howMed Know Yourself
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 |
|
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. |
Necrosis vs Apoptosis
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