Cell Injury, Types, Mechanisms, and Adaptation Quiz

Study Notes

Cell injury occurs when the integrity and functions of cells are compromised. This can happen due to a variety of reasons, both from outside (exogenous) and inside (endogenous) the body. Here, we discuss the causes, types, mechanisms, and adaptation of cell injury, along with the cell death pathways.

Causes of Cell Injury

Cells can be damaged by numerous causes, which can broadly be classified into two categories:

Exogenous causes: These include physical trauma, exposure to harmful chemicals, infectious agents like viruses or bacteria, ionizing radiation, and extreme temperatures.
Endogenous causes: These include genetically inherited disorders, aging processes, and internal biochemical imbalances within the cells themselves.

Types of Cell Injury

There are several ways to classify the type of cell injury, depending on the severity and reversibility of the damage. Some common types of cell injury include:

Swelling (Edema): This occurs when water enters the cytoplasm, causing expansion of the cell.
Shrinkage: This happens when water leaves the cell, making it smaller.
Altered cell structure: Changes in the shape or organization of cell components can impair its function.
Leakage of cellular contents: Cells lose vital materials like proteins and lipids when their membranes are damaged.
Inflammation: An inflammatory response occurs when the immune system recognizes and attempts to repair the damaged tissue.

Mechanisms of Cell Injury

Several key mechanisms trigger cell injury, regardless of the specific cause. These include:

ATP (Adenosine Triphosphate) Depletion: ATP is the energy currency of cells. When ATP levels drop, the cell can no longer carry out necessary functions.
Membrane Permeabilization: Damage to the cell membrane allows uncontrolled movement of ions and molecules in and out of the cell, affecting its physiology.
Disruption of Biochemical Pathways: Alterations in intracellular processes can disrupt normal cell functioning and survival.
DNA Damage: Direct or indirect harm to DNA can lead to mutations, impaired gene expression, and potentially, cell death.

Cell Adaptation to Injury

When cells experience injury, they employ various coping mechanisms to try and survive, including:

Autophagy: A process whereby cells break down their own damaged organelles and recycle the nutrients.
Apoptosis: Programmed cell death, triggered by signals indicating severe cell damage or abnormalities.
Necroptosis: Another form of regulated cell death initiated when apoptotic signaling fails or is overwhelmed.

Cell Death Pathways

If cells cannot repair the damage or adapt effectively, they may undergo programmed cell death. There are three main cell death pathways:

Apoptosis: Characterized by condensed chromatin, fragmentation of the nucleus, and the formation of apoptotic bodies, which are engulfed by nearby cells.
Necrosis: A passive form of cell death resulting from severe injury, characterized by swollen mitochondria, broken cell membranes, and release of cellular contents.
Autophagic cell death: A novel form of cell death involving extensive autophagy, which leads to cell demise without any apparent inflammation.