Lecture on Respiratory Physiology: Lung Compliance

Introduction to Lung Compliance

• Lung Compliance: Ability of the lungs and surrounding tissues to stretch, expand, and contract.
• Involves:
  • Alveolar walls
  • Respiratory bronchioles
  • Connective tissue surrounding lungs and chest wall

Anatomy and Physiology of the Lungs

• Lung Development:
  • Chest wall develops before lungs.
  • Lungs push into the chest cavity during development.
• Pleura and Pleural Spaces:
  • Visceral Pleura: Connective tissue sitting on lung tissue.
  • Parietal Pleura: Connective tissue on the chest wall.
  • Intrapleural Space: Contains intrapleural fluid which creates surface tension.

Pressures in the Respiratory System

• Transpulmonary Pressure: Difference between alveolar pressure and pleural pressure.
  • Typically about 4 mmHg difference.
• Alveolar Pressure: Pressure of gases inside alveoli.
• Intrapleural Pressure: Pressure in pleural cavity, usually lower than alveolar pressure.

Mechanics of Breathing

• Negative Pressure Breathing: Creating negative pressure in pleural space to draw air into lungs.
• Chest Wall and Diaphragm Movements:
  • Expansion increases negative pressure, attracting air into alveoli.
  • Relaxation causes positive pressure, pushing air out.

Lung Elasticity and Compliance

• Damage to lung tissue or chest wall (e.g., smoking) reduces elasticity.
  • Connective tissue repairs decrease lung stretchability.
• Surface Tension: Attraction of water molecules needs to be managed to prevent alveolar collapse.

Role of Surfactant

• Secreted by type 2 alveolar cells.
• Reduces surface tension, preventing alveolar collapse.
• Composed of phospholipids, proteins, and ions (e.g., phospholipid dipalmitoyl lecithin).
• Vital for newborns to begin breathing post-birth.

Summary of Breathing Mechanism

• Inhalation:
  • Diaphragm and intercostal muscles contract, expanding thoracic cage.
  • Intrapleural pressure decreases, transpulmonary pressure increases.
  • Alveoli pressure becomes negative, air is sucked in.
• Exhalation:
  • Muscles relax, thoracic cage recoils.
  • Intrapleural pressure increases, pushing air out of alveoli.

Clinical Relevance

• Punctured Lung: Loss of negative pressure causing lung collapse.
• Smoking Effects: Damaging alveoli elasticity, increasing connective tissue.

Conclusion

• Understanding lung compliance and its mechanics is crucial for grasping respiratory physiology.
• Review the concepts, and ask questions for clarity.