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→Composition of Bone
*Consists of interconnected cells embedded in a calcified, collagenous matrix
*Consists of interconnected cells embedded in a calcified, collagenous matrix
*Living, dynamic, responsive tissue, growing and remodelling throughout life
*Living, dynamic, responsive tissue, growing and remodelling throughout life
Bone is comprised of:
Bone is comprised of:
*Matrix:
*Matrix:
**Organic component: "Collagen I", which resists tension
**'''Osteoid''': Organic component
**Bone-specific proteins: Osteonectin, Osteopontin, Osteocalcin
***Uncalcified, homogeneous substance, Stains light pink with H&E
**Inorganic component: Calcium, Phosphorus, Bicarbonate, Citrate, Potassium, Magnesium, Sodium, which provide rigidity
***"Type I Collagen" (90%), which resists tension
***Bone-specific proteins(10%): Osteonectin, Osteopontin, Osteocalcin
**'''Mineral''': Inorganic component, provides rigidity
**Crystalline lattice of calcium phosphate and calcium carbonate
**Also contains Mg, Mn, Zn, Cu, Na, F
**Accounts for 65% of bone
*Cells:
*Cells:
**'''Osteoblasts''': single layer of cuboidal cells which synthesize bone extracellular matrix (ECM)
**'''Osteoblasts''': single layer of mesenchymal cells which synthesize bone extracellular matrix (ECM)
***Basophilic cytoplasm; When inactive - less cytoplasm -> flattened
***When active, appear plump and cuboidal, with basophilic cytoplasm
***Produce bone matrix = '''osteoid''' - uncalcified
****Produce bone matrix = '''osteoid'''
****Homogeneous substance, Stains light pink with H&E
****Cell membranes are rich in alkaline phosphatase (ALP)
****Possibly involved in pumping calcium across membranes
****Promoted by growth factors
****Have receptors for [[Bones - normal#Bone resorption|PTH]]: contract in response -> provide space for osteoclasts to attach
***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