Editing Heat exchanger (section)

===Humans===
The human nasal passages serve as a heat exchanger, with cool air being inhaled and warm air being exhaled.  Its effectiveness can be demonstrated by putting the hand in front of the face and exhaling, first through the nose and then through the mouth.  Air exhaled through the nose is substantially cooler.<ref>{{cite web |url=https://apps.dtic.mil/sti/citations/AD0293194 |title=Heat Loss from the Respiratory Tract in Cold |publisher=Defense Technical Information Center |date=April 1955 |last1=Webb|first1=Paul |url-status=dead |archive-url= https://web.archive.org/web/20220808095847/https://apps.dtic.mil/sti/citations/AD0293194 |archive-date= Aug 8, 2022 }}</ref><ref>{{cite book |title=Eckert animal physiology: mechanisms and adaptations |last=Randall |first=David J. |author2=Warren W. Burggren |author3=Kathleen French |author4=Roger Eckert |year=2002 |publisher=Macmillan |isbn=978-0-7167-3863-3 |page=[https://archive.org/details/eckertanimalphys00rand/page/587 587] |url-access=registration |url=https://archive.org/details/eckertanimalphys00rand/page/587 }}</ref> This effect can be enhanced with clothing, by, for example, wearing a scarf over the face while breathing in cold weather.

In species that have external testes (such as human), the artery to the testis is surrounded by a mesh of veins called the [[pampiniform plexus]]. This cools the blood heading to the testes, while reheating the returning blood.