Chap1 Cellinjury f

8/11/2019 Chap1 Cellinjury f

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CHAPTER I

CELLULAR RESPONSES TO STRESS AND TOXIC INSULTS: ADAPTATION, INJURY and DEATH

INTRODUCTION TO PATHOLOGY

Pathologyo

study of disease

o

Devoted to the study of structural, biochemical and functionalchanges in cells, tissues and organs that underlie the disease.

o

Attempts to explain the whys and wherefores of the signs andsymptoms manifested by patients while providing a rational basis forclinical care and therapy.

o

serves as bridge between the basic sciences and clinical medicineo

Scientific foundation for all of medicine.o

The study of pathology is divided into:

1.

General Pathology

- Concerned with the:a.

reactions of the cells and tissues to abnormalstimuli and

b.

to inherited defects, which are the main

causes of disease.2.

Systemic Pathology

- Examines the alterations in specialized organs and tissuesthat are responsible for disorders that involve in theseorgans.

FOUR ASPECTS OF DISEASE

o

forms the core of pathology1.

Etiology - cause of disease

2.

Pathogenesis - mechanisms of its development

3.

Molecular and Morphological Changes - the biochemical andstructural alterations induced in the cells and organs of the

body4. Clinical Manifestations - functional consequences of the

different changesEtiology

o

two major classes of etiologic factors:

1.

genetic (inherited mutations and disease associated genevariants or polymorphisms)

2.

acquired (infectious, nutritional, chemical, physical)o

The idea that one etiologic agent is the cause of one disease is notapplicable to majority of disease is not applicable.

o

Most of the common afflictions are multifactorial and arise from theeffects of various external triggers on a genetically susceptible

individual.o

The relative contribution of inherited susceptibility and external

influences varies in different disease.Pathogenesis

o

Pathogenesis refers to the sequence of events in the response of

cells or tissues to etiologic agent,o

from the initial stimulus to the ultimate expression of the disease.

Molecular and Morphologic Changeso

Morphologic changes refer to the structural alterations in cells ortissues that are either characteristic of a disease or diagnostic of an

etiologic process.o

Diagnostic pathology is devoted to identifying the nature and

progression of disease by studying morphologic changes in tissuesand chemical alterations in patients.

o

Molecular analysis by techniques such as DNA microarrays has begun

to reveal genetic differences that predict the behavior of the tumorsas well as their responsiveness to different therapies.

Functional Derangement and Clinical Manifestationo

End result of genetic, biochemical and structural changes in cells and

tissues are functional abnormalities, which lead to the clinicalmanifestations of disease as well as its progress.

o

All forms of disease start with molecular or structural alterations incells.

o

Injury to cells and to the extracellular matrix ultimately leads totissue and organ injury, which determine the morphologic and clinicalpatterns of disease.

OVERVIEW: CELLULAR RESPONSES TO STRESS AND NOXIOUS STIMULI

The normal cell is confined to a fairly narrow range of function and

structure:

- by its state of metabolism, differentiation andspecialization

- by constraints of neighboring cells

- by availability of metabolic substrates

The normal cell can handle physiologic demands, maintaining a

steady state called homeostasis. Adaptations

Are reversible functional and structural responses to morephysiologic stress and some pathologic stimuli.

new but altered steady states are achieved

Allows the cell to survive and continue to function.

the adaptive response may consist of:a.

increase in size of cells (hypertrophy) and functionaactivity

b.

increase in number of cells (hyperplasia) c.

decrease in the size and metabolic activity of the cells

(atrophy) ord.

a change in the phenotype of the cell (metaplasia)

When the stress is eliminated, the cell can recover to its original state

without having suffered any harmful consequences.

CELLULAR RESPONSES TO INJURY

Nature of Injurious Stimulus Cellular Response

Altered Physiological Stimuli; Some

Nonlethal injurious Stimuli

Cellular Adaptations

increased demand, increased stimulation

(GF,Hormomes)

decreased nutriets, decreased stimulation

Chronic irritation

Hyperplasia, hypertrophy

Atrophy

Metaplasia

Reduced Oxygen Supply, ChemicalInjury, Microbial Infection

Cell Injury

Acute and transient

Progressive and severe

Acute reversible injury

cellular swelling fattychange

irreversible injury

cedeath, necrosis, apoptosis

Metabolic alterations, genetic oracquired; chronic injury

Intracellularaccumulations,

calcification

Cumulative sublethal injry over long life

span

Cellular aging

CELL INJURY

Cell injury occurs :a.

if the limits of adaptive responses are exceededb.

if the cells are exposed to injurious agents or stressc.

if the cell is deprived of essential nutrients

d.

if the cell becomes compromised by mutations that affecessential cellular constituents

Cell injury is reversible up to a certain point.

If the stress or noxious stimuli persists, or it is severe enough fromthe beginning, the cell suffers irreversible injury and ultimately cedeath.

Adaptation, reversible cell injury and cell death may be the s tages oprogressive impairment following different types of insults.

CELL DEATH

Cell death

the end result of progressive cell injury

Most crucial events in the evolution of disease in any tissue or

organ. Results from diverse causes including ischemia (reduced blood

flow), infection and toxins.

Is a normal and essential process in embryogenesis, thedevelopment of organs and maintenance of homeostasis.

there are two principal pathway for cell death:1.

Necrosis

2.

Apoptosis

Nutrient deprivation triggers an adaptive cellular response calautophagy and may also culminate in cell death

Stresses of different types may induce changes in cells and tissuesother than typical adaptations, cell injury and cell death:

Metabolic derangements in cells and sub lethal, chronicinjury may be associated with intracellular accumulationsof a number of substances, including proteins, lipids andcarbohydrates

Calcium is often deposited at the sites of cell death

resulting in pathologic calcification

Aging is accompanied by characteristic morphologic and

functional changes in the cell.

Three other processes that affect cells and tissues are1.

intracellular accumulations2.

pathologic calcification

3.

Cell Aging


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CHAPTER I


ADAPTATION OF CELLULAR GROWTH AND DIFFERENTIATION

Adaptations are reversible changes in the number, size, phenotype,metabolic activity, or functions of cells in response to changes in their

environment.

Physiologic adaptations

Usually represent responses of cells to normalstimulation by hormones or endogenous chemical

mediators (e.g., the hormone-induced enlargementof the breast and uterus during pregnancy).

Pathologic adaptations

Are responses to stress that allow cells to modulate

their structure and function and thus escape injury. Such adaptations can take several distinct forms

HYPERTROPHY

O HYPERTROPHY

- refers to an increase in the size o f cells

- results in an increase in the size of the organ

O the hypertrophied organ has no new cells, just larger cells

O Increased size

due to the synthesis of more structural components ofthe cells.

O Cells capable of division may respond to stress by undergoing bothhyperplasia and hypertrophy

O Nondividing cells (myocardial fibers) increased tissue mass is due tohypertrophy

Ohypertrophy and hyperplasia may coexist and contribute to increasedsized

O Hypertrophy can be physiologic or pathologic and is caused byincreased functional demand or by stimulation by hormones and

growth factors.

- striated muscle cells in the heart and skeletal muscleshave only a limited capacity for division and respond toincreased metabolic demands mainly by undergoing

hypertrophy

O The most common stimulus for hypertrophy of muscle is increasedworkload.

- In the heart, the stimulus for hypertrophy is usuallychronic hemodynamic overload, resulting from eitherhypertension or faulty valves.

O

In both the heart and muscle fiber tissues, the muscle cellssynthesize more proteins and the number of myofilaments increase.

this increases the amount of force each myocyte can generateand thus increases the strength and work capacity of the

muscle as a whole.

Physiologic Hypertrophyo

massive physiologic growth of the uterus during pregnancy is a goodexample of hormone-induced increase in the size of an organ that

results mainly from hypertrophy of muscle fibers.

the cellular enlargement is stimulated by estrogenic hormones

acting on smooth muscle estrogen receptors

results in increased synthesis of smooth muscle proteins and anincrease in cell size.

MECHANISM OF HYPERTROPHY

o

Hypertrophy is the result of increased production of cellular proteins.;understanding is based on the studies of the heart.

o Hypertrophy can be induced by the linked actions of

a.

mechanical sensors (triggered by increased workload)

b.

growth factors (TGF-, insulin-like growth factor-1 [IGF-1],

fibroblast growth factor)c.

vasoactive agents (-adrenergic agonist, endothelin-1, andangiotensin II)

o

Mechanical sensors induce production of growth factors and agonist

these stimuli work coordinately to increase the synthesis ofmuscle proteins that are responsible for hypertrophy.

o

2 main biochemical pathways involved in muscle hypertrophy :1.

Phosphoinositide 3-kinase/Akt pathway

- most important in physiologic hypertrophy such as

exercise-induced hypertrophy2.

signaling downstream of G-protein coupled receptors.

- induced by many GF and vasoactive agents

- more important in pathologic hypertrophy.

o

Hypertrophy may also be associated with a switch of contractileproteins from adult to fetal or neonatal forms.

E.g. during muscle hypertrophy, the isoform of myosin heavychain is replaced by the isoform which has a slower, more

energetically economical contractions.

genes that are expressed only during early development are re

expressed in hypertrophic cells and the products of these genesparticipate in the cellular response to stress.

- gene for Atrial Natriuretic Factor (ANF) is expressed inboth the atrium and ventricle in the embryonic heart, buis down regulated after birth.

- Cardiac hypertrophy is associated with reinduction of ANF

gene expression.- ANF

peptide hormone that causesa.

salt secretion by the kidneyb.

decreases blood volume and pressurec.

serves to reduce hemodynamic load.

o

Cardiac hypertrophy eventually reaches a limit beyond whichenlargement of muscle mass is no longer able to compensate for the

increase burden.

- Several regressive changes occur in the myocardial fibebut the most important area.

lysis

b. loss of myofibrillar contractile elements.

- extreme cases: myocyte death can occur by eitheapoptosis or necrosis.

- net result: CARDIAC FAILURE, a sequence of events tha

illustrates how an adaptation to stress can progress tofunctionally significant cell injury if stress is not relieved.

o

A subcellular organelle may also undergo selective hypertrophy. hypertrophy of the smooth endoplasmic reticulum in

hepatocytes for patients treated with barbiturates.

- adaptive response that increases the amount of enzyme(cytochrome P40 mixed function oxidase) available to

detoxify the drugs.

- patient respond less to drug because of this adaptation.

HYPERPLASIA

Hyperplasia

- increase in the number of cell in an organ or tissue

- usually resulting in an increased mass of the organ tissue

- hyperplasia and hypertrophy frequently occur together, and may betriggered by the same stimulus.

- Hyperplasia takes place if the cell population is capable of dividing andthus, increasing the number of cells.

-

can by physiologic or pathologic.

PHYSIOLOGIC HYPERPLASIA - divided into1. hormonal hyperplasia

increases the functional capacity of the tissue when needed

well illustrated by the proliferation of the glandular epitheliumof the female breast at puberty and during pregnancy, usuallyaccompanied by enlargement of the glandular epithelial cells.

2.

compensatory hyperplasia

- increases tissue mass after damage or partial resection.

- e.g. in individuals who donate one lobe of the liver fotransplantation, the remaining cells proliferate so that theorgan soon grows back to its original size.

PATHOLOGIC HYPERPLASIA

- most forms are caused by excesses of hormones or growth factors actingon target cells.

- Endometrial hyperplasia is an example of abnormal hormone-inducedhyperplasia.

the balance between estrogen and progesterone is disturbed results in absolute or relative increases in the amount o

estrogen, with consequent hyperplasia of the endometria

glands.

this form of hyperplasia is a common cause of abnorma

menstrual bleeding.

- benign prostatic hyperplasia

induced by androgens.

- Benign prostatic hyperplasia and endometrial hyperplasia are abnormabut the process remains controlled because there are no mutations in

genes that regulate cell division and the hyperplasia regress if thehormonal stimulation is eliminated.

- Hyperplasia is a characteristic response to certain viral infections such a

papillomaviruses which causes skin warts and several mucosal lesionscomposed of masses of hyperplastic epithelium.

growth factors produced by viral genes or by infected cells maystimulate cellular proliferation.


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CHAPTER I


MECHANISM OF HYPERPLASIA

o

a result of growth factor-driven proliferation of mature cells and, in

some cases, by increased output of new cells from tissue stem cells. E.g. after partial hepatectomy, growth factors are produced in

the liver that engage receptors in the surviving cells andactivate signaling pathways that stimulate cell proliferation.

If the proliferative capacity of the liver cells is compromised,

hepatocytes can regenerate from intrahepatic stem cells.

ATROPHY

- reduced size of an organ or tissue

- resulting from a decrease in cell size and number

- can be physiologic or pathologic.

PHYSIOLOGIC ATROPHY

o

common during normal developmento

embryonic structures such as notochord and thyroglossal ductundergo atrophy during fetal development.

o

uterus decrease in size shorty after parturition

PATHOLOGIC ATROPHYo

depends on the underlying cause and can be local or generalized.o

common causes of atrophy are the following:

Decreased workload (atrophy of disuse)

-

when a fractured bone is immobilized in a plaster cast orwhen a patient is restricted to complete bed rest, skeletalmuscle atrophy rapidly ensues.

- initial decrease in cell size is reversible once activity isresumed.

- with more prolonged disuse, skeletal muscle fibers

decrease in number as well as in size. (this atrophy canbe accompanied by increase bone resorption, leading to

osteoporosis of disuse)

loss of innervation (denervation atrophy)

- normal metabolism and function of skeletal muscle aredependent on its nerve supply.

- Damage to nerves leads to atrophy of the muscle fibers

supplied by those nerves.

diminished blood supply

- decrease in blood supply to a tissue as a result of slowly

developing arterial occlusive disease results in atrophy ofthe tissue.

-

in late adult life, brain may undergo progressive atrophybecause of reduced blood supply as a result ofatherosclerosis. (senile atrophy, affects the heart)

inadequate nutrition

- profound protein-calorie malnutrition (marasmus) is

associated with the use of skeletal muscle as a source ofenergy after other reserves such as adipose stores have

been depleted. results in marked muscle wasting (cachexia)

- Cachexia is also seen in patients with chronicinflammatory diseases and cancer.

In CID, chronic overproduction of the inflammatory

cytokine tumor necrosis factor is responsible for

appetite suppression and lipid depletion,culminating in muscle atrophy.

loss of endocrine stimulation

- hormone responsive tissues, such as breast andreproductive organs, are dependent on endocrine

stimulation for normal metabolism and function.- loss of estrogen stimulation after menopause results in

physiologic atrophy of the endometrium, vaginal

epithelium and breast.

pressure

- tissue compression for any length of time can causeatrophy.

- enlarging benign tumor can cause atrophy in the

surrounding, uninvolved tissues.

atrophy results of ischemic changes caused by

compromise of the blood supply by the pressureexerted by the expanding mass.

o

Fundamental cellular changes associated with atrophy are identical inall pathologic settings.

o

Initial response is a decrease in cell size and organelles, which mayreduce the metabolic needs of the cell sufficiently to permit itssurvival.

o

In atrophic muscle:

- cells contain fewer mitochondria and myofilaments

- reduced amount of rough ER

MECHANISMS OF ATROPHY

o

atrophy results from:

a.

decreased protein synthesis

- protein synthesis decrease because of reduced metabolicactivity.

b.

increased protein degradation in cells- degradation of cellular proteins occurs mainly by the

ubiquitin-proteasome pathway.o

Ubiquitin-proteasome pathway

- nutrient deficiency and disuse may activate ubiquitin

ligases, which attach the small peptide ubiquitin tocellular proteins and target these proteins for degradation

in proteasomes.

- also thought to be responsible for the acceleratedproteolysis seen in a variety of catabolic conditionsincluding cancer cachexia.

o

atrophy is usually accompanied by increased autophagy with

resulting increases in the number of autophagic vacuoles.

Autophagy

- self-eating

- process in which starved cell eats its own component inan attempt to find nutrients and survive.

autophagic vacuole

-membrane bound vacuoles that contain fragments of cecomponents

- fuse with lysosomes and their contents are digested bylysosome enzymes.

some of the cell debris within the autophagic vacuole mayresist digestion and persist as membrane bound residual bodies

that may remain as sarcophagus in the cytoplasm.

- example of residual bodies is the lipofuscin granules.

when present in sufficient amounts, they impart a

brown discoloration to the tissues.

METAPLASIA

Metaplasia

- Reversible change in which one differentiated cell type (epithelial omesenchymal) is replaced by another cell type.

- represent an adaptive substitution of cells that are sensitive to stress by

cell types better able to withstand the adverse environment.

columnar to squamous epithelial metaplasia

occurs in the RT in response to chronic irritation.

habitual cigarette smoker: normal ciliated columnar epithelial cells o

the trachea and bronchi are often replaced by stratified squamousepithelial cells

stones in the excretory duct of the salivary gland, pancreas or bileducts may also cause replacement of the normal secretory columna

epithelium by stratified squamous.

deficiency in vitamin A (retinoic acid) induces squamous metaplasiain the respiratory epithelium.

the more rugged stratified squamous epithelium is able to surviveunder circumstances in which the more fragile specialized columnacells might have succumbed.

Although the epithelial lining becomes tough, important mechanismof protection against infection (mucus secretion, and the ciliary action

of the columnar epithelium) are lost.metaplasia from squamous to columnar

Barrett esophagus in which the esophageal squamous epithelium isreplaced by intestinal-like columnar cells under the influence orefluxed gastric acid.

Connective tissue metaplasia

formation of cartilage, bone or adipose tissues in tissues thanormally dont contain these elements.

Myositis ossificans

bone formation in the muscle

occurs after intramuscular hemorrhage.

may be a result of cell or tissue injury

MECHANISMS OF METAPLASIA

o

does not result from a change in the phenotype of an alreadydifferentiated cell type


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CHAPTER I


o

result of a reprogramming of stem cells that are known to exist innormal tissues or of undifferentiated mesenchymal cells present in

connective tissues.o

in a metaplastic change, these precursor cells differentiate along a

new pathway.o

differentiation of stem cells to a particular lineage is brought about bysignals generated by cytokines, growth factors and ECM componentsof the cells environment.

o

Retinoic acid regulates gene transcription directly through nuclear

retinoid receptors which can influence the differentiation of

progenitors derived from tissue stem cells.

OVERVIEW OF CELL INJURY AND CELL DEATH

REVERSIBLE CELL INJURYo

in early stages or mild forms of injury, the functional andmorphologic changes are reversible if the damaging stimulus is

removed.o

hallmarks of a reversible cell injury are:

a.

reduced oxidative phosphorylation with resultant depletion ofenergy stores in the form of ATP

b. cellular swelling caused by changes in ion concentrations and

water influx.o

various intracellular organelles (mitochondria and cytoskeleton) may

also show alteration.CELL DEATH

o

continuing damageo

injury becomes irreversibleo

cell cannot recover and eventually dieso

two principal type of cell death:1.

Necrosis

2.

Apoptosis

Necrosis

damage to membrane is severe, lysosome enzymes

enter the cytoplasm and digest the cell

cellular contents leak out Apoptosis

cells DNA or protein are damaged beyond repair,the cell kills itself.

form of cell death that is characterized bya.

nuclear dissolution

b.

fragmentation of the cell without completeloss of membrane integrity

c.

rapid removal of cellular debris

o

Necrosis is always pathologic, apoptosis serves many normal

function and is not necessarily associated with cell injury.o

Cell death is also sometimes the end result of autophagy.

o

Apoptosis can progress to necrosiso

Cell death during autophagy may show many of the biochemicalcharacteristics of apoptosis.

FEATURES OF NECROSIS AND APOPTOSIS

Feature Necrosis Apoptosis

Cell size Enlarged (swelling) Reduced (shrinkage)

NucleusPyknosiskaryorrhexis

karyolysisFragmentation intonucleosome-size fragments

Plasmamembrane

DisruptedIntact; altered structure,especially orientation of lipids

Cellular contentsEnzymatic digestion; mayleak out of cell

Intact; may be released inapoptotic bodies

Adjacentinflammation

Frequent No

Physiologic or

pathologic role

Invariably pathologic

(culmination of irreversiblecell injury)

Often physiologic, means ofeliminating unwanted cells;

may be pathologic after someforms of cell injury, especiallyDNA damage

CAUSES OF CELL INJURY

OXYGEN DEPRIVATIONo

Hypoxia

-

deficiency of oxygen

-

causes cell injury by reducing aerobic oxidative respiration.

-

extremely important and common cause of cell injury and cell

death.

- causes of hypoxia:

a.

reduced blood flow (ischemia)

b.

inadequate oxygenation of the blood due to cardiorespiratory failurec.

decreased oxygen-carrying capacity

-

anemia or

-

carbon monoxide poisoning (producing a stable carbon

monoxyhemoglobin that blocks oxygen carriage)

-

after severe blood loss

PHYSICAL AGENTSo

physical agents capable of causing ce ll injury include:

a. mechanical traumab.

extremes of temperature (burns and deep cold) c.

sudden changes in atmospheric pressure

d.

radiatione.

electric shock

CHEMICAL AGENTS AND DRUGSo

simple chemicals such as glucose or salt in hypertonicconcentration may cause cell injury directly or by derangingelectrolyte balance in cells.

o

Oxygen at high concentration is toxic

INFECTIOUS AGENTSIMMUNOLOGIC REACTIONS

o

injurious reactions to endogenous self-antigens are responsible fo

several autoimmune diseases.o

immune reactions to many external agents, such as microbes and

environmental substances are also important causes of cell and tissueinjury.

GENETIC DERANGMENTS

o

may result in a defect as severe as congenital malformationsassociated with Down syndrome caused by chromosomal anomaly o

as subtle as the decreased life span of RBC caused by a single aminoacid substitution in hemoglobin in sickle cell anemia.

o Genetic defects may cause injury because of

a.

deficiency in functional proteins, such as enzyme defects ininborn errors of metabolism or

b.

accumulation of damaged DNA or misfolded proteins

both of which trigger cell death when they are beyond repair.

NUTRITIONAL IMBALANCESo

major cause of cell injuryo

protein-calorie deficiencies cause death esp. in under privilegedpopulation

MORPHOLOGIC ALTERATIONS IN CELL INJURY

- All stresses and noxious influences exert their effects first at the moleculaor biochemical level.

- the morphologic manifestation of necrosis take more time to develop thanthose of reversible damage.

E.g. in ischemia of myocardium, cell swelling is a reversiblemorphologic change that may occur in a matter of minutes and

may progress to irreversibility within an hour or two.

Light microscopic of cell death may not be seen until 4 to 12hours after total ischemia.

-

Reversible injury is characterized by:a.

generalized swelling of the cell and its organellesb.

blebbing of the plasma membranec.

detachment of the ribosomes from the ER

d.

clumping of nuclear chromatin

these morphologic changes are associated with:

decreased generation of ATP

loss of cell membrane integrity

defects in protein synthesis

cytoskeletal damage

DNA damage

-

Irreversible injury and cell death occurs if the injurious stimulus becomespersistent or in case of excessive injury.

injurious stimuli that induces death associated with necrosisare:

a.

severe mitochondrial damage with depletion of ATPb.

rupture of lysosome and plasma membrane

-

Necrosis is the principal outcome in many commonly encountered injuries.

REVERSIBLE INJURY

o

Two features of reversible injury:1.

Cellular swelling

2. Fatty changeo

Cellular swelling

-

appears whenever cells are incapable of maintaining ionic and

fluid homeostasis


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CHAPTER I


-

result of failure of energy-dependent ion pumps in the plasmamembrane

o

Fatty change

-

occurs in hypoxic injury and various forms of toxic or metabolic

injury.

-

manifested by the appearance of lipid vacuoles in the

cytoplasm.

-

seen mainly in cells involved in and dependent on fat

metabolism such as hepatocytes and myocardial cells.

MORPHOLOGY OF REVERSIBLE CELL INJURY

cellular swelling is the first manifestation of almost all forms of injuryto cells.

- more apparent at the level of the whole organ

-

when it affects many cells, it causes some pallor, increasedturgor and increase weight in organ

On microscopic examination, small, clear vacuoles may be seen

within the cytoplasm.

represent distended and pinched off segments of the ER.

hydropic change or vacuolar degeneration.

Swelling is reversible.

Cells may show increased eosinophilic staining which becomes more

pronounced with progression to necrosis. Ultrastructural changes of reversible cell injury include:

1.

Plasma membrane alterations

-

blebbing, blunting, loss of microvilli2.

Mitochondrial changes

-

swelling and appearance of amorphous densities3.

dilation of the ER

-

with detachment of polysomes

-

intracytoplasmic figures may be present

4.

nuclear alterations

-

disaggregation of granular and fibrillar elements.

NECROSIS

o

Morphologic appearance of necrosis is the result of:

1.

denaturation of intracellular proteins2.

enzymatic digestion of lethally injured cellso

Necrotic cells are

-

unable to maintain membrane integrity and

- their contents often leak out, a process that may elicit

inflammation in the surrounding tissue.o

Enzymes that digest the necrotic cells are derived from

a.

the lysosomes of the dying cells themselves ]

b.

the lysosomes of the leukocytes that are called in as part of theinflammatory reaction.

MORPHOLOGY OF NECROTIC CELLS

Necrotic cells show increased eosinophilia

-

attributable in part to the loss of cytoplasmic RNA and in part to

the denatured cytoplasmic

Necrotic cell may have a more glassy, homogenous appearance than

do normal cells, mainly as a result of the loss of glycogen particles. When enzymes have digested the cytoplasmic organelles, the

cytoplasm becomes vacuolated and appears moth eaten.

Dead cells may be replaced by large, whorled, phospholipid massescalled myelin figures that are derived from damaged cell membranes.

- phospholipid precipitates are either phagocytized by other cellsor further degraded into fatty acids.

In EM, necrotic cells are characterized bya.

discontinuities in plasma and organelle membranes

b.

marked dilation of the mitochondria with the appearance of

large amorphous densitiesc.

intracytoplasmic myelin figuresd.

amorphous debrise.

aggregates of fluffy material probably representing denatured

protein.

Nuclear changes appear in one of the three patterns, all due tononspecific breakdown of DNA:

1.

KARYOLYSIS

-

the basophilia of the chromatin may fade

-

change that presumably reflects loss of DNA because ofenzymatic degradation by endonucleases

2.

PYKNOSIS

-

seen in apoptotic cell death

- characterized by nuclear shrinkage and increased basophilia.

-

chromatin condenses into a solid, shrunken basophilic mass

3.

KARYORHEXIS

-

pyknotic nucleus undergoes fragmentation.

PATTERNS OF TISSUE NECROSIS

Morphology

1. COAGULATIVE NECROSIS

-

architecture of dead tissues is preserved for a span of at least

some days

-

affective tissues exhibit a firm texture

-

injury denatures not only on structural proteins but also in

enzymes and so blocks proteolysis of dead cells- eosinophilic, anucleate cells persist for days or weeks.

-

E.g. ischemia caused by obstruction in a vessel may lead tocoagulative necrosis of the supplied tissue in all organs excepthe brain.

-

Infarct

a localized area of coagulative necrosis

2.

LIQUEFACTIVE NECROSIS

- characterized by digestion of the dead cells, resulting in

transformation of the tissues into a liquid, viscous mass.

- seen in focal bacteria, fungal infections

-

necrotic material is creamy yellow because of the presence othe dead leukocytes and is called pus.

-

E.g., hypoxic death of cells within the central nervous systemoften manifests as liquefactive necrosis.

3.

GANGRENOUS NECROSIS

-

usually applied to a limb, generally the lower leg that has losits blood supply and has undergone necrosis.

-

when bacterial infection is superimposed, there is moreliquefactive necrosis because of the actions of degradative

enzymes in the bacteria and the attracted leukocytes wet gangrene

4.

CASEOUS NECROSIS

-

encountered most often in the foci of tuberculosis infection.

-

caseous (cheese-like)

-

friable white appearance of the area of necrosis,

- necrotic area appears as a collection of fragmented or lysedcells and amorphous granular debris enclosed within a

distinctive inflammatory border.

- appearance is characteristic of a focus of inflammation known

as granuloma.5.

FAT NECROSIS

-

refers to focal areas of fat destruction, resulting from release oactivated pancreatic lipases into the substance of the pancrea

and the peritoneal cavity.

- occurs in acute pancreatitis.

-

necrosis takes the form of foci of shadowy outlines of necroticfat cells with basophilic calcium deposits, surrounded by aninflammatory reaction.

6.

FIBRINOID NECROSIS

- usually seen in immune reactions involving blood vessels.

-

occurs when complexes of antigens and antibodies aredeposited in the walls of arteries.

-

deposits of these immune complexes, together with fibrin thathas leaked out of vessels, result in a bright pink and

amorphous appearance in H&E stains called fibrinoid

O Most necrotic cells and their contents disappear by phagocytosis o

the debris and enzymatic digestion by the leukocytes.O

Dystrophic calcification

-

if necrotic cells and cellular debris are not promptly destroyedand reabsorbed, they tend to attract calcium salts and other

minerals and to become calcified.

MECHANISM OF CELL INJURY

principles that are relevant to most forms of cell injury:1.

Cellular response to injurious stimuli depends on the nature of the

injury, its duration and its severity.2.

Consequence of cell injury depend on the type, state and adaptability

of the injured cell.

-

cells nutritional and hormonal status and its metabolic need

are important in its response to injury.3.

Cell injury results from different biochemical mechanisms acting onseveral essential cellular components.

-

cell components that are most frequently damaged byinjurious stimuli are include


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CHAPTER I


mitochondria

cell membrane

machinery of protein synthesis and packaging

DNA nuclei

4.

Any injurious stimulus may simultaneously trigger multipleinterconnected mechanisms that damage cells.

DEPLETION OF ATP

o

ATP depletion and decreased ATP synthesis are frequently associatedwith both hypoxic and chemical injury.

o

ATP is produced in 2 ways:1.

major pathway: oxidative phosphorylation of adenosinediphosphate

reaction that results in the reduction of O2 by the electrontransfer system of mitochondria.

2.

glycolytic pathway

can generate ATP in the absence of O2 using glucose derivedfrom either body fluids or from the hydrolysis of O2.

o

the major causes of ATP depletion area.

reduced supply of oxygen and nutrients

b.

mitochondrial damagec.

actions of some toxins (e.g. cyanide)o

Tissues with greater glycolytic capacity (e.g. liver) are able to survive

loss of O2 and decreased oxidative phosphorylation better than aretissues with limited capacity for glycolysis. (e.g. brain)

o

synthetic and degradative processes within the cell that require highenergy phosphate in the form of ATP are:

membrane transport protein synthesis

lipogenesis

deacylation-reacylation reactions for phospholipidturnover

o

Depletion of ATP to 5% to 10% of normal levels has widespreadeffects on many critical cellular systems:

a.

Activity of the plasma membrane energy dependentsodium pump (ouabain-sensitive Na,K-atpase) is reduce

failure of this active transport system causes:

Na to enter and accumulate inside the cell

K to diffuse out of the cell

Net gain of solute is accompanied by isosmotic gain of water,causing cell swelling and dilation of the ER

b.

Cellular energy metabolism is altered

if supply of O2 to cells is reduced (as in ischemia),

a.

oxidative phosphorylation ceasesb.

decrease in cellular ATPc.

associated increase in adenosine monophosphate.

these changes stimulate phosphofructokinase andphosphorylase -> increased rate of anaerobic glycolysis

Anaerobic glycolysis

designed to maintain the cells energy sources by

generating ATP through metabolism of glucosederived from glycogen

glycogen stores are depleted results in the accumulation of lactic acid and

inorganic phosphates

reduces the intracellular pH

decreased activity of many cellularenzymes.

c.

Failure of the Ca pump leads to influx of Ca withdamaging effects on numerous cell components

d.

With prolonged or worsening of ATP depletion, structural

disruption of protein synthetic apparatus occurs manifested as detachment of ribosomes from rough ER and

dissociation of polysomes

consequent reduction in protein synthesis.

e.

in cells deprived of O2 or glucose, proteins may becomemisfolded.

misfolded proteins trigger a cellular reaction called unfoldedprotein response

f.

irreversible damage to mitochondrial and lysosome membranesand the cell undergoes necrosis.

MITOCHONDRIAL DAMAGE

o

Mitochondria can be damaged by:a.

increases of cytosolic Ca

b.

reactive oxygen species

c.

oxygen deprivationo

two major consequences of mitochondrial damage:

a.

Mitochondrial damage often results in the formation of a high

conductance channel in the mitochondrial membrane calledmitochondrial permeability transition pore

opening of tis conductance channel leads to:

loss of mitochondrial membrane potential resultingin depletion of ATP.

cyclophilin D

component of MPTP

target of cyclosporine

b.

Mitochondria sequester between the outer and inner membraneseveral proteins that are capable of activating apoptotic pathways includes cytochrome c and proteins

indirectly activate apoptosis inducing enzymes

called caspase.

increase permeability of the outer mitochondrial membranemay result in leakage of these proteins into the cytosol, and

death by apoptosis.

INFLUX OF CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS

o

Cytosolic free Ca (0.1 umol) is maintained at low concentrations,while extracellular levels of 1.3 nmol

o

most intracellular calcium is sequestered in mitochondria and ER.o

Ischemia and certain toxins can cause an increase in cytosolic Ca

concentration because of release of Ca from intracellular stores

resulting from increased influx of Ca across the plasma

membraneo

Increased intracellular Ca causes cell injury by several mechanisms:

a.

accumulation of Ca results in the opening of the mitochondriapermeability transition pore, and failure of ATP generation

b.

increased cytosolic Ca activates a number of enzymes that hasdeleterious cellular effects:

phospholipase - cause membrane damage

protease - breaks down both membrane and cytoskeletaproteins

endonuclease - DNA and chromatin fragmentation

ATPase - hastening ATP depletionc.

Increase cytosolic Ca levels result in the induction of apoptosis b

direct activation of caspases and by increasing mitochondriapermeability

ACCUMULATION OF OXYGEN DERIVED FREE RADICALS (OXIDATIVESTRESS)

o

Free radicals

chemical species that have a single unpaired electron in anouter orbit.

energy is released through reactions with adjacent molecules(inorganic and organic compounds)

initiate autocatalytic reactionso

Reactive oxygen species (ROS)

type of oxygen derived free radical

produced normally in cells during mitochondrial respiration andenergy generation

degraded and removed by cellular defense system.

produced in large amounts by leukocytes (neutrophils andmacrophages) as mediators for destroying microns, dead

tissues and other unwanted substances.

injury caused by ROS often accompanies inflammatory

reactions during which leukocytes are recruited and activated.o

cells are able to maintain a steady state in which free radicals arepresent transiently at lower concentrations but do not cause damage

o

When production of ROS increases or scavenging systems areineffective, result is an excess of free radicals leading to oxidative

stresso

Oxidative stress

implicated in cell injury, cancer, aging and Alzheimer disease.

GENERATION OF FREE RADICALS

1.

Reduction-Oxidation reactions that occur during normal metabolicprocess

-

different number of electrons have been transferred from O2.

- includes

Superoxide

Hydrogen peroxide

hydroxyl ions

2.

Absorption of radiant energy


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CHAPTER I


-

E.g. ionizing radiation can hydrolyze water into hydroxyl ionsand hydrogen free radicals

3.

Inflammation

-

rapid bursts of ROS are produced in activated leukocytes during

inflammations

-

reaction in plasma membrane multiprotein complex that uses

NADPH oxidase for redox reaction.

-

Intracellular oxidase (e.g. xanthane oxidase) generate

superoxide

4.

Enzymatic metabolism of exogenous chemicals or drugs can generatefree radicals that are not ROS but have similar effects

5. Transition metals such as iron and copper donate or accept freeelectrons during intracellular reactions and catalyze free radical

formation6.

Nitric oxide

- important chemical mediator generated by endothelial cells,

macrophages, neurons and other cell types

-

can act as free radical

-

can be converted to peroxynitrite anion

REMOVAL OF FREE RADICALS1.

Antioxidants

-

block the initiation of free radicals formation or inactivate freeradicals.

-

E.g. lipid soluble vitamin E and A as well as ascorbic acid and

glutathione in the cytosol

2.

Iron and Copper3.

Enzymes

Catalase

present in peroxisomes, decomposesH202

Superoxide dismutase (SODs)

convert superoxide to hydrogenperoxide

includes both manganese SOD, localizedin the mitochondria

copper-zinc-SOD, found in the cytosol

Glutathione peroxides

catalyzing free radical breakdownPATHOLOGIC EFFECTS OF FREE RADICALS

o

Lipid Peroxidation in membranes

-

in the presence of O2, free radicals may cause lipid

peroxidation within the plasma and organelle or membranes

-

Oxidative damage is initiated when the double bonds in

unsaturated fatty acids of membrane lipids are attacked by O2derived free radicals, particularly by hydroxyl ions

-

Propagation (autocatalytic chain reaction) occurs which can

result to extensive membrane damage.o

Oxidative modification of proteins

-

free radicals promotea.

oxidation of amino acid side chains,b.

formation of protein-protein cross linkagesc.

oxidation of protein backbone

-

oxidative modification of proteins may:a.

damage the active sites of enzymesb.

disrupt the conformation of structural proteins

c.

enhance proteosomal degradation of unfolded ormisfolded proteins

o

Lesions in DNA

- free radicals cause:a.

single and double strand breaks in DNA

b.

cross linking of DNA strands

c.

formation of adducts

DEFECTS IN MEMBRANE PERMEABILITY

o

Early loss of selective membrane permeability leading ultimately toovert membrane damage is a consistent feature of most forms of cellinjury (except apoptosis)

MECHANISM OF MEMBRANE DAMAGE

o in ischemic cells, membrane defects may be the result of ATP

depletion and calcium mediated activation of phospholipase.

o

toxins, viral proteins, lytic complement components, physical andchemical agents

o

Some biochemical mechanisms contribute to membrane damage:

a.

ROSb.

decreased phospholipid synthesis

c.

increased phospholipid breakdownd.

Cytoskeletal abnormalities

CONSEQUENCES OF MEMBRANE DAMAGE

o the most important sites of membrane damage during cell injury are

the mitochondrial membrane, plasma membrane and membranes o

lysosomes.

a.

Mitochondrial membrane Damage

opening of the MPTP

decreased ATP

release of proteins that trigger apoptotic deathb.

Plasma Membrane Damage

loss of osmotic balance and influx of fluids and ions

loss of cellular contents.

cells leak metabolites that are vital for thereconstitution of ATP, further depleting energystores

c.

Injury to lysosome membranes

results in leakage of enzymes into the cytoplasm

activation of the acid hydrolase in then acidic

intracellular pH of the injured cell.

cells die by necrosis.

DAMAGE TO DNA AND PROTEINS

o

Two phenomena consistently characterize irreversibility:

1.

inability to reverse mitochondria dysfunction2.

profound disturbances in membrane function.

EXAMPLES OF CELL INJRY AND NECROSIS

A.

ISCHEMIC AND HYPOXIC INJURYo

most common type of cell injury.o

Hypoxia

-

reduced oxygen availability

-

energy production by anaerobic glycolysis can continue

o

Ischemia

-

the supply of oxygen and nutrients is decreased because of

reduced blood flow as a consequence ofa.

a mechanical obstruction in the arterial system.b.

by reduced venous drainage

-

ischemia compromises the delivery of the substrates foglycolysis

-

aerobic metabolism is compromised

-

anaerobic energy generation also stops after glycolyticsubstrate are exhausted or glycolysis is inhibited by theaccumulation of metabolites that would have been removed

otherwise by blood flow.

- tends to cause more rapid and sever cell and tissue injury than

does hypoxia in the absence of ischemia.

MECHANISMS OF ISCHEMIC CELL INJURY

o

As oxygen tension within the cell decreases, there isa.

loss of oxidative phosphorylation and

b.

decreased generation of ATP

results in failure of the sodium pump, loss of potassium, influx

of calcium.

progressive loss of glycogen and decreased protein synthesis. loss of contractility does not mean cell death

o

If hypoxia continues, worsening of ATP depletion causes furthe

deterioration. they cytoskeleton disperses

resulting in the loss of Ultrastructural features such

as microvilli and the formation of blebs at the cel

surface. Myelin figures may be seen within the cytoplasm or

extracellularly.

Mitochondria are swollen as a result of loss of volume control

ER remains dilated

entire cell is markedly swollen witha.

increased concentrations of water, Na and Clb.

decreased concentration of K.

-

IF O2 is restored, all of these disturbances are reversible

o If ischemia persists, irreversible injury and necrosis ensue.

Irreversible injury is associated morphologically with

a.

severe swelling of mitochondria


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CHAPTER I


b.

extensive damage to plasma membranes (giving rise tomyelin figures)

c.

swelling of lysosomesd.

large, flocculent, amorphous densities develop in the

mitochondrial matrix.

in the myocardium, the alterations are indications of irreversibleinjury and can be seen as early as 30 to 40 minutes afterischemia.

Massive influx of Ca into the ce ll occurs

Death is mainly by necrosis but apoptosis also contributes.

Apoptotic pathway is activated by release ofproapoptotic molecules from leaky mitochondria.

Dead cells may become replaced by large masses

composed of phospholipids in the form of myelinfigures.

Myelin figures are phagocytized or degraded intofatty acids.

Calcification of fatty acid residues may occur withthe formation of Ca soaps.

o Leakage of intracellular enzymes and other proteins across the

abnormally permeable plasma membrane and into the blood providesimportant clinical indicators of cell death

Creatine Kinase MB and troponin are early signs of MI and may

be seen before the infarct is detectable morphologically.

o

Mammalian cells have developed protective responses to hypoxicstress.

Hypoxia-inducible factor-1-

promotes new blood vessel formation

-

stimulate cell survival pathway

- enhances anaerobic glycolysis.o

The strategy that is most useful in ischemic brain and SC injury is the

transient induction of hypothermia (reducing the core body temp to92F)

this treatment:a.

reduces the metabolic demands of the stressed cellsb.

decrease cell swellingc.

suppress the formation of free radicalsd.

inhibits host inflammatory response

B.

ISCHEMIA-REPERFUSION INJURY

o

When blood flow is restored to cells that have been ischemic buthave not died, injury is paradoxically exacerbated and proceed at anaccelerated phase.

As a consequence, reperfused tissue may sustain loss of cells

in addition to cells that are irreversible damaged at the end ofischemia

o

Ischemia-reperfusion injury

-

contributes to tissue damage during myocardial and cerebralinfarction

-

occurs when new damaging processes are set in motion duringreperfusion, causing the death of cells that might have

recovered.

-

the mechanisms are as follows:

a.

mew damage may be initiated during reoxygenation byincreased generation of reactive oxygen and nitrogenspecies from parenchymal and endothelial cells and from

infiltrating leukocytes.b. ischemic injury associated with inflammation as a result

of production of cytokines and increased expression ofadhesion molecules by hypoxic parenchymal and

endothelial cells.c.

Activation of the complement system

IgM antibodies have a propensity to deposit in

ischemic tissues.

When blood flow is resumed, complementproteins bind to deposited anitbodies, are

activated and cause more cell injury andinflammation.

C.

CHEMICAL (TOXIC) INJURYo

major limitation to drug therapy.

o

chemicals induce cell injury by one of two general mechanisms:1.

Chemicals injure cells directly by combining with criticalmolecular components.

2.

Most toxic chemicals are not biologically active in their nativeform but must be converted to reactive toxic metabolites, which

them act on target molecules.

This modification is accomplished by cytochrome P-450 mixedfunction oxidases in the smooth ER of the liver and othe

organs.

the toxic metabolites that cause membrane damage and ce

injury mainly by:a.

formation of free radicalsb.

subsequent lipid peroxidationc.

direct covalent binding to membrane proteins and lipidsmay also contribute.

APOPTOSIS

o

Apoptosis

-

is a pathway of cell death that is induced by a tightly regulated

suicide program

-

cells destined to die activated enzymes that degrade the cell

own nuclear DNA and nuclear and cytoplasmic proteins.o

Apoptotic cells break up into fragments called apoptotic bodies.

contain portions of cytoplasm and nucleus

plasma membrane remains intact structure is altered to become tasty targets for phagocytes.

o

dead cells and fragments are devoured before the contents haveleaked out.

o

Cell death by this pathway does not elicit an inflammatory reaction inthe host.

o

Apoptosis induced by pathologic stimuli may progress to necrosis.

CAUSES OF APOPTOSIS

APOPTOSIS IN PHYSIOLOGIC CONDITIONS

o

Embryogenesis

-

including implantation, organogenesis, developmenta

involution and metamorphosis

-

death of specific cell types at defined times during developmen

of an organism.o

Involution of hormone dependent tissues upon hormone withdrawal

-

endometrial cell breakdown during menstrual cycle

- ovarian follicular atresia in menopause

-

regression of lactating breast after weaning

-

prostatic atrophy after castration.

o

Cell loss in proliferating cell population

-

immature lymphocytes in the bone marrow and thymus that fai

to express useful antigen receptors

-

B lymphocytes in germinal centers

-

epithelial cells in intestinal crypts to maintain a constantnumber.

o

Elimination of potentially harmful self-reactive lymphocytes

- either before or after they have completed their maturation to

prevent reactions against ones own tissue.o

Death of host cells that have served useful purpose such as:

-

neutrophils in an acute inflammatory response

-

lymphocytes ate the end of an immune response

cells undergo apoptosis because they are deprived of essentiasurvival signals such as GFs.

APOPTOSIS IN PATHOLOGIC CONDITIONS

- eliminates cells that are injured beyond repair without eliciting

a host reaction, thus limiting collateral tissue damage.o

DNA Damage

- radiation, cytotoxic anticancer drugs, hypoxia

-

elimination of cells may be a better alternative than riskingmutations in damaged DNA which may result to malignantransformation.

-

larger doses may result in necrotic cell deatho

Accumulation of misfolded proteins

-

improperly folded proteins arise because of mutations in thegenes encoding thee proteins.

-

ER Stress

Excessive accumulations of misfolded proteins in the ER

culminates in apoptotic cell death

-

degenerative diseases of the CNS and other organso

cell death in certain infection

-

viral infections

-

loss of infected cells is due to apoptosis that may be induced by

the virus or by the host immune response.o

Pathologic atrophy in parenchymal organs after the duct obstruction


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CHAPTER I


MORPHOLOGIC AND BIOCHEMICAL CHANGES IN APOPTOSIS

MORPHOLOGYa.

Cell shrinkage

-

cell is smaller

- cytoplasm is dense

- organelles are normal but more tightly packed.b.

Chromatin condensation

-

most characteristic feature of apoptosis

-

chromatin aggregates peripherally-

nucleus may break up, producing two or more fragmentsc.

Formation of cytoplasmic blebs and apoptotic bodies

-

first show extensive surface blebs

-

undergoes fragmentationd.

Phagocytosis of apoptotic cells or cell bodies usually by macrophage

o

Plasma membranes are thought to remain intact during apoptosisuntil the last stages when they become permeable to normallyretained solutes.

o

Apoptosis does not elicit inflammation.BIOCHEMICAL FEATURES OF APOPTOSIS

1. Activation of Caspases

-

Caspases

c refers to cysteine protease aspase refers to unique ability of the enzymes to cleave after

aspartic acid residues.

can be divided into 2 groups:

a.

initiator

include caspase 8 and caspase 8b.

executioner

caspase 3 and caspase 6 exist as inactive pro-enzymes or zymogens

must undergo enzymatic cleavage to become active

presence of cleaved, active caspase is a marker for cellsundergoing apoptosis.

2.

DNA and protein breakdown3.

Membrane alteration and Recognition by Phagocytes

-

movement of some phospholipids (phosphatidylserene) fromthe inner leaflet to the outer leaflet of the membrane.

-

annexin V

MECHANISMS OF APOPTOSIS

o The basic mechanisms of apoptosis are conserved in multicellular

organisms.

o

The process of apoptosis may be divided into a.

initiation phase

- caspases becomes catalytically active

-

occurs principally by signals from two distinct pathways:

intrinsicor mitochondrial pathway

extrinsic or death receptor-initiatedpathway

b.

execution phase

-

other caspase trigger the degradation of critical cellularcomponents.

Initiation Phase

INTRINSIC (MITOCHONDRIAL PATHWAY

o

major mechanismo

result of increased mitochondrial permeability and release of pro

apoptotic molecule into the cytoplasmo

cytochrome c

-

proteins that when released into the cytoplasm, initiate asuicide program of apoptosis.

-

release of these proteins is controlled by balance between proand anti-apoptotic members of the Bcl family.

Growth factors are other survival signals stimulate production

of anti-apoptotic proteins , the main ones are:a.

Bcl-2

b.

Bcl-xc.

Mcl-1

these proteins reside in cytoplasm andmitochondrial membranes

control mitochondrial proteins that have theability to trigger cell death

o

When cells are deprived of survival signals, or their DNA is damaged,or misfolded proteins induce ER stress, sensors of damage or stress

are activated

these sensors are members of the Bcl family and includea.

Bim

b.

Bidc.

Bad

EXTRINSIC (DEATH RECEPTOR-INTIATED) PATHWAY OF APOPTOSIS

O

pathway is initiated by engagement of plasma membrane deathreceptors on a variety of cells.

O

Death receptors are members of the TNF receptor family that containa cytoplasmic domain called death domain because it is essential fordelivering apoptotic signals.

the best known death receptors area.

the type 1 TNF receptor

b.

Fas (CD95)

Execution Phase of Apoptosis

O

Two initiating pathways converge to a cascade of caspase activationwhich mediates the final phase of apoptosis.

O

the mitochondrial pathway leads to activation of caspase 9.; the

death receptor pathway to caspase 8 and 10.O

After the initiator caspase is cleaved to generate its active form, the

enzymatic death program is set in motion by activation of executionecaspase:

Caspase 3 and 6

- act on many cellular components

-

once activated, cleave an inhibitor of a cytoplasmic DNase and

make DNase active.

-

degrade structural components-

promote fragmentation of nuclei.

REMOVAL OF DEAD CELLS

o

in healthy cells, phosphatidylserene is present on the inner leaflet o

the membraneo

in apoptotic cells, phosphatidylserene flips out and is expressed on

the outer layer of the membrane, where it is recognized by severamacrophage receptors.

o

Cells that are dying by apoptosis secrete soluble factors that recruitphagocytes

thrombospondin

-

adhesive glycoprotein

-

recognized by phagocytes

C1q

-

natural antibodies

- proteins of complement system

CLINICOPATHOLOGIC CORRELATIONS: APOPTOSIS IN HEALTH ANDDISEASE

1.

Growth Factor deprivation

2.

DNA damage3. Protein misfolding4.

Apoptosis induced by the TNF receptor family5.

Cytotoxic T Lymphocyte Mediated Apoptosis

-

Granzymes

ability to cleave protein at aspartate resides

activate a variety of cellular caspases

kills target cells by directly inducing the effector phase ofapoptosis

Disorders Associated with Dysregulated ApoptosisA. Defective Apoptosis and Increased Cell Survival

-

low rate of apoptosis permit the survival of abnormal cells

- defective apoptosis: autoimmune disorder

B.

Increased Apoptosis and Excessive Cell Death- diseases characterized by a loss of cells

-

include:1.

neurodegenerative diseases

2.

ischemic injury3.

death of virus-infected cells

AUTOPHAGYo

Autophagy

-

cell eats its own content

- survival mechanism in times of nutrient deprivation

o

intracellular organelles and portions of cytosol are first sequesteredfrom the cytoplasm in an autophagic vacuole.

o

AV fuses with lysosomes to form autophagolysosomes, and thecellular components are digested by lysosome enzymes

o Regulated by Autophagy genes (Atgs)


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CHAPTER I


INTRACELLULAR ACCUMULATIONS

o

One manifestations of metabolic derangements in cells is theintracellular accumulation of abnormal amounts of various

substances.o

stockpiled substances fall into two categories1.

normal cellular constituent that accumulate in excess

-

water

-

lipids

- proteins

-

carbohydrates

2. abnormal substanceo

substances may be located in either the cytoplasm

(phagolysosomes) or nucleuso

most accumulations are attributable to four types of abnormalities:

a.

a normal endogenous substance is produced at a normal orincreased rate, but the rate of metabolism is inadequate to

remove it

-

fatty change in the liver

-

reabsorption protein droplets in the kidney tubules

b.

abnormal endogenous substance (product of mutated gene )accumulates because of

defects in protein folding and transport

inability to degrade the abnormal protein efficiently

-

E.g. accumulation of mutated alpha1-antitrypsin in liver cells

c. normal endogenous substance accumulates because of defectsin enzymes that are required for the metabolism

d.

abnormal exogenous substance is deposited and accumulatesbecause cell has neither the

ability to transport

enzymatic machinery to degrade the substance

LIPIDS

-

triglycerides

- cholesterol/cholesterol esters

-

phospholipidso

Phospholipids - components of myelin figures found in necrotic cells.o

Abnormal complexes of lipids and carbohydrates accumulate in thelysosome storage disease.

o

TG and cholesterol accumulation

STEATOSIS (FATTY CHANGE)

o

abnormal accumulations of TGs within parenchymal cells.o

often seen in the liver because it is the major organ involved in fatmetabolism.

o

also occurs in heart, muscle and kidney.o

causes include:

a. toxinsb.

protein malnutritionc.

DM

d.

obesitye.

anoxia

o

Mechanism may be that:

free fatty acids from adipose tissue or ingested food arenormally transported into hepatocytes

in the liver:

esterified to Tgs

converted into cholesterol or phospholipid

oxidized to ketone bodies

some are synthesized as acetate as well Excess accumulation of TGs within the liver may result from

excessive entry or defective metabolism and export of lipidso

induced by alcohol that alters mitochondrial and microsomal function,leading to increased synthesis and reduced breakdown of lipids

o

CCl and protein malnutrition cause fatty change by reducing

synthesis of apoproteinso

hypoxia inhibits fatty acid oxidationo

starvation increases fatty acid mobilization from peripheral stores.

MORPHOLOGY

- often seen in liver and heart

-

in all organs: appears as clear vacuoles within parenchymalcells.

o

Liver

-

mild fatty change may not affect the gross appearance

-

organ enlarges

-

becomes increasingly yellow

- in extreme cases, liver may weigh two to four times andtransformed into a bright yellow, soft, greasy organ.

-

fatty change begins with the development of minute membranebound inclusions closely applied to the ER.

o

Heart

-

lipid is found in cardiac muscle in the form of small dropletsoccurring in two patterns

1.

prolonged moderate hypoxia causes intracellular depositsof fat

creates grossly apparent bands of yellowedmyocardium

alternating with bands of darker red brownuninvolved myocardium (tigered effect)

2.

other pattern of fatty change is produced by moreprofound hypoxia or by some forms of myocarditis

shows more uniformly affected myocytes

CHOLESTEROL AND CHOLESTEROL ESTERS

a.

Atherosclerosis

-

smooth muscle cells within the intimal layer of the aorta andlarge arteries are filled with lipid vacuoles,

-

most are made up of cholesterol and cholesterol esters.

-

foamy appearance ; intima: yellow cholesterol-laden atheromas

- EC cholesterol esters may crystalize in the shape of long

needles, producing quite distinctive clefts in tissue sections

b.

Xanthomas

-

intracellular accumulation of cholesterol within macrophages icharacteristic of acquired and hereditary hyperlipidemic states

- clusters of foamy cells in subepithelial connective tissues of the

skin and tendons

c.

Cholesterolosis

-

focal accumulations of cholesterol-laden macrophages in the

lamina propria of the gallbladder.

- unknown mechanism of accumulation

d.

Niemann-Pick Disease, type C

- caused by mutations affecting an enzyme involved in

cholesterol trafficking = cholesterol accumulation in multipleorgans

PROTEINS

o

appearas rounded, eosinophilic droplets, vacuoles or aggregates in

the cytoplasmo

can be amorphous, fibrillar or crystalline in appearanceo

Amyloidosis: abnormal proteins deposit primarily in the extracellulaspaces

o

causes:1.

reabsorption droplets in proximal renal tubules: renal disease

with proteinuria2.

Proteins that accumulate may be normal secreted proteins tha

are produced in excessive amounts, (plasma cells engaged inactive synthesis of immunoglobulins.):

ER becomes distendedRussel bodies - large, homogenous, eosinophilicinclusions called Russell bodies.

3.

Defective intracellular transport and secretion of critical proteins4.

Accumulation of cytoskeletal proteins

- cytoskeletal proteins include:

microtubules (20-25 nm)

thin actin filaments (6-8 nm)

thick myosin filaments (15 nm) intermediate filaments (10 nm)

IF provide a flexible intracellular scaffold thaorganize the cytoplasm and resist forcesapplied to the cell

divided into 5 classes:

1.

keratin filaments - epithelial cells2.

neurofilaments - neurons

3.

desmin filaments - muscle cells4.

vimentin filaments - connective tissuecells

5.

glial cells - astrocytes; Neurofibrillarytangle found in the brain in Alzheime

disease contains neurofilaments andother proteins

5.

Aggregation of abnormal proteins - Proteinopathies

Amyloidosis


11/12

CHAPTER I


- abnormal or misfolded proteins deposit intissues and interfere with normal

funcitons

- deposits can be extracellular , or both

- aggregates may either directly orindirectly cause pathological changess

HYALINE CHANGE

o

Hyaline

refers to an alteration within cells or in the extracellular space homogenous, glassy pink

o

hyaline change is produced by a variety of alterationso

does not represent a specific pattern of accumulation.o

Extracellular hyaline

GLYCOGEN

o

Glycogen - readily available energy source stored in the cytoplasm ofhealthy cells.

o

excessive intracellular deposits of glycogen are seen in patients withan abnormality in either glucose or glycogen metabolism.

o

glycogen masses appear as clear vacuoles within the cytoplasm.

o

DM

-

prime example of glucose metabolism disorder.

- glycogen is found in renal tubular epithelial cells, within livercells, beta cells of islet of Langerhans, and heart muscle cells

o

Glycogen storage disease/ glycogenoses

- enzymatic defects in the synthesis or breakdown of glycogen

result in massive accumulation, causing cell death

PIGMENTS

o

Pigments are colored substances

EXOGENOUS PIGMENTS

o

most common is carbon (coal dust).o

when inhaled, it is picked up by macrophages within the alveoli ->transported through lymphatic channels to the regional lymph nodes

in the tracheobronchial regiono

Anthracosis

-

accumulation of pigment blacken the tissues of the lungso

Coal workers pneumoconiosis

-

aggregates of carbon dust may induce a fibroblastic reaction oreven emphysema.

o

Tattooing - form of localized exogenous pigmentation

ENDOGENOUS PIGMENTS

o

Lipofuscin

-

insoluble pigment

- also known as lipochrome or wear and tear pigment

- composed of polymers of lipid and phospholipid in complex withprotein

-

sign of free radical injury and lipid peroxidation

-

appears as yellow brown, finely granular cytoplasmic, often

perinuclear pigment.

-

seen in cells undergoing slow, regressive changes

- prominent in liver and heart of aging patients or px with severemalnutrition and cancer cachexia

o

Melanin

- endogenous, non-hemoglobin derived

-

brown black pigment

-

formed when enzyme tyrosinase catalyzes the oxidation of

tyrosine to dihydroxyphenylalanine in melanocyteso

Hemosiderin

-

hemoglobin derived, golden yellow to brown

-

granular or crystalline pigment

-

major storage form of iron

-

iron is:

transported by transferrins

stored by apoferritin, to form ferritin micelles.

Ferritin is a consistent of most cell types.

- When there is local or systemic excess in iron, ferritin formshemosiderin granules.

-

hemosiderin represents aggregates of ferritin micelles.

-

Local excess results from hemorrhage in tissues

heme moiety is converted to biliverdin then tobilirubin

-

Systemic overload : hemosiderosis; caused by:a.

increased absorption of dietary iron

b.

hemolytic anemiac.

repeated blood transfusions

MORPHOLOGY

o iron pigment appears as a coarse, golden, granular pigment lying

within the cells cytoplasm

o

Colorless potassium ferrocyanide converted by iron to blue blackferrocyanide.

o

underlying cause is the localized breakdown of red cells: hemosiderin

is only found initially in the phagocytes in the areao

Systemic hemosiderosis

- hemosiderin is found at first in the mononuclear phagocytes onthe liver, bone marrow, spleen and lymph nodes and in thescattered macrophages throughout other organs such as skin

pancreas, and kidneyso

Bilirubin

-

normal major pigment found in bile.

-

derived from hemoglobin but contains no iron

PATHOLOGIC CALCIFICATION

o

abnormal tissue deposition of Ca salts, together with small amountsof iron, magnesium and other mineral salts.

o

2 forms of pathologic calcification:1.

dystrophic calcification

- deposition occurs locally in dying tissues

-

occurs despite normal serum levels of Ca and in the absence o

derangements in Ca metabolism.2.

metastatic calcification

-

deposition of Ca in normal tissues

-

almost always results from hypercalcemia secondary to some

disturbance in Ca metabolism.Dystrophic Calcification

o encountered in area of necrosis

o

almost always present in the atheromas of advanced atherosclerosiso

commonly developed in damaged or aging heart valves

o

Appear macroscopically as fine, white granules or clumps, often felas gritty deposits.

o

tueberculous lymph node is converted to stone

MORPHOLOGY: DYSTROPHIC CALCIFICATION

-

Ca salts have a basophilic, amorphous, granular, clumpedappearance.

-

heterotrophic bone may be formed in the focus of calcification.

- single necrotic cells may constitute seed crystals that become

encrusted by mineral deposits.

- psammoma bodies

lamellated configurations caused by progressiveacquisition of outer layersresembling grain of sands

PATHOGENESIS

-

Final common pathway is the formation of crystalline Ca

phosphate mineral in the form of apatite similar to thathydroxyapatite of bone.

-

Ca is concentrated in vesicles

- steps:

1.

Ca binds to phospholipids present in vesicle membranes2.

Phosphatases associated with the membrane generatephosphate groups which bind to the Ca

3.

cycle of Ca and phosphate binding is repeated -> raisingthe local concentrations

4.

structural change occurs in the arrangement of Ca and

phosphate group, generating a microcrystal which canpropagate and lead to Ca deposition.

Metastatic Calcificationo

may occur in normal tissues whenever there is hypercalcemia.

o

Hypercalcemia accentuates dystrophic calcification.o

four principal causes:1.

increased PTH with subsequent bone resorption(hyperparathyroidism)

2.

destruction of bone tissue secondary to primary tumors or

diffuse skeletal metastasis3.

vitamin D related disorders

4.

renal failureo

may occur widely throughout the body but principally affects theinterstitial tissues of the gastric mucosa, kidneys, lungs, systemicarteries and pulmonary veins.

CELLULAR AGING


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CHAPTER I


o

result of a progressive decline in cellular function and viability causedby genetic abnormalities

o

the known changes that contribute to cellular aging include:1.

Decreased cellular replication

concept that most normal cells have a limitedcapacity for replication was developed from a simple

experimental model for aging. senescence

Werner syndrome - rare disease; characterized bysymptom of premature aging; defective in DNA

replication2.

Accumulation of metabolic and genetic changeo

Sirtuins - histone deacetylase activity; thought to promote theexpression of several genes whose products increase longevity

gssabidomd2If any of you lacks wisdom, he should ask God, who gives generously to allwithout finding fault, and it will be given to him

James 1:5

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