The Lungs (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

The lungs

Adaptations for gas exchange

• All gas exchange surfaces have features to increase the efficiency of gas exchange including:

  • Large surface area to allow faster diffusion of gases across the surface

  • Thin walls to ensure diffusion distances remain short

  • Good ventilation with air so that diffusion gradients can be maintained

  • Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster

• Remember that gas exchange occurs by the process of diffusion; breathing is essential in maintaining high concentration gradients between the air in the alveoli and the gases dissolved in the blood

  • In particular, breathing keeps the oxygen level in the alveoli high and the carbon dioxide level low

Structure of the lungs

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Structures in the lungs

• Ribs: Bone structures that surround and protect the lungs, they also aid breathing (moving up and out or down and in)

• Intercostal muscles: Muscles between the ribs which control movement, causing inhalation and exhalation

• Diaphragm: Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation

• Trachea: Windpipe that connects the mouth and nose to the lungs, lined with goblet cells (to produce mucus) and ciliated epithelial cells (with cilia which move mucus up to the mouth)

• Bronchus (plural, bronchi): Large tubes branching off the trachea with one bronchus for each lung, also lined with goblet cells and ciliated epithelial cells

• Bronchioles: The bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli

• Alveoli: Tiny moist air sacs where gas exchange takes place, each alveolus is covered in capillaries