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Cells encounter
many stresses as a result of changes in their internal and external
environments.
The patterns of
response to this stress constitute the cellular basis of disease.
If an injury
exceeds the adaptive capacity of the cell, it dies.
Pathology is the
study of cell injury and the expression of a pre-existing capacity to
adapt to such injury, on the part of either injured or intact cells.
Causes
of Cellular Injury:
Diagram showing
Structural Changes in
Reversible and Irreversible Cell Injury: click here
1. Lack of O2 supply (Hypoxia)- e.g.
Ischemia, Cardio-respiratory failure.
2. Loss of O2 carrying capacity of blood
as in Anemia, CO poisoning
3. Physical agents - heat, cold,
radiation etc.
Hypothermia
;
Hyperthermia.
4. Chemical agents including - acids,
alkali, drugs, insecticides etc.
5. Infections - bacteria, virus, fungus,
parasites etc.
Infectious Disease Online
6. Immunologic reactions such as
autoimmune diseases
7. Genetic disorders: chromosomal
alteration or mutation - e.g. Sickle cell disease
8. Nutritional injury [e.g.
Protein Calorie Malnutrition (Kwashiorkor),
Vitamin A Deficiency causing Xerophthalmia,
Keratomalacia and Night blindness].Nutritional Pathology Online
Normal cell contains higher K+ and low
Na+ than extra-cellular fluid maintained by Sodium Pump (ATP dependent
Cell membrane Transport system).
A cell needs ATP to maintain its normal
metabolic functions:
i) Membrane transport system (Failure of
Na pump causes swelling of cell).
ii) Protein synthesis (Reduced protein
synthesis causes lipid deposition).
iii) Phospholipid turnover (lack of
peroxidation causes damage of cell membrane).
Lesions:
Gross features:
The organ involved is pale and increased
in weight.
Microscopic features:
Injured cells
show cellular swelling due to increased volume of water, sodium and
potassium and are characterized by a large, pale cytoplasm and a
normally located nucleus called
hydropic or
vacuolar degeneration.
Lipid vacuoles appear later mainly in cells participating in metabolism
(e.g. hepatocytes, myocardial cells).
Ultrastructural Structures:
i) Plasma membrane shows alteration,
blebbing, blunting or distortion of microvilli and loosening of
intercellular attachment.
ii) Mitochondria show swelling and there
is appearance of phospholipid-rich amorphous densities.
Reversible cell injury:
These are the
pathologic changes that can be reversed when the stimulus is
removed or if the cause of injury is mild.
Reversible cell
injury is characterized by the cellular swelling with accumulation of
fat, protein and other substances e.g. steatosis, cholesterosis,
glycogen, and others. If the injury persists the changes become
irreversible.
Irreversible
cell injury (Cell Death):
Injury
to cell causes:
1. Change in mitochondria : Swelling and
abnormal cristae.
2. Damage of the plasma membrane causing
leakage of soluble enzymes (detected in serum in myocardial injury).
3. Fragmentation of the nuclear membrane.
Cell death:
This means the series of morphological changes which occur in relation
to a cell or group of cells following lethal injury. It is the element
of time and the action of enzymatic degradation and protein denaturation
which determine the differences between functional cell death and cell
death as morphologically defined.
Two main types:
1. Necrosis
2. Apoptosis

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