Mechanics of Breathing Lecture Notes

Anatomy of the Lungs

• Lungs Structure
  • Two lungs: Right and Left
  • Trachea branches into right and left primary bronchus
  • Smallest structural unit: Alveoli
• Pleura Layers
  • Visceral Pleura: Thin epithelial tissue layer clinging to lungs
  • Pleural Cavity: Potential space with pleural fluid
  • Parietal Pleura: Layer clinging to the chest wall

Importance of Pleural Fluid

• Prevents friction between visceral and parietal pleura during inhalation and exhalation
• Helps to avoid conditions such as pleurisy

Pressures in the Respiratory System

• Intrapulmonary Pressure (A)
  • Also known as intra-alveolar pressure
  • Located in the alveoli
  • Approximately 760 mmHg
• Intrapleural Pressure (B)
  • Present in the pleural cavity
  • Always less than intrapulmonary pressure by about 4 mmHg
  • Approximately 756 mmHg
• Atmospheric Pressure (C)
  • Also known as barometric pressure
  • Approximately 760 mmHg

Pressure Concepts

• Zero, Negative, and Positive Pressures: Compared to atmospheric pressure
• Example: Intrapulmonary pressure (760 mmHg) is zero when compared to atmospheric pressure

Factors Contributing to Negative Intrapleural Pressure

• Elasticity of the Lungs: Tendency to recoil to smallest size
• Surface Tension: From water molecules in alveoli promoting collapse
• Elasticity of the Chest Wall: Tendency to expand outward
• Gravity: Affects differences in intrapleural pressure throughout the cavity

Boyle’s Law

• Relationship: Increase in volume leads to a decrease in pressure
• Applied to the thoracic cavity to explain the negative intrapleural pressure

Transpulmonary and Transthoracic Pressures

• Transpulmonary Pressure (TP)
  • Difference between intrapulmonary and intrapleural pressure
  • Positive pressure indicates ability to inflate lungs
• Transthoracic Pressure (TTP)
  • Difference between intrapleural and atmospheric pressure
  • Negative pressure indicates tendency to deflate

Lymphatic Role

• Lymphatic vessels prevent excessive pleural fluid accumulation

Conclusion

• Recap of pressures: intrapulmonary, intrapleural, and atmospheric
• Importance of each pressure in maintaining lung inflation and deflation
• Preview of Part 2: Nervous system's role in respiratory pressure changes

Note: Continue to Part 2 for insights on nervous system influence on respiratory mechanics.