Structure of human gas exchange system

• Lungs


  Pair of loved structures made up of a series of highly branched tubules called bronchioles, which end in tiny air sacs called alveoli.
• Bronchi


  2 divisions of the trachea, leading to each lung, also produces mucus to trap dirt particles and cilia that move the dirt laden mucus towards the throat. Longer bronchi supported by cartilage, amount of cartilage reduces as bronchi gets smaller
• Trachea

  Flexible airway supported by rings of cartilage, this prevents trachea from collapsing as air pressure falls when breathing in. Tracheal walls made up of muscle lined with ciliated epithelium and goblet cells
• bronchioles 


  series of branching subdivisions of the bronchi. walls are made of muscle lined with epithelial cells. Muscle allows them to constrict so they can control the flow of air in and out the alveoli.
• Alveoli


  Minuite air sacs, with a diameter of between 100-300um at end of the bronchioles. Between the alveoli they're collagen and elastic fibres. Alveoli like with epithelium. Elastic fibres allow alveoli to stretch as they fill with air when breathing in. They're then sprung back during breathing out to expel carbon dioxide rich air. Alveolar membrane is the gas exchange surface.