Editing Sea lion (section)

===Diving adaptations===
[[File:Sea lion heart.jpg|thumb|Sea lion heart.]]
There are many components that make up sea lion physiology and these processes control aspects of their behavior. Physiology dictates thermoregulation, osmoregulation, reproduction, metabolic rate, and many other aspects of sea lion ecology including but not limited to their ability to dive to great depths. The sea lions' bodies control heart rate, gas exchange, digestion rate, and blood flow to allow individuals to dive for a long period of time and prevent side effects of high pressure at depth.

The high pressures associated with deep dives cause gases such as nitrogen to build up in tissues which are then released upon surfacing, possibly causing death. One of the ways sea lions deal with the extreme pressures is by limiting the amount of gas exchange that occurs when diving. The sea lion allows the alveoli to be compressed by the increasing water pressure thus forcing the surface air into cartilage lined airway just before the gas exchange surface.<ref name=":7" /> This process prevents any further oxygen exchange to the blood for muscles, requiring all muscles to be loaded with enough oxygen to last the duration of the dive. However, this shunt reduces the amount of compressed gases from entering tissues therefore reducing the risk of decompression sickness.<ref name=":7">{{Cite journal|last1=Kooyman|first1=G. L.|last2=Sinnett|first2=E. E.|date=1 January 1982|title=Pulmonary Shunts in Harbor Seals and Sea Lions during Simulated Dives to Depth|jstor=30158447|journal=Physiological Zoology|volume=55|issue=1|pages=105–111|doi=10.1086/physzool.55.1.30158447|s2cid=87390381}}</ref> 

The collapse of alveoli does not allow for any oxygen storage in the lungs, however. This means that sea lions must mitigate oxygen use in order to extend their dives. Oxygen availability is prolonged by the physiological control of heart rate in sea lions. By reducing heart rate to well below surface rates, oxygen is saved by reducing gas exchange as well as reducing the energy required for a high heart rate.<ref name=":8">{{Cite journal|last1=McDonald|first1=Birgitte I.|last2=Ponganis|first2=Paul J.|date=2014|title=Deep-diving sea lions exhibit extreme bradycardia in long-duration dives|journal=Journal of Experimental Biology|language=en|volume=217|issue=9|pages=1525–1534|doi=10.1242/jeb.098558|issn=0022-0949|pmid=24790100|doi-access=free|url=http://journals.biologists.com/jeb/article-pdf/217/9/1525/1883736/1525.pdf}}</ref> [[Bradycardia]] is a control mechanism to allow a switch from pulmonary oxygen to oxygen stored in the muscles which is needed when the sea lions are diving to depth.<ref name=":8" /> Another way sea lions mitigate the oxygen obtained at the surface in dives is to reduce digestion rate. Digestion requires metabolic activity and therefore energy and oxygen are consumed during this process; however, sea lions can limit digestion rate and decrease it by at least 54%.<ref name=":9">{{Cite journal|last1=Rosen|first1=David A. S.|last2=Gerlinsky|first2=Carling D.|last3=Trites|first3=Andrew W.|date=1 August 2015|title=Evidence of partial deferment of digestion during diving in Steller sea lions (''Eumetopias jubatus'')|journal=Journal of Experimental Marine Biology and Ecology|volume=469|pages=93–97|doi=10.1016/j.jembe.2015.04.017|bibcode=2015JEMBE.469...93R }}</ref> This reduction in digestion results in a proportional reduction in oxygen use in the stomach and therefore a correlated oxygen supply for diving. Digestion rate in these sea lions increases back to normal rates immediately upon resurfacing.<ref name=":9" /> 

Oxygen depletion limits dive duration, but carbon dioxide (CO<sub>2</sub>) build-up also plays a role in the dive capabilities of many [[marine mammal]]s. After a sea lion returns from a long dive, CO<sub>2</sub> is not expired as fast as oxygen is replenished in the blood, due to the unloading complications with CO<sub>2</sub>. However, having more than normal levels of CO<sub>2</sub> in the blood does not seem to adversely affect dive behavior.<ref name=":10">{{Cite journal|last1=Gerlinsky|first1=Carling D.|last2=Rosen|first2=David A. S.|last3=Trites|first3=Andrew W.|date=7 March 2014|title=Sensitivity to hypercapnia and elimination of CO<sub>2</sub> following diving in Steller sea lions (''Eumetopias jubatus'')|journal=Journal of Comparative Physiology B|language=en|volume=184|issue=4|pages=535–544|doi=10.1007/s00360-014-0819-y|pmid=24604293|s2cid=4637738|issn=0174-1578}}</ref> Compared to terrestrial mammals, sea lions have a higher tolerance to storing CO<sub>2</sub> which is what normally tells mammals that they need to breathe.<ref name=":10" /> This ability to ignore a response to CO<sub>2</sub> is likely brought on by increased carotid bodies which are sensors for oxygen levels that let the animal know its available oxygen supply.<ref name=":10" /> Yet, the sea lions cannot avoid the effects of gradual CO<sub>2</sub> build-up which eventually causes the sea lions to spend more time at the surface after multiple repeated dives to allow for enough built up CO<sub>2</sub> to be expired.<ref name=":10" />