Alveoli & Oxygen Transfer: Understanding Lung Function

The lungs contain an estimated 480 million tiny air sacs called alveoli. These alveoli are lined with capillaries, which are small blood vessels. The oxygen that is inhaled passes through the walls of the alveoli into the capillaries, and the carbon dioxide that is exhaled passes through the walls of the capillaries into the alveoli. So, there are 480 million alveoli in your lungs that pass oxygen to your blood.