Bone

Bone

1. Osteoprogenitor Cells

   • Osteoblasts
     • Osteocytes
       • Maintenance of Bone
       • Located in lacunae - one cell per lacuna
       • Cytoplasmic processes extend through canaliculi: allows oxygen and nutrients in blood to flow from haverisan canal through the bone to replenish it
         • Osteocytes connected via gap junctions
       • Secrete enzymes to maintain mineral content
     • Single layer of cuboidal/columnar cells
     • Deposits osteoid (ECM minus calcium and phosphate crystals)
     • Contains many RER and golgi => for the production of ECM
     • Osteoblasts get trapped in the ECM, mature, and become Osteocytes
     • Creation of ECM

2. ECM of Bone

   • Type I Collagen (95%)
     • Orientates according to how the osteon is organised
   • Proteoglycans
     • Chondroitin Sulfate
     • Keratan Sulfate
     • Hyaluronic Acid
   • Glycoproteins
     • Osteocalcin
     • Osteopontin
     • Osteonectin
   • Calcium Phosphate (in the form of Hydroxyapatite crystals)

3. Monocyte/Macrophage family

   • Osteoclasts
     • Reabsorbs and Renews Bone
     • Mulinucleated
     • Howship's Lacuna = leading edge of osteoclast
       • Releases acidic collagenases
         • Breaks down bone => releases Ca into blood
         • Supressed by Calcitonin - released by thyroid gland
         • Stimulated by Parathyroid hormone - released by parathyroid gland
           • Also stimulated by vitamin D
       • Ruffled membrane = increased SA for vesicle release

4. Spongy Bone

5. Compact Bone

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