1. Necrosis and apoptosis
(Foundation Block, pathology)
Lecturer name: Dr. Maha Arafah
Lecture Date:
Cell injury L2

2. Objectives List causes of cell injury List mechanisms of cell injury
Understand the changes in reversible and irreversible cell injury
Define necrosis and apoptosis
List the different conditions associated with apoptosis, its morphology and its mechanism
List the different types of necrosis, examples of each and its features
Know the difference between apoptosis and necrosis

3. DEFICIENCY OF OXYGEN Ischemia vs. Hypoxia PHYSICAL AGENTS
Etiologic agents
DEFICIENCY OF OXYGEN Ischemia vs. Hypoxia
PHYSICAL AGENTS
CHEMICAL AGENTS
INFECTION
IMUNOLOGICAL REACTIONS
GENETIC DERANGEMENTS
NUTRITIONAL IMBALANCE
AGING

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

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

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

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

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

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

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

11. morphology of cells in reversible and irreversible injury

12. myocadial cells: loss of function after 1-2 min of ischemia
However do not die until 20 to 30 min of ischemia
EM: 2-3 hours, LM 6-12 hours

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

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

17. 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.

19. IRREVERSIBLE CELL INJURY- NECROSIS

22. 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

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

24. Mechanisms of cell injury
Depletion of ATP
Damage to Mitochondria
Influx of Calcium
Free radicals production
Disruption of cell membrane and chromatin

25. Mechanisms of cell injury

26. Cell Death Death of cells occurs in two ways:
Necrosis--changes produced by enzymatic digestion ofcells after irreversible injury
Apoptosis--vital process that helps eliminate unwanted cells--an internally programmed series of events effected by dedicated gene products
Autolysis
Autolysis is the death of individual cells and tissues after the death of the whole organism.
The cells are degraded by the post-mortem release of digestive enzymes from the cytoplasmic lysosomes.
Autophagy:
Self eating in starvation

28. Necrosis
Necrosis is defined as the morphological changes that result from cell death within living tissues.
In necrosis, death of a large number of cells in one area occurs.
These changes occur because of digestion and denaturation of cellular proteins.

29. Patterns of Necrosis: In Tissues or Organs
As a result of cell death the tissues or organs display one of these six macroscopic changes:
Coagulative necrosis
Liquifactive necrosis
Caseous necrosis
Fat necrosis
Gangrenous necrosis
Fibrinoid necrosis

30. Patterns of Necrosis In Tissues or Organs
Coagulative necrosis:
Denaturation of intracellular protein leads to the pale firm nature of the tissues affected. The cells show the microscopic features of cell death but the general architecture of the tissue and cell ghosts remain discernible for a short time.
The outline of the dead cells are maintained and the tissue is somewhat firm.
Example: kidney and heart injury caused by ischaemia.

31. Removal of the dead tissue leaves behind a scar
Coagulative necrosis
Kidney: ischemia and infarction
(loss of blood supply and resultant
tissue anoxia).
Removal of the dead tissue leaves behind a scar

32. Acute renal tubular necrosis (ischemia) :
increased eosinophilia and pyknosis in necrotic cells
Normal
Necrotic

33. Coagulative necrosis:
Remember: True coagulation necrosis involves groups of cells, and is almost always accompanied, by acute inflammation (infiltrate)

34. Patterns of Necrosis In Tissues or Organs
2. Liquefactive necrosis:
The dead cells undergo disintegration and affected tissue is liquefied.
This results from release of hydrolytic lysosomal enzymes and leads to an accumulation of semi- fluid tissue.
Example:
cerebral infarction.
Abscess

35. Liquefactive necrosis in brain leads to resolution with cystic spaces.

36. Liquefactive necrosis of the brain: macrophages cleaning
up the necrotic cellular debris
Removal of the dead tissue leaves behind a cavity

37. Removal of the dead tissue leaves behind a cavity or scar
Liquefactive necrosis: two lung abscesses
Removal of the dead tissue leaves behind a cavity or scar

38. Removal of the dead tissue leaves behind a scar
Localized liquefactive necrosis liver abscess
Removal of the dead tissue leaves behind a scar

39. Patterns of Necrosis In Tissues or Organs
3. Caseous necrosis:
A form of coagulative necrosis but appear cheese-like.
The creamy white appearance of the dead tissue is probably a result of the accumulation of partly digested waxy lipid cell wall components of the TB organisms. The tissue architecture is completely destroyed.
Example:
tuberculosis lesions
fungal infections
Coccidioidomycosis
blastomycosis
histoplasmosis

40. Caseous necrosis in a hilar pulmonary lymp node infected with tuberculosis.

41. Pulmonary tuberculosis:tubercle contains amorphous finely granular, caseous ('cheesy') material typical of caseous necrosis.
Removal of the dead tissue leaves behind
a scar

42. Caseous necrosis is characterized by acellular pink areas of necrosis, surrounded by a granulomatous inflammatory process. N

43. Patterns of Necrosis In Tissues or Organs
4. Fat necrosis:
This can result from direct trauma or enzyme released from the diseased pancreas.
Example:
Necrosis of fat by pancreatic enzymes.
Traumatic fat necrosis in breast
Adipocytes rupture and the released fat undergoes lipolysis catalyzed by lipases. Macrophages ingest the oily material and a giant cell inflammatory reaction may follow. Another consequence is the combination of calcium with the released fatty acids.

44. Fat necrosis secondary to acute pancreatitis

45. Fat Necrosis 
Specific to adipose tissue with triglycerides.
With enzymatic destruction(lipases) of cells, fatty  acids are precipitated as calcium soaps.
Grossly- chalky white deposits in the tissue.
Microscopically – amorphous, basohilic /purple deposits at the periphery of necrotic adipocytes. 

46. Patterns of Necrosis In Tissues or Organs
5. Gangrenous necrosis:
This life-threatening condition occurs when coagulative necrosis of tissue is associated with superadded infection by putrefactive bacteria.
These are usually anaerobic gram-positive Clostridia spp. Derived from the gut or soil which thrive in conditions of low oxygen tension.

47. Patterns of Necrosis In Tissues or Organs
5. Gangrenous necrosis:
Gangrenous tissue is foul smelling and black.
The bacteria produce toxins which destroy collagen and enable the infection to spread rapidly. If fermentation occurs, gas gangrene ensues.
Infection can become systemic (i.e. reach the bloodstream, septicaemia).
The commonest clinical situation is gangrene of the lower limb caused by poor blood supply and superimposed bacterial infection. This is a life-threatening emergency and the limb should be amputated.

48. Example: necrosis of distal limbs, usually foot and toes in diabetes.
“Wet" gangrene “ of the lower extremity in patient with diabetes mellitus:
liquefactive component from superimposed infection
coagulative necrosis from loss of blood supply.

49. Patterns of Necrosis In Tissues or Organs
6. Fibrinoid necrosis:
typically seen in vasculitis and glomerular autoimmune diseases

50. Fibrinoid necrosis: afferent arteriole and part of the glomerulus
are infiltrated with fibrin, (bright red amorphous material)

52. Outcome of necrosis Depending on circumstances:
necrotic tissue may be walled off by scar tissue,
totally converted to scar tissue,
get destroyed (producing a cavity or cyst),
get infected (producing an abscess or "wet gangrene"),
or calcify.
If the supporting tissue framework does not die, and the dead cells are of a type capable of regeneration, you may have complete healing.

53. Apoptosis Vital process. Programmed cell death.
Can occurs in physiological or pathological conditions.

54. Physiologic process to die
Apoptosis
Physiologic process to die
This process helps to eliminate unwanted cells by an internally programmed series of events effected by dedicated gene products. It serves several vital functions and is seen under various settings.
Remember: apoptosis require energy to die

55. Apoptosis A. Physiologic
SEEN IN THE FOLLOWING CONDITIONS:
A. Physiologic
During development for removal of excess cells during embryogenesis
To maintain cell population in tissues with high turnover of cells, such as skin, bowels.
To eliminate immune cells after cytokine depletion, and autoreactive T-cells in developing thymus.
Hormone-dependent involution - Endometrium, ovary, breasts etc.

56. Apoptosis B. Pathologic To remove damaged cells by virus
Atrophy (virtually never accompanied by necrosis).
To eliminate cells after DNA damage by radiation, cytotoxic agents etc.
Cell death in tumors.

57. Morphology of Apoptosis
Shrinkage of cells
Condensation of nuclear chromatin peripherally under nuclear membrane
Formation of apoptotic bodies by fragmentation of the cells and nuclei. The fragments remain membrane- bound and contain cell organelles with or without nuclear fragments.
Phagocytosis of apoptotic  bodies by adjacent healthy cells or phagocytes.
Unlike necrosis, apoptosis is not accompanied by inflammatory reaction

59. Liver biopsy - viral hepatitis: acidophilic body (councilman body)
(apoptosis, i.e., induced, or programmed, individual cell death).
Vacuolar change is reversible.

60. Skin, apoptotic Keratinocyte

61. MECHANISMS OF APOPTOSIS
1. Chromatin condensation is mediated by calcium-sensitive endonuclease leading to internucleosomal DNA fragmentation. 2. Alteration in cell volume (shrinkage) due to action of transglutaminase. 3. Phagocytosis of apoptotic bodies is mediated by receptors on the macrophages. 4. Apoptosis is dependent on gene activation and new protein synthesis, e.g. bcl-2, c-myc oncogene and p53.

62. Apoptosis summary

64. Apoptosis regulating genes

65. Genes that regulate apoptosis:
Oncogene Bcl-2
Bcl-2 overexpression prevents apoptosis
Antagonized by cell death genes
Bcl-2 overexpression is found in follicular lymphoma.
Tumor suppressor gene p-53
Will cause cells with DNA damage to go apoptosis
Reversed by overexpression of bcl-2

66. Objectives Define necrosis and apoptosis
List the different conditions associated with apoptosis, its morphology and its mechanism
List the different types of necrosis, examples of each and its features
Know the difference between apoptosis and necrosis

67. Difference between apoptosis and necrosis
Coagulation Necrosis
Apoptosis
Stimuli
Hypoxia, Toxins
Physiologic and pathologic conditions
Histologic appearance
Cell swelling, coagulation necrosis disruption of organelles
Single cell, chromatin condensation, apoptotic bodies
DNA breakdown
Random and diffuse
internucleosomal
Mechanism
ATP depletion membrane injury
Gene activation, endonucleases, proteases
Tissue reaction
Inflammation
No inflammation, phagocytosis of apoptotic bodies
Energy
Not needed
Needed