Cell injury - B. pharma 2nd year Pathophysiology notes pdf

Cell injury 


Cell injury 

  • Principle involved in cell injury 
  • Etiology of cell injury 
  • Cellular adaptation 

At the end of this PDF, student will be able to

  • Define “ Cell injury”
  • Explain basic principles of cell injury and cell adaptation
  • Describe the etiology of cell injury   
  • Explain various forms of cellular responses to cell injury 
  • Describe various methods of cellular adaptation 

Cell injury

Pathology derived from two Greek words - Pathos – Suffering, Logos ̶ Study

“Scientific study of structure and function of the body in diseases”

Pathophysiology - Pathos – suffering, Physiology ̶ study of normal function

“Study of disordered function or breakdown of homeostasis in diseases”

Basic Principles of Cell Injury and Adaptation    

Cell injury - a variety of stresses a cell encounters as a result of changes in its internal and external environment

Cellular response to stress depends on

·         Types of cells and tissues involved

       Extent and type of cell injury

Etiology of cell injury

Cells may be broadly injured by two major ways:

A. By genetic causes

B. By acquired causes -

       Hypoxia and ischemia

       Physical agents

       Chemical agents and drugs

       Microbial agents

       Immunologic agents

       Nutritional derangements

       Psychological factors

Hypoxia and ischemia

       Deficiency of oxygen or hypoxia - failure to carry out activities

       Common cause of cell injury


        Reduced supply of blood to cells (ischemia)

        Anemia, CO poisoning, cardio respiratory insufficiency and increased demand of tissues

Physical agents

       Mechanical trauma (e.g. road accidents)

       Thermal trauma (e.g. heat and cold)


       Radiation (UV and ionizing)

       Rapid changes in atmospheric pressure

Chemicals and drugs

       Chemical poisons such as cyanide, arsenic and 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

Microbial agents

Infections caused by







       Other parasites

Immunologic agents

       Immunity protects the host against various injurious agents

       May also turn lethal and cause cell injury

Examples -

          Hypersensitive reactions

          Anaphylactic reactions

          Autoimmune diseases

          Immunologic diseases

Nutritional derangements

Nutritional deficiency diseases of

       Overall deficiency of nutrients (starvation)

       Protein calorie malnutrition (kwashiorkor, marasmus)

       Minerals (anemia) or of trace elements

       Nutritional excess - obesity, atherosclerosis, heart diseases and hypertension

Psychological factors

       Mental stress







Various forms of cellular responses to cell injury

Cellular adaptation

       Cell may adapt to the changes expressed morphologically

       Revert back to normal after the stress is removed

Reversible cell injury

       Mild to moderate stress; injured cells may recover

Irreversible cell injury

       Persistent injury; cell death may occur

Sub cellular changes 

       Residual effect of reversible cell injury may persist in the cell

       Cell injury at sub cellular level

Intracellular accumulation

       Persistence of reversible cell injury; metabolites may accumulate in the cells

Cellular adaptation


       Reduction of the number and size of parenchymal cells of an organ or its parts which was once normal

Causes – 

Physiological cause or pathological cause

       Physiological atrophy

       Pathological atrophy

Physiologic atrophy

       Normal process of aging of some tissues

       Could be due to loss of endocrine stimulation or arteriosclerosis


       Atrophy of –

       Lymphoid tissue in lymph nodes

       Gonads after menopause


Pathologic atrophy

       Starvation atrophy

       Ischemic atrophy

       Disuse atrophy

       Neuropathic atrophy

       Endocrine atrophy

       Pressure atrophy


Increase in size of the parenchymal cells

Results in the enlargement of the organ or tissue

No change in number of cells


-    Physiologic or pathologic

-          By increased functional demand

-          Or hormonal stimulation

Physiologic hypertrophy

          Enlargement of uterus in pregnancy

Pathologic hypertrophy

          Hypertrophy of heart  Systemic hypertension  Aortic valve disease Mitral insufficiency

          Hypertrophy of skeletal muscles -  hypertrophised muscles in athletes and manual labourers


       Increase in number of parenchymal cells

       Enlargement of organ or tissue

Labile cells:

-    Epithelial cells of skin and mucous membrane

-          Parenchymal cells of  liver, pancreas, kidneys adrenals and thyroid

-          Nerve cells, heart muscles and skeletal muscles – less capacity

Physiological hyperplasia

       Female breast at puberty, pregnancy and lactation

       Pregnant uterus

       Prostrate hyperplasia in old age

       Compensatory hyperplasia – after hepatectomy

Pathological hyperplasia

       Endometrium following  excess of estrogen

       Granulation tissue formation during wound healing


       Irreversible change

       One type of epithelial or mesenchymal  adult cell to another   type of epithelial or mesenchymal cells

       Response to abnormal stimuli

Epithelial metaplasia

       In bronchus  in chronic smokers

       Columnar metaplasia in Barrett’s oesophagus, in which there is change of normal squamous epithelium to columnar epithelium

Mesenchymal metaplasia

       Cartilage of larynx and bronchi in elderly people

       Scar of chronic inflammation of prolonged duration

       Fibrous stroma of tumour


       Disordered cellular development

       Accompanied with metaplasia and hyperplasia

       Referred to as atypical hyperplasia


       Increased number of layers of epithelial cells

       Disorderly arrangement of cells from basal layer to the surface layer


       Cell injury is the change in internal and external environment of cell due to variety of stress

       Cell responds to stress either by adaptation or undergoing cell injury

       Cell injury could be reversible or irreversible

       Cell adapts to the changes by undergoing atropy, hypertrophy, metaplasia, hyperplasia, dystrophy

       Causes of cell injury can be categorized as genetic and acquired 

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