The lungs

• The thorax is the top part of your body and is separated from the lower part of the body by the diaphragm
• The lungs are protected by the ribcage and surrounded by the pleural membranes
• The air that you breathe in goes through the trachea

  it splits into 2 tubes called bronchi, one going to each lung

  The bronchi split into progressively smaller tubes called bronchioles

  The bronchioles finally end at small bags called alveoli where gas exchange takes place
• alveoli are surrounded by a network of blood capillaries

  The blood passing next to the alveoli has just returned to the lungs from the rest of the body so it contains lots of CO2 and little oxygen.

  Oxygen diffuses out the alveoli( high concentration) into the blood (low concentration) CO2 diffuses out of the blood into the alveolus to be breathed out .
• Alveoli adaptations:

  1. Very thin walls (1cell) so the diffusion path is very short
  2. Have a very good blood supply, maintaining a steep concentration gradient for rapid diffusion
  3. Inner surface is moist which helps dissolve gases, making diffusion easier
  4. millions of alveoli , giving the lungs a large surface area for rapid diffusion