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20-September-2008 09:55:55 - Red blood cell Red cell redirects here. For the US military term, see Red Cell. For The NCIS episode, see 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 lungs or gills to body tissues via the blood.1 Human red blood cells Human red blood cells Red blood cells are also known as RBCs, red blood corpuscles an archaic term, haematids or erythrocytes from 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. The capitalized term Red Blood Cells is the proper name in the US for erythrocytes in storage solution used in transfusion medicine.2 Contents 1 Vertebrate erythrocytes 1.1 Nucleus 2 Mammalian erythrocytes 3 Human erythrocytes 3.1 Life cycle 3.2 Surface proteins 3.3 Separation and blood doping 4 Diseases and diagnostic tools 5 History 6 References 7 External links Vertebrate erythrocytes From left to right: human erythrocyte, thrombocyte, leukocyte. From left to right: human erythrocyte, 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 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.3 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 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 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.4 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.5 In 2007 it was reported that erythrocytes also play a part in the body's immune response: when lysed by pathogens such as bacteria, their hemoglobin releases free radicals that break down the pathogen's cell wall and membrane, killing it.67 Nucleus Erythrocytes in mammals are anucleate when mature, meaning that they lack a cell nucleus and as a result, have no DNA. In comparison, the erythrocytes of nearly all other vertebrates have nuclei; the only known exception being salamanders of the Batrachoseps genus.8 Mammalian erythrocytes Mammalian erythrocytes have nuclei during early phases of development, but extrude them as they mature in order to provide more space for hemoglobin. Mammalian erythrocytes also lose their other organelles such as their mitochondria. As a result, the cells use none of the oxygen they transport; they produce the energy carrier ATP by fermentation, via glycolysis of glucose followed by lactic acid production. Furthermore, red cells do not have an insulin receptor and thus their glucose uptake is not regulated by insulin. Because of the lack of nuclei 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 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 dogs and horses, 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. 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. 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 6-8 µm, much smaller than most other human cells. A typical erythrocyte contains about 270 million hemoglobin molecules, with each carrying four heme groups. Adult humans have roughly 2-3 × 1013 red blood cells at any given time women have about 4 to 5 million erythrocytes per 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 4,000-11,000 white blood cells and about 150,000-400,000 platelets 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.910 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 in sports. Just before and after leaving the bone marrow, they are known as reticulocytes 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 phagocytes 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 Fe3+ 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 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 proteins on the surface: Band 3 Glycophorins such as glycophorin C The blood types of humans are due to variations in surface glycoproteins of erythrocytes. Separation and blood doping Red blood cells can be separated from blood plasma by centrifugation. During 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 -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 Affected by Sickle-cell disease, red blood cells alter shape and threaten to damage internal organs. Affected by Sickle-cell disease, red blood cells alter shape and threaten to damage internal organs. Blood diseases involving the red blood cells include: Anemias 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. Polycythemias 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 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. Hemolytic transfusion reaction is the destruction of donated red blood cells after a transfusion, mediated by host antibodies, often as a result of a blood type mismatch. Several blood tests 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 Dutch biologist Jan Swammerdam, who had used an early microscope in 1658 to study the blood of a frog.11 Unaware of this work, Anton van Leeuwenhoek provided another microscopic description in 1674.12 References ^ Laura Dean. Blood Groups and Red Cell Antigens ^ Circular of Information for Blood and Blood Products pdf. US Food and Drug Administration, AABB, American Red Cross, America's Blood Centers. Retrieved on 2008-07-28. ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright 1993. Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1. ^ SNYDER, GREGORY K.; BRANDON A. SHEAFOR 1999-04-01. Red Blood Cells: Centerpiece in the Evolution of the Vertebrate Circulatory System. American Zoologist 39 2: 189-198. doi:10.1093/icb/39.2.189. ^ Ruud, J. T. 1954. Vertebrates without erythrocytes and blood pigment. Nature 117:848-850. ^ 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 ^ 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. ^ W. D. Cohen. The cytomorphic system of anucleate non-mammalian erythrocytes. Protoplasma, vol 113 no 1, February 1982 ^ Iron Metabolism, University of Virginia Pathology. Accessed 22 September 2007. ^ Iron Transport and Cellular Uptake by Kenneth R. Bridges, Information Center for Sickle Cell and Thalassemic Disorders. Accessed 22 September 2007. ^ Swammerdam, Jan 1637-1680, McGraw Hill AccessScience, 2007. Accessed 27 December 2007. ^ Red Gold - Blood History Timeline, PBS 2002. Accessed 27 December 2007. External links Blood Groups and Red Cell Antigens by Laura Dean. Searchable and downloadable online textbook in the public domain. Database of vertebrate erythrocyte sizes. Red Gold, PBS site containing facts and history v d e Transfusion medicine General concepts Apheresis Plasmapheresis, Plateletpheresis, Leukapheresis - Blood transfusion - Coombs test - Cross-matching - Exchange transfusion - International Society of Blood Transfusion - Intraoperative blood salvage - ISBT 128 - Transfusion reactions Human blood group systems - Blood type ABO - Chido-Rodgers - Colton - Cromer - Diego - Dombrock - Duffy - Gerbich - GIL - Hh - Ii - Indian - JMH - Kell Xk - Kidd - Knops - LW - Lewis - Lutheran - MNS - OK - P - Raph - Rh - Scianna - T-Tn - Xg - Yt - Other Blood products Blood donation - Blood substitutes - Cryoprecipitate - Platelets - Plasma - Red blood cells - Whole blood v d e Blood General Plasma - Hematopoietic stem cells Lymphoid - WBC T cells: Cytotoxic CD8+, Helper CD4+/Regulatory, γδ, Natural Killer T cell B cells: Plasma, Memory Natural killer cells Lymphokine-activated killer cell Null cell Myeloid - WBC Monocytes/Macrophages Histiocytes, Kupffer cells, Langhans giant cells, Microglia, Osteoclasts, Epithelioid cells Granulocytes Neutrophil, Eosinophil, Basophil - Mast cell precursors Dendritic cells Langerhans cells, Follicular dendritic cells Megakaryoblast - Megakaryocyte - Platelets Myeloid - RBC Reticulocyte - Normoblast Retrieved from http://en..org/wiki/Red_blood_cell Categories: Human cells | Blood cells | Respiration | Hematology Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Afrikaans العربية বাংলা Bosanski БългарÑ?ки Català Česky Deutsch Þ‹Þ¨ÞˆÞ¬Þ€Þ¨Þ„Þ¦Þ?Þ° Español Esperanto Euskara Ù?ارسی Français í•œêµì–´ हिनà¥?दी Hrvatski Bahasa Indonesia Interlingua Ã?slenska Italiano עברית Kapampangan ქáƒ?რთული Latina Lietuvių Magyar МакедонÑ?ки Bahasa Melayu Монгол Nederlands 日本語 ‪Norsk bokmÃ¥l‬ ‪Norsk nynorsk‬ Occitan Polski Português Română Runa Simi РуÑ?Ñ?кий Shqip Simple English SlovenÄ?ina SlovenÅ¡Ä?ina СрпÑ?ки / Srpski Basa Sunda Suomi Svenska தமிழà¯? తెలà±?à°—à±? ไทย Tiếng Việt Türkçe УкраїнÑ?ька اردو ä¸æ–‡ This page was last modified on 20 August 2008, at 06:04
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