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Cell Injury I – Cell Injury and Cell Death 

Tuesday, 9/8/09 

Michelle Dolan, M.D.

dolan009@umn.edu

Dept. of Laboratory Medicine and Pathology

    

Key Concepts 

Normal cells have a fairly narrow range of function or steady state: Homeostasis

Excess physiologic or pathologic stress may force the cell to a new steady state: Adaptation

Too much stress exceeds the cell’s adaptive capacity: Injury

    

Key Concepts (cont’d) 

Cell injury can be reversible or irreversible

Reversibility depends on the type, severity and duration of injury

Cell death is the result of irreversible injury

    

Cell Injury – General Mechanisms 

Four very interrelated cell systems are particularly vulnerable to injury:

o Membranes (cellular and organellar)

o Aerobic respiration

o Protein synthesis (enzymes, structural proteins, etc)

o Genetic apparatus (e.g., DNA, RNA)

    

Cell Injury – General Mechanisms 

Loss of calcium homeostasis

Defects in membrane permeability

ATP depletion

Oxygen and oxygen-derived free radicals

  

  

Causes of Cell Injury and Necrosis 

See Ch. 1, p. 7 

Hypoxia

o Ischemia

o Hypoxemia

o Loss of oxygen carrying capacity

Free radical damage

Chemicals, drugs, toxins

Infections

Physical agents

Immunologic reactions

Genetic abnormalities

Nutritional imbalance

    

Cell injury 

See also Chap. 1,

p. 14, Fig. 1-17    

Mechanisms of injury 

See Ch. 1, p. 17, Fig. 1-21    

Reversible Injury -- Ch. 1, pp. 13-18 

Mitochondrial oxidative phosphorylation is disrupted first Decreased ATP

o Decreased Na/K ATPase gain of intracellular Na cell swelling

o Decreased ATP-dependent Ca pumps increased cytoplasmic Ca concentration

o Altered metabolism depletion of glycogen

o Lactic acid accumulation decreased pH

o Detachment of ribosomes from RER decreased protein synthesis

End result is cytoskeletal disruption with loss of microvilli, bleb formation, etc

    

Irreversible Injury -- Ch. 1, pp. 13-18 

Mitochondrial swelling with formation of large amorphous densities in matrix

Lysosomal membrane damage leakage of proteolytic enzymes into cytoplasm

Mechanisms include:

o Irreversible mitochondrial dysfunction markedly decreased ATP

o Severe impairment of cellular and organellar membranes

Ischemic injury 

See also Ch. 1, p. 14, Fig. 1-17    

Funky mitochondria    

Cell Injury 

Membrane damage and loss of calcium homeostasis are most crucial

Some models of cell death suggest that a massive

influx of calcium “causes” cell death

Too much cytoplasmic calcium:

o Denatures proteins

o Poisons mitochondria

o Inhibits cellular enzymes

    

Calcium in cell injury 

See Ch. 1, p. 15, Fig. 1-19 

Effect of Increased Calcium

Reversible and  irreversible injury 

See Ch. 1, p. 9,

Fig. 1-9    

Clinical Correlation 

Injured membranes are leaky

Enzymes and other proteins that escape through the leaky membranes make their way to the bloodstream, where they can be measured in the serum

    

Free Radicals -- Ch. 1, pp. 15-17 

Free radicals have an unpaired electron in their outer orbit

Free radicals cause chain reactions

Generated by:

o Absorption of radiant energy

o Oxidation of endogenous constituents

o Oxidation of exogenous compounds

    

Examples of Free Radical Injury 

Chemical (e.g., CCl4, acetaminophen)

Inflammation / Microbial killing

Irradiation (e.g., UV rays skin cancer)

Oxygen (e.g., exposure to very high oxygen tension on ventilator)

Age-related changes

    

Reactive oxygen species 

See Ch. 1, p. 16, Fig. 1-20    

Mechanism of Free Radical Injury 

Lipid peroxidation damage to cellular and organellar membranes

Protein cross-linking and fragmentation due to oxidative modification of amino acids and proteins

DNA damage due to reactions of free radicals with thymine

    

Morphology of Cell Injury –  Key Concept 

(See Ch. 1, pp. 7-8) 

Morphologic changes follow functional changes

    

Reversible Injury -- Morphology 

Light microscopic changes

o Cell swelling (a/k/a hydropic change)

o Fatty change

Ultrastructural changes

o Alterations of cell membrane

o Swelling of and small amorphous deposits in mitochondria

o Swelling of RER and detachment of ribosomes

    

Irreversible Injury -- Morphology 

Light microscopic changes

o Increased cytoplasmic eosinophilia (loss of RNA, which is more basophilic)

o Cytoplasmic vacuolization

o Nuclear chromatin clumping

Ultrastructural changes

o Breaks in cellular and organellar membranes

o Larger amorphous densities in mitochondria

o Nuclear changes

    

Irreversible Injury – Nuclear Changes 

Pyknosis

o Nuclear shrinkage and increased basophilia

Karyorrhexis

o Fragmentation of the pyknotic nucleus

Karyolysis

o Fading of basophilia of chromatin

    

Karyolysis & karyorrhexis -- micro

    

Types of Cell Death 

Apoptosis

o Usually a regulated, controlled process

o Plays a role in embryogenesis

Necrosis

o Always pathologic – the result of irreversible injury

o Numerous causes

    

Apoptosis -- See Ch. 1, pp. 19-22 

Involved in many processes, some physiologic, some pathologic

o Programmed cell death during embryogenesis

o Hormone-dependent involution of organs in the adult (e.g., thymus)

o Cell deletion in proliferating cell populations

o Cell death in tumors

o Cell injury in some viral diseases (e.g., hepatitis)

    

Apoptosis – Morphologic Features 

Cell shrinkage with increased cytoplasmic density

Chromatin condensation

Formation of cytoplasmic blebs and apoptotic bodies

Phagocytosis of apoptotic cells by adjacent healthy cells

    

Events in apoptosis 

Ch. 1, p. 21, Fig. 1-23    

Apoptosis Diagram 

Ch. 1, p. 6, Fig. 1-6    

Apoptosis – Micro  

  

Types of Necrosis -- Ch. 1, pp. 10-11 

Coagulative (most common)

Liquefactive

Caseous

Fat necrosis

Gangrenous necrosis

    

Coagulative Necrosis -- Ch. 1, p. 10 

Cell’s basic outline is preserved

Homogeneous, glassy eosinophilic appearance due to loss of cytoplasmic RNA (basophilic) and glycogen (granular)

Nucleus may show pyknosis, karyolysis or karyorrhexis

    

Renal infarct -- gross    

Splenic infarcts -- gross    

Infarcted bowel -- gross    

Myocardium photomic    

Adrenal infarct -- Micro    

3 stages of coagulative necrosis (L to R) -- micro

  

  

Liquefactive Necrosis -- Ch. 1, pp. 10-11 

Usually due to enzymatic dissolution of necrotic cells (usually due to release of proteolytic enzymes from neutrophils)

Most often seen in CNS and in abscesses

Lung abscesses (liquefactive necrosis) -- gross

    

Liver abscess -- micro

    

Liquefactive necrosis -- gross

    

Liquefactive necrosis of brain 

-- micro    

Organizing liquefactive necrosis with cysts -- gross

    

Macrophages cleaning liquefactive necrosis -- micro

    

Caseous Necrosis -- Ch. 1, pp. 10-11 

Gross: Resembles cheese

Micro: Amorphous, granular eosinophilc material surrounded by a rim of inflammatory cells

o No visible cell outlines – tissue architecture is obliterated

Usually seen in infections (esp. mycobacterial and fungal infections)

    

Caseous necrosis -- gross    

Caseous -- gross    

Extensive caseous necrosis -- gross

    

Caseous necrosis -- micro

    

Enzymatic Fat Necrosis -- Ch. 1, p. 11 

Results from hydrolytic action of lipases on fat

Most often seen in and around the pancreas; can also be seen in other fatty areas of the body, usually due to trauma

Fatty acids released via hydrolysis react with calcium to form chalky

white areas “saponification”

    

Enzymatic fat necrosis of pancreas -- gross

    

Fat necrosis -- gross    

Fat necrosis -- micro    

Gangrenous Necrosis -- Ch. 1, p. 10 

Most often seen on extremities, usually due to trauma or physical injury

“Dry” gangrene – no bacterial superinfection; tissue appears dry

“Wet” gangrene – bacterial superinfection has occurred; tissue looks wet and liquefactive

    

Gangrene -- gross

    

Wet gangrene -- gross    

Gangrenous necrosis -- micro

    

Fibrinoid Necrosis -- Ch. 1, p. 11 

Usually seen in the walls of blood vessels (e.g., in vasculitides)

Glassy, eosinophilic fibrin-like material is deposited within the vascular walls

    

Cell Injury II – Cellular Adaptations 

Tuesday, 9/8/09 

Michelle Dolan, M.D.

dolan009@umn.edu

Dept. of Laboratory Medicine and Pathology

    

Slide – Adaptation diagram

    

Myocyte adaptation 

Ch. 1, p. 2, Fig. 1-2    

Hyperplasia -- Ch. 1, p. 4 

Increase in the number of cells in an organ or tissue

May or may not be seen together with hypertrophy

Can be either physiologic or pathologic

    

Physiologic Hyperplasia 

Hormonal

o Hyperplasia of uterine muscle during pregnancy

Compensatory

o Hyperplasia in an organ after partial resection

Mechanisms include increased DNA synthesis

Growth inhibitors will halt hyperplasia after sufficient growth has occurred

    

Pathologic Hyperplasia 

Due to excessive hormonal stimulation

o Endometrial proliferation due to increased absolute or relative amount of estrogen

Due to excessive growth factor stimulation

o Warts arising from papillomaviruses

Not in itself neoplastic or preneoplastic – but the underlying trigger may put the patient at increased risk for developing sequelae (e.g., dysplasia or carcinoma)

  

  

Prostatic hyperplasia -- gross    

Slide -- BPH    

Hypertrophy -- Ch. 1, p. 3 

Increase in the size of cells leading to an increase in the size of the organ (often seen in tissues made up of terminally differentiated cells – they can no longer

divide, their only response to the stress is to enlarge)

End result is that the amount of increased work that each individual cell must perform is limited

Can be either physiologic or pathologic

    

Hypertrophy (cont’d) 

Physiologic

o Due to hormonal stimulation (e.g., hypertrophy of uterine smooth muscle during pregnancy)

Pathologic

o Due to chronic stressors on the cells (e.g., left ventricular hypertrophy due to long-standing increased afterload such as HTN, stenotic valves)

    

Physiologic hypertrophy 

See Ch. 1, p. 3. Fig. 1-3    

Left ventricular hypertrophy -- gross

    

Chronic Hypertrophy 

If the stress that triggered the hypertrophy does not abate, the organ will most likely proceed to failure – e.g., heart failure due to persistently elevated HTN

Hypertrophied tissue is also at increased risk for development of ischemia, as its metabolic demands may outstrip its blood supply

    

Atrophy -- Ch. 1, p. 4 

Shrinkage in the size of the cell (with or without accompanying shrinkage of the organ or tissue)

Atrophied cells are smaller than normal but they are still viable – they do not necessarily undergo apoptosis or necrosis

Can be either physiologic or pathologic

    

Atrophy (cont’d) 

Physiologic

o Tissues / structures present in embryo or in childhood (e.g., thymus) may undergo atrophy as growth and development progress

Pathologic

o Decreased workload

o Loss of innervation

o Decreased blood supply

o Inadequate nutrition

o Decreased hormonal stimulation

o Aging

o Physical stresses (e.g., pressure)

    

Muscle atrophy -- micro    

Physiologic atrophy 

See also Ch. 1, p. 5, Fig. 1-4    

Brain atrophy (Alzheimer’s ) -- gross

    

Atrophic testis -- gross    

Metaplasia -- Ch. 1, p. 5 

A reversible change in which one mature/adult cell type (epithelial or

mesenchymal) is replaced by another mature cell type

o If injury or stress abates, the metaplastic tissue may revert to its original type

A protective mechanism rather than a premalignant change

    

Metaplasia (cont’d) 

Bronchial (pseudostratified, ciliated columnar) to squamous epithelium

o E.g., respiratory tract of smokers

Endocervical (columnar) to squamous epithelium

o E.g., chronic cervicitis

Esophageal (squamous) to gastric or intestinal epithelium

o E.g., Barrett esophagus

    

Squamous metaplasia 

See Ch. 1, p. 5, Fig. 1-5    

Gastric metaplasia in esophagus -- micro

    

Metaplasia -- Mechanism 

Reprogramming of epithelial stem cells (a/k/a reserve cells) from one type of epithelium to another

Reprogramming of mesenchymal (pluripotent) stem cells to differentiate along a different mesenchymal pathway

    

Intracellular Accumulations -- Ch. 1, pp. 23-26 

Cells may acquire (either transiently or permanently) various substances that arise either from the cell itself or from nearby cells

o Normal cellular constituents accumulated in excess (e.g., from increased production or decreased/inadequate metabolism) – e.g., lipid accumulation in hepatocytes

o Abnormal substances due to defective metabolism or excretion (e.g., storage diseases, alpha-1-AT deficiency)

o Pigments due to inability of cell to metabolize or transport them (e.g., carbon, silica/talc)

    

Intracellular accumulations 

See Ch. 1, p. 23,

Fig. 1-24    

Lipids -- Ch. 1, pp. 23-24 

Steatosis (a/k/a fatty change)

o Accumulation of lipids within hepatocytes

o Causes include EtOH, drugs, toxins

o Accumulation can occur at any step in the pathway – from entrance of

fatty acids into cell to packaging and transport of triglycerides out of cell

Cholesterol (usu. seen as needle-like clefts in tissue; washes out with processing so looks cleared out) – E.g.,

o Atherosclerotic plaque in arteries

o Accumulation within macrophages (called “foamy” macrophages) – seen in xanthomas, areas of fat necrosis, cholesterolosis in gall bladder

    

Steatosis 

See Ch. 1, p. 24,

Fig. 1-25    

Slide – Fatty liver    

Proteins -- Ch. 1, pp. 24-25 

Accumulation may be due to inability of cells to maintain proper rate of metabolism

o Increased reabsorption of protein in renal tubules eosinophilic, glassy droplets in cytoplasm

Defective protein folding

o E.g., alpha-1-AT deficiency intracellular accumulation of partially folded intermediates

o May cause toxicity – e.g., some neurodegenerative diseases

    

Alpha-1-antitrypsin accumulation -- micro

    

Gaucher’s disease -- micro    

Liver in EtOH -- micro    

Mallory hyaline -- micro    

Glycogen -- Ch. 1, p. 25 

Intracellular accumulation of glycogen can be normal (e.g., hepatocytes) or pathologic (e.g., glycogen storage diseases)

Best seen with PAS stain – deep pink to magenta color

    

Slide – Liver – normal glycogen

    

Liver – Glycogen storage disease

    

Pigments -- Ch. 1, pp. 25-26 

Exogenous pigments

o Anthracotic (carbon) pigment in the lungs

o Tattoos

    

Anthracotic pigment in lungs -- gross

    

Slide – Anthracotic lymph node

    

Anthracotic pigment in macrophages -- micro

    

Pigments 

Endogenous pigments

o Lipofuscin (“wear-and-tear” pigment)

o Melanin

o Hemosiderin

    

Lipofuscin 

Results from free radical peroxidation of membrane lipids

Finely granular yellow-brown pigment

Often seen in myocardial cells and hepatocytes

    

Lipofuscin -- micro    

Lipofuscin  

  

Melanin -- Ch. 1, p. 26 

The only endogenous brown-black pigment

Often (but not always) seen in melanomas

    

Slide -- Melanoma    

Hemosiderin -- Ch. 1, p. 26 

Derived from hemoglobin – represents aggregates of ferritin micelles

Granular or crystalline yellow-brown pigment

Often seen in macrophages in bone marrow, spleen and liver (lots of red cells and RBC breakdown); also in macrophages in areas of recent hemorrhage

Best seen with iron stains (e.g., Prussian blue), which makes the granular pigment more visible

    

Hemosiderin -- micro    

Hemosiderin    

Hemosiderin in renal tubular cells -- micro

    

Prussian Blue – hemosiderin in hepatocytes and Kupffer

cells -- micro    

Dystrophic Calcification -- Ch. 1, pp. 26-27 

Occurs in areas of nonviable or dying tissue in the setting of normal serum calcium; also occurs in aging or

damaged heart valves and in atherosclerotic plaques

Gross: Hard, gritty, tan-white, lumpy

Micro: Deeply basophilic on H&E stain; glassy, amorphous appearance; may be either crystalline or noncrystalline

    

Calcification    

Slide – Ganglioneuroblastoma with

calcification    

Dystrophic calcification in wall of stomach -- micro

    

Metastatic Calcification -- Ch. 1, p. 27 

May occur in normal, viable tissues in the setting of hypercalcemia due to any of a number of causes

o Calcification most often seen in kidney, cardiac muscle and soft tissue

    

Metastatic calcification of lung in pt with hypercalcemia

-- micro