Editing Red blood cell (section)

===Secondary functions===
When red blood cells undergo [[shear stress]] in constricted vessels, they release [[adenosine triphosphate|ATP]], which causes the vessel walls to relax and dilate so as to promote normal blood flow.<ref>{{cite journal | vauthors = Wan J, Ristenpart WD, Stone HA | title = Dynamics of shear-induced ATP release from red blood cells | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 105 | issue = 43 | pages = 16432–16437 | date = October 2008 | pmid = 18922780 | pmc = 2575437 | doi = 10.1073/pnas.0805779105 | doi-access = free | bibcode = 2008PNAS..10516432W }}</ref>

When their hemoglobin molecules are deoxygenated, red blood cells release [[S-Nitrosothiol]]s, which also act to dilate blood vessels,<ref>{{cite journal | vauthors = Diesen DL, Hess DT, Stamler JS | title = Hypoxic vasodilation by red blood cells: evidence for an s-nitrosothiol-based signal | journal = Circulation Research | volume = 103 | issue = 5 | pages = 545–553 | date = August 2008 | pmid = 18658051 | pmc = 2763414 | doi = 10.1161/CIRCRESAHA.108.176867 }}</ref> thus directing more blood to areas of the body depleted of oxygen.

Red blood cells can also synthesize [[nitric oxide]] enzymatically, using [[L-arginine]] as substrate, as do [[endothelial cell]]s.<ref>{{cite journal | vauthors = Kleinbongard P, Schulz R, Rassaf T, Lauer T, Dejam A, Jax T, Kumara I, Gharini P, Kabanova S, Ozüyaman B, Schnürch HG, Gödecke A, Weber AA, Robenek M, Robenek H, Bloch W, Rösen P, Kelm M | display-authors = 6 | title = Red blood cells express a functional endothelial nitric oxide synthase | journal = Blood | volume = 107 | issue = 7 | pages = 2943–2951 | date = April 2006 | pmid = 16368881 | doi = 10.1182/blood-2005-10-3992 | name-list-style = vanc | s2cid = 38270024 | doi-access = free }}</ref> Exposure of red blood cells to physiological levels of shear stress activates [[nitric oxide synthase]] and export of nitric oxide,<ref>{{cite journal | vauthors = Ulker P, Sati L, Celik-Ozenci C, Meiselman HJ, Baskurt OK | title = Mechanical stimulation of nitric oxide synthesizing mechanisms in erythrocytes | journal = Biorheology | volume = 46 | issue = 2 | pages = 121–132 | year = 2009 | pmid = 19458415 | doi = 10.3233/BIR-2009-0532 }}</ref> which may contribute to the regulation of vascular tonus.

Red blood cells can also produce [[hydrogen sulfide]], a signalling gas that acts to relax vessel walls. It is believed that the cardioprotective effects of garlic are due to red blood cells converting its sulfur compounds into hydrogen sulfide.<ref>{{cite journal | vauthors = Benavides GA, Squadrito GL, Mills RW, Patel HD, Isbell TS, Patel RP, Darley-Usmar VM, Doeller JE, Kraus DW | display-authors = 6 | title = Hydrogen sulfide mediates the vasoactivity of garlic | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 104 | issue = 46 | pages = 17977–17982 | date = November 2007 | pmid = 17951430 | pmc = 2084282 | doi = 10.1073/pnas.0705710104 | author-link2 = Victor Darley-Usmar | doi-access = free | bibcode = 2007PNAS..10417977B }}</ref>

Red blood cells also play a part in the body's [[immune response]]: when [[lysis|lysed]] by pathogens such as bacteria, their hemoglobin releases [[free radical]]s, which break down the pathogen's cell wall and membrane, killing it.<ref>{{cite news| vauthors = Kesava S |title=Red blood cells do more than just carry oxygen; New findings by NUS team show they aggressively attack bacteria too|url=http://www.dbs.nus.edu.sg/events/media/info/2007/dingSTsep07.pdf|access-date=26 March 2013|newspaper=The Straits Times|date=1 September 2007}}</ref><ref>{{cite journal | vauthors = Jiang N, Tan NS, Ho B, Ding JL | title = Respiratory protein-generated reactive oxygen species as an antimicrobial strategy | journal = Nature Immunology | volume = 8 | issue = 10 | pages = 1114–1122 | date = October 2007 | pmid = 17721536 | doi = 10.1038/ni1501 | s2cid = 11359246 }}</ref>