Editing Blood (section)

==={{anchor|Oxygen transport}}Oxygen transport===
{{Further|Oxygen saturation (medicine)}}
[[File:Oxyhaemoglobin dissociation curve.png|thumb|Basic hemoglobin saturation curve. It is moved to the right in higher acidity (more dissolved carbon dioxide) and to the left in lower acidity (less dissolved carbon dioxide)|left]]
About 98.5%<ref>{{Cite book|title=Fundamentals of anatomy & physiology|last=Frederic|first=Martini|date=2009|publisher=Pearson/Benjamin Cummings|others=Nath, Judi Lindsley|isbn=978-0321539106|edition= 8th |location=San Francisco|pages=657|oclc=173683666}}</ref> of the [[oxygen]] in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the [[hemoglobin]]. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in [[mammal]]s and many other species. Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O<sub>2</sub> per gram hemoglobin,<ref>{{cite journal | vauthors = Dominguez de Villota ED, Ruiz Carmona MT, Rubio JJ, de Andrés S | s2cid = 10029560 | title = Equality of the in vivo and in vitro oxygen-binding capacity of haemoglobin in patients with severe respiratory disease | journal = British Journal of Anaesthesia | volume = 53 | issue = 12 | pages = 1325–8 | date = December 1981 | pmid = 7317251 | doi = 10.1093/bja/53.12.1325 | doi-access = free }}</ref> which increases the total [[blood oxygen capacity]] seventyfold,<ref name=brsphys>{{cite book |last=Costanzo |first=Linda S. |name-list-style=vanc |title=Physiology |publisher=Lippincott Williams & Wilkins |location=Hagerstown, Maryland |year=2007 |isbn=978-0-7817-7311-9 |url-access=registration |url=https://archive.org/details/physiology00cost_0 }}</ref> compared to if oxygen solely were carried by its solubility of 0.03&nbsp;ml O<sub>2</sub> per liter blood per mm&nbsp;Hg partial pressure of oxygen (about 100&nbsp;mm&nbsp;Hg in arteries).<ref name=brsphys/>

With the exception of pulmonary and [[umbilical arteries]] and their corresponding veins, arteries carry '''oxygenated blood''' away from the heart and deliver it to the body via [[arterioles]] and [[capillaries]], where the oxygen is consumed; afterwards, [[venule]]s and veins carry '''deoxygenated blood''' back to the heart.

Under normal conditions in adult humans at rest, hemoglobin in blood leaving the lungs is about 98–99% [[Oxygen saturation (medicine)|saturated with oxygen]], achieving an oxygen delivery between 950 and 1150 ml/min<ref name=edwards>[http://www.edwards.com/SiteCollectionImages/edwards/products/presep/ar04313hemodynpocketcard.pdf Edwards Lifesciences LLC – Normal Hemodynamic Parameters – Adult] {{webarchive|url=https://web.archive.org/web/20101110081655/http://www.edwards.com/SiteCollectionImages/edwards/products/presep/ar04313hemodynpocketcard.pdf |date=10 November 2010 }} 2009</ref> to the body. In a healthy adult at rest, oxygen consumption is approximately 200–250 ml/min,<ref name=edwards/> and deoxygenated blood returning to the lungs is still roughly 75%<ref>{{cite web |url=http://home.hia.no/~stephens/ventphys.htm|archive-url=https://web.archive.org/web/20100323054138/http://home.hia.no/~stephens/ventphys.htm|url-status=dead|archive-date=23 March 2010 |title=Ventilatory Physiology and Endurance |date=23 March 2010 |access-date=4 March 2017}}</ref><ref>[https://web.archive.org/web/20040224085741/http://groups.msn.com/TransplantSupportLungHeartLungHeart/oxygen2.msnw Transplant Support- Lung, Heart/Lung, Heart] MSN groups</ref> (70 to 78%)<ref name=edwards/> saturated. Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial blood can drop to 95% or less under these conditions.<ref>{{cite journal | vauthors = Mortensen SP, Dawson EA, Yoshiga CC, Dalsgaard MK, Damsgaard R, Secher NH, González-Alonso J | title = Limitations to systemic and locomotor limb muscle oxygen delivery and uptake during maximal exercise in humans | journal = The Journal of Physiology | volume = 566 | issue = Pt 1 | pages = 273–85 | date = July 2005 | pmid = 15860533 | pmc = 1464731 | doi = 10.1113/jphysiol.2005.086025 | display-authors = etal }}</ref> Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia). Sustained hypoxia (oxygenation less than 90%), is dangerous to health, and severe hypoxia (saturations less than 30%) may be rapidly fatal.<ref>{{cite web |url=http://manbit.com/PAC/chapters/P30.cfm|archive-url=https://web.archive.org/web/20100925053056/http://manbit.com/PAC/chapters/P30.cfm|url-status=dead|archive-date=25 September 2010 |title=Blood gas and Saturation measurements |date=25 September 2010 |access-date=4 March 2017}}</ref>

A [[fetus]], receiving oxygen via the [[placenta]], is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), so fetuses produce another form of hemoglobin with a much higher affinity for oxygen ([[Fetal hemoglobin|hemoglobin F]]) to function under these conditions.<ref>{{cite web |url=http://members.aol.com/Bio50/LecNotes/lecnot20.html|archive-url=https://web.archive.org/web/19990502195422/http://members.aol.com/Bio50/LecNotes/lecnot20.html|url-status=dead|archive-date=2 May 1999 |title=Lecture Notes-20 |date=2 May 1999 |access-date=4 March 2017}}</ref>