The two lungs take up most of the space in the chest. Their key function is to get oxygen into, and waste gases out of, the bloodstream. That oxygen is used by the body’s cells to release energy, a process that produces waste carbon dioxide.
Breathing draws air rich in oxygen into the lungs through the airways, then pushes air containing carbon dioxide in the opposite direction. Lungs are spongy because they are packed with branching, air-filled tubes that get narrower and narrower before ending in tiny air sacs (alveoli). It is here that oxygen is swapped for carbon dioxide.
The lungs are like bellows. As they expand, air is sucked in for oxygen. As they compress, the exchanged carbon dioxide waste is pushed back out during exhalation.
When air enters the nose or mouth, it travels down the trachea, also called the windpipe. After this, it reaches a section called the carina. At the carina, the windpipe splits into two, creating two mainstem bronchi. One leads to the left lung and the other to the right lung.
From there, like branches on a tree, the pipe-like bronchi split again into smaller bronchi and then even smaller bronchioles. This ever-decreasing pipework eventually terminates in the alveoli, which are little air sac endings.
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