Parsons, Thomas S. Ramsay Wright Zoological Laboratories, University of Toronto, Ontario, Canada.
Randall, David J. Department of Zoology, University of British Columbia, Vancouver, Canada.
McCutcheon, F. Harold University of Pennsylvania, Philadelphia, Pennsylvania.
Last reviewed:April 2019
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- Vertebrate respiratory regulation
- Adaptations in terrestrial animals
- Related Primary Literature
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The system of organs involved in the acquisition of oxygen and the elimination of carbon dioxide by an organism. The respiratory system consists of a set of specialized organs, including anatomical structures and passages, that are responsible for the proper intake and exchange of oxygen and carbon dioxide between an organism's body and the environment. Structurally, respiratory organs usually present a vascular surface that is sufficiently extensive to provide an adequate area of absorption for gaseous exchange. This surface is moist and thin enough to allow for the passage of gases. Across the diversity of life, various respiratory structures have developed, including the lungs and airways of air-breathing vertebrates (Fig. 1), the gills of fishes and many invertebrates, and the specialized air ducts (tracheae) of insects. With regard to vertebrates, the lungs and gills are the two most important structures involved in the phase known as external respiration, or gaseous exchanges, between the blood and environment. Internal respiration refers to the gaseous exchanges that occur between the blood and cells. Certain other structures in some species of vertebrates serve as respiratory organs—for example, the integument or skin of fishes and amphibians. In particular, the moist, highly vascular skin of anuran amphibians is important in respiration. In addition, certain species of fishes have a vascular rectum that is utilized as a respiratory structure (with water being taken in and ejected regularly by the animal), whereas saclike cloacal structures occur in some aquatic species of turtles. These latter structures are vascular and are intermittently filled with, and emptied of, water; it is thought that they may function in respiration. It also should be mentioned that the yolk sac and allantois are important respiratory organs during the embryonic life of certain vertebrates. See also: Allantois; Blood; Carbon dioxide; Lung; Oxygen; Respiration; Skin; Vertebrata; Yolk sac
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