DR GOPAL MURTI / SCIENCE PHOTO LIBRARY DR GOPAL MURTI / SCIENCE PHOTO LIBRARY
Red blood cells. Coloured scanning electron micrograph (SEM) of a group of human red blood cells (erythrocytes). Mature erythrocytes are biconcave in shape, as seen here, with a diameter of about 7 microns. They have no nucleus and the cytoplasm is packed with haemoglobin, a red pigment by which oxygen is transported around the body. During its short life (about four months) a red blood cell covers about 15km every day for a total of 1500km. It transports oxygen from the lungs to the tissues where it is necessary for all metabolic processes. In a litre of blood there are normally 5000 billion red blood cells. Magnification: x2,200 at 6x7cm size.
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