Bone is 70% inorganic mineral (such as calcium- and phosphate-containing hydroxyapatite) and 30% organic i.e. collagen. The inorganic component gives it its rigidity and strength, while the organic component gives it enough flexibility to prevent shattering. Bones have special cells that build the bone matrix while at the same time dissolve it. The balance of these opposing actions determine bone volume. The bone-building cells are osteoblasts while the bone-dissolving cells are osteoclasts.
Osteoblasts grow bone by secreting the inorganic minerals. Osteoclasts break it down by resorption using acid and an enzyme that breaks down collagen – collagenase.
The roulade-like part of the bone is the building block of bone called an osteon or Harvesian system. It contains the bone components, both inorganic and organic, and has connecting channels called canaliculi so cells can communicate with a central canal containing blood vessels and nerves. The canal is called the Harvesian canal.
This rolling arrangement enables the deposition of mineral in a way that achieves the bone matrix function of conferring strength.
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