Cell injury and Adaptation complete note 2021 - Diseasecare

When cells fail to adapt to stress, they go through a series of alterations that lead to cell damage. 

Types of cell injury

The affected cells may recover from the injury called Reversible injury;(if cell may die, it is called irreversible injury,

All types of tissue injury begin with cellular molecular or structural changes.The normal cell undergoes modification in its structure and function in response to changes in demand and stress.

Until these stresses become too severe the cell is to maintain narrow range of structure and function so called- homeostasis.The cell can adapt if it is subjected to severe physiological pressures or certain pathological stimuli. Atrophy, hypertrophy, and hyperplasia are the three main cellular adaptations. The cell in development will not adapt or will have its adaptive capacity exceeded if it does not adapt. Cell injury is reversible up to a point, but severe or chronic stress causes irreparable injury, and the cell dies.In cardiac muscle, the link between adaptive, reversible, and irreversible cell injury can be seen. When myocardial fibres are subjected to greater load, such as in the case of hypertension, the cell adjusts and undergoes hypertrophy, or growth in size, and the heart is able to adequately pump against the increased stress structure.


Coagulative necrosis is a morphological characteristic of cell death induced by denaturation of cytoplasmic proteins and the destruction of cell organelles. Apoptosis is the death of a cell as a result of physiological or pathological survival processes. The main cause is condensation and fragmentation. Apoptosis is different from necrosis in terms of how it is induced.

Whether a specific stress, which induces adaptation or causes reversible or irreversible injury resulted in morphological changes, depends on many factors related to the cell only which are , differentiation, nourishment from the bloodstream and the cell's prior state

Causes of cell injury 

 Stresses that generate morphological changes in the cell, ranging from physical damage to gene abnormalities, are the root of many metabolic illnesses. The broad categories of various causes of cell injury and adaptation include: (A) Acquired and (B) Genetic causes. The acquired causes are: 1. Hypoxia and Ischemia 2. Chemical agents and drugs 3. Physical agents 4. Microbial agents 5. Immunologic agents 6. Nutritional imbalance 7. Aging. Gene faults are to blame for the genetic reasons.

(A) Acquired causes

1. Hypoxia and Ischemia: 

To generate energy and perform metabolic functions, cells in various tissues require oxygen. It occurs when arterial flow or venous drainage is restricted due to vascular disease or thrombi, and when blood oxygenation is inadequate due to cardio-respiratory failure. Hypoxia can also be caused by a reduction in the blood's oxygen carrying capacity, as in anaemia or carbon monoxide poisoning, when the creation of a stable carbon monoxyhemoglobin blocks oxygen transport.

2. Chemicals and drugs:

Chemical poisons, strong acids and alkalis, environmental pollutants, insecticides and pesticides, high-concentration oxygen, hypertonic glucose and salts, alcohol and narcotic medications, and drug therapeutic delivery are all major causes of cellular adaptation, injury, and death. Poisonous compounds cause significant cell damage, and in certain cases, death, in living beings. The mode of action is to interfere with a cell's essential functions, such as membrane permeability, osmotic balance, or the functional capability of an enzyme or cofactor.

3. Physical agents:

Mechanical trauma is one of the physical factors that causes cell harm (Road accident) The effects of thermal stress (heat and cold), electricity, radiation, and rapid changes in atmospheric pressure on the cell are numerous.

4. Microbial agents: 

Bacteria, rickettsiae, viruses, fungi, protozoa, metals, and other parasites are just some of the microbes that can cause cell death in different ways.

5. Immunologic reactions: 

The immune system works in the defense against biological hence immune response reactions such as hypersensitivity reactions, anaphylactic autoimmune diseases may cause cell injury. Anaphylactic reactions to a foreign ph example and reaction to endogenous self-antigens thought to be responsible for- autoimmune diseases.

6. Nutritional imbalance: 

Nutritional deficiency causes cell death, A deficiency or of nutrients may result in nutritional imbalances. Starvation, protein calorie shortfall (Marasmus, Kwashiorkor), mineral deficiency (anaemia), and trace element insufficiency are all examples of nutritional deficiency illnesses. High-fat diets induce atherosclerosis and obesity.

7. Aging:

 Cellular ageing may be triggered by the accumulation of harm produced by free radicals over time.Lipofucin a brownish-yellow granular intracellular pigments accumulates in a variety of tissues of heart, liver and brain as a function of age. The pigment is made up of lipid and protein complexes that are formed when polyunsaturated lipids in the subcellular membrane are oxidised.

 (B) Genetic causes

1. Developmental defect: 

Mistakes in the process of morphogenesis Developmental defects are a group of abnormalities that occur during fatal life as a result of morphogenesis errors.

2 Cytogenic defects: 

Chromosomal abnormalities are chromosomal structural or numerical abnormalities. Numerical abnormalities are caused by an increase or decrease in the number of total chromosomes.The abnormalities that occur due to changes in appearance of chromosomes is called structural abnormalities.

3. Single-gene defects (Mendelian syndrome):

Mendelian syndrome or condition refers to a defect that follows conventional mendelian inheritance patterns. There is a single gene mutation that is responsible for the problem.

4. Disorders with multifactorial inheritation:

Multiple genes combined with lifestyle and environmental factors are a cause for concern. Complex or multifactorial disorders, such as heart disease, diabetes, and obesity, are caused by a number of contributing factors.


Injury to cell may have many causes. Due to the intimate interdependence of macromolecules, enzymes, and organelles inside the cell, it may be impossible to distinguish the primary target of injury. The mechanism and location of cell harm with injurious substances are well known. In such cases, oxygen plays a critical role in cell injury. Ischemia, which is caused by a lack of oxygen, is the pathogenesis of cell injury. Clostridium perfringens (anaerobic bacterium) has elaborate phospholipids that attack phospholipids in cell membranes in partially decreased active oxygen species. These "free radical species" cause lipid oxidation and other cell-structure-damaging consequences.



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