ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY
Bone marrow. Light micrograph of stem cells forming blood cells in the bone marrow. White blood cells are large and purple, red blood cells are pale, and platelets are small purple granules. Platelet stem cells shedding platelets are visible as huge pink cells overflowing with granular cytoplasm (at centre right and upper right). Blood cells are produced constantly by the bone marrow as their lifespan is very short. Red blood cells, platelets & three types of white cell:granulocytes lymphocytes and monocytes, are all derived from a single ancestral cell known as the multipotenial stem cell. Magnification: x200 at 35mm size.
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