Red blood cells. Coloured scanning electron micrograph (SEM) of red blood cells. Amongst the red blood cells are white blood cells (yellow) and a platelet (blue) at lower right. Some of the red blood cells are in the rouleau formation, long stacks of cells, such as those seen at top right. Red blood cells often clump together in this way because of their shape. Each cubic millimetre of blood contains around five million of these tiny, flexible disc-shaped cells. The red colour comes from the protein haemoglobin, which picks up oxygen in the lungs and distributes it around the body. Magnification: x1175 at 6x7cm size.
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