7
Exchange of gases in the lungs
Read the text and write in the information in illustrations given.
The alveoli are covered with blood capillaries. Blood being transported by a capillary to the alveoli has little oxygen in it. This is called deoxygenated blood. This blood has a high concentration of carbon dioxide. Blood being transported by a capillary from the lungs is oxygenated. This means that it has a high concentration of oxygen. This blood also has a low concentration of carbon dioxide. There is a network of capillaries surrounding the alveoli. This is where the exchange of gases takes place. Firstly, deoxygenated blood flows in a capillary surrounding an alveolus. The wall of the capillary is only one cell thick. This allows gases to move in and out of the blood cells. Here, carbon dioxide leaves the deoxygenated blood and this is exhaled as we breathe. At the same time oxygen we breathe in passes through the alveolus wall, which is also only one cell thick, into the blood. Finally, the newly oxygenated blood is transported away from the lungs.