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 is lined with ciliated epithelial tissue and goblet cells. Describe the functions of these

  Beat regularly to move mucus up the airways towards the mouth to be removed. Helps keep the airways clear and prevent infections. Contain lots of mitochondria to provide energy required to move cilia
• 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