FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Platelet. Artwork showing the internal structure of platelets, fragments of white blood cells that under normal circumstances are small and biconcave in form (as here). When activated by breaks in blood vessel walls, they extend long filaments that adhere to the vessel wall and each other, forming a clot. The microtubules (white circles) around the fragment edge facilitate this change in shape. Alpha granules (green) contains growth factors that aid clotting. Also seen are mitochondria (white ovals) and glycogen granules (red), which provide energy for the platelet, and Golgi apparatus (right and left), which modify and package proteins.
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