Recall questions

• Describe the structures air passes through into the lungs?

  Mouth/nose -> Trachea -> Bronchi -> Bronchioles -> Alveoli
• Describe the role of surfactant in alveoli?

  Maintains moisture but reduces surface tension to stop alveoli collapsing when air pressure falls
• Why do alveolar walls contain elastic fibres?

  Allows alveoli to stretch when breathing in, and to recoil so that they return to original shape after exhaling
• Which tissue type comprises alveolar walls?

  Squamous epithelium
• The trachea and bronchi are lined with cartilage. Describe why

  Provides strength to trachea and bronchus. Holds the airway open - prevents collapse of the airway when air pressure falls
• Describe the roles of smooth muscle and elastic tissue in the airways

  Can contract to constrict (narrow) the airways
• Describe how alveoli are adapted to reduce diffusion distances

  Squamous epithelium are thin, flat cells which give a short diffusion distance pathway for oxygen and carbon dioxide in the alveoli, cell layer is only 0.05-0.3 micrometres wide
• Describe the pathway of oxygen from the air into the blood

  Diffuses from the alveoli > alveolar epithelium > capillary endothelium > blood down the concentration gradient. Diffuses through cell membrane as small and non-polar