Difference Between Reversible and Irreversible Cell Injury

The main difference between reversible and irreversible cell injury is that the reversible cell injury can return to the normal conditions by altering the homeostasis of the cell whereas the irreversible cell injury cannot return to the viable conditions as the cell has passed the point of no return.

Reversible and irreversible cell injury are two types of cell injury that can lead to cell death. Furthermore, reversible cell injury results in cellular swelling and fat accumulation while irreversible cell injury results in necrosis or apoptosis. 

Key Areas Covered 

1. What is Reversible Cell Injury
     – Definition, Characteristics, Response
2. What is Irreversible Cell Injury
     – Definition, Characteristics, Response
3. What are the Similarities Between Reversible and Irreversible Cell Injury
     – Outline of Common Features
4. What is the Difference Between Reversible and Irreversible Cell Injury
     – Comparison of Key Differences

Key Terms

Apoptosis, Cellular Fatty Change, Cellular Swelling, Irreversible Cell Injury, Necrosis, Reversible Cell Injury 

What is Reversible Cell Injury 

Reversible cell injury is a type of cell injury that can return to the regular state of the cell. The range of structure and function of a particular type of cell is kept in balance with respect to the challenges presented by both internal and external environment of the cell such as the food requirements, metabolic pathways, genetic information, etc. This balance is called homeostasis or the ‘steady state’. The cell has a variety of systems that maintain the steady state. Some of them are cell membrane, excretion of exogenous chemicals, defence mechanisms of the host (immune system, inflammation, phagocytosis), repair mechanisms (antioxidants, DNA repair mechanisms), etc. When the cell faces an excessive stimulus, it has the ability to adapt to the situation either by increasing the workload (hypertrophy) or decreasing the workload (atrophy). The cell may also alter its morphology, growth pattern or metabolism.  

In a short-acting or sub-lethal cell injury, this alteration of the steady state may remove the injurious agents in many instances, replenishing the cell and regenerating the lost organelles. This type of cell injuries is called reversible cell injury. The two signs of reversible cell injury are cellular swelling and cellular fatty change that can be recognized under a light microscope.  

Cellular Swelling  

Cells swell when they are unable to balance ionic and fluid homeostasis, which is a result of the loss of function of the energy-dependent ion pumps on the cell membrane. Cell swelling is the first manifestation of most forms of cell injury. Small, clear vacuoles and distended and pinched off segments of ER can be observed in the swelled cells under the microscope. 

Figure 1: Cell Membrane

Cellular Fatty Change 

Fatty change occurs in hypoxic, toxic or metabolic injuries. It is characterized by the appearance of lipid vacuoles in the cytoplasm. These changes are encountered by the cells involved in the fat metabolism such as hepatocyte and myocardial cells. 

Some ultrastructural changes can also be observed in a reversible cell injury. 

Ultrastructural Changes 

What is Irreversible Cell Injury 

Irreversible cell injury is one of the more severe and long-lasting cell injuries that lead to cell death by necrosis or apoptosis. It occurs when the cell has passed the point of no return. The characteristic features of irreversible cell injury are swelling of the mitochondria and lysosomes, damage to lysosomal membranes leading to the leakage of enzymes, damage to cell membrane, and increased acidosis in the cellular environment. The two types of cellular responses occurred by irreversible cell injury are necrosis and apoptosis.  

Necrosis 

Necrosis is a type of cell death characterized by cytoplasmic swelling, damage to cell membrane, and organelle breakdown. The components of the cytosol are leaked into the extracellular space as a result of necrosis. The six types of necrosis are coagulative necrosis, caseous necrosis, liquefactive necrosis, gangrenous necrosis, fat necrosis, and fibroid necrosis. 

Figure 2: Necrosis and Apoptosis

Apoptosis 

Apoptosis is the programmed cell death of the harmful cells. The process depends on the energy and is mediated by the enzyme caspase that cleaves specific proteins in the cytoplasm and nucleus.  

Similarities Between Reversible and Irreversible Cell Injury 

• Reversible and irreversible cell injury are two types of conditions in which the regular homeostasis of the cell is disturbed. 
• They induce stress in the cells. 
• Both types of injuries can lead to cell death.  

Difference Between Reversible and Irreversible Cell Injury 

Definition 

Reversible cell injury refers to a type of cell injury that can return to the steady state by altering cellular conditions while irreversible cell injury refers to one of the severe types of cell injury that leads to the cell death. 

Significance 

Reversible cell injury can return to the normal position while irreversible cell injury has passed the point of no return. 

Characteristics 

Reversible cell injury is sub-lethal and short-acting while irreversible cell injury is lethal and long-lasting. 

Causes 

The lack of oxygen (hypoxia or ischemia) or blood flow to the cells cause reversible cell injury while immunological responses or viral infections cause irreversible cell injury.  

Response 

Reversible cell injury results in cellular swelling and fat accumulation while irreversible cell injury results in necrosis and apoptosis.

Recovery 

Reversible cell injury can be treated with drugs while irreversible cell injury leads to permanent cell loss. 

Conclusion  

Reversible cell injury is a condition that can return to the steady state. Its cellular response is characterized by cell swelling and fatty accumulation. On the other hand, the irreversible cell injury cannot return to the viable state of the cell. It leads to cell death by necrosis or apoptosis. The main difference between reversible and irreversible cell injury is the ability to return to the normal position and cellular response.

Reference:

1. “Cell Injury.” Humpath.com – Human Pathology, Available Here
2. “Reversible Cell Injury.” Humpath.com – Human Pathology, Available Here

Image Courtesy:

1. “Cell membrane drawing-en” By This SVG image was created by Medium69.Cette image SVG a été créée par Medium69.Please credit this : William Crochot – NIST (CC BY-SA 4.0) via Commons Wikimedia    
2. “Structural changes of cells undergoing necrosis or apoptosis” By National institute on alcohol abuse and alcoholism (NIAAA) – File:Structural changes of cells undergoing necrosis or apoptosis.gif; (pubs.niaaa.nih.gov) (Public Domain) via Commons wikimedia