lower respiratory tract

The lower respiratory tract is everything from the voice box on down — the working interior of the breathing system, where air travels through branching tubes and finally reaches the surfaces that exchange gas with the blood. This is pulmonology's home turf.

It includes the trachea (windpipe), the bronchi and their finer branches the bronchioles, and the lungs with their millions of alveoli. The upper portion is purely conducting tubing; the deepest portion, the respiratory zone, is where oxygen and carbon dioxide actually cross between air and blood.

Because the lower tract leads straight to the gas-exchanging tissue, infections and diseases here are generally more dangerous than in the upper tract. Pneumonia, bronchitis, asthma, chronic obstructive pulmonary disease and lung cancer are all lower-respiratory-tract problems, and they make up the bulk of a pulmonologist's work.