Red blood cells

Red blood cells, coloured scanning electron micrograph (SEM). The main function of red blood cells (erythrocytes) is to distribute oxygen to body tissues, and to carry waste carbon dioxide back to the lungs. Each mature red blood cell lacks a nucleus and the interior is packed with haemoglobin, a red iron-containing pigment that has an oxygen-carrying capacity. Red blood cells are biconcave, giving them a large surface area for gas exchange, and highly elastic, enabling them to pass through narrow capillary vessels. Magnification: x2100 when printed at 10 centimetres wide.