Bronchus

When air travels down the trachea, that pipe does not carry it all the way into the lungs on its own: it splits in two at a point called the carina, and from there one bronchus goes to each lung. Each main bronchus enters its lung at the hilum, the doorway into the organ.

The wall of the bronchus has rings of cartilage, and those rings do what the rings in a vacuum hose do: they support the wall and keep the tube from collapsing. And once inside the lung the bronchus does not end; it keeps branching again and again, getting thinner each time, forming what is called the bronchial tree. If you turned a tree upside down and put it in your chest, the trunk would be the bronchus and the branches everything that follows.