Red blood cells. Computer artwork of red blood cells inside a blood vessel. Red blood cells, or erythrocytes, are biconcave disc-shaped cells. They contain the red pigment haemoglobin, which transports oxygen from the lungs to the body's cells, where it is used in respiration. The cells return carbon dioxide, the waste product of respiration, to the lungs to be exhaled. Red blood cells are produced in bone marrow. They have no nuclei. Blood vessels transport blood around the body. Arteries carry blood away from the heart. They branch (as seen here) forming capillaries, which supply tissues with oxygen, and then rejoin to form veins, which return to the heart.
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