What is cell injury and cell death and what are its main causes??

in #science6 years ago

The normal cell has a narrow range of function and structure to handle normal physiological demands. When there is excessive physiological or pathological stress, the cell undergoes adaptation.

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If stress exceeds the limits of adaptive capability, a sequence of events follows, termed as cell injury. The cell injury is reversible upto a certain point, but if the stress persists or severe enough from the beginning, the cell reaches the point of no return and suffers irreversible cell injury and cell death.

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Causes of Cell injury and Cell death:

The main causes of cell injury and cell death are the following:
• Anoxia and ischemia
• Physical injuries
• Injuries caused by chemical agents
• Injuries caused by biological agents
• Injuries caused by immune mechanisms
• Genetic effects
• Nutritional imbalance
• Aging

Whatever the cause of injury may be, the following four functions of the cell are disturbed resulting in derangement of metabolic and chemical functions of the cells.

  1. Aerobic respiration involving production of ATP.
  2. Synthesis of enzymic and structural proteins
  3. Reproduction
  4. Maintenance of the integrity of cellular membranes on which the ionic and osmotic homeostasis of the cell.

Anoxic causes:

Anoxia is commonly due to loss of blood supply. The arterial blood supply is cut off or venous flow is blocked. It may be either due to arterial diseases or intravascular clots. Heart attacks, myocardial infarction and strokes are best examples.

In other cases anoxia may be due to less oxygen carrying capacity of blood as in anemia and carbon mono-oxide poisoning. Anoxia produces lot of changes at cellular level starting from injury, cloudy swelling, hydropic degeneration, fatty changes and ultimately death of cell.

Physical causes:

These include extremes of cold, heat, trauma, electrical and radiant energies.
Excessive cold first of all causes a compensatory vaso-constriction of blood vessels. This impairs the blood supply to the cell. This loss of blood supply is followed by injury to the vasomotor control of blood vessels resulting in the loss of fluid and blood into the tissues.

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High temperature may cause injury by inducing hyper-metabolism beyond the capacity of available blood supply and ultimately leading to excessive accumulation of acid metabolites. The radiant energy include sunlight, UV, radiation x-rays, radio isotopes and radioactive products.

Chemical agents:

Chemical agents may be exogenous or endogenous. Both of these substances produce toxic effects because they interfere with the enzyme action.

Concentrated solution of glucose and salts disturb the osmotic equilibrium of the cell and results in cell injury. A low concentration of some of these agents destroy the cell. Some of these chemical agents have got more toxic effects on certain tissues than the others. The exogenous chemical agents may be organic and inorganic.

The endogenous type of agents are those which are produced as disturbed metabolic activity of the body itself. It is also known as auto intoxication.

Biological agents:

These include bacteria, parasites and viruses. Bacteria cause injury by producing allergic response as they act as foreign body. They produce toxins or poisons which may be exotoxins or endotoxins.

Parasites include hook worms and round worms. They deprive the tissues of essential nutrients and produce mechanical injuries.
Viruses produce injury and death of cells due to competition between the cell and the agent for essential metabolites.

Immune mechanism:

This is the mechanism which is associated with the defense of the tissues against foreign substances entering the tissues. In some cases antibodies to the tissues of the individual are produced which is known as auto immunity. Whenever antigen antibody unite in the tissues, Histamine is produced which results in the injury of the cell.

Genetic derangement:

They may arise as mutation. The environmental influences such as drugs, radiation and infection may produce mutations. The genetic injury may be as gross as the congenital malformations associated with Down’s syndrome. In general the gross malformations are associated with chromosomal abnormalities and visible changes in the karyotype.

Nutritional imbalance:

It is major cause of cell injury. Protein caloric deficiency causes a large number of deaths because it affects all cells of the body.

Nutritional excess is also an important cause of cell injury and cell death. Excess of calories, carbohydrates and lipid are thought to be the causes. Obesity is also associated with nutritional excess and obesity has been shown to have important associations with the production of pulmonary disease, hypertension and cardiac disease.

References: 1 2

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