CELL DAMAGE

ContentContent Components and functions of normal cell.Components and functions of normal cell. Cellular injury. Characteristics of the concept of “injury”. Cellular injury. Characteristics of the concept of “injury”. Mechanisms and manifestations of damage of subcellular Mechanisms and manifestations of damage of subcellular

structures: plasmatic membrane, mitochondria, structures: plasmatic membrane, mitochondria, endoplasmatic reticulum, lysosomes, microtubules and endoplasmatic reticulum, lysosomes, microtubules and microphilaments, nucleus and cytoplasm.microphilaments, nucleus and cytoplasm.

Principles of classification of cell injuries.Principles of classification of cell injuries. Molecular mechanisms of cell injury. Molecular mechanisms of cell injury. Antioxidant mechanisms of cells.Antioxidant mechanisms of cells. Cell death.Cell death. Mechanisms of apoptosis.Mechanisms of apoptosis. Ageing.Ageing.

Cellular PathologyCellular Pathology““All organ injuries start with All organ injuries start with

structural or molecular alterations in structural or molecular alterations in cells” concept began by Virchow in cells” concept began by Virchow in

1800's.1800's.

NORMAL CELL

NORMAL CELLNORMAL CELL

• at the subcellular or molecular level.• all cells share the basic organelles for the synthesis of:

• transport of ions and other substances.• to understand pathology, review normal structure and

function of cells.

“you cannot appreciate the abnormal before you understand the normal”

• Present day study of disease attempts to understand how cells react to injury.

proteinsproteins lipidslipids carbohydratescarbohydrates energy energy productionproduction

Plasma Plasma membranemembrane• phospholipid bilayerphospholipid bilayer with embedded

proteins / glycoproteins / glycolipids.• semipermeable membrane with pumps

for ionic / osmotic homeostasis

1.1. Lipid peroxidation (LPO), increased generation of free radicals2. Activation of phospholipases and lysosomal hydrolytic enzymes3. Membrane damage via amphiphilic, detergent substances4. Cell swelling membrane tension, rupture5. Inhibition of repair of the damaged membrane compounds (blockage of de novo synthesis) 6. Immune complex influence the membrane macromolecules7.Conformation disorders of macromolecules Damage to lipid bilayer damage to phospholypase, lipase activities of the membrane

Membrane Membrane damagedamage

(main causes)(main causes)

NucleusNucleus• nuclear envelope / nuclear envelope /

nuclear poresnuclear pores• chromatin chromatin

(euchromatin vs (euchromatin vs heterochromatin)heterochromatin)

• nucleolus nucleolus (synthesis of (synthesis of ribosomal RNA)ribosomal RNA)

MitochondriaMitochondria• inner & outer membranes, cristaeinner & outer membranes, cristae• intermembranous and inner matrix intermembranous and inner matrix

compartmentscompartments• oxidative phosphorylation (main source oxidative phosphorylation (main source

of ATP)of ATP)

Endoplasmic reticulum Endoplasmic reticulum (ER), Ribosomes & Golgi (ER), Ribosomes & Golgi

ApparatusApparatus• Rough (RER) vs smooth (SER)

endoplasmic reticulum• Ribosomes (free in cytosol or

attached to RER)• Polysomes (threaded by

mRNA).• Condensing vacuoles/ secretory vesicles

LysosomeLysosome• Enzymatic (acid hydrolases) digestion of materials in the cell

• Endocytosis• Phagocytosis /

phagosome; • Pinocytosis /

pinocytotic vesicle; • Receptor-mediated

endocytosis

PeroxisomePeroxisome• Enzymes (ex. catalase, catalase, oxidasesoxidases) ! metabolism of hydrogen peroxide & fatty acid

Cellular functionsCellular functions1.1. MovementMovement – muscle cells can generate forces that produce – muscle cells can generate forces that produce

motion.motion.2.2. ConductivityConductivity – is the main function of nervous cells. – is the main function of nervous cells.

Conduction as a response to a stimulus is manifested by a wave Conduction as a response to a stimulus is manifested by a wave of excitation, an electrical potential.of excitation, an electrical potential.

3.3. Metabolic absorptionMetabolic absorption – all cells take in and use nutrients and – all cells take in and use nutrients and other substances from their environment.other substances from their environment.

4.4. SecretionSecretion – certain cells are able to synthesize new substances – certain cells are able to synthesize new substances and secrete them.and secrete them.

5.5. ExcretionExcretion – all cells are able to rid themselves of waste – all cells are able to rid themselves of waste products resulting from the metabolic breakdown of nutrients. products resulting from the metabolic breakdown of nutrients.

6.6. Respiration (oxidation)Respiration (oxidation) – cells absorb oxygen which is used to – cells absorb oxygen which is used to transform nutrients into energy in the form of ATP (in transform nutrients into energy in the form of ATP (in mitochondria)mitochondria)

7.7. ReproductionReproduction – tissue growth occurs as cells enlarge and – tissue growth occurs as cells enlarge and reproduce themselves.reproduce themselves.

8.8. CommunicationCommunication – is critical for all the other functions listed – is critical for all the other functions listed above enabling the survival of the society of cells. Constant above enabling the survival of the society of cells. Constant communication allows the maintenance of a dynamic steady communication allows the maintenance of a dynamic steady state.state.

Cell InjuryCell Injury

1. Cause1. Cause intrinsic, intrinsic, extrinsic extrinsic infectious,infectious, non infectious non infectious

2. The type of influence.2. The type of influence. directdirect mediated mediated acute acute chronic chronic by the course by the course reversible reversible irreversible irreversible3. Manifestations of injury.3. Manifestations of injury.a. specifica. specific b. stereotypical (non specific)b. stereotypical (non specific) 4. In dependence on the 4. In dependence on the pathogenically mechanismspathogenically mechanisms of cells of cells

damage divide on: a) violent (forced); b) damage divide on: a) violent (forced); b) cytopath(ogen)iccytopath(ogen)ic injury. injury.

Cell injuryCell injury is defined as such a change in cell structure, metabolism, is defined as such a change in cell structure, metabolism, physico-chemical properties and function which leads to impairment of its physico-chemical properties and function which leads to impairment of its

vital activityvital activity

REVERSIBLE CELL INJURYREVERSIBLE CELL INJURY It occurs when It occurs when

environmental environmental changes exceed the changes exceed the capacity of the cell capacity of the cell to maintain normal to maintain normal homeostasis. homeostasis.

If the stress is If the stress is removed in tissue or removed in tissue or if the cell withstand if the cell withstand the assault the the assault the injury is reversible injury is reversible

IRREVERSIBLE CELL INJURYIRREVERSIBLE CELL INJURY If the stress remains the severe, the cell If the stress remains the severe, the cell

injury becomes irreversible and lead to cell injury becomes irreversible and lead to cell death death

Comparative analysis of reversible and irreversible Comparative analysis of reversible and irreversible cell injurycell injury

1. Mitochondrial oxygenation

2. ATP

3. Na+K+ pump

4. Intracellular Na +, Ca2+ , extracellular K+

glycolysis

lactate , pH

5. H20

6. Acute cell swelling

a. nuclear chromatin

shrinkingb. lysosomal swelling

Enlargement of endoplasmic reticulumRibosome order Protein synthesis

Impaired lipid deposition

Reversible injury

Inreversible injury1. Membrane damage

a. Loss of phospholipids

b. Cytoskeleton injury

c. Free radical d. Lysis of lipids2. Ca2+ influx

Increased Ca2+ load of mitochondria

Uncoupling of oxidative phosphorilation

3. Release of cytoplasmic enzymes (LDG)4. Release of lysosomal

enzymes 5. Autophagy

The main causes of The main causes of cellcell injuryinjury Internal stresses

• metabolic imbalances, nutritional deficiencies or metabolic imbalances, nutritional deficiencies or excesses excesses

• genetic abnormalities genetic abnormalities • acquired derangements acquired derangements hypoxia hypoxia impairment in impairment in

aerobic tissue respirationaerobic tissue respiration, ischemia , ischemia decrease in blood decrease in blood supplysupply

External • • physical agents (physical agents (mechanical injury, high and low mechanical injury, high and low

temperature, radiation, electrical shock, sudden temperature, radiation, electrical shock, sudden fluctuations of the barometric pressure, acceleration, fluctuations of the barometric pressure, acceleration, etcetc…) …)

• • natural toxins, venoms natural toxins, venoms • • drugs, "chemicals" (Paracelsus) drugs, "chemicals" (Paracelsus) abundant oxygen, abundant oxygen,

increase in glucose, high doses of dietary salt, poisons, increase in glucose, high doses of dietary salt, poisons, insecticides, carbon monoxide, asbestos, drugs, social insecticides, carbon monoxide, asbestos, drugs, social stimulators, e.g. alcohol, narcotics.stimulators, e.g. alcohol, narcotics.

Cell injury signsCell injury signs

a. Swellingb. Dystrophyc. Thesaurismosisd. Dysplasiae. Necrosisf. Autolysis

a. Decrease in functionb. Cellular 1. Increase in permeability 2. Cytoplasmic enzymes leakage to the bloodc. Metabolic derangementsd. Injury mediatorse. Synthesis impairmentsf. Electrolyte balance disorders

Morphological Functional

1. Lipid:1) free oxidation of lipids (FOL), Increased free radical generation and lipid peroxydation oxidative stress 2) activating of phospholipase and 3) detergent action of free fat acids. 2. Impairment in calcium homeostasis (calcium stress) 3. Electrolyte-osmotic balance disorders4. Acidosis (intracellular, extracellular) 5. Protein disorders – enzymatic derangements 6. Nucleic acid disorders (transcription, translation, DNA repair disorders) nucleic acid stress7. Violation of power providing of cell.

Molecular mechanisms of cell injuryMolecular mechanisms of cell injury

FREE FREE RADICALSRADICALS A common A common "final "final

pathway"pathway" in a variety in a variety of forms of cell injury, of forms of cell injury, including injury brought including injury brought about by inflammatory about by inflammatory cells, is generation of cells, is generation of free radicals, i.e., free radicals, i.e., molecular species with molecular species with a single unpaired a single unpaired electron available in an electron available in an outer orbital. outer orbital.

Single free radicalsSingle free radicals initiate chain reactions initiate chain reactions which destroy large which destroy large numbers of organic numbers of organic molecules molecules

Formation, Function, Types of Free RadicalsFormation, Function, Types of Free Radicals

Ionizing Radiation

Produces Hydroxyl FRs

Prod. Superoxide FRs

Damaged Mitochondria

High Concentration

of O2 Prod. Prod.

Superoxide & Superoxide & Hydroxyl FRsHydroxyl FRs

Prod. Prod. Hydrogen Hydrogen

Peroxide (H2O2)Peroxide (H2O2)

Oxidase Reactions

1. NADPH 1. NADPH oxidase in the oxidase in the

PMN & monocyte PMN & monocyte cell membranecell membrane

MyeloperoxidaseMyeloperoxidaseHypochlorouse Hypochlorouse

acidacid2. Xanthine 2. Xanthine

oxidase oxidase is a ROS is a ROS – generate FRs– generate FRs

Prod. Superoxide Prod. Superoxide FRsFRs

DrugsDrugs (e.g. (e.g.

acetaminophen)acetaminophen)Conv. to Conv. to acetaminophen acetaminophen FRs in the liverFRs in the liverCarbon Carbon tetrachloridetetrachlorideConv. to CCl3 Conv. to CCl3

FRsFRs in the liverin the liver

MetalsMetals(e.g. iron, copper)(e.g. iron, copper)

Prod. Hydroxyl FRs Prod. Hydroxyl FRs (Fenton reaction)(Fenton reaction)

Nitric OxideNitric OxideFRs prod. by FRs prod. by

macrophages & macrophages & endothelial cellsendothelial cellsIntima of elastic Intima of elastic

& muscular & muscular arteriesarteries LDL are oxidized by LDL are oxidized by

FRs, lead to FRs, lead to atherosclerotic pl.atherosclerotic pl.

FRs attack a FRs attack a molecule & molecule & “steal” its “steal” its electron electron FRs : damage FRs : damage

membranes & membranes & DNADNA

FREE-RADICAL FREE-RADICAL GENERATION GENERATION

1. 1. Oxidation of Oxidation of unsaturated fatty acids unsaturated fatty acids in membranesin membranes ("lipid ("lipid peroxidation", etc.) peroxidation", etc.) * Basic biologists: * Basic biologists: These are the same These are the same reactions that make reactions that make unsaturated fats turn unsaturated fats turn rancid. rancid.

2. Cross-linking of 2. Cross-linking of sulfhydryl groups of sulfhydryl groups of proteins. proteins.

3. Genetic mutations3. Genetic mutations Ionizing radiation: homolytic break of covalent bonds in water, DNA and other biomolecules

H 2O O H + H

ionizing rad iation

h

1. By absorbing radiant energy (UV, x-rays; striking water, these generate a hydrogen atom and a hydroxyl radical; when hydrogen peroxide contacts ferrous iron, it is cleaved into two hydroxyl radicals (* the Fenton

reaction). 2. As part of normal metabolism (for example,

xanthine oxidase and the P450 systems generate superoxide; our white cells use free radicals to attack and kill invaders)

3. As part of the metabolism of drugs and poisons (the most famous being CCl3.-, from carbon tetrachloride; even O2 in high concentrations generates enough free radicals to gravely injure the lungs).

Free radicals may Free radicals may be generated in be generated in the following the following ways:ways:

Reactive oxygen and nitrogen species ROS/RNS

Free radical – each molecule or its fragment, which can exists independently and contains one or two unpaired electronsReactive oxygen species - species, which contain one or more oxygen atoms and are much more reactive than molecular oxygen

ROS/RNSFree radicals

superoxide radical

hydroperoxyl radical

hydroxyl radical

nitric oxide

hydrogen peroxide

Some characteristics of ROS

ROS Symbol

Half-life

Properties

Superoxide radical

O2•- 10-6 s

poor oxidant, quite toxic & is deployed by theimmune system to kill invading

microorganisms.Hydroperoxyl

radicalHO2

• stronger oxidant than O2•-

Hydrogen peroxide

H2O2 minits oxidant, diffuses across membranes

Hydroxyl radical OH• 10-9 s extremely reactive, diffuses only to very low

distanceAlkoxyl radical LO• 10-6 s less reactive than OH•, but more than ROO•

Peroxyl radical LOO• 10-2 s weak oxidant, high diffusability

Singlet oxygen 1O2 10-6 s powerful oxidizing agent

Cellular sources of ROS

xanthine oxidasehemoglobinriboflavincatecholamines

Cytochrome P450

electron transport chain

lipid peroxidationNADPH oxidase (oxidative burst: phagocytes)

oxidasesflavoproteins

myeloperoxidase (oxidative burst: phagocytes)

transient metals

Oxidative Stress and Oxygen Free RadicalsOxidative Stress and Oxygen Free Radicals• Superoxide anionSuperoxide anion (O (O22

--) – ) – may be formed via the may be formed via the cytochrome Pcytochrome P450450 system system, , found in hepatocytes, found in hepatocytes, which metabolizes many which metabolizes many drugs and toxins – it drugs and toxins – it can can be removedbe removed by by superoxide superoxide dismutasedismutase

• Hydrogen peroxideHydrogen peroxide (H(H22OO22) – ) – removedremoved by by catalase catalase or or glutathione glutathione peroxidaseperoxidase

• Hydroxyl radicalHydroxyl radical ((..OH) – OH) – initiates lipid per-oxidation initiates lipid per-oxidation and DNA damageand DNA damage

Pathologic Effects of Free Pathologic Effects of Free RadicalsRadicals

Hydroxyl radicalsHydroxyl radicals initiate initiate lipid peroxidationlipid peroxidation, , leading to severe damage to membranes, especially leading to severe damage to membranes, especially in mitochondriain mitochondria

Hydroxyl radicalsHydroxyl radicals cause cause oxidative damage to oxidative damage to proteinsproteins, which may damage enzymes and , which may damage enzymes and structural proteinsstructural proteins

Hydroxyl radicalsHydroxyl radicals can induce single- and double- can induce single- and double-strand strand breaks in DNAbreaks in DNA, cross-linking, and formation , cross-linking, and formation of adducts. This could lead to of adducts. This could lead to defective transcriptiondefective transcription, , accelerated cell agingaccelerated cell aging, or , or malignant transformationmalignant transformation of of the cell to a cancerous phenotypethe cell to a cancerous phenotype

Formation of ROS and peroxynitrous acid in phagocytic vacuole of

phagocytes

SOD – superoxid dismutaseMPO - myeloperoxidase

Cellular sources of ROS - examples

O 2 O 2- H 2O 2 H 2O + O H H 2O

e- e- + 2H+ e- + H+ e- + H+

Hb(Fe 2+)-O 2 metHb(Fe 3+) + O 2-

Fe 2+ + H 2O 2 Fe 3+ + HO + O H -

Electron transport system:

Autooxidation of hemoglobin:

Fenton reaction:

LH + HO L + H2O

L + O2 LOO

LH + LOO L + LOOH

Formation of lipid (alkyl) radical initiatedby ROS:

Alkyl radical react with O2 to produceperoxyl radical:

Peroxyl radical attacks another poly-unsturated FA to produce new alkyl radical and lipid peroxide:

Oxidative damage to lipids – Oxidative damage to lipids – Lipid peroxidation (LPO)Lipid peroxidation (LPO)

ROS

Mechanisms of cell injury mediated by ROS and RNSMechanisms of cell injury mediated by ROS and RNS

ROS a RNS

Modification of aa, fragmentation and

aggregation of proteins

Lipid peroxidation DNA damage

Membrane damage

Loss of membrane integrity

Damage to Ca2+ and other ion transport systems

Inability to maintain normal ion gradients

Activation/deactivation of various enzymes

Altered gene expression

Depletion of ATP

Lipids Proteins DNA

Cell injury/ Cell death

aa – amino acids

Antioxidants and Antioxidants and secondary defense secondary defense

systemssystems Prevent ROS formation Eliminate radicals by formation of nonradicals or less reactive radicals Repair dameged molecules and cell structures Expression of genes coding for antioxidant enzymes

Antioxidants and secondary defense systems

Enzyme antioxidants

Nonenzymatic antioxidants

Chelating agents

Enzymes of repair and de

novo synthesis of damaged molecules

Water-solubleLipid-soluble

EndogenousPresent in diet

Increased production of ROS + decreased activity of Increased production of ROS + decreased activity of antioxidant system = oxidative stressantioxidant system = oxidative stress

Antioxidant systemAntioxidant system

I. Enzymatic a. Superoxide dismutase

(SOD)b. Catalasec. Glutathione peroxidase

( glutathione, GSH)d. ubiquinone

II. Non enzymatica. α-tocopherolb. Ascorbic acidc. Cysteine, mannitol,

serotonin, selenium, riboflavin, retinol, carotinoids,

d. Reduced glutathioneGlutathione systemVitaminsMicroelements (Selenium)Amino acids with SH group

Antioxidant enzymes

ENZYME TISSUE SITE ______ Superoxide dismutase

Cu/Zn SOD primarily cytosol, nucleus Mn SOD mitochondria EC SOD extracellular fluid Catalase peroxisomes Glutathione peroxidase GPx cytosol, mitochondria Glutathione reductase GRed cytosol, mitochondria _________________________________________________

Antioxidant enzymes

O 2- + O 2

- + 2H + H 2O 2 + O 2 SOD

SOD scavenges superoxide radical:SOD scavenges superoxide radical:

2H 2O 2 2H 2O + O 2

Catalase decomposes hydrogen peroxid in peroxisomes :Catalase decomposes hydrogen peroxid in peroxisomes :

Glutathione peroxidase (GPx) decomposes HGlutathione peroxidase (GPx) decomposes H22OO22 and lipid peroxides in and lipid peroxides in cytosol and mitochondria by help of GSH, NADPH and cytosol and mitochondria by help of GSH, NADPH and glutathionereductase (GRed):glutathionereductase (GRed):

GPx GRed

H2O + LOH GSSG NADPH

LOOH 2GSH NADP+

Nonenzymatic antioxidantsNonenzymatic antioxidantsEndogenous antioxidants - Synthesized in the bodyEndogenous antioxidants - Synthesized in the body bilirubín bilirubín glutathione and other thiocompounds (thioredoxin)glutathione and other thiocompounds (thioredoxin) uric aciduric acid coenzyme Q (Ubichinon-10/Ubichinol-10)coenzyme Q (Ubichinon-10/Ubichinol-10) lipooic acidlipooic acid melatoninmelatonin sex hormones sex hormones 2-oxoacids (pyruvate, 2-oxoglutarate)2-oxoacids (pyruvate, 2-oxoglutarate) dipeptides containig His (carnosine, anserine)dipeptides containig His (carnosine, anserine) albumin (-SH groups)albumin (-SH groups)

Dietary antioxidantsDietary antioxidantsascorbic acidascorbic acidvitamine Evitamine Ecarotenoidscarotenoidsflavonoids – plant phenols (catechin, quercetin etc)flavonoids – plant phenols (catechin, quercetin etc)

Synthetic antioxidantsSynthetic antioxidants N-acetylcystein (scavenger of ROS), deferoxamine (chelator), N-acetylcystein (scavenger of ROS), deferoxamine (chelator), alopurinol (inhibitor of XO), acetyl salicylic acid (feritine synthesis)alopurinol (inhibitor of XO), acetyl salicylic acid (feritine synthesis)

• Vitamin EVitamin E(fat-soluble)(fat-soluble)1) Prevents lipid 1) Prevents lipid peroxidation in cell peroxidation in cell membranes;membranes;2) Neutralizes 2) Neutralizes oxidized LDLoxidized LDL• Vitamin C Vitamin C (water-(water-soluble)soluble)1) Neutralizes FRs 1) Neutralizes FRs produced by produced by pollutants and pollutants and cigarette smokecigarette smoke• Smokers have Smokers have levels of Vit.C levels of Vit.C because they are because they are used up in used up in neutralizing FRs neutralizing FRs derived from cigarette derived from cigarette smoke.smoke.2) Best neutralizer of 2) Best neutralizer of hydroxyl FRs.hydroxyl FRs.

Oxidative StressOxidative Stress• Absorption of radiant energy with sufficient energy to initiate the radiolysis

of water, i.e., “ionizing” radiation, leads to the following reaction:

H2O .H + .OH

ACCUMULATION OF OXYGEN-ACCUMULATION OF OXYGEN-DERIVED FREE RADICALS DERIVED FREE RADICALS (OXIDATIVE STRESS)(OXIDATIVE STRESS)

Cell injury induced by free radicals, particularly reactive oxygen species, is an important mechanism of cell damage in many pathologic conditions, such as chemical and radiation injury, ischemia-reperfusion injury (induced by restoration of blood flow in ischemic tissue), cellular aging, and microbial killing by phagocytes.

Free radicals are 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, such as inorganic or organic chemicals—proteins, lipids, carbohydrates, nucleic acids—many of which are key components of cell membranes and nuclei.

Moreover, free radicals initiate autocatalytic reactions, whereby molecules with which they react are themselves converted into free radicals, thus propagating the chain of damage.

ACCUMULATION OF OXYGEN-DERIVED ACCUMULATION OF OXYGEN-DERIVED FREE RADICALS (OXIDATIVE STRESS)FREE RADICALS (OXIDATIVE STRESS)

Reactive oxygen species (ROS) are a type of oxygen-derived free are a type of oxygen-derived free radical whose role in cell injury is well established. radical whose role in cell injury is well established.

ROS are produced normally in cells during mitochondrial respiration are produced normally in cells during mitochondrial respiration and energy generation, but they are degraded and removed by cellular and energy generation, but they are degraded and removed by cellular defense systems. defense systems.

Thus, cells are able to maintain a steady state in which free radicals may be Thus, cells are able to maintain a steady state in which free radicals may be present transiently at low concentrations but do not cause damage. present transiently at low concentrations but do not cause damage.

When the production of When the production of ROS increases or the scavenging systems are or the scavenging systems are ineffective, the result is an excess of these free radicals, leading to a ineffective, the result is an excess of these free radicals, leading to a condition called condition called oxidative stress. .

Oxidative stress has been implicated in a wide variety of pathologic has been implicated in a wide variety of pathologic processes, including cell injury, cancer, aging, and some degenerative processes, including cell injury, cancer, aging, and some degenerative diseases such as diseases such as Alzheimer diseaseAlzheimer disease. .

ROS are also produced in large amounts by leukocytes, particularly are also produced in large amounts by leukocytes, particularly neutrophils and macrophages, as mediators for destroying microbes, dead neutrophils and macrophages, as mediators for destroying microbes, dead tissue, and other unwanted substances. tissue, and other unwanted substances.

Therefore, injury caused by these reactive compounds often accompanies Therefore, injury caused by these reactive compounds often accompanies inflammatory reactions, during which leukocytes are recruited and activated..

Reperfusion Injury and Reperfusion Injury and Activated OxygenActivated Oxygen

• Toxic oxygen species are generated, not during the ischemia itself, but during reperfusion, hence the term reperfusion injuryreperfusion injury

• This has clinical relevance, since reperfusion of heart muscle is commonly achieved with per-cutaneous angioplasty. Patients more than 20 minutes post-infarction

are at risk for reperfusion injury.

Reperfusion Injury and Activated OxygenReperfusion Injury and Activated OxygenGeneration of Generation of oxygen free radicalsoxygen free radicals occurs from parenchymal occurs from parenchymal and endothelial cells and from infiltrating leukocytesand endothelial cells and from infiltrating leukocytes   •    Reactive oxygen species    •    Reactive oxygen species can further damage can further damage mitochondrial membranes, which precludes generation of mitochondrial membranes, which precludes generation of ATP and leads to cell deathATP and leads to cell death   •    Ischemic injury    •    Ischemic injury is associated withis associated with inflammation,inflammation, as a as a result of the production of cytokines and increased result of the production of cytokines and increased expression of adhesion molecules by hypoxic parenchymal expression of adhesion molecules by hypoxic parenchymal and endothelial cells and endothelial cells    •       •    Recent data suggest that activation of the Recent data suggest that activation of the complement complement pathwaypathway may contribute to may contribute to ischemia-reperfusion injury. ischemia-reperfusion injury. The complement system The complement system is involved in host defense and is is involved in host defense and is an important mechanism of immune injury. Knockout mice an important mechanism of immune injury. Knockout mice lacking several complement proteins are resistant to this type lacking several complement proteins are resistant to this type of injury.of injury.

Mechanisms of membrane damage in ischemia and reperfusion

Cellular response to ischemia. ATP production by mitochondria relies on an adequate supply of oxygen and of energy substrates such as glucose. Mitochondrial function is therefore compromised soon after failure of blood supply, resulting in failure of production of ATP. One consequence of lack of ATP is failure of ATP-dependent membrane pumps, which normally pump sodium (and with it water) out of cells. Failure of membrane ion pumps leads to accumulation of sodium and water in the cell cytoplasm, with disruption of internal membrane systems. Failure of internal membrane pumps also allows free calcium to enter the cytosol, where it activates many destructive enzyme systems. Structural damage to internal membranes and the cytoskeleton, coupled with lack of ATP, leads to impairment of key synthetic pathways, including those of protein synthesis. Rupture of lysosomes and intracellular liberation of powerful hydrolytic enzymes, active at a low pH, brings about further cellular dissolution.

Summary:Summary:• Reperfusion Reperfusion generates free radicals from generates free radicals from

parenchymal, endothelial, and inflammatory parenchymal, endothelial, and inflammatory cells in the injured tissue, often producing cells in the injured tissue, often producing more cellular injury than the initial ischemia, more cellular injury than the initial ischemia, largely due to membrane damagelargely due to membrane damage

• Be able to identify grossly and Be able to identify grossly and microscopically: Myocardial infarction, renal microscopically: Myocardial infarction, renal infarction (pale infarct), gangreneinfarction (pale infarct), gangrene

Activating of membrane Activating of membrane phospholipasephospholipase

• The surplus activating of phospholipase A2 has an important value in pathogenesis of cell damage. This enzyme carries out breaking up of phospholipids of cell diaphragms to

a) unsaturated fatty acids and b) lysophospholipids. • Unsaturated fatty acids, in particular

arachidonic acid, under act of certain enzymes transform to biologically active matters - eicosanoids.

• Lysophospholipids have ability to create a micelle and they are very strong detergents. High concentration of ions of Ca2+ in a cytoplasm is the basic reason of activation of phospholipase A2.

Detergents action of surplus of free fatty acidsDetergents action of surplus of free fatty acids• Free fatty acids in large concentrations similarly as lysophospholipids

damage bimolecular lipid layer of cellular membranes.• It is possible to select 4 basic mechanisms of increase of maintenance

of free fatty acids in a cell:• 1) Entering of free fatty acids is increased cell in the presence of high

level of lipids in blood, that is observed during activating of processes of lipolysis in fatty tissues (stress, diabetes).

• 2) Formation of free fatty acids is increased in lysosomes (at atherosclerosis).

• 3) Liberation of free fatty acids is increased from phospholipids of cellular membranes under act of phospholipases.

• 4) The use of free fatty acids is broken by a cell as energy sources (diminishing of enzymes is a beta-oxidization and to the Krebs cycle during hypoxia).

CaCa2+2+ - homeostasis disorders - homeostasis disorders1. Increased entrance 1. Increased entrance a.a. HypercalciaHypercalciab.b. Impaired barrier function of the membranes Impaired barrier function of the membranes

(increase in peroxidation processes) (increase in peroxidation processes) 22. . Impaired efflux Impaired efflux Ca-accumulation Ca-accumulationa.a. Ca-pump disorder, Ca-channels impairments Ca-pump disorder, Ca-channels impairments

disorders in synaptic plasticity disorders in synaptic plasticityb.b. CaCa2+2+- Na- Na++ exchange mechanism disorder exchange mechanism disorder

Calcium Calcium mechanismsmechanisms

•Calcium functions Calcium functions as a messenger for the release of many intracellular enzymes.

•Normally, Normally, intracellular calcium intracellular calcium levels arelevels are kept extremely low compared with kept extremely low compared with extracellular levels. Theseextracellular levels. These low low intracellular levels are maintained by intracellular levels are maintained by energy-dependentenergy-dependent,, membrane-membrane-associated calcium/magnesium associated calcium/magnesium (Ca(Ca22+/Mg+/Mg22+) ATPase+) ATPase exchange exchange systems. systems. •IschemiaIschemia and certain toxins lead to an and certain toxins lead to an increaseincrease in cytosolic calciumin cytosolic calcium because because of of increased influx acrossincreased influx across the cell the cell membranemembrane and the release of calcium and the release of calcium stored in thestored in the mitochondria and mitochondria and endoplasmic reticulum. endoplasmic reticulum. •The increased calciumThe increased calcium level activates a level activates a number of enzymes with potentiallynumber of enzymes with potentially damaging effects. damaging effects. •The enzymes include the phospholipases The enzymes include the phospholipases responsibleresponsible for damaging the cell for damaging the cell membrane, proteases thatmembrane, proteases that damage the damage the cytoskeleton and membrane proteins, cytoskeleton and membrane proteins, ATPases thatATPases that break down ATP and break down ATP and hasten its depletion, and endonucleaseshasten its depletion, and endonucleases that fragment chromatinthat fragment chromatin.

Cytosolic free calcium is a potent destructive agent.

•The increase of The increase of concentration of concentration of CaCa22+ ions causes in + ions causes in a cytoplasm:a cytoplasm:

a) a) contraction ofcontraction offibrillar structuresfibrillar structuresof cellof cell(myofibrillar); (myofibrillar);

b) b) activating of activating of phospholipase Aphospholipase A22

c) c) violationviolation of of connection between connection between the processes of the processes of oxidization and oxidization and phosphorylationphosphorylation..

Mitochondria Ca2+

Endoplasmic reticulum Ca2+

Increase of cytosolicIncrease of cytosolic Ca Ca2+2+

ATP-ase Phospholipase

Proteinase Endonuclease

Reduction of phospholipid

s

Decrease ATP

Destruction of membrane and

cytoskeleton proteins

Segmentation of nuclear

chromatin

CaCa2+2+

Pathological stimuli

Pathogenetic effects of Ca stress

Electrolyte-osmotic Electrolyte-osmotic mechanismmechanism of cell of cell

damagedamage.• It connect with Na+ and K+ ions.

Aligning the concentrations of ions of Na+ and K+ on either side of cell membrane (multiplying maintenance of Na+ and degree of maintenance of K+ is in a cytoplasm) in the basis can have two mechanisms:

1) strengthening of ions diffusion through a cell membrane from extracelullar concentration and electric gradient;

2) violation of mechanisms of active transport of Na+ and K+ (Na-K-pump).

•The first mechanism will be realized in the conditions of violations water-electrolyte exchange (hypernatremia, hypokaliemia) and violation of barrier function of cell membrane (increase of its ionic permeability).

•Disorders of function of Na-K-pump can be conditioned the deficit of АТP in a cell, multiplying maintenance of cholesterol in lipids bilayer of membrane (for example, at atherosclerosis), by the action of a number of specific inhibitors Na-K-ATP-elements (for example, strophanthine (ouabaine)).•A change in maintenance of ions of Na+ and K+ is caused: •a) loss of electric potential of cellular diaphragm; •b) it was swollen cells (oedema); •c) osmotic injury of cellular membranes, which is accompanied the increase of their permeability.

Water-ion balance Water-ion balance impairmentimpairment

NaNa++ - K - K++ pump disorder leads to: pump disorder leads to:

1. Rest potential impairment changes in threshold, action potential, impulse transduction

2. Swelling of the cell3. Osmotic tension of the membrane4. Impairment of membrane barrier

function 5. Impaired electrogenesis (ECG, EEG)

As the cell membrane is highly permeable to water and water follows the osmotic gradient, the cell depends on osmotic equilibrium to maintain its volume.

In order to counterbalance the high intracellular concentration of proteins, amino acids, and other organic substrates, the cell lowers the cytosolic ionic concentration. This is done by Na+/K+-ATPase, which pumps Na+ out of the cell in exchange for K+.

Normally the cell membrane is only slightly permeable for Na+, but highly permeable for K+, so that K+ diffuses out again.

This K+-efflux creates an inside negative potential which drives Cl– out of the cell. In this ionic shift, which uses up adenosine 5"-triphosphate (ATP), reduction of the cytosolic concentration of Na+ and Cl– (adding up to ca. 230 mosm/L) is much greater than the rise in cytosolic K+ concentration (ca. 140mosm/L).

Reduction in intracellular Na+ concentration by Na+/K+-ATPase is necessary not only to avoid cell swelling, but also because the steep electrochemical gradient for Na+ is utilized for a series of transport processes.

The Na+/H+ exchanger eliminates one H+ for one Na+, while the 3 Na+/Ca2+ exchanger eliminates one Ca2+ for 3 Na+.

Na+-bound transport processes also allow the (secondarily) active uptake of amino acids, glucose, etc. into the cell.

Lastly, depolarization achieved by opening the Na+ channels serves to regulate the function of excitable cells, e.g. the signal processing and transmission in the nervous system and the triggering of muscle contractions.

• As the activity of Na+-transporting carriers and channels continuously brings Na+ into the cell, survival of the cell requires the continuous activity of Na+/K+-ATPase. • This intracellular Na+ homeostasis may be disrupted if the activity of Na+/K+-ATPase is impaired by ATP deficiency (ischemia, hypoxia, hypoglycemia). • The intracellular K+ decreases as a result, extracellular K+ rises, and the cell membrane is depolarized. • As a consequence, Cl– enters the cell and the cell swells up. These events also occur when the energy supply is compromised, or when Na+ entry exceeds the maximal transport capacity of the Na+/K+-ATPase. • Numerous endogenous substances (e.g., the neurotransmitter glutamate) and exogenous poisons (e.g., oxidants) increase the entry of Na+ and/or Ca2+ via the activation of the respective channels.• The increase in intracellular Na+ concentration not only leads to cell swelling, but also, via impairment of the 3Na+/Ca2+ exchanger, to an increase in cytosolic Ca2+ concentration. • Ca2+ produces a series of cellular effects; among others it penetrates into the mitochondria and, via inhibition of mitochondrial respiration, leads to ATP deficiency.

Mechanism Mechanism of acidosisof acidosis

Reasons of cell acidosis:Reasons of cell acidosis:• 1) there is the surplus entering of 1) there is the surplus entering of

H+ ions in cell from a extracelullar H+ ions in cell from a extracelullar environment;environment;

• 2) formation of sour products in a 2) formation of sour products in a cell during glycolysis activating cell during glycolysis activating (lactic acid – lactate), violations of (lactic acid – lactate), violations of Krebs cycle (carbons acids), Krebs cycle (carbons acids), hydrolitic breaking hydrolitic breaking up(disintegration) phospholipids up(disintegration) phospholipids of cellular membranes (free fat of cellular membranes (free fat acids, phosphoric acid) and acids, phosphoric acid) and others;others;

• 3) violation of fastening of free H+ 3) violation of fastening of free H+ ions is as a result of insufficiency ions is as a result of insufficiency of the buffer systems of cell;of the buffer systems of cell;

• 4) violation of move out H+ ions 4) violation of move out H+ ions from a cell. Reason of this is from a cell. Reason of this is disorders of Na-H-exchange disorders of Na-H-exchange mechanism, and also in the mechanism, and also in the conditions of the broken local conditions of the broken local circulation of blood in tissue.circulation of blood in tissue.

Conclusions of acidosis of cell:Conclusions of acidosis of cell: a)a) change conformation of change conformation of

protein molecules with protein molecules with violation of them function and violation of them function and properties; properties;

b)b) increase of permeability of increase of permeability of cellular membranes; cellular membranes;

c)c) activating enzymes of activating enzymes of lysosomes.lysosomes.

• If there is a lack of OIf there is a lack of O22, energy , energy metabolism switches to metabolism switches to anaerobic glycolysis. anaerobic glycolysis.

• The formation of lactic acid, The formation of lactic acid, which dissociates into lactate which dissociates into lactate and H+, causes cytosolic and H+, causes cytosolic acidosis that interferes with acidosis that interferes with the functions of the the functions of the intracellular enzymes, thus intracellular enzymes, thus resulting in the inhibition of resulting in the inhibition of the glycolysis so that this last the glycolysis so that this last source of ATP dries up.source of ATP dries up.

Mechanism Mechanism of acidosis.of acidosis.

Proteins MechanismsProteins Mechanisms• The proteins mechanisms of cell damage

contain: • 1) inhibition enzymes (reverse and irreversible); • 2) denaturation, that violation of native structure of

albumins molecules as a result of conditioned the break connections of changes of the second or tertiary structures of proteins;

• 3) proteolisis, that is carried out under the action of lysosomal enzymes.

Proteins used in diagnosis of tissue damage by blood testing

The nucleic mechanismsThe nucleic mechanisms► It’s conditioned with It’s conditioned with

violations of nucleic acids violations of nucleic acids (DNA, RNA). Its disturbance (DNA, RNA). Its disturbance of replication, transcription of replication, transcription and translation processes.and translation processes.

► Thus, universal Thus, universal mechanisms of increase of mechanisms of increase of permeability of cellular permeability of cellular membranes are: membranes are:

1) activating of FOL; 1) activating of FOL; 2) activating of 2) activating of

phospholipases; phospholipases; 3) osmotic breaking up 3) osmotic breaking up

membranes; membranes; 4) adsorption of albumens is 4) adsorption of albumens is

on a membrane. on a membrane.

The damage of mitochondrias is accompanied:

1) oppressing the processes of the cellular breathing,

2) violation of connection between the processes of oxidization and phosphorilation.

DAMAGE TO DNA AND PROTEINSDAMAGE TO DNA AND PROTEINS Cells have Cells have

mechanisms that mechanisms that repair damage to repair damage to DNA, but if this DNA, but if this damage is too severe damage is too severe to be corrected (to be corrected (e.ge.g., ., after exposure to after exposure to DNA damaging drugs, DNA damaging drugs, radiation, or radiation, or oxidative stress), the oxidative stress), the cell initiates a suicide cell initiates a suicide program that results program that results in death by in death by apoptosis. apoptosis.

A similar reaction is A similar reaction is triggered by triggered by improperly folded improperly folded proteins, which may proteins, which may be the result of be the result of inherited mutations inherited mutations or external triggers or external triggers such as free radicals. such as free radicals.

Because these Because these mechanisms of cell mechanisms of cell injury typically cause injury typically cause apoptosis, they are apoptosis, they are discussed later in the discussed later in the chapter.chapter.

› The clinical relevance of this question is The clinical relevance of this question is obvious—if we can answer it we may be able obvious—if we can answer it we may be able to devise strategies for preventing cell injury to devise strategies for preventing cell injury from having permanent deleterious from having permanent deleterious consequences. However, the molecular consequences. However, the molecular mechanisms connecting most forms of cell mechanisms connecting most forms of cell injury to ultimate cell death have proved injury to ultimate cell death have proved elusive, for several reasons. The “point of no elusive, for several reasons. The “point of no return,” at which the damage becomes return,” at which the damage becomes irreversible, is still largely undefined, and irreversible, is still largely undefined, and there are no reliable morphologic or there are no reliable morphologic or biochemical correlates of irreversibility. biochemical correlates of irreversibility. Two Two phenomenaphenomena consistently characterize consistently characterize irreversibilityirreversibility——the inability to reverse the inability to reverse mitochondrial dysfunctionmitochondrial dysfunction (lack of (lack of oxidative phosphorylation and ATP oxidative phosphorylation and ATP generation) even after resolution of the generation) even after resolution of the original injury, and original injury, and profound disturbances profound disturbances in membrane functionin membrane function. . As mentioned As mentioned earlier, injury to lysosomal membranes results earlier, injury to lysosomal membranes results in the enzymatic dissolution of the injured cell in the enzymatic dissolution of the injured cell that is characteristic of necrosis.that is characteristic of necrosis.

•Before concluding our discussion of the mechanisms of cell injury, it is useful to Before concluding our discussion of the mechanisms of cell injury, it is useful to consider the possible events that determine when reversible injury becomes consider the possible events that determine when reversible injury becomes irreversible and progresses to cell death. The clinical relevance of this question is irreversible and progresses to cell death. The clinical relevance of this question is obvious—if we can answer it we may be able to devise strategies for preventing cell obvious—if we can answer it we may be able to devise strategies for preventing cell injury from having permanent deleterious consequences. injury from having permanent deleterious consequences.

DAMAGE TO DNA AND DAMAGE TO DNA AND PROTEINSPROTEINS

Leakage of intracellular proteins through the Leakage of intracellular proteins through the damaged cell membrane and ultimately into the damaged cell membrane and ultimately into the circulation provides a means of detecting tissue-circulation provides a means of detecting tissue-specific cellular injury and necrosis using blood specific cellular injury and necrosis using blood serum samples. serum samples.

Cardiac muscle, for example, contains a Cardiac muscle, for example, contains a specific isoform of the enzyme specific isoform of the enzyme creatine creatine kinase kinase and of the contractile protein and of the contractile protein troponintroponin; ;

Liver (and specifically bile duct epithelium) Liver (and specifically bile duct epithelium) contains an isoform of the enzyme contains an isoform of the enzyme alkaline alkaline phosphatasephosphatase; and hepatocytes contain ; and hepatocytes contain transaminasestransaminases. .

Irreversible injury and cell death in these tissues Irreversible injury and cell death in these tissues are reflected in increased levels of such proteins are reflected in increased levels of such proteins in the blood, and measurement of these in the blood, and measurement of these biomarkers is used clinically to assess damage biomarkers is used clinically to assess damage to these tissues.to these tissues.

After damage to mitochondrial membranes there is failure of ATP production and loss of the normal membrane potential of the mitochondrion. The mitochondrial membrane pores (PTPC megachannels) open and release proteins into the cytosol, which can cause apoptosis, as described below. If many mitochondria in a cell fail, causing a catastrophic reduction in ATP production, the cell will die by a non-apoptotic route.

Mechanisms of cell death.Mechanisms of cell death.Terminology:Terminology:

Necrosis:Necrosis: Morphologic changes seen in Morphologic changes seen in dead cells within living tissue.dead cells within living tissue.

Autolysis:Autolysis: Dissolution of dead cells by the Dissolution of dead cells by the cells own digestive enzymes. (not seen)cells own digestive enzymes. (not seen)

Apoptosis:Apoptosis: Programmed cell death. Programmed cell death. Physiological, for cell regulation.Physiological, for cell regulation.

Mechanisms of cell deathMechanisms of cell death ““ApoptosisApoptosis is a pathway of cell death that is induced is a pathway of cell death that is induced

by a tightly-regulated suicide program in which cells by a tightly-regulated suicide program in which cells destined to die activate enzymes that degrade the destined to die activate enzymes that degrade the cell’s own nuclear DNA and nuclear and cytoplasmic cell’s own nuclear DNA and nuclear and cytoplasmic proteins”proteins”– Developmental morphogenesisDevelopmental morphogenesis– RadiationRadiation– Immune system regulationImmune system regulation– Viral infectionsViral infections– CancersCancers– ToxinsToxinsThe process was recognized in 1972 by the distinctive morphologic The process was recognized in 1972 by the distinctive morphologic

appearance of membrane-bound fragments derived from cells, and appearance of membrane-bound fragments derived from cells, and named after the Greek designation for “falling off.”named after the Greek designation for “falling off.”

General biochemical mechanismsGeneral biochemical mechanisms Defects in plasma membrane permeability.Defects in plasma membrane permeability. Oxygen deprivation or generation of reactive Oxygen deprivation or generation of reactive

oxygen species (free radical).oxygen species (free radical). Loss of calcium homeostasis.Loss of calcium homeostasis. Mitochondrial Mitochondrial damage.damage. Chemical injuryChemical injury Genetic variationGenetic variation

Receptorsª Fas, (Apo1, CD95), TNF

Trigger action of cytokines and hormones

Provider molecules of apoptotic signal to the cell Causes: moderate injury during

the entrance of O2, different actions

Conduction of intracellular apoptotic signal (Bad1)

Expression of apo-ptotic genes (bax, p53, Ced-3, p21)

Repression of apoptosis

blockaders BCL-2, XÉ

Activation of cellular cysteine – photolytic – caspases + nucleases

1) Activation of death receptors-DR, 2) Mitochondria – dependent pathway: Output of Ca, proteins, cytochrome C

Lysis of cellular proteins Fragmentation of nucleus and cytoplasm Apoptotic bodies Autophagocytosis

Without inflammation

RIP FAXDTRAD

D

Activated caspases

A p o p t o s i s

1. Cell shrinkage. 2. Nuclear chromatin condensation

and fragmentation3. Apoptotic bodies formation 4. Phagocytosis of apoptotic bodies

by adjacent cells or macrophages.5. Intacted membrane.

Morphologic features of Morphologic features of ApoptosisApoptosis

Role of apoptosis in physiology and pathologyRole of apoptosis in physiology and pathology1. During embryogenesis ( implantation, organogenesis, 1. During embryogenesis ( implantation, organogenesis, growth, metamorphosis)growth, metamorphosis)2. In adults hormone dependent involution (2. In adults hormone dependent involution (during menstrual during menstrual cycle, menopausecycle, menopause, atrophy of , atrophy of prostate and breastsprostate and breasts))3. Destruction of cells in the 3. Destruction of cells in the reproducingreproducing cellular populations cellular populations (epithelial cells of intestine ) (epithelial cells of intestine ) 4. Cell death in tumor (regression)4. Cell death in tumor (regression)5. Death of neutrophils in the active inflammatory process5. Death of neutrophils in the active inflammatory process6. Death of immune cells (B,T- lymphocytes) 6. Death of immune cells (B,T- lymphocytes) 7. Death of cytotoxic T- lymphocytes7. Death of cytotoxic T- lymphocytes8. Pathological atrophy in the 8. Pathological atrophy in the parenchimatous organs parenchimatous organs 9. During the some viral infections (hepatitis)9. During the some viral infections (hepatitis)10. Temperate action of various noxious factors10. Temperate action of various noxious factors

Confocal 3d images of nuclei from nonapoptotic (A) and apoptotic (B) cells stained with PI

A B

Morphogenesis of cell injuryMorphogenesis of cell injury

Atrophy - physiological, pathologicalTypes - local, general, dysfunctional, due to compression, blood circulation, neurogenous

Necrosis, necrobiosis (protein dystrophy)

Autolysis, caryorhexis, caryolysis, plasmorrhexis, plasmolysis, demarcation zone, inflammation around the necrosis

Morphology of necrotic cellsMorphology of necrotic cells• Cell and nuclear swelling• Vacuolization of cytoplasm• Patchy chromatin condensation• Mitochondrial swelling• Plasma membrane rupture• Dissolution of chromatin• Attraction of inflammatory cells

Relationships between sublethal and lethal cell damage. Following sublethal damage Relationships between sublethal and lethal cell damage. Following sublethal damage a cell may recover or, with persistence of the damaging stimulus, cell death may a cell may recover or, with persistence of the damaging stimulus, cell death may result. The sequential structural changes of cell death are termed 'necrosis'.result. The sequential structural changes of cell death are termed 'necrosis'.

Comparison of cell death by apoptosis and Comparison of cell death by apoptosis and necrosisnecrosis

Relationships between sublethal and lethal cell damage. Normal cells that are subject to a damaging stimulus may initiate apoptosis or may become sublethally damaged. If the stimulus abates, cells may recover by resynthesis of proteins and elimination of damaged components. If a damaging stimulus continues, either cells die through apoptosis or, when critical cell damage takes place, mainly through critical lack of ATP, cells die and undergo necrosis. Massively damaging stimuli, e.g. great heat or strong acids, cause immediate coagulation of proteins and death of cells.

Adaptive responses resulting in increased tissue mass. Increased functional demand or endocrine stimulation are what usually cause hypertrophy and hyperplasia. These new patterns of growth are stable while the causative stimulus persists, but once it is removed the tissue returns to a normal pattern of growth.

Pathology Pathology of elderlyof elderly

Ageing:Ageing:

““Progressive time related loss of Progressive time related loss of structural and functional structural and functional

capacity of cells leading to capacity of cells leading to death”death”

►Senescence, Senility, Senile Senescence, Senility, Senile changes.changes.

►Ageing of a person is intimately Ageing of a person is intimately related to cellular ageing.related to cellular ageing.

Factors affecting ageing:Factors affecting ageing:• Stress• Infections• Diseases• Malnutrition• Accidents

• Diminished stress response.

• Diminished immune response.

• Good health.

Cellular mechanisms of Cellular mechanisms of ageingageing

Cross linking proteins & Cross linking proteins & DNA.DNA.

Accumulation of toxic by-Accumulation of toxic by-products.products.

Ageing genes.Ageing genes. Loss of repair Loss of repair

mechanism.mechanism. Free radicale injuryFree radicale injury Telomerase shortening.Telomerase shortening.

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Thank you for attention!