Adaptive Changes

• Adaptive changes are modifications that cells undergo in response to chronic stress or injurious stimuli, allowing them to survive and maintain function.
• These changes can be either physiological (normal) or pathological (abnormal).
• The main types of adaptive changes include atrophy, hypertrophy, hyperplasia, metaplasia, and dysplasia.

1. Atrophy

• Description:

  • Reduction in cell size and function due to decreased demand or insufficient nutrients. Cells shrink, losing organelles and reducing metabolic activity.

• Causes:

  • Disuse (e.g., muscle atrophy from immobility)
  • Denervation (e.g., muscle atrophy from nerve loss)
  • Ischemia (e.g., reduced blood supply)
  • Malnutrition
  • Loss of endocrine stimulation (e.g., menopause-related endometrial atrophy)

• Microscopic Appearance:

  • Smaller cells with fewer organelles
  • Presence of autophagic vacuoles and lipofuscin granules

2. Hypertrophy

• Description:

  • Increase in cell size due to greater functional demand or hormonal stimulation. Cells grow larger and gain more structural proteins and organelles.

• Causes:

  • Increased workload (e.g., skeletal muscle hypertrophy from exercise)
  • Hormonal stimulation (e.g., uterine hypertrophy during pregnancy)

• Microscopic Appearance:

  • Enlarged cells with more cytoplasm and larger nuclei
  • No increase in cell number

3. Hyperplasia

• Description:

  • Increase in the number of cells in a tissue or organ due to higher demand or hormonal influence.

• Causes:

  • Hormonal (e.g., breast glandular proliferation during pregnancy)
  • Compensatory (e.g., liver regeneration)
  • Pathological (e.g., endometrial hyperplasia due to excessive estrogen)

• Microscopic Appearance:

  • More cells, but with normal morphology
  • Intact tissue architecture

4. Metaplasia

• Description:

  • Reversible replacement of one differentiated cell type with another better suited to handle stress, often due to chronic irritation.

• Causes:

  • Chronic irritation or inflammation (e.g., squamous metaplasia in smokers’ airways)

• Microscopic Appearance:

  • New, normal-appearing cell type in an abnormal location (e.g., squamous cells replacing columnar epithelium)

5. Dysplasia

• Description:

  • Abnormal growth and differentiation of cells, often considered pre-cancerous. Cells display loss of uniformity and disordered growth.

• Causes:

  • Chronic irritation or inflammation (e.g., cervical dysplasia from HPV)
  • Genetic mutations

Microscopic Appearance:

• Pleomorphism (variability in size and shape)
• Increased nuclear-to-cytoplasmic ratio
• Hyperchromatic, irregular nuclei
• Loss of normal tissue architecture

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