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1. Accidental cell death
Although the causes of accidental cell death are
many, biochemical and structural alterations are common. These alterations are
studied in details in hypoxic cell death, cell death by free radicals and cell
death by bacteria and viruses. In all these cases, two changes are common-
1) Loss of
cell membrane integrity and
2) Acute
cellular swelling
2.
Hypoxic cell injury
In normal condition
|
|
In case of hypoxia
Disturbance of mitochondria
↓
No ATP production
↓
Disturbance of energy
dependent active ionic process
↓
Loss of selective
permeability of cell
↓
Influx of Na and Ca into
cell and leak out of K and Mg from cell
↓
Increase in osmotic pressure
↓
Influx of water
↓
Acute cellular swelling
In transient period
Glycolytic pathway
↓
ATP production
↓
Production of lactic acid
↓
Reduction of pH
of cell
↓
Inhibition of
phosphofructokinase enzyme
↓
No glycolytic pathway, No
ATP
↓
Decreased pH
causes clumping of the nuclear chromatin and inhibits synthesis of RNA
In Ca influx
Influx of Ca in cell
↓
Reaction of Ca with
phosphate
↓
Initiation of phospholipase
enzyme activity
↓
Loss of phospholipid of cell
membrane
↓
Loss of integrity of cell
membrane
↓
Cell death ultimately
3. Cell injury induced by free radicals
Most of the free radicals that cause cell injury are
the toxic metabolites. Free radicals are-
-
Superoxide
-
Hydrogen peroxide
-
hydroxyl ion
Free radicals inactivate cellular enzymes and damage
the DNA of the cell. Ultimately there is acute cellular swelling.
4. Cell injury induced by chemicals
The exogenous chemicals induce cell injury and death
by either of the two mechanisms-
a. Binding directly to
structures or reactive chemicals of cellular organelles
↓
Damage of cell membranes or
the ability of cell to generate ATP
↓
Loss of homeostasis and normal function.
Or,
b. Transformation of
chemicals to more reactive metabolites
↓
Production of free radicals
↓
Permanent membrane damage and cell death
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