the lungs

• 1. the air breathed in goes through the trachea
  2. this splits into two tubes called the bronchi one going to each lung
  3. the bronchi split into smaller tubes called bronchioles
  4. the bronchioles end at small bags called alveoli where gas exchange takes place
• the lungs contain millions of alveoli surrounded by a network of blood capillaries. This is where gas exchange happens
• blood passing next to the alveoli just returned to the lungs from the body so it conatins lots of carbon dioxide and little oxygen.
• Oxygen diffuses outof the alveolus into the blood. Carbon dioxide diffuses out of the blood into the alveolus to be breathed out
• when blood reaches body cells, oxygen is released from the red blood cells and diffuses into the body cells
• carbon dioxide diffuses out of the body cells into the blood and then carried back to the lungs