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→Composition of Bone
****Have receptors for [[Bones - normal#Bone resorption|PTH]]: contract in response -> provide space for osteoclasts to attach
****Have receptors for [[Bones - normal#Bone resorption|PTH]]: contract in response -> provide space for osteoclasts to attach
***When inactive - less cytoplasm -> flattened
***When inactive - less cytoplasm -> flattened
**'''Osteocytes''': osteoblasts embedded in their own matrix; reside within '''lacunae''' and are interconnected via channels forming '''canaliculi'''
**'''Osteocytes''': osteoblasts embedded in their own matrix; reside within '''lacunae''' and are interconnected via channels forming '''canaliculi'''
***'''Canaliculi''' create connections to form a huge neural-like junctional organization
***'''Canaliculi''' create connections to form a huge neural-like junctional organization
***Reach through canaliculi in mineralised bone matrix
***Reach through canaliculi in mineralised bone matrix
***Regulate composition of bone fluid
***Regulate composition of bone fluid
**'''Osteoclasts''': giant (multinucleate monocytes) cells which act to resorb bone ECM
**'''Osteoclasts''': giant (multinucleate monocytes) cells which act to resorb bone ECM
***Histologically:
***Histologically:
****Have receptors for [[Bones - normal#Bone resorption|calcitonin]]
****Have receptors for [[Bones - normal#Bone resorption|calcitonin]]
****Involute their brush border in response
****Involute their brush border in response
**Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from stromal fibroblastic system ('''osteoprogenitor cells'''); osteoclasts from haematopoietic system
**Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from stromal fibroblastic system ('''osteoprogenitor cells'''); osteoclasts from haematopoietic system