NECROSIS AND APOPTOSIS

Cell injury L2

Lecturer name: Dr. Maha ArafahLecture Date: 17-9-2012

(Foundation Block, pathology)

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

Etiologic agents

1. DEFICIENCY OF OXYGEN Ischemia vs.

Hypoxia2. PHYSICAL AGENTS3. CHEMICAL AGENTS4. INFECTION5. IMUNOLOGICAL REACTIONS6. GENETIC DERANGEMENTS7. NUTRITIONAL IMBALANCE8. AGING

Brain – massive haemorrhagic focus (ischemia) in the cortex

This is a lesion caused by

DEFICIENCY OF OXYGEN

Abscess of the brain (bacterial)

This is a lesion caused by

infectious agent

This is a lesion caused by

chemical agent

Hepatic necrosis (patient poisoned by carbon tetrachloride)

Pulmonary caseous necrosis (coccidioidomycosis)

This is a lesion caused by

infectious agent

Gangrenous necrosis of fingers secondary to freezing

This is a lesion caused by

physical agent

The “boutonnière” (buttonhole) deformityThis is a lesion

caused by intrinsic factors

(autoimmune disease)

Liver: macronudular cirrhosis (HBV)

This is a lesion caused by

infectious agent:Viral hepatitis

(chemical:alcohol, genetic:a1-AT

deficiency)

MORPHOLOGY OF CELLS IN REVERSIBLE AND IRREVERSIBLE INJURY

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

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.

Vacuolar (hydropic) change in cells lining the proximal tubules of the kidney

Reversible changes

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.

IRREVERSIBLE CELL INJURY- NECROSIS

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 deathe.g. increased level of creatinin kinase in

blood after myocardial infarction

Myocardial infarct This is a lesion caused by

oxygen deprivation

Cell Pathology

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

chromatin

Mechanisms of cell injury

Cell DeathDeath of cells occurs in two ways:

1. Necrosis--changes produced by enzymatic digestion ofcells after irreversible injury

2. Apoptosis--vital process that helps eliminate unwanted cells--an internally programmed series of events effected by dedicated gene products

AutolysisAutolysis 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

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.

Patterns of Necrosis: In Tissues or Organs

As a result of cell death the tissues or organs display one of these six macroscopic changes:

1. Coagulative necrosis2. Liquifactive necrosis3. Caseous necrosis4. Fat necrosis5. Gangrenous necrosis6. Fibrinoid necrosis

Patterns of Necrosis In Tissues or Organs

1. 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.

Kidney: ischemia and infarction (loss of blood supply and resultant

tissue anoxia).

Coagulative necrosis

Removal of the dead tissue leaves behind a scar

Acute renal tubular necrosis (ischemia) :increased eosinophilia and pyknosis in necrotic cells

Normal

Necrotic

Coagulative necrosis:

Remember: True coagulation necrosis involves groups of cells, and is almost always

accompanied, by acute inflammation (infiltrate)

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

Liquefactive necrosis in brain leads to resolution with cystic spaces.

Liquefactive necrosis of the brain: macrophages cleaning up the necrotic cellular debris

Removal of the dead tissue leaves behind a cavity

Liquefactive necrosis: two lung abscesses

Removal of the dead tissue leaves behind a cavity or scar

Localized liquefactive necrosis liver abscess

Removal of the dead tissue leaves behind a scar

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

Caseous necrosis in a hilar pulmonary lymp node

infected with tuberculosis.

Pulmonary tuberculosis:tubercle contains amorphous finely granular, caseous ('cheesy') material typical of caseous necrosis.

Removal of the dead tissue leaves behind a scar

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

N

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 breastAdipocytes 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.

Fat necrosis secondary to acute pancreatitis

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. 

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.

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.

Example: necrosis of distal limbs, usually foot and toes in diabetes.

“Wet" gangrene “ of the lower extremity in patient with diabetes mellitus:

1. liquefactive component from superimposed infection

2. coagulative necrosis from loss of blood supply.

Patterns of Necrosis In Tissues or Organs

6. Fibrinoid necrosis: typically seen in vasculitis and glomerular

autoimmune diseases

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

Depending on circumstances: 1. necrotic tissue may be walled off by scar tissue, 2. totally converted to scar tissue, 3. get destroyed (producing a cavity or cyst), 4. get infected (producing an abscess or "wet gangrene"), 5. 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.

Outcome of necrosis

Cell Death

Apoptosis

• Vital process.• Programmed cell death.• Can occurs in physiological or pathological

conditions.

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

Apoptosis

SEEN IN THE FOLLOWING CONDITIONS: A. Physiologic

1. During development for removal of excess cells during embryogenesis

2. To maintain cell population in tissues with high turnover of cells, such as skin, bowels.

3. To eliminate immune cells after cytokine depletion, and autoreactive T-cells in developing thymus.

4. Hormone-dependent involution - Endometrium, ovary, breasts etc.

Apoptosis

B. Pathologic

1. To remove damaged cells by virus2. Atrophy (virtually never

accompanied by necrosis). 3. To eliminate cells after DNA damage

by radiation, cytotoxic agents etc. 4. Cell death in tumors.

Morphology of Apoptosis

1. Shrinkage of cells

2. Condensation of nuclear chromatin peripherally under nuclear membrane

3. 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.

4. Phagocytosis of apoptotic  bodies by adjacent healthy cells or phagocytes.

5. Unlike necrosis, apoptosis is not accompanied by inflammatory reaction

Liver biopsy - viral hepatitis: acidophilic body(councilman body)

(apoptosis, i.e., induced, or programmed, individual cell death). Vacuolar change is reversible.

Skin, apoptotic Keratinocyte

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.

Apoptosis summary

Apoptosis regulating genes

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

Genes that regulate apoptosis:

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

Difference between apoptosis and necrosis

Coagulation Necrosis ApoptosisStimuli Hypoxia, Toxins Physiologic and pathologic

conditionsHistologic 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