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A cell that contains haemoglobin and can carry oxygen to the body. Also called a red blood cell (RBC). The reddish colour is due to haemoglobin. Erythrocytes are biconcave in shape which increases the cells surface area and facilitates the diffusion of oxygen and carbon dioxide. This shape is maintained by a cytoskeleton composed of several proteins. Erythrocytes are very flexible and changes shapes when flowing through capillaries. Immature erythrocytes, called the reticulocytes normally account for 1-2 percent of red blood cells in the blood. Red blood cells erythrocytes are the most common type of blood cell and the vertebrate organism’s principal means of delivering oxygen (O2) to the body tissues through the blood flow through the circulatory system. They take up oxygen in the lungs or gills and release it while squeezing through the body’s capillaries. These cells cytoplasm is rich in haemoglobin, an iron containing biomolecules that can bind oxygen and is responsible for the blood’s red colour. In humans, mature red blood cells are oval and flexible biconcave disks. They lack a cell nucleus and most organelles to accommodate maximum space for haemoglobin. 2.4 million New erythrocytes are produced per second. The cells develop in the bone marrow and circulate for about 100-120 days in the body before their components are recycled by macrophages. Each circulation takes about 20 seconds approximately a quarter of the cells in the human body are red blood cells. Red blood corpuscles (an archaic term), haematoid, erythroid cells or erythrocytes (from Greek erythros for “red” and kytos for “hollow”, with cytes translated as “cell” in modern usage).

The first person to describe red blood cells was the young Dutch biologist Jan Swammerdam, who had used an early microscope in 1658 to study the blood of a frog. Unaware of this work, Anton Van Leeuwenhoek provided another microscopic description in 1674; this time provided a more precise description of the red blood cells, even approximating their size, “25,000 times smaller than a grain of sand. In 1901, Karl Landsteiner published his discovery of the three main blood groups, A, B, and C (which he latter renamed O). Landsteiner described the regular patterns in which reaction occurred when serum was mixed with red blood cells, thus identifying compatible and conflicting combinations between these blood groups. A year later Alfred Von Decastello and Adriano Sturli, two colleagues of Landsteiner, identified a fourth blood group, AB. In 1959, by use of x-ray crystallography Dr. Max Pentz was able to unravel the structure of haemoglobin, the red blood cell that carries oxygen.

It has been recently demonstrated that erythrocytes can also synthesize nitric oxygen enzymatically, using L-arginine as substrate, just like endocrine cells. Exposure of erythrocytes to physiological levels of shear stress activates nitric oxide synthase and export of nitric oxide, which may contribute to the regulation of vascular tonus. Erythrocytes can also produce hydrogen sulphide, a signalling gas that acts to relax vessel walls. It is believed that the cardio - protective effects of garlic are due to erythrocytes converting its sulphur compounds into human sulphide. Erythrocytes also play a part in the body’s immune response, when lysed by pathogens such as bacteria; their haemoglobin releases free radicals which break down the pathogen’s cell wall and membrane, killing it. When their haemoglobin molecules are deoxygenated, erythrocytes releases-s-nitrosothiols which also acts to dilate vessels, thus directing blood to areas of the body depleted of oxygen. When erythrocytes undergo shear stress in constricted vessels, they release ATP which causes the...
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