II. Cell Injury and Death – NUS Pathweb

Definition:

Cell injury: Sequence of events that occurs when stresses exceed ability of cells to adapt. Responses are initially reversible, but may progress to irreversible injury and cell death.

Cell death: Results when continuing injury becomes irreversible, at which time the cell cannot recover.

There are TWO principle types of cell death:

1. Necrosis - Death of cells in living tissues characterized by the breakdown of cell membranes. These changes occur because of digestion and denaturation of cellular proteins, largely by release of hydrolytic enzymes from damaged lysosomes.

There are many subtypes / morphological patterns of necrosis: Coagulative; Liquefactive; Caseous; ;

Haemorrhagic; Suppurative; Gangrenous; Fat; Fibrinoid

Common morphologic patterns of necrosis (Click to expand)

2. Apoptosis - Defined as programmed cell death characterized by nuclear dissolution, fragmentation of the cell without complete loss of membrane integrity, and rapid removal of the cellular debris.

Apoptosis can be physiological or pathological

Other processes in cellular stress

Intracellular accumulations - Accumulations of substances within cells, which are due to metabolic derangements. Substances can be endogenous (eg. lipids, proteins) or exogenous (eg. mineral dust, microbial products).

Examples are included in Mindmap 5: Morphology.

Autophagy - Process in which a cell eats its own organelles, usually during stress (eg. nutrient deprivation). This may result in the formation of residual bodies which may accumulate as lipofuscin (wear and tear pigments).

Significance - Autophagy may be a means of cell loss in some diseases (eg. degenerative disease of the CNS), but the exact mechanism is unclear.