Lungs (2)

• Approx. 300 million alveoli
• Alveoli


  • Lined with lipoprotein (surfactant) which is a mix of phospholipids and protein
  • Contain epithelial cells
  • Type 1 alveolar cells have thin cell walls and are for gas exchange
  • Type 2 alveolar cells secrete surfactant and have microvilli
• Alveolar surfactant


  Lowers surface tension at the air/liquid interface
• Air movement into lungs

  1. Pressure changes

  2. Pressure is the amount of force created by movement and collision of the gas molecules

  3. Flow = pressure difference / resistance

  4. Pressure difference = atm pressure – alv pressure
• Inhalation


  Always active
• Exhalation


  1. Can be active or passive

  2. Lungs naturally recoil so exhalation restores the lungs to their resting position