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Coronary capillary. Coloured scanning electron micrograph (SEM) of a section through a freeze- fractured coronary capillary blood vessel. Red blood cells (erythrocytes, red) are seen in the capillary. The coronary capillaries supply the contracting heart muscle with oxygen, transported from the lungs by the erythrocytes. Metabolic waste is removed from the muscle by the erythrocytes. Magnification: x3000 at 6x7cm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER)