Our lungs are the organs that bring in oxygen into our body. In them are thousands of branch-like, tiny tubules, called bronchioles, which are connected to millions of air sacs known as alveoli.
A dense network of blood capillaries is found on the surface of each alveolus. When oxygen from the air that we breathe in enters the air sacs, it diffuses into these blood capillaries.
At the same time, carbon dioxide from the blood diffuses out into the alveoli before we breathe it out.
The pathway of air: nasal cavities (or oral cavity) -> pharynx -> trachea -> right and left bronchi -> bronchioles -> alveoli (site for gaseous exchange in which oxygen enters and crbon dioxide leaves our lungs).
Notes:
- The are some 300 million alveoli in our two adult lungs. These provide a surface area of some 160m2 (almost 80 times the area of our skin).
- Only a fraction of the oxygen we inhale is taken up by the lungs.
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