Editing Lung (section)

== Other animals ==
=== Birds ===
{{Main|Bird anatomy#Respiratory system}}
[[File:BirdRespiration.svg|thumb|left|On inhalation, air travels to air sacs near the back of a bird. The air then passes through the lungs to air sacs near the front of the bird, from where the air is exhaled.]] [[File:Cross-current exchanger.jpg|thumb|right|The cross-current respiratory gas exchanger in the lungs of birds. Air is forced from the air sacs unidirectionally (from left to right in the diagram) through the parabronchi. The pulmonary capillaries surround the parabronchi in the manner shown (blood flowing from below the parabronchus to above it in the diagram).<ref name=AvResp>{{cite web| url = http://www.people.eku.edu/ritchisong/birdrespiration.html | title = BIO 554/754 – Ornithology: Avian respiration | access-date = 2009-04-23 | last = Ritchson | first = G | publisher = Department of Biological Sciences, Eastern Kentucky University }}</ref><ref name= graham>{{cite journal|last=Scott|first=Graham R.|title=Commentary: Elevated performance: the unique physiology of birds that fly at high altitudes|journal=Journal of Experimental Biology|volume= 214|issue=15|pages=2455–2462|date=2011|doi=10.1242/jeb.052548|pmid=21753038|doi-access=free}}</ref> Blood or air with a high oxygen content is shown in red; oxygen-poor air or blood is shown in various shades of purple-blue.]]
The lungs of birds are relatively small, but are connected to eight or nine [[air sacs]] that extend through much of the body, and are in turn connected to air spaces within the bones. On inhalation, air travels through the trachea of a bird into the air sacs. Air then travels continuously from the air sacs at the back, through the lungs, which are relatively fixed in size, to the air sacs at the front. From here, the air is exhaled. These fixed size lungs are called "circulatory lungs", as distinct from the "bellows-type lungs" found in most other animals.<ref name="AvResp"/><ref name="Maina2005">{{cite book|last1=Maina|first1=John N.|title=The lung air sac system of birds development, structure, and function; with 6 tables|date=2005|publisher=Springer|location=Berlin|isbn=978-3-540-25595-6|pages=3.2–3.3 "Lung", "Airway (Bronchiol) System" 66–82|url=https://books.google.com/books?id=-wtoEg7fcjkC&q=neopulmonic+parabronchi&pg=PA66}}</ref>

The lungs of birds contain millions of tiny parallel passages called [[parabronchi]]. Small sacs called ''atria'' radiate from the walls of the tiny passages; these, like the alveoli in other lungs, are the site of [[gas exchange]] by simple diffusion.<ref name=Maina2005 /> The blood flow around the parabronchi and their atria forms a cross-current process of gas exchange (see diagram on the right).<ref name=AvResp /><ref name= graham />

The air sacs, which hold air, do not contribute much to gas exchange, despite being thin-walled, as they are poorly vascularised. The air sacs expand and contract due to changes in the volume in the thorax and abdomen. This volume change is caused by the movement of the sternum and ribs and this movement is often synchronised with movement of the flight muscles.<ref name=VB>{{Cite book|last1=Romer |first1=Alfred Sherwood |last2=Parsons |first2=Thomas S. |year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location=Philadelphia |pages=330–334 |isbn=978-0-03-910284-5}}</ref>

Parabronchi in which the air flow is unidirectional are called ''paleopulmonic parabronchi'' and are found in all birds. Some birds, however, have, in addition, a lung structure where the air flow in the parabronchi is bidirectional. These are termed ''neopulmonic parabronchi''.<ref name=Maina2005 />

=== Reptiles ===
{{Main|Reptile anatomy#Respiratory system}}
The lungs of most reptiles have a single bronchus running down the centre, from which numerous branches reach out to individual pockets throughout the lungs. These pockets are similar to alveoli in mammals, but much larger and fewer in number. These give the lung a sponge-like texture. In [[tuatara]]s, [[snake]]s, and some [[lizard]]s, the lungs are simpler in structure, similar to that of typical amphibians.<ref name=VB />

Snakes and limbless lizards typically possess only the right lung as a major respiratory organ; the left lung is greatly reduced, or even absent. [[Amphisbaenian]]s, however, have the opposite arrangement, with a major left lung, and a reduced or absent right lung.<ref name=VB />

Both [[Crocodylia|crocodilians]] and [[Monitor Lizard|monitor lizards]] have lungs similar to those of birds, providing a unidirectional airflow and even possessing air sacs.<ref>{{cite web|title=Unidirectional airflow in the lungs of birds, crocs…and now monitor lizards!?|url=http://svpow.com/2013/12/11/unidirectional-airflow-in-the-lungs-of-birds-crocs-and-now-monitor-lizards/|website=Sauropod Vertebra picture of the week|access-date=9 February 2016|date=2013-12-11}}</ref> The now extinct [[Pterosauria|pterosaurs]] have seemingly even further refined this type of lung, extending the airsacs into the wing membranes and, in the case of [[Lonchodectidae|lonchodectids]], ''[[Tupuxuara]]'', and [[Azhdarchoidea|azhdarchoids]], the hindlimbs.<ref>{{cite journal|last1=Claessens|first1=Leon P.A.M.|last2=O'Connor|first2=Patrick M.|last3=Unwin|first3=David M.|last4=Sereno|first4=Paul|title=Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism|journal=PLOS ONE|date=18 February 2009|volume=4|issue=2|pages=e4497|doi=10.1371/journal.pone.0004497|pmid=19223979|pmc=2637988|bibcode=2009PLoSO...4.4497C|doi-access=free}}</ref>

[[Reptile|Reptilian]] lungs typically receive air via expansion and contraction of the ribs driven by [[axial skeleton|axial muscles]] and buccal pumping. [[Crocodilian]]s also rely on the [[hepatic]] piston method, in which the liver is pulled back by a muscle anchored to the [[pubis (bone)|pubic bone]] (part of the pelvis) called the diaphragmaticus,<ref name="Munns">{{cite journal|last1=Munns |first1=SL |last2=Owerkowicz |first2=T |last3=Andrewartha |first3=SJ |last4=Frappell |first4=PB |title=The accessory role of the diaphragmaticus muscle in lung ventilation in the estuarine crocodile Crocodylus porosus|journal=The Journal of Experimental Biology|date=1 March 2012|volume=215|issue=Pt 5|pages=845–852|pmid=22323207|doi=10.1242/jeb.061952|doi-access=free}}</ref> which in turn creates negative pressure in the crocodile's thoracic cavity, allowing air to be moved into the lungs by [[Boyle's law]]. [[Turtle]]s, which are unable to move their ribs, instead use their forelimbs and [[pectoral girdle]] to force air in and out of the lungs.<ref name=VB />

=== Amphibians ===
{{Further|Frog#Respiration and circulation}}
[[File:Axolotl ganz.jpg|thumb|right|alt=Axolotl|The [[axolotl]] (''Ambystoma mexicanum'') retains its larval form with gills into adulthood.]]
The lungs of most [[frog]]s and other [[amphibian]]s are simple and balloon-like, with gas exchange limited to the outer surface of the lung. This is not very efficient, but amphibians have low metabolic demands and can also quickly dispose of carbon dioxide by diffusion across their skin in water, and supplement their oxygen supply by the same method. Amphibians employ a [[positive pressure]] system to get air to their lungs, forcing air down into the lungs by [[buccal pumping]]. This is distinct from most higher vertebrates, who use a breathing system driven by [[negative room pressure|negative pressure]] where the lungs are inflated by expanding the rib cage.<ref name=Breathing>{{cite journal |last1=Janis |first1=Christine M. |last2=Keller |first2=Julia C. |title=Modes of ventilation in early tetrapods: Costal aspiration as a key feature of amniotes  |journal=Acta Palaeontologica Polonica |date=2001 |volume=46 |issue=2 |pages=137–170 |url=https://www.app.pan.pl/article/item/app46-137.html }}</ref> In buccal pumping, the floor of the mouth is lowered, filling the mouth cavity with air. The throat muscles then presses the throat against the underside of the [[skull]], forcing the air into the lungs.<ref name="review">{{cite journal |last1=Brainerd |first1=E. L. |title=New perspectives on the evolution of lung ventilation mechanisms in vertebrates |journal=Experimental Biology Online |date=December 1999 |volume=4 |issue=2 |pages=1–28 |doi=10.1007/s00898-999-0002-1 |bibcode=1999EvBO....4b...1B |s2cid=35368264 }}</ref>

Due to the possibility of respiration across the skin combined with small size, all known lungless [[tetrapod]]s are amphibians. The majority of salamander species are [[lungless salamander]]s, which respirate through their skin and tissues lining their mouth. This necessarily restricts their size: all are small and rather thread-like in appearance, maximising skin surface relative to body volume.<ref name=Duellman&Trueb>{{cite book|last1=Duellman|first1=W.E.|last2=Trueb|first2=L. |others=illustrated by L. Trueb |title=Biology of amphibians|year=1994|publisher=Johns Hopkins University Press|isbn=978-0-8018-4780-6}}</ref> Other known lungless tetrapods are the [[Bornean flat-headed frog]]<ref>{{cite news |last1=Bickford |first1=David |title=First Lungless Frog Discovered in Indonesia |url=https://www.scientificamerican.com/gallery/first-lungless-frog-discovered-in-indonesia/ |work=Scientific American |date=April 15, 2008 }}</ref> and ''[[Atretochoana eiselti]]'', a [[caecilian]].<ref>{{cite journal |last1=Wilkinson |first1=M. |last2=Sebben |first2=A. |last3=Schwartz |first3=E.N.F. |last4=Schwartz |first4=C.A. |title=The largest lungless tetrapod: report on a second specimen of (Amphibia: Gymnophiona: Typhlonectidae) from Brazil |journal=Journal of Natural History |date=April 1998 |volume=32 |issue=4 |pages=617–627 |doi=10.1080/00222939800770321 }}</ref>

The lungs of amphibians typically have a few narrow internal walls ([[:wikt:septum|septa]]) of soft tissue around the outer walls, increasing the respiratory surface area and giving the lung a honeycomb appearance. In some salamanders, even these are lacking, and the lung has a smooth wall. In caecilians, as in snakes, only the right lung attains any size or development.<ref name=VB />

===Fish===
Lungs are found in three groups of fish; the [[coelacanth]]s, the [[bichir]]s and the [[lungfish]]. Like in tetrapods, but unlike fish with swim bladder, the opening is at the ventral side of the oesophagus. The coelacanth has a nonfunctional and unpaired vestigial lung surrounded by a fatty organ.<ref>{{cite journal | pmc=5717702 | date=2017 | last1=Lambertz | first1=M. | title=The vestigial lung of the coelacanth and its implications for understanding pulmonary diversity among vertebrates: New perspectives and open questions | journal=Royal Society Open Science | volume=4 | issue=11 | doi=10.1098/rsos.171518 | pmid=29291127 | bibcode=2017RSOS....471518L }}</ref> Bichirs, the only group of [[Actinopterygii|ray-finned fish]] with lungs, have a pair which are hollow unchambered sacs, where the gas-exchange occurs on very flat folds that increase their inner surface area. The lungs of [[lungfish]] show more resemblance to tetrapod lungs. There is an elaborate network of parenchymal septa, dividing them into numerous respiration chambers.<ref>{{cite book | url=https://books.google.com/books?id=3bsgS125KH0C&dq=Lungfish+complex+respiratory+surface+septa+honeycomb&pg=PA1864 | title=Encyclopedia of Fish Physiology: From Genome to Environment | date=June 2011 | publisher=Academic Press | isbn=978-0-08-092323-9 }}</ref><ref>{{cite journal | url=https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.20576 | doi=10.1002/ar.20576 | title=Innervation and Neurotransmitter Localization in the Lung of the Nile bichir ''Polypterus bichir bichir'' | date=2007 | last1=Zaccone | first1=Giacomo | last2=Mauceri | first2=Angela | last3=Maisano | first3=Maria | last4=Giannetto | first4=Alessia | last5=Parrino | first5=Vincenzo | last6=Fasulo | first6=Salvatore | journal=The Anatomical Record | volume=290 | issue=9 | pages=1166–1177 | pmid=17722050 }}</ref> In the [[Australian lungfish]], there is only a single lung, albeit divided into two lobes. Other lungfish, however, have traditionally been considered having two lungs, but newer research defines paired lungs as bilateral lung buds that arise simultaneously and are both connected directly to the foregut, which is only seen in tetrapods.<ref>Camila Cupello, Tatsuya Hirasawa, Norifumi Tatsumi, Yoshitaka Yabumoto, Pierre Gueriau, Sumio Isogai, Ryoko Matsumoto, Toshiro Saruwatari, Andrew King, Masato Hoshino, Kentaro Uesugi, Masataka Okabe, Paulo M Brito (2022) [https://elifesciences.org/articles/77156 Lung evolution in vertebrates and the water-to-land transition], ''[[eLife]]''</ref> In all lungfish, including the Australian, the lungs are located in the upper dorsal part of the body, with the connecting duct curving around and above the oesophagus. The blood supply also twists around the oesophagus, suggesting that the lungs originally evolved in the ventral part of the body, as in other vertebrates.<ref name=VB />

=== Invertebrates ===
{{further|Respiratory system of gastropods}}
[[File:Spider internal anatomy-en.svg|thumb|[[Book lung]]s of a female spider (shown in pink)]]
A number of [[invertebrate]]s have lung-like structures that serve a similar respiratory purpose to true vertebrate lungs, but are not evolutionarily related and only arise out of [[convergent evolution]]. Some [[arachnid]]s, such as [[spider]]s and [[scorpion]]s, have structures called [[book lung]]s used for atmospheric gas exchange. Some species of spider have four pairs of book lungs but most have two pairs.<ref>{{Cite web
| url = https://www.britannica.com/science/book-lung
| title = book lung {{!}} anatomy
| website = Encyclopædia Britannica
| access-date = 2016-02-24
}}</ref> Scorpions have [[Spiracle (arthropods)|spiracle]]s on their body for the entrance of air to the book lungs.<ref>{{Cite web
| url = https://www.britannica.com/science/spiracle
| title = spiracle {{!}} anatomy
| website = Encyclopædia Britannica
| access-date = 2016-02-24
}}</ref>

The [[coconut crab]] is terrestrial and uses structures called [[branchiostegal lung]]s to breathe air.<ref name="Farrelly2005">{{cite journal|vauthors=Farrelly CA, Greenaway P|year=2005|title=The morphology and vasculature of the respiratory organs of terrestrial hermit crabs (''Coenobita'' and ''Birgus''): gills, branchiostegal lungs and abdominal lungs |journal=Arthropod Structure & Development|volume=34 |issue=1 |pages=63–87 |doi=10.1016/j.asd.2004.11.002|bibcode=2005ArtSD..34...63F }}</ref> Juveniles are released into the ocean, however adults cannot swim and possess an only rudimentary set of gills. The adult crabs can breathe on land and hold their breath underwater.<ref>{{Cite book
| url = https://books.google.com/books?id=RR09AAAAIAAJ
| title = Biology of the Land Crabs
| last1 = Burggren
| first1 = Warren W.
| last2 = McMahon
| first2 = Brian R.
| year = 1988
| publisher = Cambridge University Press
| isbn = 978-0-521-30690-4
| page = 25
| language = en
}}</ref> The branchiostegal lungs are seen as a developmental adaptive stage from water-living to enable land-living, or from fish to amphibian.<ref>{{Cite book
| url = https://books.google.com/books?id=RR09AAAAIAAJ
| title = Biology of the Land Crabs
| last1 = Burggren
| first1 = Warren W.
| last2 = McMahon
| first2 = Brian R.
| year = 1988
| publisher = Cambridge University Press
| isbn = 978-0-521-30690-4
| page = 331
| language = en
}}</ref>

[[Pulmonates]] are mostly [[land snail]]s and [[slug]]s that have developed a simple lung from the [[mantle cavity]]. An externally located opening called the [[pneumostome]] allows air to be taken into the mantle cavity lung.<ref>Land Snails (& other Air-Breathers in Pulmonata Subclass & Sorbeconcha Clade).
at Washington State University Tri-Cities Natural History Museum. Accessed 25 February 2016. http://shells.tricity.wsu.edu/ArcherdShellCollection/Gastropoda/Pulmonates.html {{Webarchive|url=https://web.archive.org/web/20181109010506/http://shells.tricity.wsu.edu/ArcherdShellCollection/Gastropoda/Pulmonates.html |date=2018-11-09 }}</ref><ref>{{Cite book
| url = https://books.google.com/books?id=7UyeBQAAQBAJ
| title = Mollusca: Metabolic Biochemistry and Molecular Biomechanics
| last = Hochachka
| first = Peter W.
| year = 2014
| publisher = Academic Press
| isbn = 978-1-4832-7603-8
| language = en
}}</ref>