Cell Injury Overview

Cell Injury

• Cell injury is a process in which cells are damaged.
• The response to injury depends on the type, duration, and severity of the injury.
• The response depends on the type of cell, the cell's adaptive capacity, and the cell's genetic composition.
• Cells experience functional and biochemical abnormalities.
• Cell function is lost before biochemical and morphological changes are visible.

Introduction

• Body cells adapt to their environment.
• Homeostasis is the maintenance of a stable internal environment within acceptable limits.
• Cells adapt to physical stress (increased workload), or harmful conditions (nutrient deficiency).
• Cells maintain viability and function after adapting.
• Cell injury occurs when the capacity to adapt or stress exceeds a certain level.
• Cell injury can be reversible; cells can return to their original state.
• Irreversible injury occurs with prolonged exposure to stressors; the cell dies.
• Cell death is a normal and significant process in embryogenesis, organ development, and maintenance of homeostasis.

Causes of Cell Injury

• Hypoxia and Ischemia:
  • Hypoxia is reduced oxygen supply below physiological levels.
  • Ischemia is a reduced blood supply.
  • They are common causes of cell injury.
• Toxins:
  • Found in the environment (carbon dioxide, smoke, alcohol, drugs).
  • Some medicine at therapeutic dosages can damage cells and tissues.
  • All viruses, bacteria, fungi, and protozoa can damage cells.
• Physical agents:
  • Trauma, high temperatures, radiation, electric current.
  • Changes in atmospheric pressure can damage cells.
• Immunological Reactions:
  • Autoimmune reactions and allergic reactions damage cells.
• Genetic Abnormalities:
  • Deficiencies in functional proteins can damage cells.
• Nutritional Imbalances:
  • A major cause of cell injury.
• Aging:
  • Reduces a cell's ability to respond to stress and can lead to cell death.

Reversible Injury

• Reversible injury is a stage where impaired cell function and morphology can be eliminated if the harmful stimuli are removed.
• Cells and intracellular organelles generally swell due to water absorption.
• Cell homeostasis is disrupted during reversible injury.

Morphological Changes in Reversible Injury

• Cellular edema: clearly visible at the organ level. Paleness, increased turgor, and increased organ mass are observed during macroscopic examination. Small vacuoles are visible in the cytoplasm under a microscope.
• Fatty changes: occur in the cytoplasm of cells.
• Other changes include: increased redness of the cytoplasm, plasma membrane swelling, weakening of intercellular connections, accumulation of chromatin, and amorphous formations (myelin figures - aggregations of phospholipids).

General Principles of Cell Injury

• Cellular response to injury depends on the type, duration, and severity of the injury.
• The outcome of exposure depends on the cell type, its adaptive capacity, and its genetic makeup.
• Cell injury typically arises from functional and biochemical abnormalities within one or more major cellular components.
• Cell function often declines before detectable biochemical or morphological signs of injury appear.

Mechanism of Cell Injury (Hypoxia and Ischemia)

• Hypoxia is a decrease in oxygen supply to tissues below normal levels.
• A critical and common cause of cell injury and death.
• Reduced ATP production.
• Failure of Na+-K+ pumps.
• Glycolysis increases; lactic acid and inorganic phosphates accumulate.
• Protein synthesis decreases; lipids accumulate.
• All of these changes are reversible if the oxygen supply is restored.

Mechanism of Cell Injury (Toxins)

• Toxins cause cell injury through distinct mechanisms.
• Some toxins directly bind to crucial molecular components or organelles.
• Other toxins transform into reactive metabolites that affect cells.

Types of Hypoxia

• Anemic: decreased blood oxygen due to low hemoglobin (e.g., hemolytic anemia).
• Histotoxic: impaired oxygen use by tissues (e.g., carbon monoxide poisoning)
• Hypoxic (or ischemia): insufficient oxygen supply to the blood (e.g., drowning).
• Ischemic: reduced blood supply to cells.
• Stagnant: insufficient blood supply (e.g., circulatory failure).