Cell injury results when cells are stressed so severely that they are no longer able to adapt or when cells are exposed to inherently damaging agents.

1. Prof.Dr.Mulazim Hussain Bukhari
MBBS,DCP,CHPE,MPhil, FCPS, PhD
HOD Pathology UCMD, University of Lahore
CELL INJURY

2. CELL INJURY
Cell injury results when cells are stressed so severely that
they are no longer able to adapt or when cells are
exposed to inherently damaging agents.

3. REVERSIBLE /IRREVERSIBLE CELL INJURY
• Reversible cell injury: Certain functional and morphologic
changes that are eversible if the damaging stimulus is
removed.
• Irreversible cell injury: It results with continuing damage up
to a stage from where cells can not recover, ultimately
leading to cell death.

4. CAUSES
OF CELL
INJURY
HYPOXI
A
INFECTION
S
IMMUNOLOGI
C REACTIONS
CONGENITA
L
DISORDERS
CHEMICA
L INJURY
PHYSICAL
INJURY
NUTRITION
AL
IMBALANCE

5. 1. HYPOXIA• Most common cause of injury
• It is the lack of oxygen leading to inability of the cell to synthesize sufficient ATP by
aerobic oxidation.
• Major mechanisms leading to hypoxia
I. Ischemia e.g., Thromboembolism, Hypoxemia (Respiratory acidosis, ventilation
defect,perfusion defect,diffusion defect)
II. Cardiopulmonary failure
III. Decreased oxygen carrying capacity of blood
(Anaemia,Methaemoglobinemia,CO poisoning,

6. 2. INFECTIONS
• Viruses, bacteria, parasites, fungi & prions
• Mechanism of injury
I. Direct infection of cells
II. Production of toxins
III. Host inflammatory responses
3. IMMUNOLOGIC REACTIONS
o Hypersensitivity reactions
o Autoimmune diseases

7. 4. CONGENITAL DISORDERS
o Inborn errors of metabolism
5. CHEMICAL INJURY
o Drugs
o Poisons e.g., cyanide, arsenic and mercury
o Pollution
o Occupational exposures e.g., CCl4 , Asbestos and CO
o Lifestyle changes
6. PHYSICAL FORMS OF INJURY
o Trauma e.g., blunt, penetrating, crush injuries
o Burns
o Frostbite
o Radiation
o Pressure changes

8. 7. NUTRITIONAL IMBALANCE
• Inadequate calorie/protein intake
I. Marasmus and kwashiorkor
II. Anorexia nervosa
• Excess calorie intake
I. Obesity
II. Atherosclerosis
• Vitamin deficiency
I. Vitamin A ….. Xerophthalmia
II. Vitamin B 12 ….. Megaloblastic anemia, Subacute combined degeneration of spinal cord
III.Vitamin C ….. Scurvy
IV.Vitamin D ….. Rickets and osteomalacia
V. Folate ….. Megaloblastic anemia and neural tube defects
VI.Niacin ….. Pellagra (Diarrhea, dementia and dermatitis)

9. Causes of Hypoxia in detail
• Ischemia
• Decreased arterial blood flow
• Coronary artery atherosclerosis, thrombosis of splenic veins
• Hypoxemia
• Decreased PaO2

10. Causes of Hypoxaemia
• Respiratory acidosis( PaO2 and PCo2
• CO2 retention in lungs due to decreased in PaO2
• Examples: Medullary center depression (Barbiturates), Paralysis of diaphragm,chronic Bronchitis,
• Ventilation defect
• Impaired O2 delivery to alveoli
• Reparatory distress syndrome with collapse of distal airways
• No O2 exchange in the lungs that are perfused but not ventilated
• Produces intrapulmunary shuntings of blood
• Administration of Oxygen does not increase PaO2

11. Causes of Hypoxaemia II
• Perfusion defect
• Absence of blood flow to alveoli
• Pulmonary embolism
• No O2 exchange in the lungs that are ventilated but not perfused
• Produces increase in Pathological dead space
• Administration of Oxygen increases PaO2

12. Causes of Hypoxaemia III
• Diffusion Defect
• Decrease O2 diffusion through the alveolar capillary interface
• Examples: Interstitial fibrosis, Pulmunary edema

13. Hb Related abnormalities
• Anaemia
• Decreased Hb Conc in blood
• Decreased production of Hb (IDA)
• Increased destruction (Hereditary spherocytosis)
• Decreased production of RBC (Aplastic anaeima)
• Increased destruction of RBC (Spenomegaly)
• (There is normal Pa2 and SaO2)

14. Hb Related abnormalities II• Methaemoglobinemia
• With oxidised Fe+3
• Causes : Oxidizing agents
• Nitrite containing drugs: Nitroglycerine
• Sulpher containg drug: Trimethoprim, Sulphamethazole
• Deficiency of Methb reductase which normally reduces Fe3+ to Fe 2+
• No binding of Fe3 with oxygen
• There is normal Pa2 but decreased SaO2
• Patients have cyanosis, skin colour does not return to normal even administration of O2
• Rx is meth-Blue and ascorbic acid both activates MetHb Reductase which reduces Fe3+ to Fe 2+

15. Hb Related abnormalities III• CO poisoning
• Produced by incomplete combustions of carbon containing compounds
• Caused by automobile exhaust,
• Pathogenesis
• Co2 competes with O2 to combine with Hb with decreases SaO2 with normal PaO2
• Electron Transport Chain inhibition of cytochrome oxidase
• It causes the left shift of O2 binding curve (OBC)
• Clinical findings: chery red discourlarion of skin and MM, headache, coma, necrosis of
globus pallidus

16. Hb Related abnormalities III• Factors causing left shift of OBC
• Decreased 2,3 biphosphoglycerate (BPG)
• Intermediate of gylcolysis
• CO, Alkalosis, metHb, hypothermia
• Enzyme inhibition of Oxidative Phosphoryylation
• Cyanide (use of nitroprusside) and CO poisoning (combustion of polyurethane products in house fires)
• Uncoupling of Oxidative Phosphoryylation
• Hyperthermia

17. Tissue susceptibility of Hypoxia
• Water shed area between two arteries
• Anterior cerebral artery and middle cerebral artery
• Superior and inferior mesenteric arteries (Spenic flexure)
• Subendocardial area
• Renal cortex and medulla

18. Consequences of Hypoxia
• Decreased synthesis of ATP
• Anerobic gylcolysis
• Decreased Protein synthesis due to detachment of ribosomes
• Irreversible cell changes

19. CELLULAR RESPONSES TO INJURY

20. Three types of Responses
• Adaptation
• Reversible injury
• Irreversible injury and cell death

21. FACTORS AFFECTING CELLULAR RESPONSE
• Type of injury
• Duration and pattern
• Severity and intensity
• Type of cell affected
• Cell’s metabolic state
• Cell’s ability to adapt

22. MECHANISMS OF CELL INJURY
• ATP depletion
• Mitochondrial damage
• Loss of calcium homeostasis
• Oxidative stress
• Defects in membrane permeability

23. 1. ATP Depletion
• Depletion of ATP to less than 5% leads to
I. Decreased Na-K ATPase activity
II. Anaerobic glycolysis
III. Lactic acid accumulation
IV. Ca-pump failure
V. Ribosomal disaggregation
VI. Unfolded protein response

24. 2. MITOCHONDRIAL DAMAGE

25. 3. LOSS OF CALCIUM HOMEOSTSIS

26. 4. OXIDATIVE STRESS
• Imbalance between free radical generating and scavenging systems results in
oxidative stress e.g.,
I. Ischemia-reperfusion injury
II. Cellular aging
III.Microbial killing.

27. Types of Free Radicals
• Compounds with a single unpaired electron in an outer orbit
• Oxygen derived free Radicals
• Superoxide O2+
• Hydroxyl ions OH+
• Hydrogen peroxidase H2O2
• Drugs and chemical free radicals
• Liver cytochrome P-450 system
• Acetaminophen and Carbon tetrachloride poisoning

28. Free radicals may be generated within cells in
several ways• The reduction-oxidation reactions that occur during normal metabolic processes.
• During normal respiration, molecular O2 is reduced by the transfer of four electrons to H2 to generate two
water molecules.
• This conversion is catalyzed by oxidative enzymes in the ER, cytosol, mitochondria, peroxisomes, and
lysosomes.
• During this process small amounts of partially reduced intermediates are produced in which different
numbers of electrons have been transferred from O2, these include superoxide anion

29. Absorption of radiant energy (e.g., ultraviolet light, x-
rays).
• For example, ionizing radiation can hydrolyze water into •OH and hydrogen (H) free
radicals.

30. Rapid bursts of ROS (Reactive Oxygen species)• Rapid bursts of ROS are produced in activated leukocytes during inflammation.
• This occurs by a precisely controlled reaction in a plasma membrane multiprotein
complex that uses NADPH oxidase for the redox reaction to NADP and H oins are
released

31. Enzymatic metabolism of exogenous chemicals or drugs• can generate free radicals that are not ROS but have similar effects (e.g., CCl4 can
generate CCl3, described later in the chapter).

32. Transition metals• Transition metals such as iron and copper donate or accept free electrons during intracellular reactions and
catalyze free radical formation, as in the Fenton reaction (H2O2 + Fe2+ → Fe3+ + OH + OH-).
• Because most of the intracellular free iron is in the ferric (Fe3+) state, it must be reduced to the ferrous (Fe2+)
form to participate in the Fenton reaction.
• This reduction can be enhanced by
, and thus sources of iron and may cooperate in oxidative cell damage.

33. Nitric oxide (NO),• It is an important chemical mediator generated by endothelial cells, macrophages,
neurons, and other cell types can act as a free radical and can also be converted to
highly reactive peroxynitrite anion (ONOO-) as well as NO2 (Nitrite)and NO3
-
.(Nitrate)

34. Properties O- H2O2
•OH ONOO- (peroxynitrite)
MECHANISMS OF
PRODUCTION
Incomplete reduction of O2
during oxidative phosphorylation;
by phagocyte oxidase in
leukocytes
Generated by SOD from O2
- and
by oxidases in peroxisomes
Generated from H2O by
hydrolysis, e.g., by radiation;
from H2O2 by Fenton
reaction; from
Produced by interaction of
and NO generated by NO
synthase in many cell types
(endothelial cells, leukocytes,
neurons, others)
MECHANISMS OF
INACTIVATION
Conversion to H2O2 and O2 by
SOD
Conversion to H2O and O2 by
catalase (peroxisomes),
glutathione peroxidase (cytosol,
mitochondria)
Conversion to H2O by
glutathione peroxidase
Conversion to HNO2 by
peroxiredoxins (cytosol,
mitochondria)
PATHOLOGIC
EFFECTS
Stimulates production of
degradative enzymes in leukocytes
and other cells; may directly
damage lipids, proteins, DNA;
acts close to site of production
Can be converted to •OH and
OCl-, which destroy microbes and
cells; can act distant from site of
production
Most reactive oxygen-derived
free radical; principal ROS
responsible for damaging
lipids, proteins, and DNA
Damages lipids, proteins, DNA

35. Neutralizing of free Radicals
• Superoxide dismutase
• superoxides
• Glutathion peroxidase
• Peroxides, hydroxyl and acetamonophin radical
• Catalase
• Peroxidase radicals
• Vitanin A,E and Beta carotenes
• Blocks free radical formations and degrades already synthesised Free radicals

37. Examples of free radical Injuries
• Acetaminophen Free radicals
• Fulminant hepatitis
• Renal Papillary necrosis
• CCL4 free radical
• Liver necrosis and fatty degenerations
• Ischemia and reperfusion injury
• Iron over load
• Retinopathy

38. 5. DEFECTS IN MEMBRANE PERMEABILITY

40. REVERSIBLE CELL INJURY
Hallmarks include
• Cell membrane pump failure
I. Hydropic change
II. Swelling of endoplasmic reticulum
• Ribosomal disaggregation
• Stimulation of Phosphoructokinase activity
• Reversible clumping of nuclear chromatin
• Mylein figures and cell blebs

41. IRREVERSIBLE CELL INJURY
Hallmarks include
• Severe membrane damage
• Efflux of intracellular enzymes and proteins
• Mitochondrial swelling
• Accumulation of large densities in miotochondria
• Lysosomal rupture followed by autolysis
• Nulear changes
I. Pyknosis … degeneration and condensation of nuclear chromatin
II. Karyorrhexis … nuclear fragmentation
III. Karyolysis … dissolution of the nucleus

42. Injury to the cell organelles
• Mitochondrial Injury
• Release of cytochrome C from the injured Mitochondria causes appotosis
• Injurious agents include Alcohol, salicylates, and increased cystolic ca2+
• Smooth Endoplasmic Reticulum
• alcohol, barbiturates, and phynentoin
• Causes hyperplsia and increased drugs toxifications with lower than expected therapeutic dose
• Inhibition of enzymes P-450 cytochrome system
• Proton recpetor blockers (emiprazole), and macrolides (erythrocine)
• decreased drugs toxifications with higher than expected therapeutic dose

43. Other organelles• Lyosomes
• Primary lysosomes
• Hydrolytic enzymes
• Deficiency of enzymes
• Gaucher’s Disease with deficiency of glucocerebrosidase causes its accumulation
• Secondary Lysosome
• Arise with fusion of primaryb lysosomes with phagocytic vacuoles
• Defect in Chediak-Higashi Syndrom (CHS) with giant granues no auzurophilic granules action results in repeated
infection of staphylococcus aureus

44. • Cytoskeleton
• Mitotic spindle defect
• Intermediate filaments defect
• Lewis bodies eosinophilic granules in substantia nigra
• Mallory bodies in alcoholic liver
• Rigor mortis

45. Adaptations of Cellular Growth and
Differentiation

46. HYPERTROPHY• Hypertrophy refers to an increase in the size of cells, resulting in an increase in the size of the organ.
• The hypertrophied organ has no new cells, just larger cells.
• The increased size of the cells is due to the synthesis of more structural components of the cells.
• Cells capable of division may respond to stress by undergoing both hyperplasia (described below) and
hypertrophy, whereas in nondividing cells (e.g., myocardial fibers) increased tissue mass is due to hypertrophy.
• In many organs hypertrophy and hyperplasia may coexist and contribute to increased size.

47. • Hypertrophy can be physiologic or pathologic and is caused by increased functional
demand or by stimulation by hormones and growth factors

50. HYPERPLASIA• Hyperplasia is an increase in the number of cells in an organ or tissue, usually resulting in increased mass of the
organ or tissue.
• Although hyperplasia and hypertrophy are distinct processes, frequently they occur together, and
they may be triggered by the same external stimulus. Hyperplasia takes place if the cell population
is capable of dividing, and thus increasing the number of cells.
• Hyperplasia can be physiologic or pathologic.

51. Mechanisms of Hyperplasia
• Hyperplasia is the result of growth factor-driven proliferation of mature cells
and, in some cases, by increased output of new cells from tissue stem cells.

52. ATROPHY
• Atrophy is reduced size of an organ or tissue resulting from a decrease in cell size and number.
• Atrophy can be physiologic or pathologic.
• Physiologic atrophy is common during normal development.
• Some embryonic structures, such as the notochord and thyroglossal duct, undergo
atrophy during fetal development.
• The uterus decreases in size shortly after parturition, and this is a form of
physiologic atrophy

53. Mechanisms of Atrophy• Atrophy results from decreased protein synthesis and increased protein degradation in cells
• Protein synthesis decreases because of reduced metabolic activity.
• The degradation of cellular proteins occurs mainly by the ubiquitin-proteasome pathway.
• Nutrient deficiency and disuse may activate ubiquitin ligases, which attach the small peptide ubiquitin to
cellular proteins and target these proteins for degradation in proteasomes

54. Causes of atrophy
• Decreased workload (atrophy of disuse)
• Loss of innervation (denervation atrophy).
• Diminished blood supply
• Inadequate nutrition
• Loss of endocrine stimulation
• Pressure

56. METAPLASIA• Metaplasia is a reversible change in which one differentiated cell type (epithelial or
mesenchymal) is replaced by another cell type.
• It may represent an adaptive substitution of cells that are sensitive to stress by cell types
better able to withstand the adverse environment.

58. Mechanism• Metaplasia does not result from a change in the phenotype of an already differentiated cell
type;
• instead it is the result of a reprogramming of stem cells that are known to exist in normal
tissues, or of undifferentiated mesenchymal cells present in connective tissue.
• In a metaplastic change, these precursor cells differentiate along a new pathway.

60. 1
• A comatose 35-year-old man is admitted to the hospital after being involved in a motorcycle collision. He is
• intubated and mechanically ventilated. He dies 8 weeks later. A photomicrograph of tracheal tissue obtained
at
• autopsy is shown. Which of the following processes best describes these findings?
• (A) Atrophy
• (B) Dysplasia
• (C) Hyperplasia
• (D) Hypertrophy
• (E) Metaplasia
• (F) Neoplasia

61. • A 57-year-old woman with a 30-year x 2 pack/day history of cigarette smoking undergoes
bronchoscopy. Biopsy of bronchial tissue show
s replacement of the normal pseudostratified ciliated columnar epithelium with stratified squamous
epithelium. This change represents
A. dysplasia
B. hyperplasia
C. malignant transformation
D. metaplasia
E. necrosis and repair

62. MORPHOLOGY OF CELL INJURY
& NECROSIS

63. MORPHOLOGY OF REVERSIBLE CELL
INJURY
• Two patterns of reversible cell injury can be recognized under light
microscope
a) Cellular swelling
b) Fatty change/ Vacuolar degeneration

64. a) CELLULAR SWELLING
• First manifestation of all forms of injury
• Appears when cells are incapable of maintaining ionic and fluid homeostasis
• Difficult to appreciate with light microscope
• Grossly it is represented by
Pallor
Turgor
Weight of the organ

65. b) VACUOLAR DEGENERATION / FATTY
CHANGE
• Occurs due to hypoxia, toxins and metabolic injury
• Microscopic examination reveals distended and pinched off segments of ER
in form of small clear vacuoles in cytoplasm
• Also known as HYDROPIC CHANGE

66. MORPHOLOGY•Intracellular accumulations of water or polysaccharides (e.g., glycogen) may
produce clear vacuoles,
•it becomes necessary to resort to special techniques to distinguish three types of
clear vacuoles.
•The identification of lipids requires the avoidance of fat solvents commonly used
in paraffin embedding for routine hematoxylin and eosin stains.

67.  To identify the fat, it is necessary to prepare frozen tissue sections of either fresh or aqueous
formalin-fixed tissues.
 The sections may then be stained with Sudan IV or Oil Red-O, both of which impart an
orange-red color to the contained lipids.
Identification of Fat

68. PAS
• The periodic acid-Schiff (PAS) reaction is commonly employed to identify
glycogen, although it is by no means specific.
• When neither fat nor polysaccharide can be demonstrated within a clear
vacuole, it is presumed to contain water or fluid with a low protein content.

69. Electron micrograph of PCT of kidney
NORMAL REVERSIBLE IRREVERSIBLE

70. Necrosis is summary
• Necrosis is a word that describes the morphological changes that occur to a cell
after its death.
• These include the following:
• (1) cellular swelling
• (2) denaturation of cytoplasmic proteins (gives rise to eosinophilia)
• (3) breakdown of cell organelles
• (4) a sequence of nuclear changes which include (a) karyolysis (b) pyknosis (c) karyorrhexis.
• (5) There is inflammation.

71. NECROSIS• Necrosis is the sum of degradative and inflammatory reactions occurring after tissue death caused
by injury.
• Always pathologic
• Occurs within living organisms
• NOTE : In pathological specimens fixed cells with well preserved morphology are dead
but not necrosed.

72. AUTOLYSIS / HETEROLYSIS• Autolysis refers to degradative reactions in cells caused by intracellullar enzymes
endogenous to the cells
• Post mortem autolysis occurs after death of entire organism and is not necrosis
• Heterolysis refers to cellular degradation by enzymes derived from exogenous
sources (Bacteria and leucocytes)

73. TYPES OF NECROSIS
• Especially in heart and kidney1. COAGULATIVE
2. LIQUEFACTIVE
•Tuberculosis3. CASEOUS
4. GANGRENOUS
• In Blood vessels
5. FIBRINOID
6. FAT NECROSIS
• Especially in CNS and Bacterial infection
• Lower extremities and bowel
• Pancreas and breast

74. MORPHOLOGY OF NECROSIS
Light microscopy reveals
• Increased eosinophilia due to
I. Loss of normal basophilia
II. Increased binding of eosin with denatured proteins
• Glassy appearance due to
I. Loss of glycogen particles
II. Enzymatic digestion of organelles
• Formation of myelin figures (Large whorled phospholipid masses)

75. MORPHOLOGY OF NECROSIS
Electron microscopy reveals
• Overt discontinuity in the plasma and organelle membranes
• Mitochondrial swelling with amorphous densities
• Intracytoplasmic myelin figures
• Amorphous osmiophilic debris
• Nuclear changes

76. MORPHOLOGY OF NECROSIS
• Nuclear changes appear in the form of one of the following three patterns
I. Pyknosis … degeneration and condensation of nuclear chromatin
II. Karyorrhexis … nuclear fragmentation
III. Karyolysis … dissolution of the nucleus
• NOTE : With the passage of time nucleus of necrotic cell totally disappears

77. A. COAGULATIVE NECROSIS
• CAUSE … Interruption of blood supply
• ORGANS … Seen in organs supplied by end arteries with limited collateral
circulation e.g., Heart and Kidney
• PATHOLOGICAL CHANGES … Preservation of General architecture
and increased eosinophilia

78. Ischemic necrosis of the myocardium.
A. Normal myocardium
B. Myocardium with coagulation necrosis showing strongly eosinophilic anucleate
myocardial fibers. Leukocytes in the interstitium are an early reaction to necrotic
muscle

79. Kidney infarct exhibiting coagulative necrosis, with loss of nuclei and clumping of cytoplasm but with
preservation of basic outlines of glomerular and tubular architecture

80. B. LIQUIFACTIVE NECROSIS
• CAUSE … Focal bacterial & Occasionally Fungal infections and hypoxic CNS insults
• ORGANS … CNS and Abscesses
• PATHOLOGICAL CHANGES … Transformation of a tissue into a liquid viscous mass
creamy yellow in colour and is called pus

81. A focus of liquefactive necrosis in the kidney caused by fungal infection. The focus is filled with white cells
and cellular debris, creating a renal abscess that obliterates the normal architecture.

82. C. CASEOUS NECROSIS
• CAUSE … Tuberculosis
• ORGANS … Every organ affected by TB
• PATHOLOGICAL CHANGES … Cheesy white on gross appearance.
Microscopically architechture is not preserved but tissue is not liquified. It is
enclosed within a distinctive inflammatory border known as a
GRANULOMATOUS REACTION.

83. A tuberculous lung with a large area of caseous necrosis. The caseous debris is yellow-white and cheesy

84. central caseation surrounded by epithelioid and multinucleated giant cells

85. D. GANGRENOUS NECROSIS
• CAUSE … Interruption of blood supply
• ORGANS … Extremeties and Bowel
• PATHOLOGICAL CHANGES … Not a distinctive pattern of necrosis
I. Dry gangrene … if coagulative necrosis is dominant
II. Wet gangrene … when complicated with infective heterolysis and
consequent liquifactive necrosis

86. E. FIBRINOID NECROSIS
• CAUSE … Immune mediated vascular damage
• ORGANS … Blood vessels
• PATHOLOGICAL CHANGES … smudgy pink appearance due to
deposition of fibrin like proteinaceous material in wall of arteries

87. Acute vascular injury with fibrinoid necrosis and edema after exposure to ionizing radiation

88. F. FAT NECROSIS
• CAUSE … Liberation of pancreatic enzymes and trauma to fat cells
• ORGANS … Pancreas and Breast
• PATHOLOGICAL CHANGES … Foci of shadowy outlines of necrotic
fat cells with basophilic calcium deposits surrounded by inflammatory
reactions.

89. Foci of fat necrosis with saponification in the mesentery. The areas of white chalky deposits represent calcium
soap formation at sites of lipid breakdown.

90. Acute pancreatitis. The microscopic field shows a region of fat necrosis on the right and focal pancreatic
parenchymal necrosis

91. Acute pancreatitis. The pancreas has been sectioned across to reveal dark areas of hemorrhage in the head of
the pancreas and a focal area of pale fat necrosis in the peripancreatic fat

92. TABLE: FEATURES OF NECROSIS AND APOPTOSIS

93. NECROSIS & APOPTOSIS