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 many smaller tubes called bronchioles
• The bronchioles end in tiny air sacs called alveoli which is where gases diffuse in and out of the bloodstream
• Oxygen in the air diffuses into the bloodstream whilst carbon dioxide in the bloodstream diffuses into the air.
• The alveoli are adapted through:

  • Millions of alveoli = Huge surface area
  • Very thin walls = Short diffusion path
  • Very good blood supply

  Meaning that oxygen rapidly diffuses into the bloodstream and carbon dioxide diffuses rapidly out
• Through breathing, we increase the rate of diffusion, as it brings fresh oxygen into the alveoli and takes away carbon dioxide. This makes the concentration gradients high for these gases, increasing the rate of diffusion.