CELLULAR RESPONSES TO
STRESS AND TOXIC INSULTS
Pathology – Chapter 1
Introduction

Pathology
 Study
(logos) of disease (pathos)
 Structural,

biochemical, and functional changes
Cells, tissues, and organs that underlie disease
Introduction

Four aspects of a disease process
 Cause
(etiology)
 Mechanisms of its development (pathogenesis)
 Biochemical and structural alterations (molecular and
morphologic changes)
 Functional consequences of these changes (clinical
manifestations)
Etiology

Two major classes
 Genetic
 Inherited
mutations
 Disease-associated gene variants
 Acquired
 Infectious
 Nutritional
 Chemical
 Physical
Pathogenesis

Sequence of events in the response of cells or tissues
to the etiologic agent
 From
the initial stimulus to the ultimate expression of the
disease

One of the main domains of pathology
Molecular and Morphologic Changes

Structural alterations in cells or tissues
 Characteristic
of a disease
 Diagnostic of an etiologic process
Functional Derangements and Clinical
Manifestations

Functional abnormalities
 End
results of genetic, biochemical, and structural changes
in cells and tissues
 Lead to the clinical manifestations (symptoms and signs)
Lead to the progression of disease (clinical course and
outcome)
Functional Derangements and Clinical
Manifestations

Disease
 Starts
with molecular or structural alterations in cells
 Concept

 Injury
Father of modern pathology
to cells and to extracellular matrix
 Tissue

first put forth by Rudolf Virchow (19th century)
and organ injury
Determine the morphologic and clinical patterns of disease
Cellular Responses to Stress and
Noxious Stimuli

Normal cell
 Confined
to a narrow range of function and structure
 State
of metabolism, differentiation, and specialization
 Constraints of neighboring cells
 Availability of metabolic substrates
 Maintains
homeostasis (steady state)
Cellular Responses to Stress and
Noxious Stimuli

Adaptations
 Reversible
 Usually
functional and structural responses
due to physiologic stresses and pathologic stimuli
 Hypertrophy
(increase in the size of cells)
 Hyperplasia (increase in the number of cells)
 Atrophy (decrease in the size and metabolic activity of
cells)
 Metaplasia (change in the phenotype of cells)
Cellular Responses to Stress and
Noxious Stimuli

Cell injury
 Exposure
to injurious agents or stress
 Deprivation of essential nutrients
 Compromised by mutations that affect essential cellular
constituents
 Reversible
 Up
to a certain point
 Irreversible
 Stimulus
injury and cell death
persists
Cellular Responses to Stress and
Noxious Stimuli

Cell death
 End
result of progressive cell injury
 One of the most crucial events in the evolution of
disease
 Results from diverse causes
 Ischemia
 Infection
 Toxins
(reduced blood flow)
Cellular Responses to Stress and
Noxious Stimuli

Cell death
 Normal
and essential process
 Embryogenesis
 Maintenance
 Two
of homeostasis
principal pathways of cell death
 Necrosis
and apoptosis
Adaptations of Cellular Growth and
Differentiation

Hypertrophy
 Increase
 Results
in the size of cells
in an increase in the size of the organ
 No
new cells, just larger cells
 Due to synthesis of structural components of the cells
 Cellular
proteins
Adaptations of Cellular Growth and
Differentiation

Hypertrophy
 Physiologic
or pathologic
 Cause
 Increased
functional demand
 Stimulation by hormones and growth factors
Adaptations of Cellular Growth and
Differentiation

Hypertrophy
 Example:
Striated muscle cells (heart and skeletal muscle)
 Limited
capacity for division
 Respond to increased metabolic demands

Hypertrophy
 Most


common stimulus
Increased workload
Example: Bodybuilders "pumping iron"
 Increase in size of the individual muscle fibers
Hypertrophy

Mechanisms
 Induced
by linked actions
 Mechanical
sensors
 Growth factors
 Vasoactive agents

Two main biochemical pathways
 Phosphoinositide
3-kinase/Akt pathway
 Signaling downstream of G protein-coupled receptors
Hypertrophy


Usually refers to increase in size of cells or tissues
HOWEVER, a subcellular organelle may undergo
selective hypertrophy
 Example:
Individuals treated with drugs
(barbiturates)
 Hypertrophy
of the smooth endoplamic reticulum (SER) in
hepatocytes




Adaptive response
Increases the amount of enzymes (cytochrome P-450 mixed
function oxidases) available to detoxify the drugs
Eventually, patients respond less to the drug
May result in an increased capacity to metabolize other drugs
Hyperplasia

Increase in the number of cells in an organ or tissue
 Results
in increased mass of the organ or tissue
 May occur in the setting of hypertrophy
 Physiologic and pathologic
Hyperplasia

Increase in the number of cells in an organ or tissue
 Physiologic
 Hormonal

hyperplasia
hyperplasia
Increases the functional capacity of a tissue when needed
 Compensatory

hyperplasia
Increases tissue mass after damage or partial resection
Hyperplasia

Physiologic hyperplasia
 Hormonal
hyperplasia
 Proliferation
of the glandular epithelium of the female
breast


Puberty
Pregnancy
 Compensatory
 Myth
hyperplasia
of Prometheus
 Ancient Greeks recognized the capacity of the liver to
regenerate
 Liver transplantation (donor)
Hyperplasia

Pathologic Hyperplasia
 Caused
by excesses of hormones or growth factors
acting on target cells
 Endometrial hyperplasia
 Abnormal
hormone-induced hyperplasia
 Common cause of abnormal menstrual bleeding
Hyperplasia

Pathologic Hyperplasia
 Benign
prostatic hyperplasia
 Induced
by responses to androgens
 Constitutes
a fertile soil in which cancerous proliferation
may eventually arise
Atrophy



Reduced size of an organ or tissue
Results from a decrease in cell size and number
Physiologic atrophy
 Common
during normal development
 Embryonic


structures
Notochord
Thyroglossal duct
 Uterus

Decreased size shortly after parturition
Atrophy

Pathologic atrophy
 Depends
on the underlying cause
 Local or generalized

Common causes of atrophy
 Decreased
 Muscle
 Loss
workload (atrophy of disuse)
atrophy secondary to immobilization/bedrest
of innervation (denervation atrophy)
 Diminished blood supply
Atrophy

Common causes of atrophy
 Inadequate
 Profound

 Loss
nutrition
protein-calorie malnutrition (marasmus)
Use of skeletal muscle as a source of energy after other reserves
(adipose stores) have been depleted
of endocrine stimulation
 Hormone-responsive
tissues (breast and reproductive organs)
 Pressure
 Tissue
compression for any length of time
Atrophy

Mechanisms
 Results
from decreased protein synthesis
 Reduced
 Results
metabolic activity
from increased protein degradation in cells
 Ubiquitin-proteasome

pathway
Responsible for the accelerated proteolysis
 Catabolic conditions (cancer cachexia)
Atrophy

Accompanied by increased autophagy
 Increases

in the number of autophagic vacuoles
Autophagy ("self eating")
 Process
in which the starved cell eats its own components
to survive
Atrophy

Autophagic vacuoles
 Membrane-bound
vacuoles that contain fragments of cell
components
 Vacuoles
ultimately fuse with lysosomes
 Contents are digested by lysosomal enzymes
 Some cell debris (in the autophagic vacuoles) resist digestion

Persist as membrane-bound residual bodies
 Lipofuscin granules (brown atrophy)
Metaplasia



Reversible change
One differentiated cell type replaced by another
cell type
Adaptive substitution of cells (sensitive to stress)
 Cell
types better able to withstand adverse
environments
Metaplasia

Most common epithelial metaplasia
 Columnar
to squamous
 Occurs in the respiratory tract
 Chronic


irritation
Cigarette smoker
 Normal PCCE replaced by stratified squamous epithelial
cells
 Lack of mucociliary elevator
If persistent, may initiate malignant transformation
in metaplastic epithelium
Metaplasia

Metaplasia from squamous to columnar type
 Barrett
esophagus
 Esophageal
squamous epithelium is replaced by intestinallike columnar cells


Influence of refluxed gastric acid
Connective tissue metaplasia
 Formation
of cartilage, bone, or adipose tissue
(mesenchymal tissues) in tissues that do not contain these
elements
 Bone

formation in muscle (myositis ossificans)
Can occur following an intramuscular hemorrhage
Metaplasia

Mechanisms
 Does
not result from a change in the phenotype of an
already differentiated cell type
 Result of reprogramming
 Stem
cells (known to exist in normal tissues)
 Undifferentiated mesenchymal cells present in connective
tissue
 Precursor
cells differentiate along a new pathway
Practice Question

A 43-year-old man has complained of mild burning substernal pain
following meals for the past 3 years. Upper GI endoscopy is performed
and biopsies are taken of an erythematous area of the lower esophageal
mucosa 3 cm above the gastroesophageal junction. There is no mass lesion,
no ulceration, and no hemorrhage noted. The biopsies show the presence of
columnar epithelium with goblet cells. Which of the following mucosal
alterations is most likely represented by these findings?

A. Dysplasia

B. Metaplasia

C. Hypertrophy

D. Hyperplasia

E. Ischemia
Practice Question






A 19-year-old woman gives birth to her first child. She
begins breast feeding the infant. She continues breast
feeding for almost a year with no difficulties and no
complications. Which of the following cellular processes
that began in the breast during pregnancy allowed her
to nurse the infant for this period of time?
A. Lobular hyperplasia
B. Stromal hypertrophy
C. Epithelial dysplasia
D. Steatocyte atrophy
E. Ductal epithelial metaplasia
Practice Question






A study is performed involving the microscopic analysis of tissues
obtained from surgical procedures. Some of these tissues have the
microscopic appearance of an increased cell size of multiple cells
within the tissue, due to an increase in the amount of cytoplasm, with
nuclei remaining uniform in size. Which of the following conditions is
most likely to have resulted in this finding?
A. Uterine myometrium in pregnancy
B. Female breast at puberty
C. Liver following partial resection
D. Ovary following menopause
E. Cervix with chronic inflammation
Practice Question






A 38-year-old man incurs a traumatic blow to his upper
left arm. He continues to have pain and tenderness
even after 3 months have passed. A plain film
radiograph reveals a 4 cm circumscribed mass in the
soft tissue adjacent to the humerus. The mass contains
areas of brightness on the x-ray. Over the next year
this process gradually resolves. Which of the following
terms best describes this process?
A. Dysplasia
B. Hyperplasia
C. Hypertrophy
D. Metaplasia
E. Neoplasia
Practice Question





A 21-year-old woman has a routine Pap smear performed
for a health screening examination. The pathology report
indicates that some cells are found cytologically to have
larger, more irregular nuclei. A follow-up cervical biopsy
microscopically demonstrates disordered maturation of the
squamous epithelium, with hyperchromatic and pleomorphic
nuclei extending nearly the full thickness of the epithelial
surface. No inflammatory cells are present. Which of the
following descriptive terms is best applied to these Pap
smear and biopsy findings?
A. Dysplasia
B. Metaplasia
C. Anaplasia
D. Hyperplasia
Practice Question






A 3-year-old child has been diagnosed with ornithine
transcarbamylase deficiency and has developed hepatic
failure. The left lobe of an adult donor liver is used as an
orthotopic transplant. A year later, the size of each liver in
donor and recipient is greater than at the time of
transplantation. Which of the following cellular alterations is
most likely to explain this phenomenon?
A. Metaplasia
B. Dysplasia
C. Hyperplasia
D. Anaplasia
E. Neoplasia
CELLULAR ADAPTATIONS
LECTURE #2
Causes of Cell Injury







Oxygen deprivation
Physical agents
Chemical agents and drugs
Infectious agents
Immunologic reactions
Genetic derangements
Nutritional imbalances
Injurious Stimuli

Oxygen Deprivation
 Hypoxia
 Deficiency
of oxygen
 Reduces aerobic oxidative respiration
 Causes


Reduced blood flow (ischemia)
Inadequate oxygenation of the blood
 Cardiorespiratory failure
Injurious Stimuli

Oxygen Deprivation
 Hypoxia
 Causes,

continued
Decreased oxygen-carrying capacity of the blood
 Anemia
 Carbon monoxide poisoning
 Severe blood loss
 Depending

on the severity
Cells may adapt, undergo injury, or die
Injurious Stimuli

Physical Agents
 Mechanical
trauma
 Extremes of temperature (burns and deep cold)
 Sudden changes in atmospheric pressure
 Radiation
 Electric shock
Injurious Stimuli

Chemical Agents and Drugs
 Chemicals
(too many to list)
 Glucose or salt in hypertonic concentrations
 Oxygen at high concentrations
 Trace amounts of poisons
 Environmental and air pollutants
 Insecticides, herbicides
 Industrial and occupational hazards
 Recreational drugs (alcohol)
 Therapeutic drugs
Injurious Stimuli

Infectious Agents
 Submicroscopic
viruses to the large tapeworms
 Rickettsiae
 Bacteria
 Fungi
 Higher
forms of parasites
Injurious Stimuli

Immunologic Reactions
 Injurious
reactions to endogenous self-antigens
 Several
 Immune
autoimmune diseases
reactions to external agents
 Microbes
 Environmental
substances
Injurious Stimuli

Genetic Derangements
 Severe
defects
 Congenital

Chromosomal anomaly
 Subtle
defects
 Decreased

malformations associated with Down syndrome
life span of red blood cells
Single amino acid substitution in hemoglobin in sickle cell anemia
 Variations
 Influence
in the genetic makeup
the susceptibility of cells by chemicals and other
environmental insults
Injurious Stimuli

Nutritional Imbalances
 Protein-calorie
deficiencies
 Underprivileged
populations
 Deficiencies
of specific vitamins
 Self-imposed problems
 Anorexia
 Nutritional
 Excess
nervosa
excesses
of cholesterol
 Obesity
Morphologic Alterations

Sequential morphologic changes in cell injury

Reversible injury
Generalized swelling of the cell and its organelles
 Blebbing of the plasma membrane
 Detachment of ribosomes from the ER
 Clumping of nuclear chromatin


Associations
Decreased generation of ATP
 Loss of cell membrane integrity
 Defects in protein synthesis
 Cytoskeletal damage
 DNA damage

Reversible Injury

Two features of reversible cell injury

Cellular swelling
Cells are incapable of maintaining ionic and fluid homeostasis
 Result of failure of energy-dependent ion pumps in the plasma
membrane


Fatty change
Hypoxic injury
 Various forms of toxic or metabolic injury
 Manifested by the appearance of lipid vacuoles in the cytoplasm
 Hepatocytes and myocardial cells

Reversible Injury

Morphology
 Cellular
swelling
 First
manifestation of almost all forms of injury to cells
 Difficult morphologic change to appreciate with the light
microscope

More apparent at the level of the whole organ
 Pallor,
increased turgor, and increase in weight of the organ
 Microscopic examination

Small clear cytoplasmic vacuoles (distended and pinched-off ER)
 Hydropic change or vacuolar degeneration
Reversible Injury

Ultrastructural changes

Plasma membrane alterations


Blebbing, blunting, and loss of microvilli
Mitochondrial changes
Swelling
 Appearance of small amorphous densities


Dilation of the ER
Detachment of polysomes
 Intracytoplasmic myelin figures may be present


Nuclear alterations

Disaggregation of granular and fibrillar elements
Irreversible Cell Injury and Cell Death

Continuous damage

Cell injury becomes irreversible


Cell cannot recover and it dies
Two principal types of cell death

Necrosis

Severe membrane damage



Lysosomal enzymes enter the cytoplasm and digest the cell, and cellular
contents leak out
Always a pathologic process
Apoptosis

Cell's DNA or proteins are damaged beyond repair



Cell kills itself by nuclear dissolution, fragmentation of the cell without
complete loss of membrane integrity, and rapid removal of the cellular
debris
Serves many normal functions
Not necessarily associated with cell injury
Necrosis

Morphologic appearance
 Result
of denaturation of intracellular proteins and
enzymatic digestion of the lethally injured cell
 Necrotic cells
 Unable

to maintain membrane integrity
Contents leak
 Elicits inflammation in the surrounding tissue
Necrosis

Necrotic cells

Increased eosinophilia in hematoxylin and eosin (H & E)
stains
Loss of cytoplasmic RNA (which binds the blue dye, hematoxylin)
 Denatured cytoplasmic proteins (which bind the red dye, eosin)


Glassy homogeneous appearance

Loss of glycogen particles
Digestion of cytoplasmic organelles---vacuolated cytoplasm
(moth-eaten)
 Dead cells


Replaced by large, whorled phospholipid masses (myelin figures)


Derived from damaged cell membranes
Phospholipid precipitates
 Phagocytosed by other cells
 Further degraded into fatty acids
Necrosis

Necrotic cells

Nuclear changes
Due to nonspecific breakdown of DNA
 Karyolysis




Pyknosis




Fading of the basophilia of the chromatin
A change that presumably reflects loss of DNA because of
enzymatic degradation by endonucleases
Nuclear shrinkage
Increased basophilia
Chromatin condenses into a solid, shrunken basophilic mass
Karyorrhexis


Pyknotic nucleus undergoes fragmentation
Nucleus in the necrotic cell totally disappears (1 or 2 days)
Patterns of Tissue Necrosis

Coagulative necrosis
Architecture of dead tissues is preserved for a span of a
few days
 Tissue displays a firm texture
 Eosinophilic, anucleate cells persist for days or weeks

Removed by phagocytosis of the cellular debris by infiltrating
leukocytes
 Digestion of the dead cells by the action of lysosomal enzymes of
the leukocytes


Example:


Ischemia caused by obstruction in a vessel may lead to
coagulative necrosis of the supplied tissue
Localized area

Infarct
Patterns of Tissue Necrosis

Liquefactive necrosis
 Characterized
 Resulting
by digestion of the dead cells
in transformation of the tissue into a liquid viscous
mass
 Seen
in focal bacterial infections
 Occasionally seen in fungal infections
 Creamy yellow
 Dead
leukocytes
 Purulent matter (aka pus)
 Hypoxic
death of cells in the CNS
Patterns of Tissue Necrosis

Gangrenous necrosis
 Not
a specific pattern of cell death
 Commonly used in clinical practice
 Applied to a limb (usually lower leg)
 Lost
its blood supply and has undergone necrosis (typically
coagulative necrosis)

 Add
Involving multiple tissue planes
in a bacterial infection
 More

liquefactive necrosis
Because of the actions of degradative enzymes in the bacteria
and the attracted leukocytes
 Wet gangrene
Patterns of Tissue Necrosis

Caseous necrosis
 Encountered
most often in foci of tuberculous infection
 “Caseous" (cheeselike)
 Derived
from the friable white appearance of the area of
necrosis
 Microscopic
examination
 Collection
of fragmented or lysed cells
 Amorphous granular debris enclosed within a distinctive
inflammatory border

Characteristic of a focus of inflammation known as a granuloma
Patterns of Tissue Necrosis

Fat necrosis
 Term
that is well fixed in medical parlance
 Does
 Focal
not denote a specific pattern of necrosis
areas of fat destruction
 Release
of activated pancreatic lipases into the substance of
the pancreas and the peritoneal cavity
 Microscopic
 Foci
examination
of shadowy outlines of necrotic fat cells
 Basophilic calcium deposits
 Inflammatory reaction
Patterns of Tissue Necrosis

Fibrinoid necrosis
 Special
form of necrosis
 Seen in immune reactions involving blood vessels
 Complexes of antigens and antibodies
 Deposited
 Microscopic
 Deposits

in the walls of arteries
examination
of these "immune complexes" and fibrin
Bright pink and amorphous appearance (“fibrinoid”)
Mechanisms of Cell Injury

Principles that are relevant to most forms of cell
injury
 Cellular
response to injurious stimuli
 Depends
on the nature of the injury, its duration, and its
severity
 Small doses of a chemical toxin or brief periods of ischemia
may induce reversible injury
 Large doses of the same toxin or more prolonged ischemia


Instantaneous cell death
Slow, irreversible injury leading in time to cell death
 Consequences
of cell injury depend on the type, state,
and adaptability of the injured cell
Mechanisms of Cell Injury

Principles that are relevant to most forms of cell injury

Cell injury results from different biochemical mechanisms
acting on several essential cellular components
Mitochondria
 Cell membranes
 DNA in nuclei


Any injurious stimulus may simultaneously trigger multiple
interconnected mechanisms that damage cells

Difficult to ascribe cell injury in a particular situation to a single or
even dominant biochemical derangement
ATP

ATP is produced in two ways
 Major
pathway (mammalian cells)
 Oxidative

Reaction that results in reduction of oxygen by the electron
transfer system of mitochondria
 Second
pathway
 Glycolytic


phosphorylation of adenosine diphosphate
pathway
Generates ATP in the absence of oxygen
Uses glucose derived either from body fluids or from the
hydrolysis of glycogen
Depletion of ATP

ATP depletion and decreased ATP synthesis
 Associated
with both hypoxic and chemical (toxic) injury
 Major causes
 Reduced
supply of oxygen and nutrients
 Mitochondrial damage
 Actions of toxins (e.g., cyanide)
ATP

High-energy phosphate in the form of ATP
 Required
for virtually all synthetic and degradative
processes within the cell
 Depletion of ATP to 5% to 10% of normal levels
 Widespread
effects on many critical cellular systems
Depletion of ATP

Effects on critical cellular systems

Activity of the plasma membrane energy-dependent sodium
pump is reduced
Failure of this active transport system causes sodium to enter and
accumulate inside cells and potassium to diffuse out
 The net gain of solute is accompanied by isosmotic gain of water,
causing cell swelling, and dilation of the ER


Cellular energy metabolism is altered
Reduced supply of oxygen to cells (i.e. ischemia)
 Oxidative phosphorylation ceases




Decrease in cellular ATP
Increase in adenosine monophosphate
Glycogen stores are rapidly depleted
Depletion of ATP

Effects on critical cellular systems
 Failure
of the Ca2+ pump leads to influx of Ca2+
 Damages
 Prolonged
 Structural
intracellular organelles
or worsening depletion of ATP
disruption of the protein synthetic apparatus
occurs


Manifested as detachment of ribosomes from the rough ER
Dissociation of polysomes
 Consequent reduction in protein synthesis
Depletion of ATP

Effects on critical cellular systems
 Oxygen
or glucose deprivation
 Proteins

may become misfolded
Trigger a cellular reaction (unfolded protein response)
 Cell injury and even death
 Irreversible
damage to mitochondrial and lysosomal
membranes
 Cell
necrosis
Mitochondrial Damage

Mitochondria
 Cell's
suppliers of life-sustaining energy in the form of
ATP
 Critical players in cell injury and death
 Damaged by:
of cytosolic Ca2+
 Reactive oxygen species
 Oxygen deprivation
 Increases
 Mutations
in mitochondrial genes are the cause of some
inherited diseases
Mitochondrial Damage

Formation of a high-conductance channel in the
mitochondrial membrane
 Mitochondrial
permeability transition pore
 Opening
of this conductance channel leads to the loss of
mitochondrial membrane potential

Resulting in failure of oxidative phosphorylation and progressive
depletion of ATP
 Necrosis of the cell
Mitochondrial Damage

Mitochondria
 Sequester
proteins between their outer and inner
membranes
 Capable


of activating apoptotic pathways
Cytochrome c and caspases (indirectly activate apoptosis-inducing
enzymes)
Increased permeability of the outer mitochondrial membrane
 Leakage of these proteins into the cytosol
 Death by apoptosis
Calcium Homeostasis


Calcium ions are important mediators of cell injury
Cytosolic free calcium
 Normally
maintained at very low concentrations (∼0.1
μmol)
 Intracellular calcium is sequestered in mitochondria and
the ER

Increased cytosolic Ca2+ activates a number of
enzymes
 Deleterious
cellular effects
 Phospholipases (membrane damage)
Calcium Homeostasis

Increased cytosolic Ca2+ activates a number of enzymes
Proteases (break down both membrane and cytoskeletal
proteins)
 Endonucleases (responsible for DNA and chromatin
fragmentation)
 ATPases (hastening ATP depletion)


Increased intracellular Ca2+ levels

Induction of apoptosis

Direct activation of caspases and by increasing mitochondrial
permeability
Free Radicals

Free radicals
Chemical species that have a single unpaired electron in an
outer orbit
 Energy created by this unstable configuration is released
through reactions with adjacent molecules



Inorganic or organic chemicals-proteins, lipids, carbohydrates,
nucleic acids
Reactive oxygen species (ROS)
Type of oxygen-derived free radical
 Produced normally in cells during mitochondrial respiration and
energy generation
 Degraded and removed by cellular defense systems
 Produced in large amounts by leukocytes, particularly neutrophils
and macrophages

Generation of Free Radicals


The reduction-oxidation reactions that occur during
normal metabolic processes
Absorption of radiant energy (ultraviolet light, xrays)
radiation can hydrolyze water into •OH and
hydrogen (H) free radicals
 Ionizing

Rapid bursts of ROS
 Produced

in activated leukocytes during inflammation
Enzymatic metabolism of exogenous chemicals or
drugs
Generation of Free Radicals


Transition metals such as iron and copper donate or
accept free electrons during intracellular reactions
(Fenton reaction (H2O2 + Fe2+ → Fe3+ + OH + OH
Nitric oxide
 Important
chemical mediator that can act as a free
radical
 Generated by endothelial cells, macrophages, neurons,
and other cell types
Removal of Free Radicals


Free radicals are inherently unstable and generally
decay spontaneously
Cells have developed multiple nonenzymatic and
enzymatic mechanisms to remove free radicals


Iron and copper can catalyze the formation of ROS


Minimize injury
Levels of these reactive metals are minimized by binding of
the ions to storage and transport proteins (e.g., transferrin,
ferritin, lactoferrin, and ceruloplasmin), thereby minimizing
the formation of ROS
Enzymes acts as free radical-scavenging systems
Pathologic Effects of Free Radicals

Three reactions

Lipid peroxidation in membranes

Presence of O2, free radicals may cause peroxidation of lipids
within plasma and organellar membranes


Oxidative modification of proteins

Free radicals promote:




Oxidative damage is initiated when the double bonds in
unsaturated fatty acids of membrane lipids are attacked by O2derived free radicals
Oxidation of amino acid side chains
Formation of protein-protein cross-linkages (e.g., disulfide bonds)
Oxidation of the protein backbone
Lesions in DNA
Single- and double-strand breaks in DNA
 Cross-linking of DNA strands
 Formation of adducts

Membrane Damage

Several biochemical mechanisms may contribute to
membrane damage
 Reactive
oxygen species
 Decreased phospholipid synthesis
 Increased phospholipid breakdown
 Cytoskeletal abnormalities
Membrane Damage

Consequences

The most important sites of membrane damage during cell injury

Mitochondrial membrane damage



Plasma membrane damage




Opening of the mitochondrial permeability transition pore leading to
decreased ATP
Release of proteins that trigger apoptotic death
Loss of osmotic balance and influx of fluids and ions
Loss of cellular contents
Cells may also leak metabolites
 Vital for the reconstitution of ATP, thus further depleting energy stores
Injury to lysosomal membranes




Leakage of their enzymes into the cytoplasm
Activation of the acid hydrolases in the acidic intracellular pH of the injured
cell
Activation of these enzymes leads to enzymatic digestion
Cells die by necrosis
CELLULAR RESPONSES
PART THREE
Ischemic and Hypoxic Injury


Most common type of cell injury in clinical medicine
Studied extensively
 Humans
 Experimental
animals
 Culture systems

Hypoxia
 Reduced
oxygen availability
 Occurs in a variety of clinical settings
Ischemic and Hypoxic Injury

Ischemia
 Supply
of oxygen and nutrients is decreased
 Because of reduced blood flow
 Consequence
of a mechanical obstruction in the arterial
system/reduced venous drainage
 Compromises
the delivery of substrates for glycolysis
Ischemic and Hypoxic Injury

Ischemic tissues
 Aerobic
metabolism compromised
 Anaerobic energy generation stopped
 Glycolytic
substrates are exhausted
 Glycolysis is inhibited


Accumulation of metabolites
Ischemia tends to cause more rapid and severe cell
and tissue injury than does hypoxia in the absence of
ischemia
Mechanisms of Ischemic Cell Injury

Sequence of events (post-hypoxia or ischemia)

Oxygen tension within the cell decreases
Loss of oxidative phosphorylation
 Decreased generation of ATP


Failure of the sodium pump
 Loss of potassium
 Influx of sodium and water
 Cell swelling
Influx of Ca2+
 Progressive loss of glycogen
 Decreased protein synthesis


Functional consequences may be severe at this stage
Mechanisms of Ischemic Cell Injury

Example:
 Heart
muscle ceases to contract within 60 seconds of
coronary occlusion
 Loss of contractility does not mean cell death
 Continued hypoxia
 Worsening

ATP depletion
Further deterioration
 Cytoskeleton disperses
 Loss of ultrastructural features (microvilli and the formation of
blebs)
 Myelin figures (degenerating cellular membranes)
 Seen within the cytoplasm (in autophagic vacuoles) or
extracellularly
Mechanisms of Ischemic Cell Injury

Example:
 Continued

hypoxia (continued from previous slide)
Cytoskeleton disperses
 Mitochondria—swollen
 Due to loss of volume control in these organelles
 ER remains dilated
 Entire cell is markedly swollen
 Increased concentrations of water, sodium, and chloride
 Decreased concentration of potassium

If oxygen is restored, all of these disturbances are
reversible!!!!
Mechanisms of Ischemic Cell Injury


If ischemia persists, irreversible injury and
necrosis ensue!!!!
Irreversible injury
 Severe
swelling of mitochondria
 Extensive damage to plasma membranes (giving rise
to myelin figures)
 Swelling of lysosomes
 Large, flocculent, amorphous densities develop in the
mitochondrial matrix
Mechanisms of Ischemic Cell Injury

Example:
 Myocardium
 Irreversible
injury can be seen as early as 30 to 40
minutes after ischemia





Massive influx of calcium into the cell (ischemic zone)
Death is mainly by necrosis, but apoptosis also contributes
 Apoptotic pathway is activated by release of proapoptotic molecules from leaky mitochondria
Cell's components are progressively degraded
Widespread leakage of cellular enzymes into the
extracellular space
Dead cells replaced by large masses (myelin figures)
 Either phagocytosed by leukocytes
 Degraded further into fatty acids
Mechanisms of Ischemic Cell Injury

Despite many investigations
 No
reliable therapeutic approaches for reducing the
injurious consequences of ischemia in clinical situations
 Most useful strategy in ischemic (and traumatic) brain
and spinal cord injury
 Transient
induction of hypothermia (core body temperature
to 92°F)




Reduces the metabolic demands of the stressed cells
Decreases cell swelling
Suppresses the formation of free radicals
Inhibits the host inflammatory response
Ischemia-Reperfusion Injury

Restoration of blood flow to ischemic tissues


Promotes recovery of cells (reversibly injured)
Certain circumstances

Blood flow is restored to cells that have been ischemic but
have not died

Paradoxical injury is exacerbated


Proceeds at an accelerated pace
Reperfused tissues may sustain loss of cells in addition to the
cells that are irreversibly damaged at the end of ischemia
Ischemia-reperfusion injury
 Clinically important


Contributes to tissue damage during myocardial and cerebral
infarction and following therapies to restore blood
Ischemia-Reperfusion Injury

Reperfusion injury occur
 New
damaging processes are set in motion during
reperfusion
 Causes
the death of cells that might have recovered
otherwise
 Several proposed mechanisms

Damage may be initiated during reoxygenation
 Increased generation of reactive oxygen and nitrogen
species
 Produced in reperfused tissue as a result of mitochondrial
damage

Cellular antioxidant defense mechanisms may be compromised
by ischemia
 Accumulation of free radicals
 Mediators
of cell injury (calcium) may also enter reperfused
Ischemia-Reperfusion Injury

Ischemic injury
 Associated
with inflammation
 Result
of the production of cytokines
 Causes additional tissue injury

Activation of the complement system
 May
contribute to ischemia-reperfusion injury
 Involved in host defense
 Important mechanism of immune injury
Chemical (Toxic) Injury



Chemical injury remains a frequent problem in
clinical medicine
Major limitation to drug therapy
Many drugs are metabolized in the liver
 Frequent
target of drug toxicity
 Toxic liver injury
 Most
frequent reason for terminating the therapeutic use or
development of a drug
Chemical (Toxic) Injury

Chemicals induce cell injury
 Direct
injury
 Combining

with critical molecular components
Example: Mercuric chloride poisoning
 Mercury binds to the sulfhydryl groups of cell membrane
proteins
 Causes increased membrane permeability and inhibition of ion
transport
 Damage is usually to the cells that use, absorb, excrete, or
concentrate the chemicals
 Cells of the gastrointestinal tract and kidney
Apoptosis


Pathway of cell death
Induced by a tightly regulated suicide program


Cells destined to die activate enzymes that degrade the
cells' own nuclear DNA and nuclear and cytoplasmic proteins
Cells break up into fragments (apoptotic bodies)
Contain portions of the cytoplasm and nucleus
 Plasma membrane of the apoptotic cell and bodies remains
intact

Structure is altered
 Tasty targets for phagocytes


Dead cell and its fragments are rapidly devoured

Before the contents have leaked out

Cell death by this pathway does not elicit an inflammatory reaction
in the host
Apoptosis

Death by apoptosis
 Normal
phenomenon that serves to eliminate cells that
are no longer needed
 Maintains a steady number of various cell populations
in tissues

Causes of Apoptosis
 Involution
of hormone-dependent tissues upon hormone
withdrawal
 Endometrial
cell breakdown during the menstrual cycle
 Ovarian follicular atresia in menopause
 Regression of the lactating breast after weaning
 Prostatic atrophy after castration
Apoptosis

Causes of Apoptosis, continued
 Cell
loss in proliferating cell populations to maintain a
constant number (homeostasis)
 Immature
lymphocytes in the bone marrow
 Thymus that fails to express useful antigen receptors
 B lymphocytes in germinal centers
 Epithelial cells in intestinal crypts
Apoptosis

Causes of Apoptosis, continued
 Elimination
of potentially harmful self-reactive
lymphocytes
 Before

or after they have completed their maturation
Prevent reactions against one's own tissues
 Death
of host cells that have served their useful
purpose
 Neutrophils
in an acute inflammatory response
 Lymphocytes at the end of an immune response
Apoptosis in Pathologic Conditions

Apoptosis eliminates cells that are injured beyond
repair without eliciting a host reaction
 Thus

limiting collateral tissue damage
Death by apoptosis is responsible for loss of cells in
a variety of pathologic states
 DNA

damage
Radiation, cytotoxic anticancer drugs, and hypoxia

Production of free radicals
Apoptosis in Pathologic Conditions

Death by apoptosis is responsible for loss of cells
in a variety of pathologic states
 Accumulation
 Improperly



of misfolded proteins
folded proteins
Mutations in the genes encoding these proteins
Damage caused by free radicals
Accumulation of these proteins in the ER
 ER stress
Apoptosis in Pathologic Conditions

Death by apoptosis is responsible for loss of cells
in a variety of pathologic states
 Cell
death in certain infections
 Viral

infections
Apoptosis is induced by the virus (as in adenovirus and HIV
infections) or by the host immune response (as in viral
hepatitis)
 Pathologic
atrophy in parenchymal organs after duct
obstruction
 Pancreas,
parotid gland, and kidney
Morphology of Apoptosis

Cell shrinkage
 Smaller
in size
 Cytoplasm is dense
 Organelles are more tightly packed
 Recall
that in other forms of cell injury, an early feature is
cell swelling, not shrinkage

Chromatin condensation
 Most
characteristic feature of apoptosis
 Chromatin aggregates peripherally, under the nuclear
membrane, into dense masses of various shapes and
sizes
Morphology of Apoptosis

Formation of cytoplasmic blebs and apoptotic
bodies
 Extensive
surface blebbing
 Fragmentation into membrane-bound apoptotic bodies

Phagocytosis of apoptotic cells or cell bodies
 Macrophages
Biochemical Features of Apoptosis

A specific feature of apoptosis is the activation
of several members of a family of cysteine
proteases
 Caspases
 Two


properties of this family of enzymes
The “c" refers to a cysteine protease
The "aspase" refers to the unique ability of these enzymes to
cleave after aspartic acid residues
Biochemical Features of Apoptosis

The caspase family
 Divided
functionally into two groups
 Initiator

Caspase-8 and caspase-9
 Executioner

 Exist
Caspase-3 and caspase-6
as inactive pro-enzymes, or zymogens, and
must undergo an enzymatic cleavage to become
active
 The presence of cleaved, active caspases is a
marker for cells undergoing apoptosis
Mechanisms of Apoptosis

Process of apoptosis
 Divided
 Initiation

phase
Caspases become catalytically active
 Execution

 Two
phase
Caspases trigger the degradation of critical cellular components
pathways
 Intrinsic
(mitochondrial)
 Extrinsic (death-receptor initiated)
Mechanisms of Apoptosis

The Intrinsic (Mitochondrial) Pathway of Apoptosis
 Major
mechanism of apoptosis in all mammalian
cells
 Result of increased mitochondrial permeability
 Result of release of pro-apoptotic molecules (death
inducers) into the cytoplasm
 leads to activation of the initiator caspase-9
Mechanisms of Apoptosis

The Extrinsic (Death Receptor-Initiated) Pathway of
Apoptosis
 Initiated
by engagement of plasma membrane death
receptors on a variety of cells
 Death receptors are members of the TNF receptor
family
 Contain
a cytoplasmic domain involved in protein-protein
interactions that is called the death domain

Delivering apoptotic signals
 Leads
to activation of the caspase-8 and -10
Mechanisms of Apoptosis

The Execution Phase of Apoptosis
 Two
initiating pathways converge to a cascade of
caspase activation
 Mediates
the final phase of apoptosis
 Enzymatic
death program is set in motion by rapid and
sequential activation of the executioner caspases
 Caspase-3

and -6
Act on many cellular components
Mechanisms of Apoptosis

Removal of Dead Cells
 Formation
of apoptotic bodies breaks cells up into
"bite-sized"
 Edible
 Healthy
for phagocytes
cells
 Phosphatidylserine
is present on the inner leaflet of the
plasma membrane
 Apoptotic
cells
 Phospholipid
"flips" out and is expressed on the outer layer
of the membrane


Recognized by several macrophage receptors
Cells that are dying by apoptosis secrete soluble factors that
recruit phagocytes
Clinico-pathologic Correlations

Examples of Apoptosis
 Growth
Factor Deprivation
 Hormone-sensitive
cells deprived of the relevant hormone
 Lymphocytes that are not stimulated by antigens and
cytokines
 Neurons deprived of nerve growth factor die by apoptosis
 DNA
Damage
 Exposure
of cells to radiation or chemotherapeutic agents
Autophagy




Process in which a cell eats its own contents
Survival mechanism in times of nutrient deprivation
Starved cell lives by cannibalizing itself and
recycling the digested contents
Intracellular organelles and portions of cytosol are
first sequestered from the cytoplasm in an
autophagic vacuole
 Subsequently
fuses with lysosomes to form an
autophagolysosome
 Cellular
components are digested by lysosomal enzymes
Intracellular Accumulations

Manifestation of metabolic derangements in cells
 Intracellular
accumulation of abnormal amounts of
various substances
 Stockpiled


substances fall into two categories
Normal cellular constituent
 Water, lipids, proteins, and carbohydrates
 Accumulates in excess
Abnormal substance
 Exogenous (mineral or products of infectious agents)
 Endogenous (product of abnormal synthesis or
metabolism)
 May be harmless to the cells
 Occasionally they are severely toxic
 Located in either the cytoplasm (frequently within
phagolysosomes) or the nucleus
Intracellular Accumulations

Attributable to four types of abnormalities
A
normal endogenous substance is produced at a
normal or increased rate, but the rate of metabolism
is inadequate to remove it
 Fatty
change in the liver and reabsorption protein
droplets in the tubules of the kidneys
 An
abnormal endogenous substance, accumulates
because of defects in protein folding and transport
and an inability to degrade the abnormal protein
efficiently
 Accumulation
of mutated α1-antitrypsin in liver cells
 Various mutated proteins in degenerative disorders of
the central nervous system
Intracellular Accumulations

Attributable to four types of abnormalities
A
normal endogenous substance accumulates
because of defects, usually inherited, in enzymes
that are required for the metabolism of the
substance
 Storage
diseases (genetic defects in enzymes involved in
the metabolism of lipid and carbohydrates, resulting in
intracellular deposition of these substances)
 An
abnormal exogenous substance is deposited and
accumulates because the cell has neither the
enzymatic machinery to degrade the substance nor
the ability to transport it to other sites
 Accumulations
of carbon particles and nonmetabolizable
Lipids

All major classes of lipids can accumulate in cells
 Triglycerides
 Cholesterol/cholesterol
esters
 Phospholipids
 Components
of the myelin figures found in necrotic cells
Lipids

Steatosis (Fatty Change)
 Abnormal
accumulations of triglycerides within
parenchymal cells
 Seen in the liver
 The
major organ involved in fat metabolism
 Occurs
in heart, muscle, and kidney
Lipids

Steatosis (Fatty Change)
 Causes
 Toxins,
protein malnutrition, diabetes mellitus, obesity, and
anoxia
 Most common causes of significant fatty change in the liver
(developed countries)


Alcohol abuse
Nonalcoholic fatty liver disease
 Associated with diabetes and obesity
Lipids

Mechanisms for triglyceride accumulation in the liver
 Free
fatty acids from adipose tissue or ingested food
are normally transported into hepatocytes
Esterified to triglycerides, converted into cholesterol or
phospholipids, or oxidized to ketone bodies
 Excess accumulation of triglycerides within the liver may
result from excessive entry or defective metabolism and
export of lipids


Such defects are induced by alcohol
 Hepatotoxin that alters mitochondrial and microsomal
functions
 Leading to increased synthesis and reduced breakdown of lipids
Lipids

Morphology
 Fatty
change is most often seen in the liver and heart
 Appears as clear vacuoles within parenchymal cells
 Intracellular
accumulations of water or polysaccharides (e.g.,
glycogen) may also produce clear vacuoles
 Identification
of lipids requires the avoidance of fat
solvents commonly used in tissue preparation
 Prepare
frozen tissue sections of either fresh or aqueous
formalin-fixed tissues
 Sections may then be stained with Sudan IV or Oil Red-O

Orange-red color to the contained lipids
Lipids

Gross examination--Liver
 Mild
fatty change may not affect the gross appearance
 Progressive accumulation
 Organ
enlarges and becomes increasingly yellow
 Extreme instances, the liver may weigh two to four times
normal


Bright yellow, soft, greasy organ
Gross examination—Heart

Grossly apparent bands of yellowed myocardium
 Alternating with bands of darker, red-brown, uninvolved
myocardium (tigered effect)
Cholesterol and Cholesterol Esters

Most cells use cholesterol for the synthesis of cell
membranes
 Without
intracellular accumulation of cholesterol or
cholesterol esters

Accumulations manifested histologically by
intracellular vacuoles are seen in several pathologic
processes
 Atherosclerosis
 Atherosclerotic

plaques
Smooth muscle cells and macrophages within the intimal layer of
the aorta and large arteries are filled with lipid vacuoles, most
of which are made up of cholesterol and cholesterol esters
Cholesterol and Cholesterol Esters

Xanthomas
 Intracellular
accumulation of cholesterol within
macrophages (acquired and hereditary
hyperlipidemic states)
 Clusters of foamy cells are found in the subepithelial
connective tissue of the skin and in tendons

Cholesterolosis
 Focal
accumulations of cholesterol-laden
macrophages in the lamina propria of the
gallbladder

Niemann-Pick disease, type C
 Lysosomal
storage disease
 Caused by mutations affecting an enzyme involved
Proteins

Intracellular accumulations of proteins
 Appear
as rounded, eosinophilic droplets, vacuoles, or
aggregates in the cytoplasm
 Reabsorption droplets in proximal renal tubules
 Seen
in renal diseases associated with protein loss in the
urine
 May
be normal secreted proteins that are produced in
excessive amounts
 Plasma
cells engaged in active synthesis of immunoglobulins
Proteins

Defective intracellular transport and secretion of
critical proteins

α1-antitrypsin deficiency


Emphysema
Accumulation of cytoskeletal proteins

Microtubules, thin actin filaments ,thick myosin filaments,
and intermediate filaments
Alcoholic hyaline is an eosinophilic cytoplasmic inclusion in liver
cells and is composed predominantly of keratin intermediate
filaments
 Neurofibrillary tangle found in the brain in Alzheimer disease
contains neurofilaments and other proteins


Aggregation of abnormal proteins
Hyaline Change





Alteration within cells or in the extracellular space
Gives a homogeneous, glassy, pink appearance
Widely used as a descriptive histologic term rather
than a specific marker for cell injury
Produced by a variety of alterations
Does not represent a specific pattern of
accumulation
Glycogen


Readily available energy source stored in the
cytoplasm of healthy cells
Excessive intracellular deposits of glycogen
 Seen
in patients with an abnormality in either glucose
or glycogen metabolism


Appear as clear vacuoles within the cytoplasm
Dissolves in aqueous fixatives
 Tissues
are best fixed in absolute alcohol
 Staining with Best carmine or the PAS reaction
 Rose-to-violet
color to the glycogen
Pigments



Pigments are colored substances, some of which are
normal constituents of cells (melanin)
Others are abnormal and accumulate in cells only
under special circumstances
Exogenous pigments (coming from outside the
body)
 Carbon
(coal dust)
 Ubiquitous
air pollutant of urban life
 Accumulations of this pigment blacken the tissues of the lungs
(anthracosis) and the involved lymph nodes
 Tattooing
 Localized,
pigmentation of the skin
 Pigments inoculated are phagocytosed by dermal
Pigments

Endogenous pigments (synthesized within the body
itself)
 Lipofuscin
 Insoluble
pigment
 Also known as lipochrome or wear-and-tear pigment
 Composed of polymers of lipids and phospholipids in
complex with protein
 Not injurious to the cell or its functions
 Telltale sign of free radical injury and lipid peroxidation
 Yellow-brown, finely granular cytoplasmic, often perinuclear,
pigment in tissue sections
 Seen in cells undergoing slow, regressive changes
 Prominent in the liver and heart of aging patients or patients
with severe malnutrition and cancer cachexia
Pigments

Melanin
 Endogenous,
non-hemoglobin-derived, brown-black
pigment
 Formed when the enzyme tyrosinase catalyzes the
oxidation of tyrosine to dihydroxyphenylalanine in
melanocytes
 The only endogenous brown-black pigment
Pigments

Hemosiderin
 Hemoglobin-derived,
golden yellow-to-brown, granular
or crystalline pigment
 Serves as one of the major storage forms of iron
 Represents aggregates of ferritin micelles
 Seen normally in mononuclear phagocytes of the bone
marrow, spleen, and liver
 Actively
engaged in red cell breakdown
Pigments




Iron pigment appears as a coarse, golden, granular
pigment
Within the cell's cytoplasm
Visualized in tissues by the Prussian blue
histochemical reaction
Underlying cause is the localized breakdown of red
cells
 Hemosiderin
is found initially in the phagocytes in the
area

Systemic hemosiderosis
 Mononuclear
phagocytes of the liver, bone marrow,
Pigments

Bilirubin
 Normal
major pigment found in bile
 Derived from hemoglobin
 Contains no iron
Pathologic Calcification


Abnormal tissue deposition of calcium salts, together
with smaller amounts of iron, magnesium, and other
mineral salts
Two forms of pathologic calcification
 Dystrophic
calcification
 Local
deposition in dying tissues
 It occurs despite normal serum levels of calcium and in the
absence of derangements in calcium metabolism
 Encountered
in areas of necrosis
 Coagulative,
 Metastatic
caseous, or liquefactive type
calcification
 Deposition
of calcium salts in otherwise normal tissues
 Hypercalcemia secondary to some disturbance in calcium
Pathologic Calcification

Morphology
 Calcium
salts
 Basophilic,
amorphous granular, clumped appearance
 Intracellular or extracellular, or in both locations
 Over time, heterotopic bone may be formed in the focus of
calcification
 Lamellations (psammoma bodies)

Present in benign and malignant conditions
Cellular Aging




Result of a progressive decline in cellular function
and viability
Caused by genetic abnormalities and the
accumulation of cellular and molecular damage due
to the effects of exposure to exogenous influences
Aging is a regulated process that is influenced by a
limited number of genes
Aging is associated with definable mechanistic
alterations
Cellular Aging

The known changes that contribute to cellular
aging
 Decreased
cellular replication
 Accumulation of metabolic and genetic damage

Cellular life span
 Determined
by a balance between damage
resulting from metabolic events occurring within the
cell and counteracting molecular responses that can
repair the damage