DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Bone cells (osteocytes, yellow) in two bone lacunae (orange) from a fractured compact bone (grey), coloured scanning electron micrograph (SEM). A bone-producing cell is called an osteoblast. During bone formation osteoblasts become progressively trapped in the bone matrix at sites called lacunae (orange). The osteoblast produces osteoid, the organic bone matrix that is a mass of collagen fibres and glycoprotein cement. As soon as osteoid is formed, calcium salts crystallize inside it to form mineralized, compact bone. Osteoblasts that become trapped in lacunae (orange) in the bone become osteocytes. The osteocyte (yellow) has many processes or thread-like extensions that enter the bone through the bone canaliculi (orange), a network of minute channels linking nearby lacunae. Compact bone is made of collagen fibres and ground substances arranged in concentric sheets. Magnification: x600 when shortest axis printed at 25 millimetres.
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