Electron micrographs of three different functional stages of an osteocyte. a. Relatively quiescent osteocyte that contains only a few profiles of rER and a few mitochondria (M). The cell virtually fills the lacuna that it occupies; the arrows indicate where cytoplasmic processes extend into canaliculi. Hydroxyapatite crystals have been lost from the matrix, which is ordinarily mineralized (MM), but some hydroxyapatite crystals fill the pericellular space. The hydroxyapatite crystals obscure the other substances within the pericellular space. The dark band marking the boundary of the lacuna is the osmiophilic lamina (OL). x25,000. b. A formative osteocyte containing larger
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