Red blood cells. Coloured scanning electron micrograph (SEM) of normal human red blood cells (erythrocytes). They are rounded and flattened into a biconcave shape, an adaptation which provides the maximum surface area for the exchange of gases. The principal function of red blood cells is to distribute and transport oxygen around the body. As the cell matures the nucleus and other internal organelles are lost, and it becomes filled with haemoglobin, a red iron- containing pigment with an efficient capacity to carry oxygen. Magnification: x800 at 35mm size.
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