CELLULAR RESPONSES TO STRESS AND TOXIC INSULTS (1)
1) Pathology
a) Study of Disease – the structural, biochemical and functional changes (cells/tissues/organs that underlie disease)
2) Four Aspects of disease process
a) Cause (etiology)
i) Two Major Classes
(1) Genetic : Inherited Mutations / Disease Associated Gene Variants
(2) Acquired : Infectious / Nutritional / Chemical / Physical
b) Mechanism of development (pathogenesis)
i) Response of cells/tissues to etiological agent (stimulus  expression of disease)
c) Biochemical/Structural Alterations (Molecular/Morphological Changes)
i) Characteristic of a disease, diagnostic of etiological process
d) Function Consequences of the Changes (Clinical Manifestations)
i) Functional abnormalities
(1) End result in changes to cells/tissues
(2) Symptoms and Signs
(3) Lead to the progression of disease (clinical course/outcome)
ii) Disease
(1) Molecular/Structural alteration of disease
(2) Leads to injury to cell/extracellular matrix (determine morphological/clinical patterns of disease)
3) Normal Cell
a) Narrow range of function/structure (State of
metabolism, differentiation, specialization)
i) Constraints of neighboring cells
ii) Availability of metabolic substrates
b) Maintains homeostasis
4)
Cell Injury
a) Due To
i) Injurious agent / Stress
ii) Deprivation of Essential Nutrients
iii) Mutations that affect essential cellular
constituents
b) Reversible – to a certain point
c) Irreversible Injury (Stimulus persists)  Cell Death
5) Cell Death
a) End result (progressive cell injury)
b) Crucial event in evolution of disease
c) Results From
i) Ischemia / Infection / Toxin
d) Normal/Essential
i) Embryogenesis / Maintenance of
Homeostasis
e) Principal Pathways
i) Necrosis / Apoptosis
6) Stress / Injury to the Cell
a) Adaptations (Cell adapts due to the stress or injury inflicted on it, if the cell can’t adapt  Injured)
i) Reversible functional/structural responses
ii) Types
(1) Hypertrophy (Increase in SIZE of cells)
(a) General
(i) Results in increased organ size
(ii) NO new cells  Just larger
(iii) Due To: Synthesis of structural components of cell (cell proteins)
(b) Cause
(i) Physiological or Pathological
1. Increased functional demand
2. Stimulation by hormones/growth factors
(c) Example: Striated Muscle Cells (Heart/Skeletal)
(i) Limited division
(ii) Response to increased metabolic demand = HYPERTROPHY
(iii) Most common stimulus  Increased workload (body builders) – increased size of muscle fibers
(d) Example : Uterus
(i) Image of Uterus which has never given birth vs.
uterus that has given birth (and the histological
differences)
(e) Example: Barbiturates
(i) Hypertrophy USUALLY refers to size of
cells/tissues, can refer to sub-cellular organells
(ii) Barbiturates
1. Hypertrophy of sER in Hepatocytes
a. Adaptive Response, Increase enzymes available for detoxification of drugs
b. Patients eventually respond less to drugs
c. May result in increased capacity to metabolize other drugs
(f) Mechanisms
(i) Induced by linked action
1. Mechanical Sensors / Growth Factors / Vasoactive Agents
(g) Biochemical Pathways
(i) (Physiological)  Phosphoinositide 3-kinase/AKt Pathway
(ii) (Pathological)  Signaling downstream of G-protein coupled
receptors
(2) Hyperplasia (Increase in NUMBER of cells)
(a) General
(i) Increased Mass of Organ/Tissue
(ii) May occur along with hypertrophy
(iii) May lead to cancer (doesn’t have to)
(b) Physiological Hyperplasia
(i) Hormonal hyperplasia (increases functional capacity of tissue when needed)
1. Ex: Female Breast in Puberty (Proliferation of glandular epilthelium – puberty/pregnancy)
(ii) Compensatory hyperplasia (Increases tissue mass after damage/resection)
1. Ex: Liver Transplant
(c) Pathological Hyperplasia
(i) Caused by excess of hormones/growth factor acting on target cells
(ii) Ex: Endometrial hyperplasia
1. Abnormal hormone induced hyperplasia, common cause of abnormal menstrual bleeding
2. Nothing to oppose estrogen
(iii) Ex: Benign Prostatic Hyperplasia
1. Induced by androgens (fertile soil for cancer to arise)
(3) Atrophy (Decrease in SIZE/METABOLIC ACTIVITY of cells)
(a) General
(i) Reduced size of organ/tissue
(b) Physiological Atrophy
(i) Common during development
1. Ex: Embryonic structure (Notochord/Thyroglossal Duct)
2. Ex: Uterus (Decreased size shortly after birth)
(ii) Ex: Uterus (decrease after parturition)
(c) Pathological Atrophy
(i) Depends on underlying cause (local or generalized)
(ii) Common Causes
1. Decreased workload (dis-use)  Muscle atrophy secondary to immobilization
2. Loss of innervation (de-nervation atrophy)
3. Diminished Blood Supply
4. Inadequate Nutrition (marasmus) – Use skeletal muscle as source of energy after fat stores are
depleted
5. Loss of endocrine stimulation (hormone-responsive tissues  Breast and Reproductive Organs)
6. Pressure – Tissue compression
(d) Mechanisms
(i) Result of decreased protein synthesis (reduced metabolic activity)
(ii) Result of increased protein degradation in cells (Ubiquitin-proteasome pathway  Responsible for
the accelerated proteolysis (catabolic conditions- cancer cachexia))
(e) Accompanied by: Increased autophagy (self-eating)
(i) Starved cell eats its own components to survive
(ii) Autophagic Vacuoles
1. Vacuoles ultimately fuse with lysosomes
2. Contents digested by lysosomal enzymes
3. Some cell debris (in vacuoles) resist digestion  persist as
membrane-bound residual bodies
a. Ex: Lipofuscin granules (brown atrophy)
(4) Metaplasia (CHANGE in type of cells)- Reversible
(a) One cell type replaced by another cell type
(b) Adaptive substitution of cells (to stress)  Cells better able withstand environment
(c) Types
(i) Most Common Epithelial Metaplasia - Columnar  Squamous (Respiratory Tract)
a. Chronic Irritation (cigarette smoker)  Normal PCEE replaced by stratified squamous, lack
of muco-cilliary elevator
b. Persistant  ay initiate malignant transformation in meta-plastic epithelium
(ii) Squamous  Columnar (Barrett esophagus)
1. Esophageal squamous epithelium replaced by
intestinal-like columnar cells
2. Caused by – Influence of refluxed gastric acid
(iii) Connective Tissue Metaplasia
1. Form cartilage, bone or adipose tissue in tissues that
don’t contain those elements
2. **Bone Formation in muscle (myositis ossificans) –
can occur following intramuscular hemorrhage
(d) Mechanisms
(i) Phenotype of already differentiated cell DOES NOT change (not squamouscolumnar)
(ii) Stem Cells / Undifferentiated MEsenchymal cells (in CT)  Different cell type than others in tissue
(iii) Pre-cursor cells differentiate along a new pathway
CELLULAR RESPONSES TO STRESS AND TOXIC INSULT (2)
1) Causes of Cell Injury
a) Oxygen Deprivation
i) Hypoxia (Deficiency of oxygen)
(1) Reduces aerobic oxidative repiration
(2) Causes:
(a) Reduced Blood Flow (Ischemia)
(b) Inadequate Oxygenation of the Blood (Cardio-respiratory failure)
(c) Decreased oxygen-carrying capacity of the blood (Anemia/CO poisoning/Severe Blood Loss)
(3) Depending on Severity  Cells adapt, undergo injury or die
b) Physical Agents
i) Mechanical Trauma / Extremes of Temp (Burns/Cold) / Change in Atmospheric Pressure / Radiation / Electric
Shock
c) Chemical Agents & Drugs
i) Chemicals / Glucose or Salt in hypertonic conc. / Oxygen at High conc. / Poisons / Environmental & Air
Pollutants / Insecticides & Herbicides / Industrial & Occupational Hazards / Recreational Drugs / Therapeutic
Drugs
d) Infectious Agents
i) Viruses  Large Tapeworms / Rickettsiae / Bacteria / Fungi / Higher Forms of Parasites
e) Immunological Reactions
i) Injurious reactions to endogenous self-antigens (several autoimmune diseases)
ii) Immune reactions to external agents (Microbes / Environmental Substances)
f) Genetic Derangements
i) Severe Defects
(1) Congenital Malformations associated w. Down Syndrome (Chromosomal anomaly)
ii) Subtle Defects
(1) Decreased lifespan of RBC’s (Single AA substitution in hemoglobin in sickle cell anemia)
iii) Variations in genetic makeup
(1) Influence susceptibility of cells by chemicals / other
environmental insults
g) Nutritional Imbalances
i) Protein-calorie deficiencies (underprivileged)
ii) Deficiencies of specific vitamins
iii) Self-imposed problems (anorexia)
iv) Nutritional Excess (excess of cholesterol / obesity)
2) Morphological Alterations
a) Reversible Injury
i) Swelling of cell & organelles / Blebbing of Plasma Membrane / Detachment of ribosomes from ER / Clumping of
nuclear chromatin
ii) Associated with
(1) Decreased ATP prod / Lose cell mem Integrity / Defects in protein syn. / Cytoskeletal damage /DNA damage
iii) Features
(1) Cell Swelling
(a) Failure of energy dep. Ion pumps in plasma membrane
(b) 1st manifestation of almost all forms of injury to a cell
(c) Difficult to appreciate at microscopic level (w. light micro.)  Apparent at whole organ level
(i) Small clear cytoplasmic vacuoles (distended/pinched off ER)
(d) Pallor, increased turgor, and increase in weight of organ
(2) Fatty Change
(a) Hypoxic Injury / Various Forms of Toxic & Metabolic
Injury / Appearance of lipid vacuoles in cytoplasm
(b) Ex: Hepatocytes and Myocardial Cells
iv) Ultra-structural changes
(1) Plasma Mem. – Blebbing, Blunting, Loss of Microvilli
(2) Mitochondrial Changes – Swelling, Small amorphous densities
(3) Dilation of the ER
(a) Detachment of polysomes / Intra-cytoplasmic myelin figures
(4) Nuclear alterations – Disaggregation of granular/fibrillar elements
b) Irreversible Cell Injury / Death
i) Continuous damage  injury becomes irreversible (cell can’t recover
and dies!)
ii) Two Principle Types of Cell Death
(1) Necrosis
(a) Severe Membrane Damage – Lysosomal enzymes enter
cytoplasm and digest cell (Cellular Contents Leak Out)
(b) ALWAYS PATHOLOGICAL process
(c) Morphological Appearance
(i) Result of denaturation of intracellular proteins, and
enzymatic digestion of lethally injured cell
(ii) Necrotic cells – unable to maintain membrane, contents
leak  Elicits inflammation in surrounding tissue
(d) Necrotic Cells
(i) Increased Eosinophilia in H&E stain
1. Loss of cytoplasmic RNA – Binds H (blue dye)
2. Denatured cytoplasmic proteins – Binds E (red dye)
(ii) Glassy homogenous appearance  Loss of glycogen particles
(iii) Digestion of cytoplasmic organelles  Vacuolated cytoplasm (“moth-eaten”)
(iv) Nuclear Changes of Necrotic Cells
1. Kayolysis – Fading of Chromatin, DNA loss bc of enzymatic degradation by endonucleases
2. Pyknosis – Nuclear shrinks, increased color, chromatin condenses into solid shrunken mass
3. Kayorrhexis – Nucleus undergoes fragmentation, nucleus totally disappears (1-2 days)
(e) Dead Cells
(i) Replaced by large phospholipid masses  derived from damaged cell membranes
(ii) Phospholipid precipitates  Phagocytosed by other cells, further degraded into FA’s
(2) Apoptosis
(a) Cell’s DNA or Proteins damaged beyond repair
(i) Cell kills itself: Nuclear dissolution / Fragmentation of cell WITHOUT complete loss of membrane
integrity
(ii) Rapid removal of cellular debris
(b) Serves normal functions  NOT necessarily associated with cell injury
PATTERNS OF TISSUE NECROSIS
Types
Coagulative Necrosis
General
Associate w. Ischemia
Identification
Tissue – Firm
Architecture of dead tissue Dead Cells persist for dayspreserved for a few days
weeks  Removed by
phagocytosis (leukocytes),
digestion by lysosomal
enzymes of leukocytes
Liquefactive Necrosis
FOCAL BACTERIAL
INFECTION (occasionally in
fungal)
Example
Infarct  Ischemia (obstruction)
– coaqulative necrosis of
supplied tissue
Creamy Yellow purulent
matter (dead leukocytes)
Infarct in Brain (Dissolution of
Tissue)
Applied to limb (usually
lower leg)  Loss of blood
supply (Coag. Nec.) –
involves multiple tissue
planes
Add bacterial infection
(liquefactive nec.)  Wet
Gangrene
Microscopic – collection of
fragmented/lysed cells,
amorphous granular debris
w. distinctive inflamed
border (granuloma)
Tuberculosis
Digestion of dead cell 
Transform tissue to liquid
Gangrenous Necrosis
Caseous Necrosis
Hypoxic death of cells
(CNS)
No specific pattern of cell
death
Most often seen in TB
infection
“Cheese-like” – friable
white appearance in area
of necrosis
Fat Necrosis
Doesn’t denote a specific
pattern of necrosis
Release of activated
pancreatic lipases into
substance of pancreas /
peritoneal cavity
Fibrinoid Necrosis
Immune Reactions
involving blood vessels
Complexes of Ag-Abs
deposited in walls of
arteries
Microscopic – Foci of
shadowy outlines of necrotic
fat cells, basophilic calcium
deposits, inflammatory
reaction “Spongiform
Appearance”
White chalky deposits (foci of
fat necrosis)
Microscopic – Bright pink and Arteries
amorphous appearance
(Deposits of immune
complexes and fibrin)
3) Mechanisms of Cell Injury
a) Principles of Cell injury
i) Cell Response to Injurious Stimulus
(1) Depends on: Nature of Injury, Duration, and Severity
(2) Small doses of toxin or brief period of ischemia may induce reversible change
(3) Large doses of toxin or prolonged ischemia  Instantaneous Cell Death / Slow irreversible injury  cell
death
ii) Consequences  Depend on type, state, and adaptability of injured cell
iii) Cell injury (result of different biochemical mechanisms)
(1) Act on several essential cellular component (mitochondria, cell membrane, DNA in nuclei)
iv) Any injurious stimulus  May simultaneously trigger multiple connected mechanisms that damage cells (can’t
attribute injury to a single or dominant biochemical activity)
b) ATP
i) Production (Two Ways)
(1) Major – Oxidative phosphorylation of adenosine diphosphate (reduction of oxygen – ETC in mitochondria)
(2) Minor – Glycolytic Pathway (ATP in absence of oxygen – uses glucose)
ii) ATP Depletion/Decreased synthesis
(1) Associated w. hypoxia and chemical injury
(2) Major Causes
(a) Reduced oxygen supply and nutrients / Mitochondrial
Damage / Action of toxins (ex: CN)
(3) High-Energy phosphate in form of ATP
(a) Required for all processes in the body
(b) Depletion of ATP to 5-10% of normal levels  WIDESPREAD
effect on critical cellular systems
(4) Effects on Cellular Systems
(a) Reduced activity of plasma membrane Na-K pump
(i) Failure Na enters/accumulate inside cells, K diffuses
out
(ii) Gain of Solute  Isoosmotic gain of water (cell
swelling/dilation of ER)
(b) Cellular Metabolism altered
(i) Reduced supply of oxygen to cells (ischemia)
(ii) Oxidative phosphorylation ceases (Decrease in cellular ATP / Increase in adenosine monophosphate
/ glycogen stores rapidly depleted)
(c) Failure of Ca pump  Influx of Ca (damages intracellular organelles)
(d) Prolonged or Worsening depletion of ATP
(i) Structural disruption of protein synthetic apparatus  detachment of ribosomes from rough ER /
Dissociation of polysomes (reduction in protein synthesis)
(e) Oxygen/Glucose deprivation
(i) Protein misfoldinng  Trigger cellular reaction (Cell Injury or even Death)
(f) Irreversible damage to mitochondrial and lysosomal membranes  Cell Necrosis
c) Mitochondrial Damage
i) General
(1) Cells supplier of energy (ATP)  Critical Player in cell injury/death
ii) Damaged by:
(1) Increases cytosolic Ca / Reactive oxygen species / Oxygen deprivation
(2) Mutations in mitochondrial genes (cause of some inherited diseases)
iii) Formation of a high-conductance channel in mito. membrane
(1) Mito. permeability transition pore  Loss of mito. mem. Potential (Failure of
oxidative phosphorylation and progressive depletion of ATP)  NECROSIS of the cell
iv) Sequester proteins between inner and outer membrane
(1) Capable of activating apoptatic pathways
(a) Cytochrome C and Caspases  indirectly activate apoptosis inducing enzymes
(b) Increased permeability of outer mito. mem. (leakage of proteins into cytosol)  Death by apoptosis
d) Calcium Homeostasis
i) General
(1) Ca Ions (important mediators of cell injury)
(2) Cytosolic free Ca (maintained at low levels)
(3) Intracellular Ca (Sequestered in mitochondria and ER)
ii) Increased cytosolic Ca  Activates enzymes
(1) Proteases  Break down membrane and cytoskeletal proteins
(2) Endonucleases  Responsible for DNA / Chromatin fragmentation
(3) ATPases  hasten ATP depletion
iii) Increased intracellular Ca levels
(1) Induction of apoptosis (direct activation of capases) – increases mitochondrial
permeability
e) Free Radicals
i) General
(1) Chemical species with single unpaired electron in outer orbit
(2) Energy created by unstable configuration
(a) Released through reactions with adjacent molecules (inorganic/organic chemicals, Lipids, Carbs, Nucleic
Acids)
(3) Decay spontaneously
(4) Multiple non-enzymatic/enzymatic mechanisms in cells remove free radicals (minimize injury)
(5) Iron/Copper catalyze formation of ROS (Min. levels by binding ions to storage/transport proteins :
Transferrin, ferritin, lactoferrin  Min. formation of ROS)
(6) Reactive Oxygen Species (ROS)
(a) Oxygen-derived free radical
(b) Produced normally in cells (during respiration/energy generation)
(c) Degraded & removed by cellular defense systems
(d) Produced in large amounts by leukocytes (neutrophils / macrophages)
ii) Generation of Free Radicals
(1) Reduction-Oxidation Reactions occur during normal metabolic processes
(2) Absorption of radiant energy (Ultraviolet light, X-rays, ionizing radiation- hydrolyzes water into ‘OH and H
free radicals)
(3) Rapid bursts of ROS (production in activated leukocytes- inflammation)
(4) Enzymatic metabolism of exogenous chemicals or drugs
(5) Metals (Iron/Copper) donate or accept free electrons during intracellular reactions
(6) Nitric Oxide (Important chemical mediator- acts as free radical) – generated by endothelial cell,
macrophages, and neurons
iii) Three Reactions of Free Radicals
(1) Lipid Peroxidation in Membranes (Presence of O2)
(a) Cause peroxidation of lipids within plasma and organelle membranes
(b) Oxidative damage (Initiated when double bond in unsaturated FA’s of mem. lipids are attacked by O2
derived free radicals
(2) Oxidative modification of proteins (Free Radicals promote)
(a) Oxidation of AA side chains / Formation of protein-protein cross-links (disulfide bond) / Oxidation of
protein backbone
(3) Lesions in DNA
(a) Single & Dbl strand breaks in DNA / Cross-linking of DNA Strands / Formation of adducts
f) Membrane Damage
i) Biochemical Mechanisms:
(1) Reactive oxygen species / Dec. phospholipid synthesis & Inc. breakdown / Cytoskeletal abnormalities
ii) Important Sites of Membrane Damage during Cell Injury
(1) Mito: Opening mitochondrial permeability pore = dec. ATP / Release of proteins  Apoptotic Death
(2) Plasma Mem: Lose Osmotic Balance/Loss of Cellular Contents/Cells may leak metabolites – even lower ATP
(3) Lysosomal Membrane
(a) Leak Enzymes/Activate acid hydrolases/Activate of enzymes  Enzymatic Digestion/Cells Die (Necrosis)
CELLULAR RESPONSES TO STRESS & TOXIC INSULTS (3)
1) Hypoxia – Reduced oxygen availability
2) Ischemia
a) General
i) Supply of oxygen/nutrients decreased (reduced blood flow) – obstruction in artery or reduced venous drain
ii) Compromise delivery of glycolysis substrates (no energy!)
iii) More rapid/severe cell & tissue damage than hypoxia w/o ischemia
iv) No reliable way for reducing injurious consequences of ischemia
b) Ischemic Tissues
i) Aerobic metabolism compromised
ii) Anaerobic energy generation stopped – glycolytic sub gone, glycolysis inhibited (accumulation of metabolites)
c) Mechanisms of Ischemic Cell Injury
i) Sequence of Events
(1) Oxygen tension w.i cell decreases
(a) Lose oxidative phosphorylation
(b) Decreased generation of ATP  Failure of Na pump (Loss of K / Influx Na & H20 / Cell Swelling)
(2) Influx of Ca
(3) Progressive loss of glycogen
(4) Decreased Protein Synthesis
ii) Ex: Heart Muscles (stop contracting w.i 60 seconds of coronary occlusion)
(1) Loss of contraction = NOT CELL DEATH
(2) Continued Hypoxia
(a) ATP depletion  Deterioration
(i) Cytoskeleton disperses
1. Loss of Ultra-structural features-microvilli/blebbing
2. Myelin figures (degen. cell mem. seen w.i cytoplasm or extracellularly)
3. Mitochondria – swollen (loss of volume control in organelle)
4. ER remains dilated
5. Entire cell markedly swollen (Increased water, Na, Cl / Decreased K)
(b) ***OXYGEN RESTORED – REVERSIBLE***
(3) Ischemia persists  Irreversible Damage
(a) Severe Swell of Mito / Damage to Plasma Mem. / Swelling Lysosomes / Large densities in mito matrix
iii) Ex: Myocardium
(1) Irreversible injury – 30/40 min after ischemia
(a) Massive Influx of Ca (Ischemic zone)
(b) Death – mainly necrosis, also apoptosis(activated -release of pro-apoptotic molecules from leaky mito)
(c) Leakage of cell enzymes into extracellular space
(d) Dead cells replaced by large masses (myelin figures)
(i) Phagocytosed by leukocytes / Degraded into FA’s
d) Treatment(?) – None reliable for
i) MOST useful (ischemic brain/spinal cord)
(1) Induction of hypothermia (lower body temp to 92degrees)
(a) Reduce metabolic demands / Decreases Cell Swelling / Inhibit host inflammatory response
ii) Restoration of Blood Supply to Ischemic Tissues
(1) Promote cell recovery (cells MUST be reversibly injured – can’t have died
(2) Ischemic-Reperfusion Cell Injury
(a) Reperfusion can contribute to tissue damage (heart/brain inf.) – Cells might have otherwise recovered
(i) Mechanism
1. Reoxygenation (Inc. generation of reactive oxygen/nitrogen species)
2. Cellular antioxidant defense mechanism (compromised by ischemia/accumulate free radicals)
3. Mediator of cell injury (Ca may re-enter reperfused cells) – damage organelles, increase free
radical production
4. Associated w. Inflammation – production of cytokines/inflamm. causes additional tissue injury
5. Activation of complement (involved in host defense Immune Injury)
3) Chemical (Toxic) Injury
a) General
i) Can be caused by drugs (limitation of drug therapy) – metabolized in Liver
(1) Liver = frequent site of drug toxicity
(2) Toxic Liver Injury (most frequent reason for stopping a drug)
b) Mechanism
i) Chemicals Induce Cell Injury
(1) Direct Injury
(a) Combine with critical molecular components
(b) Ex: Mercuric Chloride Poisoning
(i) Mercury binds to sulfhydryl group (Cell mem. proteins)  Inc. Membrane permeability/inhibition
of ion transport
(ii) Damage to cells that use/absorb/excrete or concentration the chemicals (GI Tract/Kidneys)
(c) Apoptosis
(i) Induced by suicide program (activate enzymes – degrade nuclear DNA / degrade nuclear,
cytoplasmic proteins) **Cell Membrane remains INTACT**
4) Apoptosis
a) General
i) Pathway of Cell Death
ii) Cells destined to die  Activate enzymes (degrade nuclear DNA, degrade nuclear/cytoplasmic proteins)
iii) Cell breaks into apoptotic bodies (fragments)  Portion of cytoplasm/nucleus
iv) Plasma membrane remains INTACT (structure altered – easy target for macrophages)
v) Dead cells / Fragments – Rapidly Devoured (Cell Contents NOT leaked)
vi) Does NOT elicit inflammatory reaction in host
b) Death By Apoptosis
i) Normal – eliminate cells no longer needed (maintain steady numbers)
NORMAL CAUSES OF CELL APOPTOSIS
CAUSES
Hormone withdrawal of
Hormone-dependent
Tissue
EXAMPLES o Endometrial cell
breakdown (menstrual
cycle)
o Ovarian follicular atresia in
menopause
o Regression of lactating
breast after weaning
o Prostatic atrophy after
castration
Cell loss in proliferating
populations to
maintain homeostasis
Elimination of
potentially harmful selfreactive lymphocytes
Death of host
cells that have
served purpose
o Immature lymphocytes
in BM
o Thymus – fails to
express useful Ag
receptor
o B-lymphocytes in
germinal centers
o Epithelial cell in
intestinal crypts
o Before or after
maturation – prevent
autoimmune reactions
o Neutrophils in
acute
inflammatory
response
o Lymphocytes at
end of Immune
Response
ii) Pathological Apoptosis
(1) Elimination of cells beyond repair (w.o eliciting host reaction – minimize collateral tissue damage)
(a) DNA damage – radiation, cytotoxic anticancer drugs, hypoxia  Prod. Of Free Radicals
(b) Accumulation of mis-folded proteins
(i) Mutations in genes encoding them, damage caused by free radicals, accumulation in ER (ER stress)
(c) Certain Infections (Viral)
(i) Apoptosis induced by the virus  Adenovirus/HIV infections
(ii) Host Immune Response  Viral Hepatitis
(d) Pathological Atrophy in parenchymal organs after duct obstruction
(i) Pancreas, parotid gland, kidney
c) Morphology of Apoptosis
i) Cell shrinkage (Smaller, Dense cytoplasm, Tightly packed organelles) – ALL OTHER
CELL INJURY = SWELL
(1) Chromatin Condensation
(a) Most characteristic – aggregate peripherally in dense masses, nucleus
may fragment to 2+ pieces
(2) Cytoplasmic blebs/apoptotic bodies
(a) Extensive surface blebbing, Fragmentation into membrane-bound
apoptotic bodies
(3) Phagocytosis of apoptotic cells or cell bodies (by macrophage)
d) Biochemical Features of Apoptosis
i) Specific
(1) Activation of cysteine proteases
(2) Caspases
(a) “C”=cysteine proteases, “aspase”=unique ability to cleave after aspartic residues
(b) Divided into two groups: Initiators (Caspase 8 & 9) and Executioners (Caspase 3 & 6)
(c) Exist as zymogens – cleaved to activate (cleaved caspases= marker- cell undergoing apoptosis)
e) Mechanisms
i) Process
(1) Phases
(a) Initiation – caspases become active
(b) Execution – caspases trigger degradation of critical cell
components
(i) Initiation pathways converge to a cascade of caspase
activation
(ii) Enzymatic Death Program
1. Set in motion by activation of executioner caspases
(caspases 3 & 6  Act on many cell processes)
(2) Pathways
(a) Intrinsic (mitochondria)
(i) Major mechanism in mammalian cells
(ii) Result of increased mitochondrial permeability and
release of pro-apoptotic molecules (death inducers) into
cytoplasm
(iii) Leads to activation of initiator caspase 9
(b) Extrinsic (death-receptor initiated)
(i) Engagement of plasma membrane death receptors on
variety of cells
(ii) Death receptors (Member of TNF receptor family)
1. Cytoplasmic domain- protein-protein interactions
2. Delivers apoptatic signals
(iii) Leads to activation of the caspase 8 & 10
(c) Removal of Dead cells
(i) Apoptotic bodies break cells into “bite-sized” pieces – edible by phagocytes
(ii) Healthy cells – phophatidylserine present on inner leaflet of plasma membrane
1. Apoptotic cells  phospholipid “flips” out – recognized by macrophage receptors
5) Autophagy
a) General
i) Cell eats its own contents (survival mechanism or nutrient deprivation)
ii) Starved cell cannibalizes itself and recycles digested contents
iii) “Eaten”: Intracellular Organelles and Portions of Cytosol
(1) Sequestered from cytoplasm in autophagic vacuole – fuses with lysosome (cellular components digested by
lysosomal enzymes)
6) Intracellular Accumulations
a) Manifestation of metabolic derangements in cells (intracellular accumulation of abnormal amounts of substances) f
i) Abnormal accumulation of normal cellular constituent
(1) Water, Lipids, Proteins, Carbs
ii) Abnormal accumulation of abnormal substance
(1) Types
(a) Exogenous (mineral or products of infectious agent)
(b) Endogenous (product of abnormal synthesis or metabolism)
(2) May be harmless - occasionally severely toxic
(3) Location: Cytoplasm / Nucleus
b) Types
i) Normal Endogenous substance (prod. at norm. or inc. rate) – metabolism
not sufficient to remove it
(1) Fatty change in Liver
(2) Reabsorption Protein Droplets (Tubules of Kidneys)
ii) Abnormal Endogenous substance accumulates (defect in protein
folding/transport  Inability to degrade abnormal protein)
(1) Accumulation of mutated α-1 antitrypsin in liver
(2) Mutated protein in degenerative CNS disorders
iii) Normal Endogenous substance accumulates (defect (inherited) in
enzymes required for metabolism of substance)
(1) Storage Disorders of Lipids/Carbs
iv) Abnormal Exogenous substance – deposited/accumulates (cell doesn’t
have enzymatic machinery to degrade or ability to transport)
(1) Accumulation of carbon particles and non-metabolizable
chemicals (silica)
c) Materials which Accumulate
i) Lipids
(1) Morphology
(a) Fatty change (often Liver/Heart)
(b) Clear Vacuoles w.i parenchymal cells
(c) Identification of Lipids (Avoid fat solvents used in tissue prep / Sections
stained with Sudan IV or Oil Red-O – Orange-Red color of lipid)
(2) Gross Examination (Liver)
(a) Mild Fatty Change – doesn’t affect gross appearance
(b) Progressive accumulation: Organ Enlarges, Becomes Yellow
Fatty Liver
(c) Extreme Cases: Organ 2-4 times normal weight, Bright Yellow soft and greasy
(3) Gross Examination (Heart)
(a) Bands of yellowed myocardium, alternating red-brown uninvolved myocardium (“TIGER”)
ii) Cholesterol/Cholesterol Esters
(1) Intracellular Vacuoles – Several Pathological Processes
(a) Atherosclerosis
(i) Plaques (Smooth Muscles/Macrophages – Intimal layer of aorta
and large arteries, filled with lipid vacuoles)
(ii) Foamy appearance, yellow cholesterol laden atheromas
(b) Xanthomas
(i) Intracell. Accum. of cholesterol in macrophages (acquired and
hereditary hyperlipidemia states)
(ii) Clusters of foamy cells in CT of skin and in tendons
(c) Cholesterolosis
(i) Focal accumulations of cholesterol-laden macrophages in lamina proper of gallbladder
(d) Niemann-Pick Disease (Type C)
(i) Lysosomal storage disorder (mutation  defective enzyme involved in cholesterol trafficking)
(ii) Cholesterol accumulation in multiple organs
iii) Protein
(1) Intracelluar accumulation found in: rounded, eosin-loving droplets in cytoplasm
(2) Reabsorption droplets in proximal renal tubules
(a) Renal disease associated with protein loss in urine
(b) May be normal secreted proteins- produced in excessive
amounts
(3) Defective intracellular transport/secretion of critical proteins
(a) α1-antitrypsin deficiency  Emphysema
(4) Accumulation of cytoskeleton proteins
(a) Alcoholic Hyaline
(i) Eosin-loving cytoplasmic inclusion in liver cells,
composed predominantly of keratin intermediate fibers
(b) Neurofibrillary tangle (Alzheimer’s disease)
(i) Neuro-filaments and other proteins
iv) Hyaline Cartilage
(1) Alteration w.i cell or in extracellular space – homogenous, glassy pink
appearance
(2) Produced by a variety of alterations
(3) No specific pattern of accumulation
v) Glycogen
(1) Stored in cytoplasm of healthy cells
(2) Visualization: Tissues fixed w. absolute alcohol, stained w. carmine or PAS
(rose-violet color) – Less grainy than cholesterol esters
(3) Excessive intracellular deposits
(a) Abnormality in glucose or glycogen metabolism
vi) Pigments
(1) Colored Substances – normal in some cells (melanin)
(2) “Abnormal Pigments”
(a) Exogenous pigments
(i) Carbon (coal dust) – pollutants in urban cities
1. Blackens the tissues of lungs (anthracosis), and lymph nodes involved
(ii) Tatoos
1. Localized pigmentation of skin (phagocytosed by dermal macrophages)
(b) Endogenous pigments
(i) Lipofuscin
1. Insoluble pigment (not injurious – sign of free radical injury/lipid
peroxidation)
2. Yellow-brown finely granular cytoplasmic, often peri-nuclear
3. Seen in cells undergoing slow regressive changes
4. Prominent in heart and liver (Aging / Severe Malnutrition / Caner
Cachexia Patients)
(ii) Melanin
1. Non-hemoglobin derived brown-black pigment
2. Formation: Oxidation of tyrosine to dihydroxyphenyalanine in
melanocytes
(iii) Hemosiderin
1. Hemoglobin-derived (major form of iron storage)
2. Aggregates of ferritin micelles
3. Seen in mononuclear phagocytes of BM, spleen and liver (actively
engaged in RBC breakdown)
4. Golden yellow-brown (granular/crystalline pigment)
5. Systemic Hemosiderosis: Mononuclear Phagocytes – Liver, BM,
Spleen, Lymph Nodes, scattered throughout other organs
(iv) Iron
1. Coarse, Golden, Granular (Cell Cytoplasm)
2. Visualized with Prussian Blue
3. Cause: Localized breakdown of RBC’s
(v) Bilirubin
1. Normal pigment found in bile (derived from hemoglobin – no Iron)
vii) Calcification
(1) Two types (Pathological Calcification)
(a) Dystrophic Calcification
(i) Local Deposition in dying tissues (normal serum levels)  Areas of Necrosis
(ii) Absence of derangements in Ca metabolism
(iii) Ex: Calcification of the aortic valve
(b) Metastatic Calcification
(i) Deposition of Ca salts in otherwise normal tissue
(ii) Hypercalcemia (secondary to some disturbance in Ca
metabolism)
(2) Morpholgy
(a) Basophilic, amorphous granular, clumped (intracellular, extracellular or both)
(b) Can become heterotopic bone over time
(c) Lamellations (psammoma bodies – in benign/malignant conditions)
7) Cell Aging
a) Progressive decline in function/viability (caused by genetic abnormality)
b) Accumulation of cellular/molecular damage (effect of exogenous influences)
c) Aging
i) Regulated process (Influenced by a number of genes)
ii) Associated with definable mechanistic alterations
d) Changes contributing to cellular aging
i) Decreased cellular replication, accumulation of metabolic/genetic damage
e) Cellular Life Span
i) Balance between
(1) Damage from metabolic events w.i cell
(2) Molecular Response to repair the damage