[Origin and evolution of the respiratory tract in vertebrates].
The description of the evolution of Vertebrate lung is based on comparative anatomy and physiology, combined with phylogenetics. An air-breathing organ (ABO), in addition to gill respiration, appeared in fishes about 400 M years ago. It consisted of a single primitive lung ventilated by a buccal pump. This breathing system was adopted by the first terrestrial tetrapods, and is largely preserved in current amphibians. In the Amniotes, the buccal pulsing pump has been replaced with a costal aspiration pump. In mammals, this ABO evolved into a bronchoalveolar lung. In "Reptiles", the ABO is a partitioned lung with one or several cavities. It serves as a gas exchanger but also as an O(2) reserve, which allows for long periods of apnoea. In birds, the ABO is a tubular structure ventilated by unidirectional airflow. Such a breathing system allows for high rates of O(2) consumption. The diversity of structure and function of the Vertebrate lung should not be analysed as a progression of increasing complexity towards mammal lungs, but rather as diverse responses to varying environmental conditions and phylogenic constraints, and to the challenge of acquiring oxygen necessary for aerobic metabolism.
Roux
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Laboratoire de Physiologie cellulaire respiratoire EMI 9937, Université Victor Segalen, Bordeaux 2, France.
D000818:Animals; D008168:Lung / Q000033:anatomy & histology* / Q000502:physiology; D010802:Phylogeny; D011650:Pulmonary Alveoli / Q000502:physiology; D012119:Respiration; D014714:Vertebrates