Structure

• Cartilage (in trachea): prevents the trachea from collapsing during absence of air and also to protect it
• Ribs: to protect vital organs and blood vessels and expands and contracts (and efficient breathing)
• Intercostal (internal & external) muscles: situated between the ribs that create and move the chest wall
• Diaphragm: produces volume and pressure changes in the thorax leading to the ventilation of the lungs
• Oxygen:

  • Inspired air: 21%
  • Expired air: 16%
• Carbon dioxide:

  • Inspired air: 0.04%
  • Expired air: 4%
• Nitrogen:

  • Inspired air: 78%
  • Expired air: 78%
• Water:

  • Inspired air: varies to climate
  • Expired air: Saturated water vapour
• Temperature:

  • Inspired air: varies to climate
  • Expired air: always warm
• Test for $CO_2$ : Blow $CO_2$ through limewater. +ve result = turn cloudy