Cell injury

11.1. What is cell injury and what principles of its classification exist?

Cell injury is a typical pathological process which is caused by action of pathogenic matters and reveals as the breaches of intracellular homeostasis which lead to violation of structural integrity of a cell and its functional abilities.

There are several classifications of cell injury types:

1) acute and chronic (depending on speed of development and expressiveness of main reveals of cell injury);

2) convertible and inreversible (depending on a degree of disruption of an intracellular homeostasis);

3) mitotic and interphase (depending on the period of life cycle on which action of the injuring agent have place);

4) violent and cytopathic (depending on initiating pathogenetic mechanisms of cell injury).

11.2. What factors can cause the cell injury?

Direct (primary) cell injury results from direct action on a cell such factors as:

1) the physical nature (mechanical trauma, high and low temperature, radiation, etc.);

2) the chemical nature (an acid, alkalis, low-molecular organic substances, enzymes, etc.);

3) the biological nature (viruses, bacteria, the simplest).

Mediated (secondary) cell injury arises as consequences of primary violations of the homeostasis of organism (hypoxia, acidosis and alkalosis, hyperosmia and hyposmia, hypoglycemia, etc.).

11.3. What attributes has the cell injury?

There are following attributes of cell injury:

1. Structural. Are found out with the help of histological and electron-microscopic methods of research and they are studying subject of pathological anatomy.

2. Functional. They are: violations of electrophysiological processes (depolarization of plasmatic membrane, change of properties of excitability and conductivity, development of parabiosis); breaches of contractility, exocytosis and endocytosis; violations of cellular division, intercellular contacts and interactions; changes in cell perception of nervous and humoral regulatory influences.

3. Physical and chemical which include violations of the cellular colloids (reduction of a degree of dispersivity of colloids of cytoplasm and nucleus, increase of viscosity of cytoplasm, change sorption properties in relation to vital dyes) and water and electrolyte imbalance (increasing of concentration in cytoplasm of sodium and calcium ions and reduction of concentration of potassium ions, edema of cell and its organoids, accumulation of hydrogen ions - acidic cell injury).

4. Biochemical: 1) the reduction of concentration of macroergic substances - phosphocreatine and adenosine triphosphate - and increase in concentration of their products hydrolytic splitting - creatine, adenosine diphosphate, adenosine monophosphate, inorganic phosphate; 2) inhibition of tissue breath; 3) decoupling of oxidation and phosphorylation; 4) activation of glycolysis; 5) activation of processes of proteolysis; 6) increasing of desamination intensity.

5. Thermodynamic. It is decompartmentalisation, i.e. violation of relative isolation of endocellular compartments; conformational changes of macromolecules occurring in a direction of the most favorable thermodynamic condition (denaturation); disintegration of large (more complex) molecules on little (less complex); alignment of concentration gradients between cellular compartments, and between cytoplasm and the extracellular environment.

11.4. What are the essential differences between two pathogenic variants of cell injury: violent and cytopathic?

Violent cell injury develops at action on initially healthy cell of physical, chemical and biological factors which intensity exceeds usual influences to which the cell is adapted.

Cytopathic cell injury develops in case of previously breaches of protective-compensatory homeostatic mechanisms of a cell. In this case injury of abnormal (ill) cells initiates by such degree of influence, which is natural for normal (healthy) cells. Cytopathic variant includes all kinds of cell injury caused by absence of any components necessary for it (under hypoxia, starvation, hypo- and avitaminosises, antioxidant insufficiency, genetic defects, breaches of nerve trophic, etc.).

11.5. What molecular mechanisms can take place in pathogenesis of cell injury?

There are 6 groups of molecular mechanisms which play important role in pathogenesis of cell injury:

1. Lipid mechanisms (LPO, activation of membranous phospholipases, detergent action of free fatty acids).