1.7
Cellular Injury I: Introduction
Cellular injury occurs when a cell cannot maintain homeostasis or adapt to stressors such as hypoxia, toxins, or trauma. Depending on severity and dur…
Cellular injury happens when a cell is unable to maintain balance under stress, such as a lack of oxygen, known as hypoxia, or exposure to toxins.
When oxygen levels fall, ATP —the cell’s primary energy source —decreases, and vital cellular processes begin to fail.
Loss of ATP impairs ion pumps, such as the sodium–potassium ATPase, causing sodium and water influx, which results in cellular swelling.
While this swelling can be reversible, sustained injury leads to irreversible damage and cell death — either through necrosis or apoptosis.
Necrosis happens when a cell dies, leading to inflammation, whereas apoptosis is a programmed, controlled process that removes damaged cells in an orderly manner.
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Q1: What happens to a cell when oxygen levels drop?
When oxygen levels fall, ATP production decreases, depriving cells of their primary energy source. This impairs vital processes like ion pump function, causing sodium and water to accumulate inside the cell. The resulting cellular swelling can initially be reversible, but sustained hypoxia leads to irreversible damage and cell death.
Q2: How does ATP depletion damage cellular ion pumps?
ATP powers the sodium-potassium ATPase and other ion pumps that maintain cellular balance. When ATP levels drop due to reduced oxygen or mitochondrial dysfunction, these pumps fail to function. Sodium and water then flow into the cell uncontrolled, causing swelling and disrupting normal cellular operations.
Q3: What role do reactive oxygen species play in cellular injury?
Reactive oxygen species, including superoxide, hydrogen peroxide, and hydroxyl radicals, are generated during hypoxia and reoxygenation. These free radicals damage cellular membranes, proteins, mitochondria, and DNA, amplifying cellular dysfunction. ROS-driven mitochondrial damage further reduces ATP production and triggers cell death pathways, accelerating injury progression.
Q4: How does calcium influx contribute to cellular damage?
When ischemia or toxins disrupt membrane integrity, calcium floods into the cell cytoplasm. Elevated calcium activates destructive enzymes like phospholipases, proteases, and endonucleases that degrade cellular structures and organelles. Combined with mitochondrial damage, calcium overload accelerates the progression toward irreversible cell death.
Q5: What is the difference between necrosis and apoptosis?
Necrosis occurs when a cell dies uncontrollably, triggering inflammation and tissue damage. Apoptosis is a programmed, controlled process that removes damaged cells in an orderly manner without inflammation. Both result from severe or sustained cellular injury, but apoptosis is a regulated response while necrosis is chaotic cell death.
Q6: Why is membrane damage an early feature of cellular injury?
Membrane damage increases permeability, allowing harmful substances like calcium to enter the cell uncontrolled. Lysosomal membrane rupture releases digestive enzymes that cause self-digestion and structural breakdown of cellular components. Early membrane compromise amplifies other injury mechanisms and accelerates progression toward irreversible damage and cell death.
Q7: Can cellular swelling from injury always be reversed?
Initial cellular swelling from ATP depletion and ion pump failure can be reversible if the stress is removed quickly and homeostasis is restored. However, sustained injury leads to irreversible damage involving mitochondrial dysfunction, protein misfolding, and DNA damage. Once cells reach this point, recovery is impossible and cell death becomes inevitable.