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Red Blood Cells


Red blood cells are also known as RBCs, red cells, red blood corpuscles (an archaic term), haematids, erythroid cells or erythrocytes (from Greek erythros for “red“ and kytos for “hollow vessel“, with -cyte translated as “cell“ in modern usage). RBCs are the most common type of blood cell and the vertebrate organism’s principal means of delivering oxygen (O2) to the body tissues – via blood flow through the circulatory system. RBCs take up oxygen in the lungs or gills and release it into tissues while squeezing through the body’s 1) ___. The cytoplasm of erythrocytes is rich in hemoglobin, which is an iron-containing biomolecule that can bind oxygen and is responsible for the 2) ___ color of the cells. The cell membrane is composed of proteins and lipids, and this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and specifically the capillary network. In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell 3) ___ and most organelles, in order to accommodate maximum space for hemoglobin.


Approximately 2.4 million new erythrocytes are produced per second in human adults. The cells develop in the bone 4) ___ 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. Packed red blood cells (pRBC) are red blood cells that have been donated, processed, and stored in a blood bank for blood5) ___.


As a result of not containing mitochondria, these RBCs use none of the oxygen they transport; instead they produce the energy carrier ATP by the glycolysis of glucose and lactic acid fermentation on the resulting pyruvate. Because of the lack of nuclei and organelles, mature red blood cells do not contain DNA and cannot synthesize any RNA, and consequently cannot divide. They have limited repair capabilities. This also ensures that no virus can evolve to target mammalian red blood 6) ___. When erythrocytes undergo shear stress in constricted vessels, they release ATP, which causes the vessel walls to relax and dilate so as to promote normal blood 7) ___. When their hemoglobin molecules are deoxygenated, erythrocytes release S-nitrosothiols, which also act to dilate blood vessels, thus directing more blood to areas of the body depleted of 8) ___. Erythrocytes can also synthesize nitric oxide enzymatically, using L-arginine as substrate, as do endothelial cells. Exposure of erythrocytes to physiological levels of shear stress activates nitric 9) ___ synthase and export of nitric oxide, which may contribute to the regulation of vascular tonus. Erythrocytes can also produce hydrogen sulfide, a signaling gas that acts to relax vessel walls. It is believed that the cardioprotective effects of garlic are due to erythrocytes converting its sulfur compounds into hydrogen sulfide. Erythrocytes also play a part in the body’s immune response: when lysed by pathogens such as bacteria, their hemoglobin releases free 10) ___, which break down the pathogen’s cell wall and membrane, killing it. Sources: WebMD; Wikipedia; ScienceDaily


ANSWERS: 1) capillaries; 2) red; 3) nucleus; 4) marrow; 5) transfusions; 6) cells; 7) flow; 8) oxygen; 9) oxide; 10) radicals



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