Red blood cells. Coloured scanning electron micro- graph (SEM) of clusters of red blood cells (erythrocytes). Mature erythrocytes are biconcave in shape, as seen here. They have no nucleus and their 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 body tissues where it is necessary for all metabolic processes. In a litre of blood there are normally 5000 billion red blood cells. Magnification: unknown.
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