Editing Megabat (section)

===Internal systems===
[[File:Hypsignathus monstrosus anatomy.png|thumb|alt=A scientific illustration of the internal anatomy of a megabat. Its organs are individually labeled.|Internal anatomy of the [[hammer-headed bat]] (''Hypsignathus monstrosus'')]]
Flight is very energetically expensive, requiring several adaptations to the [[cardiovascular system]]. During flight, bats can raise their [[oxygen consumption]] by twenty times or more for sustained periods; human athletes can achieve an increase of a factor of twenty for a few minutes at most.<ref name="Maina">{{cite journal|url=http://jeb.biologists.org/content/jexbio/111/1/43.full.pdf| title=Correlations between structure and function in the design of the bat lung: a morphometric study| first1=J. N.| last1= Maina| first2= A. S.| last2= King| journal=[[Journal of Experimental Biology]]| year= 1984| volume= 11| issue=1| page=44| doi=10.1242/jeb.111.1.43| bibcode=1984JExpB.111...43M}}</ref> A 1994 study of the [[straw-coloured fruit bat]] (''Eidolon helvum'') and [[hammer-headed bat]] (''Hypsignathus monstrosus'') found a mean [[respiratory exchange ratio]] (carbon dioxide produced:oxygen used) of approximately 0.78. Among these two species, the [[gray-headed flying fox]] (''Pteropus poliocephalus'') and the [[Egyptian fruit bat]] (''Rousettus aegyptiacus''), maximum heart rates in flight varied between 476 beats per minute (gray-headed flying fox) and 728 beats per minute (Egyptian fruit bat). The maximum number of breaths per minute ranged from 163 (gray-headed flying fox) to 316 (straw-colored fruit bat).<ref>{{cite journal|url=http://jeb.biologists.org/content/jexbio/120/1/79.full.pdf| title=Flight Physiology of Intermediate-Sized Fruit Bats (Pteropodidae)| journal=Journal of Experimental Biology|year= 1986| volume= 120| pages= 84–93|first=R. E.| last=Carpenter| issue=1| doi=10.1242/jeb.120.1.79| bibcode=1986JExpB.120...79C}}</ref> Additionally, megabats have exceptionally large [[lung volumes]] relative to their sizes. While terrestrial mammals such as [[shrew]]s have a lung volume of 0.03&nbsp;cm<sup>3</sup> per gram of body weight (0.05&nbsp;in<sup>3</sup> per ounce of body weight), species such as the [[Wahlberg's epauletted fruit bat]] (''Epomophorus wahlbergi'') have lung volumes 4.3 times greater at 0.13&nbsp;cm<sup>3</sup> per gram (0.22&nbsp;in<sup>3</sup> per ounce).<ref name="Maina"/>

Megabats have rapid digestive systems, with a gut transit time of half an hour or less.<ref name="Nelson">{{cite report|url=https://www.environment.gov.au/system/files/pages/a117ced5-9a94-4586-afdb-1f333618e1e3/files/37-ind.pdf| title=Fauna of Australia| last=Nelson| first=J. E.| volume=1B|publisher=[[Department of the Environment and Energy|Australian Government Department of the Environment and Energy]]}}</ref> The digestive system is structured to a [[herbivorous]] diet sometimes restricted to soft fruit or nectar.<ref name="Richards1983" /> The length of the digestive system is short for a herbivore (as well as shorter than those of [[insectivorous]] microchiropterans),<ref name="Richards1983"/> as the fibrous content is mostly separated by the action of the palate, tongue, and teeth, and then discarded.<ref name="Richards1983" /> Many megabats have U-shaped stomachs. There is no distinct difference between the small and large intestine, nor a distinct beginning of the [[rectum]]. They have very high densities of intestinal [[microvillus|microvilli]], which creates a large surface area for the absorption of nutrients.<ref>{{cite book| title=Comparative Anatomy of the Gastrointestinal Tract in Eutheria II| editor-first=A.| editor-last= Schmidt-Rhaesa| isbn=9783110560671| publisher=[[Walter de Gruyter GmbH & Co KG]]| year=2017|pages=328–330}}</ref>