1. Cell injury Dr. Maha Arafah Assistant Professor
Department of Pathology
King Khalid University Hospital and King Saud University
Saturday, Oct 9, 2010
9:00 to 10:00 am

2. CONCEPT OF INJURY AND CELLULAR RESPONSE TO INJURY
Overview of Cell Injury and Cell Death
L2:
Necrosis and Apoptosis
L3:
Cellular accumulation and Calcification
L4:
Adaptation to environmental stress

3. Overview of Cell Injury and Cell Death
Definition
Causes
Reversible cell injury ( nonlethal hit)
Irreversible injury and cell death ( lethal hit)
Mechanisms of Cell Injury
Free radical injury
Morphology of cells in injury

4. Objectives
Upon completion of this lecture, the student should:
Understand the concepts of reversible and irreversible (lethal) cell injury.
Know the causes of cell injury.
Be aware of the mechanisms of cell injury which include the actions of:
Bacterial toxins.
Free radicals.
Hypoxia.
Chemical injury
Effects of viruses.
Radiation.
Be aware of the morphology of cells in reversible and irreversible injury

5. CELLULAR RESPONSE TO INJURY
CONCEPT OF INJURY AND
CELLULAR RESPONSE TO INJURY
Cells are constantly exposed to a variety of stresses.
When too severe, INJURY results.
Injury alters the preceding normal steady state of the cell.

6. ALL CELLS

7. ALL ORGANISMS

8. Living in the World

9. Must cope with…

10. Stress!!!

11. Etiologic agents

12. MECHANISMS OF CELL INJURY
General principles:
The cellular response to injurious stimuli depends on
1. type of injury
2. Its duration
3. Severity
The consequences depend on
the type, status, adaptability, and genetic makeup of the injured cell.
The structural and biochemical components of a cell are so integrally connected that multiple secondary effects rapidly occur
Cellular function is lost far before cell death occurs

13. Objectives Know the causes of cell injury.
Upon completion of this lecture, the student should:
Understand the concepts of reversible and irreversible (lethal) cell injury.
Know the causes of cell injury.
Be aware of the mechanisms of cell injury which include the actions of:
Bacterial toxins.
Free radicals.
Hypoxia.
Chemical injury
Effects of viruses.
Radiation.
Be aware of the morphology of cells in reversible and irreversible injury

14. Causes of cell injury EXCESS or DEFICIENCY OF OXYGEN PHYSICAL AGENTS
CHEMICAL AGENTS
INFECTION
IMUNOLOGICAL REACTIONS
GENETIC DERANGEMENTS
NUTRITIONAL IMBALANCE
AGING

16. Brain – massive haemorrhagic focus (ischemia) in the cortex
This is a lesion
caused by
DEFICIENCY OF OXYGEN

17. Abscess of the brain (bacterial)
This is a lesion
caused by
infectious agent

18. Hepatic necrosis (patient poisoned by carbon tetrachloride)
This is a lesion
caused by
chemical agent

19. Pulmonary caseous necrosis (coccidioidomycosis)
This is a lesion
caused by
infectious agent

20. Gangrenous necrosis of fingers secondary to freezing
This is a lesion
caused by
physical agent

21. The “boutonnière” (buttonhole) deformity
This is a lesion
caused by
intrinsic factors
(autoimmune disease)

22. Liver: macronudular cirrhosis (HBV)
This is a lesion
caused by
infectious agent:
Viral hepatitis
(chemical:alcohol, genetic:a1-AT deficiency)

23. (chemical:alcohol, genetic:a1AT deficiency)
This is a lesion
caused by HBV
infectious agent
(chemical:alcohol, genetic:a1AT deficiency)
Liver: cirrhosis

24. Objectives
Upon completion of this lecture, the student should:
Understand the concepts of reversible and irreversible (lethal) cell injury.
Know the causes of cell injury.
Be aware of the mechanisms of cell injury which include the actions of:
Bacterial toxins.
Free radicals.
Hypoxia.
Chemical injury.
Effects of viruses.
Radiation.
Be aware of the morphology of cells in reversible and irreversible injury

25. Mechanisms of cell injury
Cell membrane damage
Complement-mediated cell membrane lysis via the membrane attack complex (MAC)
Bacterial toxins
Free radicals
Mitochondrial damage leading to inadequate aerobic respiration
Hypoxia (lack of oxygen)
Cyanide poisoning
Ribosomal damage leading to altered protein synthesis
Alcohol in liver cells
Antibiotics in bacteria
Nuclear change
Viruses
Radiation

27. MECHANISMS OF CELL INJURY
Integrity of Cell Membranes
Mechanisms of membrane damage in cell injury:
Decreased O2 and increased cytosolic Ca2+ are typically seen in ischemia but may accompany other forms of cell injury.
Production of reactive oxygen species
Lysis of enzymes
Activation of complement system
Lysis by viruses

29. MECHANISMS OF CELL INJURY
Effect of plasma membrane damage
Loss of structural integrity
Loss of function

30. MECHANISMS OF CELL INJURY
DEPLETION OF ATP
ATP depletion and decreased ATP synthesis are frequently associated with both hypoxic and chemical (toxic) injury
Depletion of ATP to <5% to 10% of normal levels has widespread effects on many critical cellular systems:
Plasma membrane energy-dependent sodium pump is reduced, resulting in cell swelling
increased rate of anaerobic glycolysis, glycogen stores are rapidly depleted. Glycolysis results in the accumulation of lactic acid. This reduces the intracellular pH, resulting in decreased activity of many cellular enzymes.
Failure of the Ca2+ pump leads to influx of Ca2+
In cells deprived of oxygen or glucose, unfolded protein formed, that may lead to cell injury and even death.

31. MECHANISMS OF CELL INJURY Heat shock proteins:
Definition:
They are proteins which stabilize other cellular proteins.
Function:
Guide the newly synthesized protein and the misfolded proteins to degradation.
Protect proteins from cellular stresses.

32. Chaperones

33. Repair of Protein Damage

35. MECHANISMS OF CELL INJURY
MITOCHONDRIAL DAMAGE
Mitochondria are important targets for virtually all types of injurious stimuli, including hypoxia and toxins.
Cell injury is frequently accompanied by morphologic changes in mitochondria.

36. GENERAL MECHANISMS OF INJURY
Result in apoptosis

37. INFLUX OF INTRACELLULAR CALCIUM AND LOSS OF CALCIUM HOMEOSTASIS
Calcium ions are important mediators of cell injury.
Cytosolic free calcium is maintained at extremely low concentrations (<0.1 μmol) compared with extracellular levels of 1.3 mmol (most intracellular calcium is sequestered in mitochondria and endoplasmic reticulum)
Such gradients are modulated by membrane-associated, energy-dependent Ca2+, Mg2+-ATPases.
Ischemia and certain toxins cause an early increase in cytosolic calcium concentration, owing to the net influx of Ca2+ across the plasma membrane and the release of Ca2+ from mitochondria and endoplasmic reticulum

38. Failure of intracellular calcium homeostasis

39. MECHANISMS OF CELL INJURY
the integrity of the genetic apparatus of the cell
Caused by:
Ionizing radiation
Viruses
Mutagenic chemicals

40. MECHANISMS OF CELL INJURY
(4) the integrity of the genetic apparatus of the cell
Effect of DNA abnormalities:
1. Failure of synthesis of proteins and enzyme
2. Failure of mitosis
3. Progression to cancer

41. Free radicals and cell membrane damage

42. MECHANISMS OF INJURY BY FREE RADICALS
Free radicals are highly reactive atoms which have an unpaired electron in an outer orbital.
This state is unstable and react with organic and inorganic chemical.
The most important free radicals are derived from oxygen  
Superoxide
Hydrogen peroxide
Hydroxy radical 

43. Injury by free radical
Free radical can be produced in cells in response to a variety of processes, including radiation, normal metabolic oxidation reactions and drug metabolism processes.

44. MECHANISMS OF INJURY BY FREE RADICALS
What happen when the cell is injured by free radicals?
Lipid peroxidation
Protein damage
DNA damage 

46. A. Superoxide dismutase. 2O2- + 2H ---> H2O2 + O2
Normal mechanism to protect against free radical injury
1. Enzyme
A. Superoxide dismutase.
2O2- + 2H ---> H2O2 + O2
B. Glutathione peroxidase.
H2O2 + 2 GSH ---> 2H2O + GSSG
C. Catalase.
2H2O2 ----> O2 + 2 H2O
2. Antioxidant:
vit E, vit C
Sulfhydryl containing compounds e.g. cysteine
Proteins e.g., transferrin and albumin

47. ISCHEMIC AND HYPOXIC INJURY

48. ISCHEMIC AND HYPOXIC INJURY
Oxygen is required for oxidative phosphorylation.
Hypoxia and ischemia occur in:
a] Hypoglycaemia.
b] Hypoxia due to :
1. Respiratory obstruction or disease.
2. Ischemia.
3. Anaemia.
4. Alteration of hemoglobin.
c] Enzyme inhibition by cyanide.
d] Uncoupling of oxidative phosphorylation.

49. ISCHEMIC AND HYPOXIC INJURY
The result is defective ATP production
First cells affected are those with highest demand of oxygen.

51. How Ionizing Radiation Kills Cells 
Proliferating Cells - by DNA damage.
Leads to apoptosis. 
Nonproliferating cells- by lipid peroxidation.

52. How Viruses Kill Cells Directly Cytopathic Viruses – e.g. Poliovirus
Indirectly cytopathic Viruses -  e.g. hepatitis B

53. How Viruses Kill Cells
Direct cytopathic viruses insert their proteins into the plasma membranes, disrupting the cells permeability (membrane damage)
Indirect cytopathic viruses also in insert their proteins into the plasma membrane, but to create an antigenic target for cytotoxic T lymphocytes. 

55. How Chemicals Kill Cells :
Group I : interact directly with cellular contents to cause damage (mercury, lead and iron (toxic heavy metals) 
Group II: whose metabolite is toxic e.g. hepatotoxins: (Carbon tetrachloride(CCl4), acetominophen, bromobenzene)
Group III: bind cytochrome P450 (the mixed function oxygenase involved in drug metabolism)   

56. Reversible and irreversible cell injury : time and exposure factors
Chemical injury
Reversible and irreversible cell injury : time and exposure factors

57. Sequelae of cell injury
Depend on: A. cell features
Specialization. Cells that are enzyme rich, nucleated or have specialized organelles within the cytoplasm may be more vulnerable.
Cell state. Cells that have an inadequate supply of oxygen are more prone to injury.
Regenerative ability. The potential of a cell population to divide is important in the response of tissues to injury.

58. Sequelae of cell injury
Depend on: B. Injury features:
Type of injury. The injury may be ischaemic, toxic, chemical, etc.
Exposure time. The length of time of exposure to a toxin or reduced oxygen concentration will affect the change of a cell surviving the insult.
Severity. The ability to survive an injury will also depend upon its severity, e.g. is the lack of oxygen partial (hypoxia) or complete (anoxia).

59. Objectives
Upon completion of this lecture, the student should:
Understand the concepts of reversible and irreversible (lethal) cell injury.
Know the causes of cell injury.
Be aware of the mechanisms of cell injury which include the actions of:
Bacterial toxins.
Free radicals.
Hypoxia.
Chemical injury
Effects of viruses.
Radiation.
Be aware of the morphology of cells in reversible and irreversible injury

60. morphology of cells in reversible and irreversible injury

61. Morphologic changes in Reversible Injury
Early changes:
(1) Cloudy swelling or hydropic changes: Cytoplasmic swelling and vacuolation due to intracellular accumulation of water and electrolytes secodary to failure of energy-dependent sodium pump.
(2) Mitochondrial and endoplasmic reticulum swelling due to
loss of osmotic regulation.
(3) Clumping of nuclear chromatin.

62. Vacuolar (hydropic) change in cells lining the proximal tubules of the kidney
Reversible
changes

63. Hydropic vacuoles in the endoplasmic reticulum of hepatocyte
Reversible changes

64. Nucleus Hydropic vacuoles in the endoplasmic reticulum of hepatocyte

65. Morphologic changes in irreversible injury:
1. Severe vacuolization of the mitochondria, with
accumulation of calcium-rich densities.
2. Extensive damage to plasma membranes.
3. Massive calcium influx activate phospholipase, proteases, ATPase and endonucleases with break down of cell component.
4. Leak of proteins, ribonucleic acid and metabolite.
5. Breakdown of lysosomes with autolysis.
6. Nuclear changes: Pyknosis, karyolysis, karyorrhexis.

66. IRREVERSIBLE CELL INJURY- NECROSIS

69. Morphologic changes in irreversible injury
- Dead cell are either collapsed and form a whorled phospholipid masses or degraded into fatty acid with calcification. - Cellular enzymes are released into circula- tion. This provides important clinical parameter of cell death e.g. increased level of creatinin kinase in blood after myocardial infarction

71. Myocardial infarct This is a lesion caused by oxygen deprivation
Cell Pathology
This is a lesion
caused by
oxygen
deprivation
Myocardial infarct

73. Following ischemic heart injury, the following sequence is observed:
rapid biochemical and ultrastructural responses
light microscopic evidence of reversible injury after several minutes
ultrastructural evidence of irreversible injury in minutes
unequivocal light microscopic evidence of cell death after hours

74. MECHANISMS OF INJURY: Ischemia

75. TAKE HOME MESSAGES:
Cellular injury is caused by various elements include bacterial toxins,, hypoxia, alcohol, viruses and radiation.
Depletion of ATP, free radicals production, disruption of cell membrane and chromatin are important mechanism in cell injury
Cellular injury could be reversible (sublethal) or irreversible (lethal).