Structural and functional changes is produced by pathology is called cell injury. There are two types of cell injuries:

• Reversible (caused by mild stressors)
• Irreversible (caused by moderate or severe stressors)

CAUSES OF CELL INJURY

1. Ischemia
2. Infectious reactions
3. Immune reactions
4. Chemical factors
5. Physical factors
6. Psychosocial factors
7. Nutritional factors
8. Cellular aging

1. Ischemia

It occurs when there is decreased blood flow or increased metabolism in the cells. Lack of blood flow can leads to nutritional deficit and decreased removal of waste products from the tissues. Partial lack of oxygen is called hypoxia and complete absence of oxygen is called anoxia. Ischemia is the major cause of Myocardial infarction and cerebrovascular accidents.

2. Infectious reactions

Commonly bacteria and viruses can cause infections in human body. These microbes enter into the host cell and release exotoxins and endotoxins. Then, it cause damage, degradation of cells and spread of infections across the cells. When micro-organism or their toxin is present in the blood is called sepsis. It can affect blood vessels and cause septic shock.

3. Immune reactions

Although immune system acts against foreign bodies, sometimes it acts against body tissues (immunity is double edged sword). It can range from mild allergy (hypersensitivity) to life-threatening anaphylactic reactions or autoimmune disorders. For example, increased level of IgE is in allergic conditions like asthma. In this case, omalizumab is the commonly used medication for treating allergic asthma. Omalizumab binds with free IgE and lowers IgE level. Thus, it helps in treating allergies. In some cases like organ transplantation, body will not accept the foreign body (e.g. transplanted organ). To prevent this incident, surgeons prescribe immunosuppressants which lowers immunity or immune reactions.

4. Chemical factors

An ever-increasing list of chemical agents and drugs may cause cell injury. Important examples include the following: Chemical poisons such as cyanide, arsenic, mercury;

• Strong acids and alkalis
• Environmental pollutants
• Insecticides and pesticides
• Oxygen at high concentrations
• Hypertonic glucose and salt
• Social agents such as alcohol and narcotic drugs
• Therapeutic administration of drugs.

5. Physical factors

Physical agents in causation of disease are as under:

• Mechanical / blunt trauma (e.g. road accidents)
• Penetrating trauma (e.g. weapons)
• Thermal trauma (e.g. by heat and cold)
• Electricity
• Radiation (e.g. ultraviolet and ionizing or irradiation of normal cells during cancer treatment)
• Rapid changes in atmospheric pressure (e.g. Barotrauma during scuba diving).

6. Psychosocial factors

Mental stress, tension, strain, overload or frustration can cause musculoskeletal pain. This is the reason, every physiotherapy assessment should be based on biopsychosocial model.

7. Nutritional factors

Deficiency or excess of nutrition can cause nutritional imbalances.

• Nutritional deficiency diseases are:
• Marasmus
• Kwashokar
• Anemia
• Nutritional excess diseases are:
• Obesity
• Atherosclerosis
• Heart diseases

8. Cellular aging

Impaired ability of the cells to undergo replication and repair. Normally, degenerative processes of tissues occur after 60 years in males and 45 years in females.

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1. Harsh mohan., General pathology.
2. Catherine cavellaro Goodman., pathological implications for physical therapist., fourth edition.