Cell Adaptive Changes

When cells are stressed, they can undergo several adaptive changes. These changes help the cell adapt to new conditions and can be classified into four main types: atrophy, hypertrophy, hyperplasia, and dysplasia.

Atrophy

• Definition: Reversible reduction in the size of the cell.
• Mnemonic: "Use it or lose it."
• Causes:
  • Disuse
  • Insufficient blood flow
  • Malnutrition
  • Denervation
  • Reduced endocrine stimulation
• Example: Muscular atrophy after several days of disuse.

Hypertrophy

• Definition: Increase in cell size due to increased workload.
• Types:
  • Pathologic: Can be a disease state (e.g., hypertrophy of the heart).
  • Physiologic: Normal adaptation (e.g., muscular hypertrophy from vigorous exercise).

Hyperplasia

• Definition: Increase in the number of cells.
• Causes:
  • Increased workload
  • Hormonal stimulation
  • Decreased tissue
• Example: Breast enlargement and hyperplasia during pregnancy.

Metaplasia

• Definition: Replacement of one adult cell type by another adult cell type that can better endure the stress.
• Cause: Chronic inflammation or irritation.
• Example: Barrett's esophagus, where squamous epithelium is replaced by columnar epithelium in response to chronic irritation by gastric acids.

Dysplasia

• Definition: Disorganized cell growth resulting in cells of abnormal size, shape, and appearance.
• Possible Consequence: Can precede carcinogenic changes.
• Example: Cervical dysplasia, referring to abnormal cells on the surface of the cervix.