Cell Adaptation Lecture Notes

Introduction

• Topic: How cells respond to stress to keep the organism alive.
• Key Concept: Cells adapt to stressors to maintain homeostasis.

Schematic Diagram Explanation

• Normal Cell: Maintains homeostasis.
• Stress Response: Cells subjected to stress (e.g. workload, pH, nutrition, chemicals) adapt to return to homeostasis.
  • Injury Response: Cells face mechanical, chemical, or physical trauma, or oxygen reduction; cells can either repair (reversibly) or die (irreversibly).
• Cell Death Types: Necrosis and apoptosis (covered in another video).
• Main focus: How cells adapt to stressors.

Types of Cell Adaptation

1. Atrophy
2. Hypertrophy
3. Hyperplasia
4. Metaplasia
5. Dysplasia

Cell Categorization by Activity

• Labile Cells: Constantly replicating (mitotically active).
• Quiescent (Stable) Cells: Not currently replicating but can if needed.
• Permanent Cells: Cannot replicate (e.g., muscle and neuronal cells).

Stress Response in Different Cell Types

• Example: Heart muscle cells adapt to oxygen reduction or increased workload (e.g., exercise).
  • Hypertrophy: Increase in cell size in response to increased demand (common in non-replicating cells like heart muscle).

Detailed Adaptation Types

Atrophy

• Definition: Reduction in cell size due to decreased demand or stimulation.
• Causes:
  • Disuse (e.g., muscles in a cast).
  • Denervation, malnutrition, reduced hormone stimulation, and reduced blood flow.
• Examples:
  • Physiological: Uterine muscles reduce post-pregnancy.
  • Pathophysiological: Ischemia (reduced blood flow leading to smaller leg muscles).

Hypertrophy

• Definition: Increase in cell size due to increased demand.
• Causes:
  • Mechanical stress, hormonal stimulation, growth factors.
• Examples:
  • Physiological: Muscle growth from exercise; uterine growth during pregnancy.
  • Pathophysiological: Cardiac hypertrophy in heart disease (inefficient muscle growth).

Hyperplasia

• Definition: Increase in cell number (not size).
• Cell Types: Labile or stable cells (e.g., epithelial cells, liver cells, glandular cells).
• Causes:
  • Hormonal changes, increased demand for cells.
• Examples:
  • Physiological: Breast tissue growth during puberty/pregnancy; liver regeneration.
  • Pathophysiological: Prostate gland enlargement, viral-induced warts.

Metaplasia

• Definition: Change in cell type to better withstand chronic irritation or inflammation.
• Causes: Chronic irritation (e.g., smoking, acid reflux).
• Examples:
  • Bronchial ciliated cells change to stratified squamous cells in smokers.
  • Esophageal cells change to columnar cells in response to stomach acid in GERD.

Dysplasia

• Definition: Disordered growth leading to varied cell size and shape, often a precursor to cancer.
• Causes: Chronic irritation or inflammation.
• Examples:
  • Cervical dysplasia due to HPV.
  • Bronchopulmonary dysplasia in preterm infants.
• Note: Can be reversible but less likely compared to other adaptations.

Summary

• Cell Adaptation Mechanism: Cells adapt (size, number, type) in response to environmental stress to survive.
• Importance: Understanding how different cell types respond helps in recognizing disease progressions and treatment strategies.