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Necrosis vs Apoptosis

 
Necrosis
Apoptosis
Definition Morphologic changes caused by progressive degradative actions of enzymes on lethally injured cells. A form of cell death, designed to eliminate the unwanted host cell through the activation of co-ordinated internally programmed series of events affected by set of genes
Outcome Always fatal May be beneficial
Types Coagulative

Liquefactive

Caseous

Enzymatic –fat

Fibrinoid

Gangrene –wet or dry

No types
Causes
  1. Ischemia and hypoxia
  2. Free radical mediated
  3. Chemical mediated injury
  4. Cellular aging
Cytotoxic T lymphocytes

Withdrawal of growth factors/hormones

Receptor ligand interaction

  1. FAS
  2. TNF receptors
Cell size/form Swollen Shrinked
Plasma membrane Disrupted Intact –altered structure esp. orientation of lipids
Membrane permeability Definitely altered Preserved till advanced stages
Severity of stimuli determine pathway of cell death (not nature) ATP depletion

Radiation, hypoxia, anticancer –high dose

Low dose
Histology Affects contagious cells

Exudation present

Cellular lysis with released lysosomes

Affects single cell

Exudation absent

Pigmentation without release of enzymes

Cytoplasm Swollen with membrane fragmentation Condensed with loss of specialized surface structure
Cellular contents Enzymatic digestion

Contents may leak out of cell

Intact

Released in apoptotic bodies

Mitochondria Swollen Intact (preserved)
Endoplasmic reticulum Swollen Intact
Nucleus Pyknosis

Karyorrhesis

Karyolysis

Nuclear condensation followed by fragmentation into nucleosome sized fragments
Chromatin Fine aggregation beneath nuclear membrane Coarse lumps beneath nuclear membrane
Nucleolus Conserved Dispersed
DNA degradation Random Formation of 185-200 base pairs DNA fragments
Apoptotic bodies None Formed
Myelin Formed Not formed
Elimination Enzymatic digestion

  1. Autolysis
  2. Heterolysis
Apoptotic bodies are formed which are phagocytosed by macrophages
Adjacent inflammation Frequent None
Physiologic/pathologic Invariably pathologic

 

Often physiologic

May be pathologic

Protein synthesis Not required Required
Protein cleavage(caspases) No Yes
Examples All hypoxic deaths esp. MI

Caseous necrosis Mycobacterium T.B

Programmed cell destruction during embryogenesis

Viral hepatitis in which loss of infected cell is largely because of apoptotic bodies.

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