Editing Gas exchange (section)

===Amphibians===
Amphibians have three main organs involved in gas exchange: the lungs, the skin, and the gills, which can be used singly or in a variety of different combinations. The relative importance of these structures differs according to the age, the environment and species of the amphibian. The skin of amphibians and their larvae are highly vascularised, leading to relatively efficient gas exchange when the skin is moist. The larvae of amphibians, such as the pre-metamorphosis [[tadpole]] stage of [[frog]]s, also have external [[gills]]. The gills are absorbed into the body during [[metamorphosis]], after which the lungs will then take over. The lungs are usually simpler than in the [[amniote|other land vertebrates]], with few internal septa and larger alveoli; however, toads, which spend more time on land, have a larger alveolar surface with more developed lungs. To increase the rate of gas exchange by diffusion, amphibians maintain the concentration gradient across the respiratory surface using a process called [[buccal pumping]].<ref name="Brainerd">{{cite journal |last=Brainerd |first=E. L.  |date=1999 |title=New perspectives on the evolution of lung ventilation mechanisms in invertebrates|journal=Experimental Biology Online |volume=4 |issue= 2|pages=1–28 |doi=10.1007/s00898-999-0002-1 |bibcode=1999EvBO....4b...1B |s2cid=35368264 }}</ref> The lower floor of the mouth is moved in a "pumping" manner, which can be observed by the naked eye.