From the outside, lungs are pink and a bit squishy, like a sponge. But the inside contains the real lowdown on the lungs! At the bottom of the trachea (say: tray-kee-uh), or windpipe, there are two large tubes. These tubes are called the main stem bronchi (say: brong-kye), and one heads left into the left lung, while the other heads right into the right lung.
Each main stem bronchus (say: brong-kuss) — the name for just one of the bronchi — then branches off into tubes, or bronchi, that get smaller and even smaller still, like branches on a big tree. The tiniest tubes are called bronchioles (say: brong-kee-oles), and there are about 30,000 of them in each lung. Each bronchiole is about the same thickness as a hair.
At the end of each bronchiole is a special area that leads into clumps of teeny tiny air sacs called alveoli (say: al-vee-oh-lie). There are about 600 million alveoli in your lungs and if you stretched them out, they would cover an entire tennis court. Now that's a load of alveoli! Each alveolus (say: al-vee-oh-luss) — what we call just one of the alveoli — has a mesh-like covering of very small blood vessels called capillaries (say: cap-ill-er-ees). These capillaries are so tiny that the cells in your blood need to line up single file just to march through them.
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