Gas exchange in the Lungs

• Air passes into the lungs through a tube called the trachea.

  
• Rings of cartilage prevent the trachea from collapsing during inhalation.
• The trachea splits into two smaller tubes called bronchi, with one passing to each lung
• Further into the lungs, the bronchi subdivide into smaller tubes caller bronchioles.
• The bronchioles end in tiny air sacs called alveoli.
• The lungs contain millions of alveoli, and each one is microscopic.
• Alveoli are where gases diffuse in and out of the bloodstream.
• The millions of alveoli means that the lungs have a huge surface area

  
• The alveoli have very thin walls so the diffusion path is very short.
• The alveoli have a very good blood supply.
• Once the oxygen diffuses into the blood, it is rapidly removed. This ensures that the concentration gradient is as steep as possible.
• By breathing, we also increase the rate of diffusion. Breathing brings fresh oxygen into the alveoli and takes away the carbon dioxide. This makes the concentration gradient high for these gases. This increases the rate of diffusion.