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Red blood cells are the most common type of Blood Cell and are the Vertebrate Body 's principal means of delivering Oxygen from the Lung s or Gill s to body tissues via the Blood . Red blood cells are also known as RBCs or '''erythrocytes''' (from Greek ''erythros'' for "red" and ''kytos'' for "hollow", with ''cyte'' nowadays translated as "cell"). A '''schistocyte''' is a red blood cell undergoing fragmentation, or a fragmented part of a red blood cell. VERTEBRATE ERYTHROCYTES 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. 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, are held in solution in the Blood Plasma ). A related compound, Myoglobin , acts to store oxygen in Muscle cells. The color of erythrocytes is due to the heme group of hemoglobin. The blood plasma is straw-colored alone, but the red blood cells change colors due to 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 blood vessel walls. The keeping of oxygen-binding proteins in cells (rather than having them dissolved in body fluid) was an important step in the evolution of vertebrates; it allows for less Viscous blood and longer transport ways of oxygen. MAMMALIAN ERYTHROCYTES Erythrocytes in Mammal s are ''anucleate'' when mature, meaning that they don't have a Cell Nucleus and thus no DNA . In comparison, the erythrocytes of nearly all other Vertebrate s have nuclei; the only known exception is Salamander s of the '' Batrachoseps '' genus. Mammalian erythrocytes also lose their other Organelle s including their Mitochondria and produce energy by Fermentation , via Glycolysis of Glucose followed by Lactic Acid production. Like most cell types, red cells do not have an Insulin Receptor and thus glucose uptake is not regulated by Insulin . Mammalian erythrocytes are bi, 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 that are dumped into the blood during times of exertion stress, yielding a higher oxygen transport capacity. HUMAN ERYTHROCYTES The diameter of a typical human erythrocyte disk is 6–8 µm ; they are thus 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 s in a cubic millimeter of human blood. The red blood cells store collectively about 3.5 grams of Iron ; that's more than five times the iron stored by all the other tissues combined. 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. (In the Embryo , the Liver is the main site of red blood cell production.) The production can be stimulated by the Hormone Erythropoietin (EPO), which is used for Doping In Sports . Erythrocytes develop in about 7 days and live a total of about 120 days. The aging cells swell up to a sphere-like shape and are engulfed by Phagocyte s, destroyed and their materials are released into the blood. The main sites of destruction are the liver and the Spleen . The heme constituent of hemoglobin is eventually excreted as Bilirubin . The Blood Type s of humans are due to variations in surface Glycoprotein s of erythrocytes. Red blood cells can be separated from which is not equipped to deal with blood of the resulting higher Viscosity . DISEASES AND DIAGNOSTIC TOOLS , red blood cells alter shape and threaten to damage internal organs.]] Blood Diseases involving the red blood cells include:
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 In 1658 , the Dutch Jan Swammerdam was the first to describe red blood cells; he had used an early Microscope . EXTERNAL LINKS |
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