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

Causes 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)

•       Electricity

•       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

•       Bacteria

•       Fungi

•       Protozoa

•       Metazoa

•       Rickettsiae

•       Virus

•       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

•       Strain

•       Anxiety

•       Overwork

•       Frustration

•       Alcoholism

•       smoking

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 Atrophy

•       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

Examples-

•       Atrophy of –

•       Lymphoid tissue in lymph nodes

•       Gonads after menopause

•      Brain

Pathologic atrophy

•       Starvation atrophy

•       Ischemic atrophy

•       Disuse atrophy

•       Neuropathic atrophy

•       Endocrine atrophy

•       Pressure atrophy

Hypertrophy

Increase in size of the parenchymal cells

Results in the enlargement of the organ or tissue

No change in number of cells

Causes:

–    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

Hyperplasia

•       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

Metaplasia

•       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

Dysplasia

•       Disordered cellular development

•       Accompanied with metaplasia and hyperplasia

•       Referred to as atypical hyperplasia

Examples

•       Increased number of layers of epithelial cells

•       Disorderly arrangement of cells from basal layer to the surface layer

Summary

•       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

Cell injury PDF Notes