Editing Exhalation (section)

==Exhalation and gas exchange==

The main reason for exhalation is to rid the body of carbon dioxide, which is the waste product of gas exchange in humans.  Air is brought into the lungs through inhalation. Diffusion in the alveoli allows for the exchange of O<sub>2</sub> into the pulmonary capillaries and the removal of CO<sub>2</sub> and other gases from the pulmonary capillaries to be exhaled.  In order for the lungs to expel air the diaphragm relaxes, which pushes up on the lungs.  The air then flows through the trachea then through the larynx and pharynx to the nasal cavity and oral cavity where it is expelled out of the body.<ref name="secondary anatomy">{{cite journal |doi=10.1513/pats.201007-050RN |pmid=21364219 |title=Anatomy and Physiology of the Upper Airway |journal=Proceedings of the American Thoracic Society |volume=8 |issue=1 |pages=31–9 |year=2011 |last1=Sahin-Yilmaz |first1=A. |last2=Naclerio |first2=R. M. }}</ref> Exhalation takes longer than inhalation and it is believed to facilitate better exchange of gases.  Parts of the nervous system help to regulate respiration in humans. The exhaled air is not just carbon dioxide; it contains a mixture of other gases.  Human breath contains [[volatile organic compounds]] (VOCs).  These compounds consist of methanol, isoprene, acetone, ethanol and other alcohols.  The exhaled mixture also contains ketones, water and other hydrocarbons.<ref name=VOCs>{{cite journal |doi=10.1080/10473289.1999.10463831 |pmid=10352577 |title=Human Breath Emissions of VOCs |journal=Journal of the Air & Waste Management Association |volume=49 |issue=5 |pages=594–8 |year=1999 |last1=Fenske |first1=Jill D. |last2=Paulson |first2=Suzanne E. |doi-access=free }}</ref><ref name="secondary VOC">{{cite journal |pmid=20056112 |pmc=4009073 |year=2010 |last1=Weisel |first1=C. P. |title=Benzene exposure: An overview of monitoring methods and their findings |journal=Chemico-Biological Interactions |volume=184 |issue=1–2 |pages=58–66 |doi=10.1016/j.cbi.2009.12.030 }}</ref>   
           
It is during exhalation that the [[olfaction]] contribution to [[Flavor (taste)|flavor]] occurs in contrast to that of ordinary smell which occurs during the inhalation phase.<ref>{{cite journal |doi=10.1016/j.neulet.2010.02.024 |pmid=20171264 |title=Expiration: The moment we experience retronasal olfaction in flavor |journal=Neuroscience Letters |volume=473 |issue=2 |pages=92–6 |year=2010 |last1=Masaoka |first1=Yuri |last2=Satoh |first2=Hironori |last3=Akai |first3=Lena |last4=Homma |first4=Ikuo |s2cid=2671577 }}</ref>