Red blood cell 67158 220023633 2008-06-17T22:38:47Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Redirect6|Red cell|the US military term|Red Cell|The NCIS episode|Red Cell (NCIS)}}'''Red blood cells''' are the most common type of [[blood cell]] and the [[vertebrate]] [[body]]'s principal means of delivering [[oxygen]] from the [[lung]]s or [[gill]]s to body tissues via the [[blood]].<ref>Laura Dean. [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=rbcantigen.TOC&depth=2 ''Blood Groups and Red Cell Antigens'']</ref> [[Image:redbloodcells.jpg|right|frame|Human red blood cells]] Red blood cells are also known as '''RBCs''', '''red blood corpuscles''' (an archaic term), '''haematids''' or '''erythrocytes''' (from [[Greek language|Greek]] ''erythros'' for "red" and ''kytos'' for "hollow", with ''cyte'' translated as "cell" in modern usage). A '''schistocyte''' is a red blood cell undergoing [[cell fragmentation]], or a fragmented part of a red blood cell. ==Vertebrate erythrocytes== [[Image:Red White Blood cells.jpg|thumb|From left to right: human [[erythrocyte]], [[Platelet|thrombocyte]], [[leukocyte]].]] Erythrocytes consist mainly of [[hemoglobin]], a complex [[molecule]] containing [[heme]] groups whose [[iron]] atoms temporarily link to oxygen molecules in the lungs or gills and release them throughout the body. Oxygen can easily [[diffusion|diffuse]] through the red blood cell's [[cell membrane]]. Hemoglobin also carries some of the waste product [[carbon dioxide]] back from the tissues. (In humans, less than 2% of the total oxygen, and most of the carbon dioxide, is held in solution in the [[blood plasma]]). A related compound, [[myoglobin]], acts to store oxygen in [[muscle]] cells.<ref>{{cite book | last = Maton | first = Anthea | authorlink = | coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | date = 1993 | location = Englewood Cliffs, New Jersey, USA | pages = | url = | doi = | id = | isbn = 0-13-981176-1}}</ref> The color of erythrocytes is due to the heme group of hemoglobin. The [[blood plasma]] alone is straw-colored, but the red blood cells change color depending on the state of the hemoglobin: when combined with oxygen the resulting oxyhemoglobin is scarlet, and when oxygen has been released the resulting deoxyhemoglobin is darker, appearing bluish through the vessel wall and skin. [[Pulse oximetry]] takes advantage of this color change to directly measure the [[artery|arterial]] blood [[oxygen saturation]] using [[colorimetric]] techniques. The sequestration of oxygen carrying proteins inside specialized cells (rather than having them dissolved in body fluid) was an important step in the [[evolution]] of [[vertebrates]]; it allows for less [[viscosity|viscous]] blood, higher concentrations of oxygen, and better diffusion of oxygen from the blood to the tissues. The size of erythrocytes varies widely among vertebrate species; erythrocyte width is on average about 25% larger than [[capillary]] diameter and it has been hypothesized that this improves the oxygen transfer from erythrocytes to tissues.<ref name=snyder>{{Cite journal | doi = 10.1093/icb/39.2.189 | volume = 39 | issue = 2 | pages = 189–198 | last = SNYDER | first = GREGORY K. | coauthors = BRANDON A. SHEAFOR | title = Red Blood Cells: Centerpiece in the Evolution of the Vertebrate Circulatory System | journal = American Zoologist | date = 1999-04-01 | url = http://icb.oxfordjournals.org/cgi/content/abstract/39/2/189 }}</ref> The only known vertebrates that don't use erythrocytes for oxygen transport are the ice fishes (family [[Channichthyidae]]); they live in very oxygen rich cold water and transport oxygen freely dissolved in their blood.<ref>Ruud, J. T. 1954. Vertebrates without erythrocytes and blood pigment. ''Nature'' 117:848-850.</ref> In 2007 it was reported that erythrocytes also play a part in the body's [[immune response]]: when [[lysis|lysed]] by pathogens such as bacteria, their hemoglobin releases [[free radical]]s that break down the pathogen's cell wall and membrane, killing it.<ref>[http://www.dbs.nus.edu.sg/eventlist/happenings/details/2007/dingSTsep07.pdf Red blood cells do more than just carry oxygen. New findings by NUS team show they aggressively attack bacteria too.], ''[[The Straits Times]]'', 1 September 2007</ref><ref> Jiang N, Tan NS, Ho B, Ding JL. Respiratory protein-generated reactive oxygen species as an antimicrobial strategy. ''Nature Immunology'', 26 August 2007. PMID 17721536.</ref> ==Mammalian erythrocytes== Erythrocytes in [[mammal]]s are ''anucleate'' when mature, meaning that they lack a [[cell nucleus]] and as a result, have no [[DNA]]. Red blood cells have nuclei during early phases of development, but extrude them as they mature in order to provide more space for [[hemoglobin]]. In comparison, the erythrocytes of nearly all other [[vertebrate]]s have nuclei; the only known exception being [[salamander]]s of the ''[[Batrachoseps]]'' genus.<ref>W. D. Cohen. [http://www.springerlink.com/content/q88qv27q77620746/ The cytomorphic system of anucleate non-mammalian erythrocytes.] ''Protoplasma'', vol 113 no 1, February 1982</ref> Mammalian erythrocytes also lose their other [[organelle]]s such as their [[mitochondrion|mitochondria]]. As a result, red blood use ''none'' of the oxygen they transport; they produce the energy carrier [[Adenosine triphosphate|ATP]] by [[fermentation (biochemistry)|fermentation]], via [[glycolysis]] of [[glucose]] followed by [[lactic acid]] production. Furthermore, red cells do not have an [[insulin receptor]] and thus glucose uptake is not regulated by [[insulin]]. Because of the lack of nucleus and organelles, the red blood cells cannot synthesize any [[RNA]], and consequently they cannot divide or repair themselves. Mammalian erythrocytes are biconcave disks: flattened and depressed in the center, with a dumbbell-shaped cross section. This shape (as well as the loss of organelles and nucleus) optimizes the cell for the exchange of oxygen with its surroundings. The cells are flexible so as to fit through tiny [[capillary|capillaries]], where they release their oxygen load. Erythrocytes are circular, except in the [[camel]] family [[Camelidae]], where they are oval. In large blood vessels, red blood cells sometimes occur as a stack, flat side next to flat side. This is known as ''rouleaux formation'', and it occurs more often if the levels of certain serum proteins are elevated, as for instance during [[inflammation]]. The [[spleen]] acts as a reservoir of red blood cells, but this effect is somewhat limited in humans. In some other mammals such as [[dog]]s and [[horse]]s, the spleen sequesters large numbers of red blood cells which are dumped into the blood during times of exertion stress, yielding a higher oxygen transport capacity. [[Image:Gray453.png|thumb|400px|Erythrocytes: (a) seen from surface; (b) in profile, forming rouleaux; (c) rendered spherical by water; (d) rendered crenate by salt. (c) and (d) do not normally occur in the body.]] ==Human erythrocytes== The diameter of a typical human erythrocyte disk is [[1 E-6 m|6&ndash;8 µm]], much smaller than most other [[List of distinct cell types in the adult human body|human cells]]. A typical erythrocyte contains about 270 million hemoglobin molecules, with each carrying four heme groups. Adult humans have roughly [[1 E12|2&ndash;3 &times; 10<sup>13</sup>]] red blood cells at any given time (women have about 4 to 5 million erythrocytes per [[liter|microliter]] (cubic millimeter) of blood and men about 5 to 6 million; people living at high altitudes with low oxygen tension will have more). Red blood cells are thus much more common than the other blood particles: There are about 4,000&ndash;11,000 [[white blood cells]] and about 150,000&ndash;400,000 [[platelet]]s in each microliter of human blood. The red blood cells of an average adult human male store collectively about 2.5 grams of [[iron]], representing about 65% of the total iron contained in the body.<ref>[http://www.med-ed.virginia.edu/courses/path/innes/nh/iron.cfm Iron Metabolism], University of Virginia Pathology. Accessed 22 September 2007.</ref><ref>[http://sickle.bwh.harvard.edu/iron_transport.html Iron Transport and Cellular Uptake] by Kenneth R. Bridges, Information Center for Sickle Cell and Thalassemic Disorders. Accessed 22 September 2007.</ref> (See [[Human iron metabolism]].) ===Life cycle=== The process by which red blood cells are produced is called [[erythropoiesis]]. Erythrocytes are continuously being produced in the red [[bone marrow]] of large bones, at a rate of about 2 million per second. (In the [[embryo]], the [[liver]] is the main site of red blood cell production.) The production can be stimulated by the [[hormone]] [[erythropoietin]] (EPO), synthesised by the kidney; which is used for [[Doping (sport)|doping in sports]]. Just before and after leaving the bone marrow, they are known as [[reticulocyte]]s which comprise about 1% of circulating red blood cells. Erythrocytes develop from committed stem cells through reticulocytes to mature erythrocytes in about 7 days and live a total of about 120 days. The aging erythrocyte undergoes changes in its [[plasma membrane]], making it susceptible to recognition by [[phagocyte]]s and subsequent [[phagocytosis]] in the [[spleen]], liver and bone marrow. Much of the important breakdown products are recirculated in the body. The heme constituent of hemoglobin are broken down into Fe<sup>3+</sup> and [[biliverdin]]. The biliverdin is reduced to [[bilirubin]], which is released into the plasma and recirculated to the liver bound to [[albumin]]. The iron is released into the plasma to be recirculated by a carrier protein called [[transferrin]]. Almost all erythrocytes are removed in this manner from the circulation before they are old enough to [[Hemolysis|hemolyze]]. Hemolyzed hemoglobin is bound to a protein in plasma called [[haptoglobin]] which is not excreted by the kidney. ===Surface proteins=== There are two main types of [[protein]]s on the surface: * [[Band 3]] * [[Glycophorin]]s such as [[glycophorin C]] The [[blood type]]s of humans are due to variations in surface [[glycoprotein]]s of erythrocytes. ===Separation and blood doping=== Red blood cells can be separated from [[blood plasma]] by [[centrifugation]]. During [[blood donation|plasma donation]], the red blood cells are pumped back into the body right away, and the plasma is collected. Some athletes have tried to improve their performance by [[blood doping]]: first about 1 litre of their blood is extracted, then the red blood cells are isolated, frozen and stored, to be reinjected shortly before the competition. (Red blood cells can be conserved for 5 weeks at &minus;79 °C.) This practice is hard to detect but may endanger the human [[cardiovascular system]] which is not equipped to deal with blood of the resulting higher [[viscosity]]. == Diseases and diagnostic tools == [[Image:Sicklecells.jpg|frame|right|Affected by [[Sickle-cell disease]], red blood cells alter shape and threaten to damage internal organs.]] [[Blood diseases]] involving the red blood cells include: * [[Anemia]]s (or anaemias) are diseases characterized by low oxygen transport capacity of the blood, because of low red cell count or some abnormality of the red blood cells or the hemoglobin. ** [[Iron deficiency anemia]] is the most common anemia; it occurs when the dietary intake or absorption of [[iron]] is insufficient, and hemoglobin, which contains iron, cannot be formed ** [[Sickle-cell disease]] is a genetic disease that results in abnormal hemoglobin molecules. When these release their oxygen load in the tissues, they become insoluble, leading to mis-shaped red blood cells. These sickle shaped red cells are rigid and cause blood vessel blockage, pain, strokes, and other tissue damage. ** [[Thalassemia]] is a genetic disease that results in the production of an abnormal ratio of hemoglobin subunits. ** [[Spherocytosis]] is a genetic disease that causes a defect in the red blood cell's [[cytoskeleton]], causing the red blood cells to be small, sphere-shaped, and fragile instead of donut-shaped and flexible. ** [[Pernicious anemia]] is an [[autoimmune disease]] wherein the body lacks [[intrinsic factor]], required to absorb [[vitamin B12]] from food. Vitamin B12 is needed for the production of hemoglobin. ** [[Aplastic anemia]] is caused by the inability of the [[bone marrow]] to produce blood cells. ** [[Pure red cell aplasia]] is caused by the inability of the bone marrow to produce only red blood cells. ** [[Hemolysis]] is the general term for excessive breakdown of red blood cells. It can have several causes. * The [[malaria]] parasite spends part of its life-cycle in red blood cells, feeds on their hemoglobin and then breaks them apart, causing fever. Both [[sickle-cell disease]] and [[thalassemia]] are more common in malaria areas, because these mutations convey some protection against the parasite. * [[Polycythemia]]s (or erythrocytoses) are diseases characterized by a surplus of red blood cells. The increased viscosity of the blood can cause a number of symptoms. **In [[polycythemia vera]] the increased number of red blood cells results from an abnormality in the bone marrow. * Several [[microangiopathy|microangiopathic diseases]], including [[disseminated intravascular coagulation]] and [[thrombotic microangiopathies]], present with [[pathognomonic]] (diagnostic) RBC fragments called schistocytes. These pathologies generate [[fibrin]] strands that sever RBCs as they try to move past a [[thrombus]]. Several [[blood test]]s involve red blood cells, including the ''RBC count'' (the number of red blood cells per volume of blood) and the [[hematocrit]] (percentage of blood volume occupied by red blood cells). The [[blood type]] needs to be determined to prepare for a [[blood transfusion]] or an [[organ transplantation]]. == History == The first person to describe red blood cells was probably the young [[Netherlands|Dutch]] biologist [[Jan Swammerdam]], who had used an early [[microscope]] in [[1658]] to study the blood of a frog.<ref>"Swammerdam, Jan (1637–1680)", McGraw Hill AccessScience, 2007. Accessed 27 December 2007.</ref> Unaware of this work, [[Anton van Leeuwenhoek]] provided another microscopic description in [[1674]].<ref>[http://www.pbs.org/wnet/redgold Red Gold - Blood History Timeline], [[PBS]] 2002. Accessed 27 December 2007.</ref> ==References== {{reflist}} == External links == * [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowTOC&rid=rbcantigen.TOC&depth=2 ''Blood Groups and Red Cell Antigens''] by Laura Dean. Searchable and downloadable online textbook in the public domain. * [http://www.genomesize.com/cellsize/ Database of vertebrate erythrocyte sizes]. * [http://www.pbs.org/wnet/redgold Red Gold], [[PBS]] site containing facts and history {{Transfusion medicine}} {{Blood}} [[Category:Human cells]] [[Category:Blood cells]] [[Category:Respiration]] [[Category:Hematology]] [[af:Rooibloedsel]] [[ar:خلية حمراء]] [[bn:লোহিত রক্তকণিকা]] [[bs:Crvene krvne ćelije]] [[bg:Еритроцит]] [[ca:Glòbul vermell]] [[cs:Červená krvinka]] [[de:Erythrozyt]] [[dv:ލޭގެ ރަތް ސެލް]] [[es:Eritrocito]] [[eo:Eritrocito]] [[eu:Globulu gorri]] [[fa:گویچه سرخ]] [[fr:Érythrocyte]] [[ko:적혈구]] [[hr:Eritrociti]] [[id:Sel darah merah]] [[ia:Erythrocyto]] [[is:Rauð blóðkorn]] [[it:Globulo rosso]] [[he:תא דם אדום]] [[pam:Erythrocyte]] [[ka:ერითროციტები]] [[la:Erythrocyti]] [[lt:Raudonasis kraujo kūnelis]] [[hu:Vörösvértest]] [[mk:Еритроцит]] [[mn:Цусны улаан эс]] [[nl:Rode bloedcel]] [[ja:赤血球]] [[no:Rødt blodlegeme]] [[nn:Raud blodlekam]] [[oc:Eritrocit]] [[pl:Erytrocyt]] [[pt:Hemácia]] [[ro:Eritrocit]] [[qu:Puka yawar kawsaykuq]] [[ru:Эритроциты]] [[sq:Eritrociti]] [[simple:Red blood cell]] [[sk:Červená krvinka]] [[sl:Eritrocit]] [[sr:Црвена крвна зрнца]] [[su:Sél getih beureum]] [[fi:Punasolu]] [[sv:Röd blodkropp]] [[ta:இரத்தச் சிவப்பணு]] [[te:ఎర్ర రక్త కణం]] [[th:เม็ดเลือดแดง]] [[vi:Hồng cầu]] [[tr:Alyuvar]] [[uk:Еритроцити]] [[ur:سرخ خونی خلیہ]] [[zh:红血球]]