Red blood cells. Coloured scanning electron micrograph (SEM) of human red blood cells (erythrocytes). Red blood cells are biconcave in shape giving them a large surface area for gas exchange, and highly elastic enabling them to pass through narrow capillary vessels. The nucleus and other organelles are lost as the cell matures. Each cell is packed with haemoglobin, a red iron- containing pigment with an efficient oxygen carrying capacity. The main function of red blood cells is to distribute oxygen to body tissues and to carry the carbon dioxide waste product back to the lungs. Magnification: x3,150 at 5x7cm size.
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