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

Cell injury 

Content 

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

Causes:

−        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