The essential organs of respiration are the lungs, in which gaseous exchange takes place between the inspired air and the bloodstream.

The ancillary organs comprise the passages through which air is led to and from the lungs. The nose is included, although it may alternatively be considered among the organs of special sense as it evolved as the organ of olfaction. The pharynx, in which the air and food streams cross, is more conveniently considered among the digestive organs, although its upper part (nasopharynx) is purely an airway. A short account of the development follows the description of the adult anatomy.