Any external or internal factor that disrupts homeostasis can cause cell injury. The most common cause of cell injury is hypoxia, which is a lack of oxygen that prevents aerobic respiration. Hypoxia can be caused by ischemia, a reduction in blood flow; hypoxemia, low oxygen levels in the blood; or a decreased oxygen-carrying capacity in the blood due to conditions like anemia. Other common causes of cell injury include physical insults like trauma or radiation; chemicals and drugs; inflammation; genetic abnormalities; and nutritional imbalances.

1. Any external or internal agent that acts
over the cells and affect their capacity to
keep the state called homeostasis.
INJURY AGENT

2. Causes of cell injury
• Hypoxia and ischemia
• Physical agents
• Chemical agents and drugs
• Inflammation
• Genetic derangements
• Nutritional imbalances

3. Hypoxia is a deficiency of oxygen, which
causes cell injury by reducing aerobic
oxidative respiration.
It is the most common cause of cell injury.
.
Hypoxia

4. Causes of hypoxia
Ischemia
Hypoxemia
Decreased O2- carrying capacity of blood

5. Ischemia
Ischemia is a reduction of blood flow, compromises the supply not only
of oxygen, but also of metabolic substrates, including glucose. Usually
as a consequence of mechanical obstruction in the arterial system, fall
in blood pressure or loss of blood

6. Hypoxemia
Low partial pressure of O2 in blood (PaO2<60 mmHg,
SaO2<90%)

7. Decreased O2-carrying capacity arise with Hb loss or
dysfunction.
Anemia
CO poisoning ( smoke from fires and exhaust from cars or
gas heaters)
Methemoglobinemia

8. Physical agents
• Mechanical trauma (e.g. road accidents);
• Thermal trauma (e.g. by heat and cold);
• Electricity;
• Radiation (e.g. ultraviolet and ionising);
• Rapid changes in atmospheric pressure.

9. Chemicals and Drugs
• Chemical poisons such as cyanide, arsenic,
mercury;
• Strong acids and alkalis;
• Environmental pollutants;
• Insecticides and pesticides;
• Oxygen at high concentration;
• Hypertonic glucose and salt;
• Social agents such as alcohol and narcotic
drugs;
• Therapeutic administration of drugs.

10. Infection agents
• Bacteria;
• Rickettsiae;
• Viruses;
• Fungi;
• Protozoa;
• Metazoa;
• Other parasites.

11. Immunologic reaction
Immunity is a “double-edged sword”
--- it protects the host against various
injurious agents but it may also turn lethal
and cause cell injury e.g.
• Hypersensitivity reactions;
• Anaphylactic reactions;
• Autoimmune reactions.

12. Genetic Derangements
Genetic defects as causes of cell injury are of
major interest to scientists and physicians
today.
• The genetic injury may result in a defect
caused by a chromosomal abnormality (e.g. the
congenital malformations associated with Down
syndrome).
• Variations in the genetic makeup can also
influence the susceptibility of cells to injury by
chemicals and other environmental insults.

13. Nutritional imbalances
A deficiency or an excess of nutrients may result
in nutritional imbalances.
• Nutritional deficiency diseases may be due to
overall deficiency of nutrients (e.g. starvation), of
protein calorie (e.g. marasmus, kwashiorkor), of
minerals (e.g. anaemia), or of trace elements.
• Nutritional excess is a problem of affluent
societies resulting in obesity, atherosclerosis,
heart disease and hypertension.