ROGER HARRIS / SCIENCE PHOTO LIBRARY ROGER HARRIS / SCIENCE PHOTO LIBRARY
Red and white blood cells. Computer artwork of a blood vessel containing red and white blood cells. 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. White blood cells, or leucocytes, defend the body from foreign pathogens, for example bacteria. Some leucocytes produce antibodies, whereas others engulf foreign cells (phagocytosis). Red blood cells are produced in bone marrow. White cells are produced there also but some migrate through blood vessels to mature elsewhere, for example in the thymus gland.
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