BSIP VEM / SCIENCE PHOTO LIBRARY BSIP VEM / SCIENCE PHOTO LIBRARY
Red blood cells in arteriole. Coloured Scanning Electron Micrograph (SEM) of red blood cells flow- ing through an arteriole in the wall of the lung's air sacs (alveoli). The cavities around the blood vessel are air spaces inside the lung. Red blood cells are tiny, flexible, disc-shaped cells that take up 40% of the volume of blood. Each cubic millimetre of blood contains about five million. Their colour comes from the protein haemoglobin, which picks up oxygen in the lungs and releases around the body. Constant physical pounding means that each red blood cell only lasts about four months. Magnification unknown.
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