Necrosis vs Apoptosis – howMed

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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	Ischemia and hypoxia Free radical mediated Chemical mediated injury Cellular aging	Cytotoxic T lymphocytes Withdrawal of growth factors/hormones Receptor ligand interaction
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	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.

2012-07-06

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