Cell Injury I Cell Injury and Cell Death

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Cell Injury I Cell Injury and Cell Death

• Tuesday, 9/8/09
• Michelle Dolan, M.D.
• dolan009_at_umn.edu
• Dept. of Laboratory Medicine and Pathology

2
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 cells adaptive
  capacity Injury

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Key Concepts (contd)

• 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

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Cell Injury General Mechanisms

• Four very interrelated cell systems are
  particularly vulnerable to injury
• Membranes (cellular and organellar)
• Aerobic respiration
• Protein synthesis (enzymes, structural proteins,
  etc)
• Genetic apparatus (e.g., DNA, RNA)

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Cell Injury General Mechanisms

• Loss of calcium homeostasis
• Defects in membrane permeability
• ATP depletion
• Oxygen and oxygen-derived free radicals

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Causes of Cell Injury and NecrosisSee Ch. 1, p. 7

• Hypoxia
• Ischemia
• Hypoxemia
• Loss of oxygen carrying capacity
• Free radical damage
• Chemicals, drugs, toxins
• Infections
• Physical agents
• Immunologic reactions
• Genetic abnormalities
• Nutritional imbalance

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Cell injury
See also Chap. 1, p. 14, Fig. 1-17
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Mechanisms of injury
See Ch. 1, p. 17, Fig. 1-21
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Reversible Injury -- Ch. 1, pp. 13-18

• Mitochondrial oxidative phosphorylation is
  disrupted first ? Decreased ATP ?
• Decreased Na/K ATPase ? gain of intracellular Na
  ? cell swelling
• Decreased ATP-dependent Ca pumps ? increased
  cytoplasmic Ca concentration
• Altered metabolism ? depletion of glycogen
• Lactic acid accumulation ? decreased pH
• Detachment of ribosomes from RER ? decreased
  protein synthesis
• End result is cytoskeletal disruption with loss
  of microvilli, bleb formation, etc

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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
• Irreversible mitochondrial dysfunction ? markedly
  decreased ATP
• Severe impairment of cellular and organellar
  membranes

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Ischemic injury
See also Ch. 1, p. 14, Fig. 1-17
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Funky mitochondria
13
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
• Denatures proteins
• Poisons mitochondria
• Inhibits cellular enzymes

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Calcium in cell injury
See Ch. 1, p. 15, Fig. 1-19
Effect of Increased Calcium
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Reversible and irreversible injury
See Ch. 1, p. 9, Fig. 1-9
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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

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Free Radicals -- Ch. 1, pp. 15-17

• Free radicals have an unpaired electron in their
  outer orbit
• Free radicals cause chain reactions
• Generated by
• Absorption of radiant energy
• Oxidation of endogenous constituents
• Oxidation of exogenous compounds

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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

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Reactive oxygen species
See Ch. 1, p. 16, Fig. 1-20
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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

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Morphology of Cell Injury Key Concept(See Ch.
1, pp. 7-8)

• Morphologic changes follow functional changes

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Reversible Injury -- Morphology

• Light microscopic changes
• Cell swelling (a/k/a hydropic change)
• Fatty change
• Ultrastructural changes
• Alterations of cell membrane
• Swelling of and small amorphous deposits in
  mitochondria
• Swelling of RER and detachment of ribosomes

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Irreversible Injury -- Morphology

• Light microscopic changes
• Increased cytoplasmic eosinophilia (loss of RNA,
  which is more basophilic)
• Cytoplasmic vacuolization
• Nuclear chromatin clumping
• Ultrastructural changes
• Breaks in cellular and organellar membranes
• Larger amorphous densities in mitochondria
• Nuclear changes

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Irreversible Injury Nuclear Changes

• Pyknosis
• Nuclear shrinkage and increased basophilia
• Karyorrhexis
• Fragmentation of the pyknotic nucleus
• Karyolysis
• Fading of basophilia of chromatin

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Karyolysis karyorrhexis -- micro
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Types of Cell Death

• Apoptosis
• Usually a regulated, controlled process
• Plays a role in embryogenesis
• Necrosis
• Always pathologic the result of irreversible
  injury
• Numerous causes

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Apoptosis -- See Ch. 1, pp. 19-22

• Involved in many processes, some physiologic,
  some pathologic
• Programmed cell death during embryogenesis
• Hormone-dependent involution of organs in the
  adult (e.g., thymus)
• Cell deletion in proliferating cell populations
• Cell death in tumors
• Cell injury in some viral diseases (e.g.,
  hepatitis)

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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

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Events in apoptosis
Ch. 1, p. 21, Fig. 1-23
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Apoptosis Diagram
Ch. 1, p. 6, Fig. 1-6
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Apoptosis Micro
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Types of Necrosis -- Ch. 1, pp. 10-11

• Coagulative (most common)
• Liquefactive
• Caseous
• Fat necrosis
• Gangrenous necrosis

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Coagulative Necrosis -- Ch. 1, p. 10

• Cells 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

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Renal infarct -- gross
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Splenic infarcts -- gross
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Infarcted bowel -- gross
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Myocardium photomic
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Adrenal infarct -- Micro
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3 stages of coagulative necrosis (L to R) -- micro
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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

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Lung abscesses (liquefactive necrosis) -- gross
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Liver abscess -- micro
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Liquefactive necrosis -- gross
44
Liquefactive necrosis of brain-- micro
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Organizing liquefactive necrosis with cysts --
gross
46
Macrophages cleaning liquefactive necrosis --
micro
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Caseous Necrosis -- Ch. 1, pp. 10-11

• Gross Resembles cheese
• Micro Amorphous, granular eosinophilc material
  surrounded by a rim of inflammatory cells
• No visible cell outlines tissue architecture is
  obliterated
• Usually seen in infections (esp. mycobacterial
  and fungal infections)

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Caseous necrosis -- gross
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Caseous -- gross
50
Extensive caseous necrosis -- gross
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Caseous necrosis -- micro
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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

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Enzymatic fat necrosis of pancreas -- gross
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Fat necrosis -- gross
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Fat necrosis -- micro
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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

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Gangrene -- gross
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Wet gangrene -- gross
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Gangrenous necrosis -- micro
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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

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Cell Injury II Cellular Adaptations

• Tuesday, 9/8/09
• Michelle Dolan, M.D.
• dolan009_at_umn.edu
• Dept. of Laboratory Medicine and Pathology

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Slide Adaptation diagram
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Myocyte adaptation
Ch. 1, p. 2, Fig. 1-2
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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

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Physiologic Hyperplasia

• Hormonal
• Hyperplasia of uterine muscle during pregnancy
• Compensatory
• Hyperplasia in an organ after partial resection
• Mechanisms include increased DNA synthesis
• Growth inhibitors will halt hyperplasia after
  sufficient growth has occurred

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Pathologic Hyperplasia

• Due to excessive hormonal stimulation
• Endometrial proliferation due to increased
  absolute or relative amount of estrogen
• Due to excessive growth factor stimulation
• 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)

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Prostatic hyperplasia -- gross
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Slide -- BPH
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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

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Hypertrophy (contd)

• Physiologic
• Due to hormonal stimulation (e.g., hypertrophy of
  uterine smooth muscle during pregnancy)
• Pathologic
• Due to chronic stressors on the cells (e.g., left
  ventricular hypertrophy due to long-standing
  increased afterload such as HTN, stenotic valves)

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Physiologic hypertrophy
See Ch. 1, p. 3. Fig. 1-3
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Left ventricular hypertrophy -- gross
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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

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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

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Atrophy (contd)

• Physiologic
• Tissues / structures present in embryo or in
  childhood (e.g., thymus) may undergo atrophy as
  growth and development progress
• Pathologic
• Decreased workload
• Loss of innervation
• Decreased blood supply
• Inadequate nutrition
• Decreased hormonal stimulation
• Aging
• Physical stresses (e.g., pressure)

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Muscle atrophy -- micro
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Physiologic atrophy
See also Ch. 1, p. 5, Fig. 1-4
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Brain atrophy (Alzheimers ) -- gross
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Atrophic testis -- gross
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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
• If injury or stress abates, the metaplastic
  tissue may revert to its original type
• A protective mechanism rather than a premalignant
  change

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Metaplasia (contd)

• Bronchial (pseudostratified, ciliated columnar)
  to squamous epithelium
• E.g., respiratory tract of smokers
• Endocervical (columnar) to squamous epithelium
• E.g., chronic cervicitis
• Esophageal (squamous) to gastric or intestinal
  epithelium
• E.g., Barrett esophagus

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Squamous metaplasia
See Ch. 1, p. 5, Fig. 1-5
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Gastric metaplasia in esophagus -- micro
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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

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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
• Normal cellular constituents accumulated in
  excess (e.g., from increased production or
  decreased/inadequate metabolism) e.g., lipid
  accumulation in hepatocytes
• Abnormal substances due to defective metabolism
  or excretion (e.g., storage diseases, alpha-1-AT
  deficiency)
• Pigments due to inability of cell to metabolize
  or transport them (e.g., carbon, silica/talc)

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Intracellular accumulations
See Ch. 1, p. 23, Fig. 1-24
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Lipids -- Ch. 1, pp. 23-24

• Steatosis (a/k/a fatty change)
• Accumulation of lipids within hepatocytes
• Causes include EtOH, drugs, toxins
• 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.,
• Atherosclerotic plaque in arteries
• Accumulation within macrophages (called foamy
  macrophages) seen in xanthomas, areas of fat
  necrosis, cholesterolosis in gall bladder

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Steatosis
See Ch. 1, p. 24, Fig. 1-25
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Slide Fatty liver
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Proteins -- Ch. 1, pp. 24-25

• Accumulation may be due to inability of cells to
  maintain proper rate of metabolism
• Increased reabsorption of protein in renal
  tubules ? eosinophilic, glassy droplets in
  cytoplasm
• Defective protein folding
• E.g., alpha-1-AT deficiency ? intracellular
  accumulation of partially folded intermediates
• May cause toxicity e.g., some neurodegenerative
  diseases

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Alpha-1-antitrypsin accumulation -- micro
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Gauchers disease -- micro
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Liver in EtOH -- micro
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Mallory hyaline -- micro
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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

96
Slide Liver normal glycogen
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Liver Glycogen storage disease
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Pigments -- Ch. 1, pp. 25-26

• Exogenous pigments
• Anthracotic (carbon) pigment in the lungs
• Tattoos

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Anthracotic pigment in lungs -- gross
100
Slide Anthracotic lymph node
101
Anthracotic pigment in macrophages -- micro
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Pigments

• Endogenous pigments
• Lipofuscin (wear-and-tear pigment)
• Melanin
• Hemosiderin

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Lipofuscin

• Results from free radical peroxidation of
  membrane lipids
• Finely granular yellow-brown pigment
• Often seen in myocardial cells and hepatocytes

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Lipofuscin -- micro
105
Lipofuscin
106
Melanin -- Ch. 1, p. 26

• The only endogenous brown-black pigment
• Often (but not always) seen in melanomas

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Slide -- Melanoma
108
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

109
Hemosiderin -- micro
110
Hemosiderin
111
Hemosiderin in renal tubular cells -- micro
112
Prussian Blue hemosiderin in hepatocytes and
Kupffer cells -- micro
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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 HE stain glassy,
  amorphous appearance may be either crystalline
  or noncrystalline

114
Calcification
115
Slide Ganglioneuroblastoma with calcification
116
Dystrophic calcification in wall of stomach --
micro
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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
• Calcification most often seen in kidney, cardiac
  muscle and soft tissue

118
Metastatic calcification of lung in pt with
hypercalcemia -- micro