Cell injury and death can occur through various mechanisms including hypoxia, physical or chemical insults, and microbial or immunological agents. The cellular response to injury depends on the cell type, extent, and type of injury. Initial responses include cellular adaptation, subcellular changes, or intracellular accumulations. Injury may result in reversible or irreversible cell damage and cell death. Irreversible injury is characterized by mitochondrial dysfunction and membrane damage, leading to necrosis or apoptosis. Different patterns of necrosis include coagulative, liquefactive, caseous, and gangrenous necrosis.

1. Cell Injury
Cell Death
Apoptosis
DR. NIDHI RAI

2.  Most forms of disease state begin with cell injury and consequently loss of cellular
function.
 Cell injury is defined as- a variety of stresses a cell encounters as a result of
changes in its internal and external environment.
 The cellular response to injury varies and depends upon
 type of cell and tissue involved
 Extent of injury
 Type of injury

3. Cellular reponse to injury
1. Cellular Adaptation- the cell may adapt to the change and revert back to normal
after the stress removal
2. Sub Cellular changes- the residual effects may persist in the cell as evidence of
injury.
3. Intracellular accumulations- metabolites may accumulate within the cell.
4. Reversible cell injury- injury may recover
5. Irreversible cell injury- the cell dies.

5. Etiology of Cell Injury
 Genetic cause
 Acquired causes

6. Acquired Causes
Based on underlying agent:
 Hypoxia and ischaemia
 Physical agents
 Chemical agents and drugs
 Microbial agents
 Immunologic agents
 Nutritional derangement
 Psychological factors

7. Hypoxia & Ischemia
 Deficiency of oxygen or hypoxia results in failure to carry out cellular
activities.
 Most common, causes of hypoxia are: reduced supply of blood to cells-
ischemia
 Oxygen deprivation can result from other causes like anemia, carbon
monoxide poisoning,cardio respiratory insufficiency and increase in
demand of tissues

8. Physical agents
 Mechanical trauma
 Thermal trauma
 Electricity
 Radiation rapid changes in atmospheric pressure

9. Chemical Agents
 Chemical poisons: cyanide, arsenic, mercury.
 Strong acid and alkalis
 Insecticides and pesticides
 High oxygen concentration
 Hypertonic glucose and salt
 Alcohol and narcotic drugs
 Theraputic drugs

10.  Microbial Agents
 Immunologic agent
Immunity is a double edged sword :
Hypersensitivity reactions
Anaphylactic reactions
Autoimmune diseases
 Nutritional derangement
 Psychological

11. Pathogenesis of Ischemic/Hypoxic
Injury
 Reversible cell injury
 Irreversible cell injury

12. Reversible Cell Injury
Hypoxia/Ischemia
ATP
Damaged Na Pump (
Membrane)
Intercellular pH Protein Synthesis
Ultrastructural /
Functional Changes
REVERSIBLE CELL
INJURY

14. Irreversible Cell Injury
 2 essential features:
 Inability of the cell to reverse Mitochondrial Dysfunction
 Disturbance in cell membrane function
 In addition: depletion of proteins, leakage of lysosomal enzymes into cytoplasm,
reduced intracellular pH and further reduction in ATP.

15. Mitochondrial Damage/Dysfunction
 Mitochondria – critical players in cell injury and cell death
 Mitochondria can be damaged by
 Cytosolic Calcium
 ROS
 Oxygen Deprivation ( Hypoxia, Toxins)
 Two major consequences of mitochondrial damage
 Loss of mitochondrial membrane potential and pH
changes, resulting in failure of oxidative
phosphorylation and progressive depletion of ATP.
 Leakage of cyt C and other proteins into cytosol and to
cell death by apoptosis

16. Mitochondrial Dysfunction
 Morphological mitochondrial changes:
 Vacuoles in mitochondria
 Deposition of amorphous Ca in mitochondrial matrix.

17. Q. first step inhibited due to hypoxic injury is:
a. Oxidative phosphorylation
b. Glycogenesis
c. Detachment of ribosomes from RER
d. Cell shrinkage
Ans. A The first point of attack of hypoxia id the cells aerobic respiration, i.e. oxidative
phosphorylation by mitochondria ATP production is decreased → Na-K Pump stops →
more Na inside → cell becomes hyperosmolar →water enters → swelling of cell → bleb
formation → along with this ribosomes also detach. This process is reversible if O2 is
supplied.

18. Membrane Damage
 Consistent feature of most form of cell injury except apoptosis.
 Mechanism:
 Accelerated degradation of membrane phospholipids.
 Cytoskeletal damage
 Toxic oxygen radicals
 Hydrolytic enzymes
 Serum estimation of liberated intracellular enzymes

19. Restoration of blood flow to ishemic tissue can
promote recovery of cells if they are reversibly
unjured, but can also paradoxiucallt exacerbate the
injury and cause cell death. Called Ishcemia-
reperfusion injury

20. Membrane Damage
Nuclear Changes
(Pyknosis,Karyolysis,Karyorrhaxis)
Cell Death (Myelin
Figure)
Serum Enzyme estimation
(SGOT,LDH)
Liberation of Intercellular Enzymes

24. Normal Kidney

25. Normal Kidney tubules
 Epithelial cells stain evenly pink
(eosinophilic) in cytoplasm, with
purple, basophilic, nucleic acids
confined to the nuclei
 Apical surfaces are ciliated
 Interstitia not infiltrated with immune
cells nor congested with proteins

26. Swollen kidney tubules
 Increased eosinophilic staining
 Decreased basophilic staining (RNA)
 Plasma membrane rounding, blebbing, loss of
cilia, due to loss of connections with
cytoskeleton
 Integrity of tubules degrading, but basement
membranes intact
 Nuclei largely intact, slightly narrowed, pyknotic

27. Reversible damage –cellular swelling

28. Reversible damage –fatty change
Intracellular accumulations of a variety of materials can occur in response to cellular injury. Here
is fatty metamorphosis (fatty change) of the liver in which deranged lipoprotein transport from
injury (most often alcoholism) leads to accumulation of lipid in the cytoplasm of hepatocytes.

29.  The characteristic feature of hypoxic irreversible injury is/are:
a. Vacuolization of mitochondria
b. Swelling of lysosomes
c. Calcium densities
d. All of the above
Ans: D
 Cellular swelling and fatty change are example of:
a. Reversible injury
b. Irreversible injury
c. Cellular swelling is reversible but fatty change is`irreversible
d. None of the above
Ans: A Fatty change is an indicator of reversible cell injury, manifested by
appearance of small or large lipid vacuoles in cytoplasm and occurs with hypoxia.
Basically seen in cells involved in fat metabolism as in liver.

30. Free Radical Mediated Cell Injury
 Ischaemic reperfusion injury
 Radiolysis of water
 Chemical toxicity
 Hyperoxia (toxicity due to oxygen therapy)
 Cellular aging
 Killing of exogenous biologic agents
 Inflammatory damage
 Destruction of tumour cells
 Chemical carcinogenesis
 Atherosclerosis

32.  Generation of oxygen radicals begins within mitochondrial inner membrane.
 When cytochrome oxidase catalyzes of oxygen (O2 ) to water (H2O)
 Intermediates between O2 and H2O are:
 Superoxide oxygen O’2 : 1 electrón
 Hydrogen peroxide H2O2 : 2 electrones
 Hydroxyl radical OH- : 3 electrons

36. Morphology of Irreversible Cell
Injury
 Cell death is a state of irreversible injury.
 In living body it may occur as:
 Local or focal change (autolysis, necrosis and apoptosis)
Necrosis-pathologic
Apoptosis-normal and pathologic
Autophagy-normal and pathologic
 Changes that follow( gangrene and pathologic calcification)
 End of life ( somatic death)

37. Autophagy/Self Digestion
 Disintegration of the cell by its own hydrolytic enzymes liberated from lysosomes.
 It is rapid in some tissues rich in hydrolytic enzymes such as pancreas and gastric
mucosa.
 Morphologically , autolysis is identified by :
 Homogeneous and eosinophilic cytoplasm
 Loss of cellular details
 Remains of cell as debris

38. Necrosis
 Defined as- focal death along with
degradation of tissue by hydrolytic
enzymes liberated by cells,
accompanied by inflammation.
 2 essential features:
 Cell digestion by lytic enzymes
 Denaturation of proteins

39. Digestion of cellular contents and the host response may take hours to develop. The earliest
histologic evidence of necrosis may not become apparent until 4 to 12 hours.

40.  Cytoplasmic Changes:
 Homogenous and intensely eosinophilic (H&E)
 Occasionally: When enzymes have digested the cytoplasmic
organelles, the cytoplasm becomes vacuolated and appears moth-
eaten.

41.  Nuclear Changes
Nuclear changes assume one of the 3 patterns, all due to the non-specific
breakdown of the DNA.
Pyknosis- condensation of nuclear chromatin
Karyolysis – undergo dissolution
Karyorrhexis- fragmentation into many clumps

42. Types of Tissue Necrosis
 Coagulative
 Liquefactive
 Caseous
 Fat
 Fibrinoid
 Gangrenous

43. Coagulative Necrosis
 Most common type
 Caused by
irreversible focal injury, mostly from sudden cessation of blood flow
(ischemia)and less often from bacterial and chemical agents
 Organs affected are: heart, kidney and spleen.

44. Ischemic injury to cell
Architecture of dead tissue is preserved ( for few days)
Cell Death
Denaturation of proteins & enzymes
Firm Texture of tissue
Proteolysis of dead cells
dead cells are phagocytosed leaving granular debris and fragments of
cells
Necrosed focus is infiltrated by inflammatory cells
Eosinophilic anucleate cells
v
v
Microscopic changes are
the result of:
 Denaturation of proteins
 Enzymatic digestion of
the cell.

45. Gross Appearance
 Foci of coagulative necrosis:
In early stages:
pale, firm and slightly swollen.
With progression:
become more yellowish,
softer, and shrunken.
Wedge shaped kidney infarct
(coagulative necrosis)

46. Microscopic Appearance:
 Hallmark of coagulative necrosis:
conversion of normal cells into their
‘tombstones’ i.e. outlines of the cells
are retained so that the cell type can still
be recognised but their cytoplasm and
nuclear details are lost.
 Necrosed cells are swollen and appear
more eosinophilic than normal

47. Microscopic view of the edge of the infarct ,with normal kidney (N)and necrotic cell in the infarct
(I) showing preserved cellular outlines with loss of nuclei and an inflammatory infiltrate which is
difficult to discern at this magnification

48. Coagulative Necrosis: Myocardial infarction
Here is myocardium in which the cells are dying as a result of ischemic injury from coronary
artery occlusion. This is early in the process of necrosis. The nuclei of the myocardial fibers are
being lost. The cytoplasm is losing its structure, because no well-defined cross-striations are
seen

49.  It occurs commonly due to ischemic injury and bacterial or fungal infections.
 It occurs due to degradation of tissue by the action of powerful hydrolytic enzymes.
 Transformation of the tissue into a liquid viscous mass.
 The necrotic material is frequently creamy yellow because of the presence of dead
leukocytes and is called pus.
 Common e.g. Infarct brain and abscess cavity.
Liquefactive Necrosis
(Colliquative Necrosis)

50. Caseous Necrosis
 Caseous (cheese like) is derived from the friable white appearance of the area of
necrosis.
 It is a combined feature of coagulative and liquefactive necrosis.
 Found in the center of foci of tuberculous infection.

51. Gross Appearance
 Foci of caseous necrosis, as the
name implies, resemble dry cheese
and are soft, granular and
yellowish.
 This appearance is partly attributed
to the histotoxic effects of
lipopolysaccharides present in
the capsule of the tubercle
bacilli, Mycobacterium
tuberculosis.

52. Microscopic Findings
 The necrosed foci are structureless,
eosinophilic and contain granular debris.
 The surrounding tissue shows
characteristic granulomatous
inflammatory reaction consisting of
epithelioid cells with interspersed giant
cells of langhan’s or foreign body type
and peripherally lymphocytes

53. Fat Necrosis
 Not a specific pattern
 These are:
 Following pancreatic necrosis
 Traumatic fat necrosis commonly in breast
 Fat necrosis in either of the 2 instances results in hydrolysis of neutral fat present in
adipose cells due to release to activated lipase into glycerol and free fatty acids.
 The damaged adipose cells assume cloudy appearance when only free fatty remain
behind , after glycerol leaks out.
 The leaked out free fatty acids, complex with Ca to form Ca soaps (saponification)

54. Gross Appearance
 Appears as yellowish-white and firm
deposits.
 Ca soap imparts the necrosed foci firmer
and chalky white appearance

55. Microscopic Findings
 Cloudy appearance of necrosed cell.
 Surrounded by inflammatory reaction.
 Formation of calcium soaps is identified
in the tissue sections as amorphous,
granular and basophilic material.

56. Fibrinoid Necrosis
 It is characterized by the deposition of fibrin like material which has the
staining properties of fibrin.
 Usually seen in immune reactions involving blood vessels.
 Example: Autoimmune diseases, arthus reaction arterioles in hypertension,
peptic ulcer etc.

57. Microscopic Findings
 Identified by brightly eosinophilic,
hyaline-like deposition in the vessel
wall or on the luminal surface of a peptic
ulcer.
 Local haemorrhages may occur due to
rupture of these blood vessels.

58. Gangrenous Necrosis
 Not a specific pattern.
 Term is commonly used in clinical
practice.
 Usually applied to a limb, generally the
lower leg, that has lost its blood supply
and has undergone, typically, coagulative
necrosis

59. Gangrene
 Potentially life-threatening condition
 caused by a critically insufficient blood supply(necrosis) to tissue.
 This may occur after an injury or infection, or in people suffering from any
chronic health problem affecting blood circulation.
 Risk factors: Diabetes and long-term smoking

60. 3 Types
 Dry
 Wet
 Gas
 In either type of gangrene, coagulation necrosis undergo liquefaction by the
action of putrefactive bacteria.

61. Dry Gangrene
 Form of coagulative necrosis.
 develops in ischemic tissue.
 Etiopathogenesis:
Causes
• Peripheral artery disease (c/m)
• Acute limb ischemia
Limit oxygen
in ishchemic
limb
• Bacteria fails to survive
• Limits putrefaction
Dry
Gangrene
• Affected part is dry, shrunken and dark reddish black.
• Line of separation present

62. Wet Gangrene
 Characterized by thriving bacteria.
 Poor prognosis (compared to dry gangrene) due to septicemia resulting from the
free communication between infected fluid and circulatory fluid.
 The tissue is infected by saprogenic microorganisms eg.Clostridium perfringens or
Bacillus fusiformis , which cause tissue to swell and emit a fetid smell.
 The affected part is edematous,soft, putrid, rotten and dark
Blockage of
venous(mainly)
&/or arterial
blood
Stagnation of
blood
Rapid growth of
bacteria
Toxin production
Septicemia &
cell death

63. Gas Gangrene
 Bacterial infection that produces gas within tissues.
 Caused by Clostridium, most commonly alpha toxin (exotoxin)producing
Clostridium perfringens, or various non-clostridial species.
 These environmental bacteria may enter the muscle through a wound and subsequently
proliferate in necrotic tissue and secrete powerful toxins.
 Infection spreads rapidly as the gases produced by bacteria expand and infiltrate
healthy tissue in the vicinity.
 Because of its ability to quickly spread to surrounding tissues, gas gangrene
should be treated as a medical emergency.

64. Q. Myocardial infarct is an example of:
a. Coagulation necrosis
b. Liquefactive necrosis
c. Caseous necrosis
d. Cell death nut not of necrosis
Ans. A
Q. Hypoxic death leads to:
a. Coagulation necrosis
b. Liquefactive necrosis
c. Caseous necrosis
d. Cell death nut not of necrosis
Ans. A

65. Q. Disappearance of nuclear chromatin is called as:
A. Pyknosis
B. Karyolysis
C. Karyorrhexis
D. None
Ans. (A) pyknosis, characterized by nuclear shrinkage & increased basophilia. Here. the DNA
apparently condenses into a solid, shrunken basophilia mass.
Q. The fading of Nuclear chromatin is
a. Karyolysis b. Karyorrhexis c. Pyknosis d. Cytolysis
Ans. A
Q. Pyknosis is characterized by
a. Nuclear basophilia
b. Nuclear Shrinkage
c. Nucleus disintegration
d. Nucleolus disintegration
Ans. B

66. Q. A glassy homogenous, increased eosinophilia with moth eaten appearance in a cell is indicated of:
a. Reversible fatty change
b. Reversible hypoxia
c. Necrosis
d. B and C
Ans. C
Q. Karyolysis leads to:
a. Decreased eosinophilia
b. Increased eosinophilia
c. Decreased basophilia
d. Increased basophilia
Ans. C
Due to Karyolysis the basophilia decreases but a necrotic cell in initial stages is characterized by
increased eosinophilia. Increase in basophilia is typical of pyknosis

67. Q.Which of the following is correctly matched
a. Caseating necrosis – Tuberculosis
b. Caseation - yellow fever
c. Fat necrosis – Pancreatitis
d. Gumma – infarction
Ans. A & C
Q. Caseation necrosis is suggestive of-
A. Tuberculosis B. Sarcoidosis C. Leprosy D. Mid line lethal granuloma
Ans. ‘A’
Q. Liquefaction necrosis is commonly seen in
a. Brain b. Lung c. Liver d.Spleen
Ans. A

68. Q. Liquefaction necrosis is commonly seen in
a. Brain b. Lung c. Liver d. Spleen
Ans. A
Q. Coagulation necrosis is seen in all cells (except in):
a. Liver b. Heart c. Brain d. Lungs
Ans. C
The process of coagulative necrosis is characteristic of hypoxic death of cells
in all tissues except the brain.
Q. Hypoxic death leads to:
a. Coagulation necrosis b. Liquefactive necrosis
c. Caseous necrosis d. Cell death nut not of necrosis
Ans. A

69. Q. Gangrene is the death of a part accompanied by
a. Suppuration b. Putrefaction c. Calcification d. Coagulation
Ans. B Gangrene is a form of necrosis of tissue with superadded putrefaction.
Q. Gangrene is defined as:
a. Necrosis of body parts
b. Coagulative necrosis of body parts
c. Necrosis with putrefaction
d. All are true
Ans. C

70. Apoptosis
 Apoptosis in Greek meaning ‘falling off’ or‘dropping off’.
 Defined as:
 coordinated and internally programmed cell death
Pathway of cell death which is induced by a tightly regulated suicide program in
which cell destined to die activate intrinsic enzymes that degrade the cells own
nuclear DNA and nuclear and cytoplasmic protein.

71. Cellular changes
 Shrinking of cell with dense cytoplasm and almost
normal but tightly packed organelles.
 Chromatin condensation around the periphery of nucleus
(most characteristic feature)
 Cytoplasmic blebbing with formation of membrane bound
near-spherical bodies called apoptotic bodies containing
compacted organelles.
 Phagocytosis of apoptotic bodies by macrophages
 No acute inflammation

72. Histopathological examintaion
 Apoptotic cell appear as
 Round or oval mass
 Intensely eosinophilic cytoplasm
 Fragments of dense nuclear chromatin

73. Causes of Apoptosis
Physiological
DNA damage
(Radiation/cytotox
ic drug/hypoxia)
Embryogenesis &
fetal
Development
Organ atrophy
after duct
obstruction
Viral Infections
like HIV/Adeno
Pathological
Hormone
dependent
involution
Accumulation of
missfolded
proteins
Death of the cells have served
their function E.g. neutrophil &
lymphocyte
Elimination of
self-Reactive
lymphocytes
Cell loss in
proliferating cell
population

74. Molecular Mechanism of Apoptosis
 Result from activation of enzyme called caspases (cysteine-aspartic-acid-
proteases)
 Two Phases:
1. Initiation phase: activation of caspases
2. Execution phase: degradation of cellular component by caspases.
 Two pathways on caspase activation:
 The Intrinsic Pathway (Mitochondrial)
 The Extrinsic Pathway ( Death receptor initiated)

75.  Initiators of apoptosis
1. Absence of stimuli e.g. Hormone, growth factors, cytokines.
2. Activators of programmed cell death. E.g.TNF receptors.
3. Intracellular stimuli e.g. Heat, radiation, hypoxia
 Regulators of apoptosis
 Anti-apoptotic: BCL 2, BCL-XL and MCL1
 Pro-apoptotic: BAX & BAK
 Sensors: BAD, BIM, BID, Puma & Noxa

76. Intrinsic -Mitochondrial pathway
• Synthesis of anti-
apoptotic molecules
(Bcl-2) promoted by
Growth factors & other
survival signals
1.Deprivation of
growth factors
2.ER Stress
3. DNA damage
• Activation of
sensor BH3
only protein
Activate
Proapoptotic
protein BAX &
BAN
• Proapoptotic
protein
increase mito.
Permeability
Leak out of mito.
Proteins in to
cytoplasm like Cyt
c
• Binding of Cyt c to a
protein called APAF
• Forms apoptosomes
Apoptosome bind with
casepase-9 (Initiater
caspase )which initiate
autoamplification
process of activation
• Activated
Executers
Caspases
(caspase-3)
Execution Phse
 BH3 Also bind to and block the function of
antiapoptotic protein
 The synthesis of Antiapoptotic protein is
declined due to def of survival signals
• Bcl-2 is over expressed in most follicular B-cell
lymphomas – allowing abnormal cells to
proliferate.

77. Essence of intrinsic
(mitochondrial) pathway
 Pro-apoptotic and protective molecules that regulate mitochondrial permeability
and the release of death molecules sequestered in the mitochondria are
maintained in balance normally.
 Imbalance initiates the death pathway.

78. Extrinsic pathway
(Death Receptor Initiated)
 Death receptors are members of the tumor necrosis factor receptor family and a
related protein called Fas (CD95).
 These molecules contain a death domain.

79. Fas expressed on
the surface linked
death domain if
activated apoptosis
is intitated

81. Mechanism of
Apoptosis
Initiators of apoptosis
(transmembrane, intracellar)
Regulators of apoptosis
(bcl-2, others)
Programmed cell death
Fas receptor
activation
(cytotoxic T cells)
DNA damage
(radiation,
chemotherapy,
free radicals
PHAGOCYTOSIS
APOPTOSIS
Mitochondrial injury
DNA damage
P53
Bax
ceramide
Caspases

82. Difference between Necrosis &
Apoptosis

83. Agarose Gel Electrophoresis
Normal Cell Apoptotic cell with
step ladder pattern
Necrotic cells,
DNA in all
different length.
Smearing patterbn

84. Necroptosis:
 Form of cell death which resemble necrosis morphologically and apoptosis
mechanistically as a form of programmed cell death
 Triggered by
• Ligation of TNFR1
• Viral proteins
 Caspase independent
 RIP1 & RIP 3 complex dependent
 Inflammation present
Pyroptosis:
 Inflammatory form of programmed cell death
 Infection with intracellular pathogens
 Involve activation of caspase 1 & caspase 11

85. Q. Gene inhibiting apoptosis is:
a. bcl2 b. P53 c.Ras d. N-myc
Ans. A
Q. Which of the following features is seen in apoptosis but not in necrosis?
A. Inter nucleosome cleavage of DNA
B. Inflammation
C. Pyknosis
D. Cytoplasmic hyper eosinoplilia
E. Karyolysis
Ans:A

86. Necrosis or Apoptosis ?
Ans: Necrosis
Lots of leukocytes
Does apoptosis involve an
inflammatory response?

88. THANK YOU