lungs

• alveoli - minute airsacs, site of gas exchange in lungs
• inspiration:

  • external intercostal muscles contract
  • diaphragm contracts and flattens
  • internal intercostal muscles relax
  • ribs are pulled upwards and outwards
  • increasing volume of thoracic cavity
  • decreasing pressure in lungs
  • pulling air into the lungs down the pressure gradient
• expiration:

  • external intercostal muscles relax
  • diaphragm relaxes and curves back
  • internal intercostal muscles contract
  • ribs are pulled down and inwards
  • this decreases volume in the thoracic cavity
  • increasing pressure in the lungs
  • air is forced out the lungs down the pressure gradient
• pathway of air:

  • trachea
  • bronchi
  • bronchioles
  • alveoli
  • alveolar epithelium
  • capillary endothelium
  • blood
• tidal volume = volume of air breathed in or out per breath
• minute ventilation = amount of air breathed in or out per minute
• breathing rate = amount of breaths per minute
• minute ventilation = tidal volume x breathing rate