The air is warmed up before passing down the windpipe, where it's divided at the bottom between two airways called bronchi that lead to either lung.

IN THE hierarchy of transplant surgery,replacing a bronchus (the passage from the main windpipe, the trachea, into alung) does not sound difficult compared with, say, plumbing in a new heart.

The left and right bronchi branch off from the trachea and carry oxygen further into the lungs.