
generate acts to maintain vascular tone and as a neurotransmitter, respectively
-
iNOS, is involved in microbial killing, is expressed when macrophages are
activated by cytokines (IFN-γ) or microbial products, and induces the production
of NO
Products of coagulation
-
Inhibiting coagulation reduced the inflammatory reaction to some microbes
Coagulation and inflammation are linked processes.
Protease-activated receptors (PARs)
 Activated by thrombin (protease that cleaves fibrinogen to produce fibrin)
 Expressed on leukocytes, suggesting a role in inflammation
 Clearest role is in platelets
 Thrombin activation of a PAR known as the thrombin receptor
 Potent trigger of platelet aggregation during the clot formation
-
All forms of tissue injury that lead to clotting also induce inflammation
Inflammation causes changes in endothelial cells that ↑ the abnormal clotting.
Clotting / Fibrinolytic system
-
-
Fibrin clot at site of injury helps in containing the cause.
Fibrin clot provides a framework for inflammatory cells.
Xa causes increased vascular permeability and leukocytes emigration
Thrombin causes
 Leukocytes adhesion
 Platelets aggregation
 Generation of fibrinopeptides: chemotactic & induce vasopermeability
 Chemotactic
XIIa also activates the fibrinolytic pathway to prevent widespread thrombosis.
Fibrin split products increase vascular permeability.
Plasmin
 Cleaves C3 to form C3a, leading to dilatation and increased permeability.
 Activates XIIa amplifying the entire process.
Thrombin as an Inflammatory Mediator
-
Binds to protease-activated receptors (PARs) expressed on platelets, endothelial
cells, smooth muscles leading to:
 P-selectin mobilization
 Expression of integrin ligands
 Chemokine production
 Prostaglandin production by activating cyclooxygenase-2
 Production of PAF
 Production of NO
Kinin System
-
Vasoactive peptides
 Derived from plasma proteins, called kininogens
 By the action of specific proteases called kallikreins
 Leads to formation of bradykinin from HMWK
-
Effects of bradykinin
 Increased vascular permeability
 Arteriolar dilatation
 Bronchial smooth muscle contraction
 Pain
-
Short half-life (inactivated by kininases)
The Complement System in Inflammation
-
Collection of soluble proteins and their membrane receptors
Function mainly in host defense against microbes and in inflammatory reactions
More than 20 complement proteins, some of which are numbered C1-C9
Function in both innate and adaptive immunity for defense against microbes
-
Several cleavage products of complement proteins are elaborated that cause
 Increased vascular permeability
 Chemotaxis
 Opsonization
-
C3a and C5a (anaphylatoxins)
 Increase vascular permeability
 Cause mast cell to secrete histamine
-
C5a
 Activates lipoxygenase pathway of AA
 Activates leukocytes
 Increased integrins affinity
 Chemotactic
-
C3b and iC3b are opsonins
Plasmin and proteolytic enzymes split C3 and C5
Membrane attack complex (C5-9) lyse bacterial membranes
Defects in the Complement System
-
Deficiency of C3 → susceptibility to infections.
Deficiency of C2 and C4 → susceptibility to SLE.
Deficiency of late components → low MAC → Neisseria infections.
↓ inhibitors of C3 and C5 convertase (↓ DAF [Decay-accelerating Factor or
CD55]) → hemolytic anemia (PNH)
↓C1 inhibitor → angioneurotic edema
Morphologic Appearance of Acute Inflammation
-
Special morphologic patterns depends on
 The severity of the reaction
 Its specific cause
 The particular tissue and site involved
1- Catarrhal
 Acute inflammation + mucous hypersecretion
 Example: common cold
2- Serous
 Abundant protein-poor fluid with low cellular content
 Example: skin blisters and body cavities (peritoneum, pleura, or pericardium)
3- Fibrinous:
 Accumulation of thick exudate rich in fibrin
 May resolve by fibrinolysis or organize into thick fibrous tissue
 Example: acute pericarditis
4- Suppurative (purulent):
 Pus: Creamy yellow or blood stained fluid consisting of neutrophils,
microorganisms & tissue debris
 Example: acute appendicitis
 Abscess: Focal localized collection of pus
 Empyema: Collection of pus within a hollow organ
5- Ulcers
 Defect of the surface lining of an organ or tissue
 Mostly GI tract or skin
Outcomes of Acute Inflammation
1- Complete resolution (back to normal)
 Clearance of injurious stimuli
 Removal of the exudate, fibrin & debris
 Reversal of the changes in the microvasculature
 Replacement of lost cells (regeneration)
2- Healing
 Organization by fibrosis through formation of Granulation tissue
 Substantial tissue destruction or
 Tissue cannot regenerate or
 Extensive fibrinous exudates
3- Abscess formation
4- Progression to chronic inflammation
Effects of Acute Inflammation
Beneficial
Elimination of injurious stimulus
Dilution of toxins
Entry of antibodies
Drug transport
Fibrin formation
Delivery of nutrients and oxygen
Stimulation of the immune response
Harmful
Digestion of normal tissue
Swelling
Inappropriate inflammatory response
Chronic inflammation
-
-
Inflammation of prolonged duration (weeks, months, or years)
Starts either rapidly or slowly
Characterized by:
 Persistent injurious agent
 Inability of the host to overcome the injurious agent
Characteristics:
 Chronic inflammatory cell infiltrate (mononuclear cells)
 Lymphocytes
 Plasma cells
 Macrophages
 Tissue destruction
 Repair
 Neovascularization
 Fibrosis (like in liver cirrhosis)
Feature
Duration
Predominant cells
Vascular events
-
-
Acute inflammation
Minutes to days
Neutrophils
Chronic inflammation
Days to years
Lymphocytes and
macrophages
Vascular proliferation &
fibrosis
Fluid & plasma protein
exudation
Develops under special circumstances
 Progression from acute inflammation (tonsillitis, osteomyelitis)
 Repeated exposure to toxic agent (Silicosis, asbestosis, hyperlipidemia)
 Viral infections like hepatitis B & C
 Persistent microbial infections (Mycobacteria, Treponema, Fungi)
 Autoimmune disorders (Rheumatoid arthritis, SLE)
Macrophages & the mononuclear phagocytic system
 Macrophages:
 Derived from circulating monocytes
 Scattered in tissues:
 Kupffer cells (liver)
 Sinus histiocytes (spleen & LN)
 Alveolar macrophages (lung)
 Microglia (CNS)
 Activated mainly by IFN-γ secreted from T lymphocytes
 Increased cell size
 Increased lysosomal enzymes
 More active metabolism = greater ability to kill ingested organisms
 Epithelioid appearance
-
Macrophages accumulation at site of infection
 Recruitment of monocytes from circulation by chemotactic factors:
 Chemokines & C5a
 PDGF, TGFα
 Fibrinopeptides & fibronectin
 Collagen breakdown fragments
 Proliferation of macrophages at foci of inflammation
 Immobilization of macrophages at sites of inflammation
-
Products of activated macrophages
 Proteases
 Complement and clotting factors
 Oxygen species and NO
 AA metabolites
 IL-1 & TNF
 Growth factors (PDGF, FGF, TGFβ)
 Neutrophil chemotactic factors
-
Granuolmatous Inflammation
 Distinctive form of chronic inflammation
 Collections of epithelioid macrophages
 May have one or more of the following
 Surrounding rim lymphocytes & plasma
cells
 A surrounding rim of fibroblasts & fibrosis
 Giant cells (either giant cell with scattered nuclei or Langerhans cells
with horseshoe nuclei)
 Central necrosis (caseating granulomas is most common in TB [acid
fast])
Bacterial
Mycobacterium tuberculosis
Mycobacterium Leprae
Trepnema pallidum
Bartonella henslae
Parasitic Schistosomiasis
Fungal
Histoplasma capsulatum
Blastomycosis
Cryptococcus neoformans
Coccidioides immitis
Inorganic Silicosis
metals
Byrelliosis
Foreign
Foreign body
body
Other prosthesis
Keratin
Unknown Sarcoidosis
-
Morphologic appearance of chronic inflammation
 Ulceration: local defect or loss of continuity in surface epithelia
 Chronic abscess cavity
 Induration & fibrosis
 Thickening of the wall of a hollow viscus
 Caseous necrosis
-
Systemic inflammatory effects (acute phase response)
 Mediated by IL-1, IL6, TNF, which interact with
vascular receptors in the thermoregulatory center
of hypothalamus via local PG-E production
 Systemic manifestations include:
 Fever
 Catabolism
 Increased slow wave sleep, decreased appetite
 Hypotension & other hemodynamic changes
 Acute-phase proteins by liver (CRP, fibrinogen, serum amyloid A protein)
 Leukocytosis:
 Neutrophilia: bacterial infection
 Lymphocytosis: viral infection
 Eosinophilia: parasitic infection
 Leukopenia
 Increased ESR
-
Consequences of Defective Inflammation
 Susceptibility to infections (defective innate immunity)
 Delayed repair
 Delayed clearance of debris and necrotic tissue
 Lack of stimuli for repair
-
Consequences of excessive inflammation
 Allergic reactions
 Autoimmune disorders
 Atherosclerosis
 Ischemic heart disease
Repair
Stem cells
-
Characteristics:
 Self-renewal capacity
 Asymmetric replication
 Capacity to develop into multiple lineages
 Extensive proliferative potential
-
Types:
 Embryonic: pluripotent cells that can give rise to all tissues of the body
 Adult: restricted differentiation capacity (lineage specific)
 Induced pluripotent
 Introducing into mature cells genes that are characteristic of ES cell
 Acquire many characteristics of stem cells
-
Impact of embryonic stem cells on medicine
 Study of specific cell signaling and differentiation steps
 Production of knockout mice
 Generation of cells to regenerate damaged tissue (regenerative medicine)
-
Examples of adult stem cells
 Bone marrow: Hematopoietic stem cells
 Liver: Hering canal
 Skeletal muscle: Satellite cells
 Intestine: Base of crypts
 Skin: Hair follicle bulge
Polypeptide growth factors
-
Chemical mediators that affect cell growth
Produced transiently in response to an external stimulus
Binding to specific receptors on the cell surface or intracellularly
The most important mediators affecting cell growth
Present in serum or produced locally
Pleiotropic effects: proliferation, migration, differentiation, tissue remodeling
Regulate growth of cells
Controlling expression of genes that regulate cell proliferation (proto-oncogenes)
Growth factors such as epidermal growth factor (EGF) & hepatocyte GF (HGF)
 Bind to receptors with intrinsic kinase activity
 Triggering a cascade of phosphorylating events through MAP kinases
 Culminate in transcription factor activation and DNA replication
Examples of growth factors
1- EGF (epidermal growth factor) & TGF-α
 Binds to its receptor ERB B1
 Mitogenic for epithelial cells & fibroblasts
 Migration of epithelial cells
2- PDGF (platelet-derived growth factor)
 Migration & proliferation of fibroblast, smooth muscle cell & monocyte
 Chemotactic
3- FGFs (fibroblast growth factors)
 Mitogenic for fibroblast & epithelial cells
 Angiogenesis
 Chemotactic for fibroblasts
 Wound healing
4- VEGF (vascular endothelial growth factor)
 Angiogenesis
 Increased vascular permeability
5- HGF/scatter factor (hepatocyte growth factor)
 Mitogenic to most epithelial cells including hepatocytes
 Promotes scattering and migration of cells
Transforming Growth Factor Beta (TGF-β)
-
TGF-β binds to 2 receptors (types I &II) with serine/threonine kinase activity
Receptors phosphorylates cytoplasmic transcription factors smads
Smads enter the nucleus and associate with other DNA binding proteins
Activating or inhibiting gene transcription
Inhibitor of most epithelial cells and leukocytes
Increases expression of cell cycle inhibitors (Cip/Kip, INK4/ARF)
Stimulates proliferation of fibroblasts & smooth muscles
Fibrosis (fibroblasts chemotaxis, ECM synthesis, ↓ proteases, ↑ protease inh.)
Strong anti-inflammatory effect
Intercellular signaling
1- Autocrine: GF acts on the same cells that produced it
2- Paracrine: GF acts on the adjacent cells
3- Endocrine: GF or hormone travels by blood and acts on a distant cell
Receptors for growth factors
-
-
Receptors with built-in intrinsic tyrosine kinase activity (GFs)
Receptors lacking intrinsic tyrosine kinase activity that recruit kinases (cytokines)
Seven transmembrane G-protein coupled receptors
 Produce multiple effects via the cAMP and Ca2+ pathways
 Chemokines utilize such receptors
Steroid hormone receptors (intracellular, bind hormone & enter the nucleus)
Extracellular matrix
-
A major component of all tissues
Provides the backbone & support
Regulates growth, movement and differentiation of cells
Divided into
 Basement membrane:
 Type IV collagen
 Adhesive glycoproteins
 Laminin
 Interstitial matrix:
 Fibrillary and nonfibrillar collagens
 Elastin
 Proteoglycans
 Fibronectin
Components of the extracellular matrix
-
Collagen
 The most common protein in animals
 Fibrillar & non-fibrillar
 Hydroxylation, mediated by vit C, provides strength
 Fibrillar collagens form most of CT in wounds & scars
 Non-fibrillar (type IV): main component of BM
Labile cells: continuously dividing
Quiescent (stable cells):
- Hepatocytes, Kidney cells, SMCs
- At G0 phase of cell cycle
- Can enter G1 phase
- Limited proliferation (except liver)
Permanent cells:
- Neurons & cardiac myocytes
- At G0 phase of cell cycle
- No proliferative capacity
-
Elastin
 Provides elasticity
 Surrounded by mesh-like network of fibrillin to
supports elastin deposition
 Defective fibrillin leads to Marfan syndrome
-
Proteoglycans
 Form highly hydrated gel like material
 Protein core with many attached long polysaccharides (glycosaminoglycans)
 Act as a reservoir for bFGF
 Integral cell membrane proteins (syndecan)
-
Adhesive glycoproteins
 Fibronectin
 Domains bind collagen, elastin, proteoglycans
 Bind to integrins via RGD (arginine-glycine-aspartic acid ) domains
 Laminin: connects cells to collagen and heparan sulfate
Repair by regeneration
-
-
Replacing injured tissue by same type of original tissue cells.
Labile (stem cells) & stable cells (liver, kidney & smooth muscles)
Involves two tissue components:
 Cellular proliferation, regulated by growth factors & growth inhibitors
 Extracellular matrix (ECM) & cell-matrix interaction
An intact basement membrane is essential for its orderly regeneration
Repair by connective tissue
-
In cases of
 Severe injury with damage to parenchymal cells and stroma
 Permanent (nondividing) cells: cardiac muscle and neurons
-
Components of CT repair:
1- Neovascularization (angiogenesis)
2- Proliferation of fibroblasts
3- Deposition of ECM
4- Remodeling
Angiogenesis
-
-
Either from
 Endothelial precursor cells
 Pre-existing vessels
VEGF effects on ECs : ↑ migration, proliferation, differentiation & permeability
Angioipoietins 1&2, PDGF, and TGF-β stabilize newly formed vessels
-
Angiogenesis from Endothelial Precursor Cells (EPCs)
 Hemangioblast → Hematopoietic stem cells & angioblasts
 Angioblasts = Endothelial Precursor Cells = EPCs
 EPCs
 Stored in bone marrow
 Markers of hematopoietic stem cells and endothelial cells
 Play a role in neovascularization, replacement of endothelial cells, reendothelialization of vascular implants
-
Angiogenesis from Pre-existing Vessels
 A parent vessel sends out capillary sprouts to produce new vessels
 Steps involved:
 Degradation of the parent vessel BM
 Migration of endothelial cells (EC)
 Proliferation of endothelial cells
 Maturation of EC and organization into capillary tubes
 Growth factors involved:
 Basic fibroblast growth factor (βFGF)
 Vascular endothelial growth factor (VEGF)
Healing
-
Healing by first intention
 Focal disruption of basement membrane
 Loss of only a few epithelial cells
 Seen in surgical Incision
-
Healing by second intention
 Larger injury, abscess, infarction
 Results in much larger scar and then CONTRACTION
-
Steps of wound healing
1- Fibrin clot formation → filling the gap
2- Induction of acute inflammatory response by an initial injury
 Neutrophils (1st 24 h)
 Monocytes by 3rd day
3- Parenchymal cell regeneration
4- Migration & proliferation of parenchymal and CT cells & granulation tissue
5- Synthesis of ECM proteins
6- Remodeling of parenchymal elements to restore tissue function
7- Remodeling of connective tissue to achieve wound strength
Fibrosis
-
Emigration and proliferation of fibroblasts: PDGF, FGF, EGF, TGF-β
Deposition of ECM: PDGF, FGF, TGF-β and cytokines (IL-1 &TNF)
Scar remodeling
-
Shift and change of the composition of the ECM of the scar
Metalloproteinases:
 Zn-dependent enzymes produced by many cells
 Capable of degrading different ECM constituents
 Inactivated by tissue inhibitors of metalloproteinases (TIMP) and steroids
 Include
 Interstitial collagenases
 Gelatinases
 Stromelysins
Wound strength
-
Sutured wounds have 70% of the strength of unwounded skin
After sutures are removed at one week, wound strength is only 10%
By 3-4 months, wound strength is about 80% of unwounded skin
Factors affecting healing:
-
Systemic
 Nutritional
 Protein deficiency
 Vitamin C deficiency
 Zinc deficiency
 Systemic diseases
 Diabetes mellitus
 Arteriosclerosis
 Renal failure
 Infections (systemic)
 Corticosteroid treatment
 Age
 Immune status
-
Local
 Infection
 Poor blood supply
 Type of tissue
 Presence of foreign body material
 Ionizing irradiation
 Mechanical factors
 Excessive movement
 Hematoma
 Apposition
Pathologic Aspects of Repair
-
Aberrations of growth may occur
1- Exuberant granulation:
 Excessive granulation tissue during wound healing
 Hypertrophic scar (temporary and self-limited)
2- Keloid:
 Excessive collagen accumulation during wound healing
 Resulting in raised tumorous scar
 Histologically: thick rope collagen
 Tumor-like mass
3- Excessive fibrosis: cirrhosis, pulmonary fibrosis, rheumatoid arthritis (RA)
4- Tissue damage:
 Collagen destruction by collagenases in RA
 Formation of nodules