Cell injury implies such changes in cell structure, metabolism, physico-chemical properties or function, that seriously compromise cellular viability or the ability to adapt to noxious stimuli.
Common causes of cell injury
1. Chemical agents and drugs.
2. Physical agents (e.g. mechanical trauma, extremes of temperature (burns and deep cold), radiation, electric shock, sudden changes in barometric pressure).
3. Biological agents (infectious agents including viruses, rickettsiae, bacteria, fungi, and higher forms of parasites; genetic derangements: nutritional imbalance).
Mechanisms of cell injury
I. Derangements in the energy supply and utilization.
1. Decrease in the rate or efficiency of ATP production.
2. Decreased transport of ATP to the sites of utilization.
3. Impaired ATP utilization in metabolic processes.
II. Loss of the integrity of cell membranes.
1. An imbalance between production and utilization of free radicals causing lipid peroxidation.
2. Activation of intracellular hydrolases.
3. Defects in membrane permeability.
4. Detergent effect of amphyphyllic compounds.
5. Impaired resynthesis of the damaged membrane constituents.
6. Overextension and the following rupture of membranes in the swelled cells or cellular organelles.
III. Ionic and water imbalance.
1. Imbalance of the particular ions.
2. Abnormal redistribution of ions in intracellular compartments.
3. Overhydration of a cell.
4. Dehydration of a cell.
IV. Changes in the genome and/or its abnormal realization.
A. Changes in the genome.
1. Changes in the gene structure.
2. Derepression of pathogenic genes.
3. Repression of the «vital» genes.
4. Insertion of the alien DNA fragment with pathological information.
B. Disorders of the gene realization program.