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Bone and Joint

Osteocytes and bone matrix

Osteocyte lacuno-canalicular network, its mechanosensory role and the organic/inorganic matrix

10 questions 2 source pages

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10 questions
Q1What is an osteocyte?▸
  • Described as an osteoblast trapped in osteoid
  • Makes up 90% of cells in the mature skeleton
Q2What are the functions of osteocytes?▸
  • Regulate bone response to hormonal and mechanical stimuli
  • Regulate calcium and phosphorus concentration in bone
  • Stimulated by calcitonin, inhibited by PTH
Q3What are the characteristics of osteocytes?▸
  • High NC (minimal organelle)
  • Long cytoplasmic processes
  • No ALP expression
Q4What are bone lining cells?▸
  • Inactive osteoblasts
  • Reactive for bone formation, or prepare bone for osteoclastic resorption upon PTH stimulation
Q5What are the proportions of organic and inorganic bone matrix?▸
  • Organic 40%
  • Inorganic 60%
Q6What does the organic matrix contain and what strength does it provide?▸
  • Collagen type I (90%) for tensile strength; hydroxyproline forms the triple helix with glycine
  • Proteoglycans for compressive strength
  • Non-collagen matrix proteins: osteocalcin, osteonectin, osteopontin
  • Growth factors and cytokines (TGF, IL-1, IL-6)
Q7What are the roles of osteocalcin?▸
  • From the mature osteoblast (marker of osteoblastic differentiation)
  • Controls osteoclasts: stimulates 1,25 vitamin D, inhibits PTH
  • Urine detection indicates bone maturation
Q8What are the roles of osteonectin and osteopontin?▸
  • Osteonectin: from osteoblast/platelets, regulates mineralisation, binds calcium
  • Osteopontin (pont = bond): cell binding
Q9What is the inorganic component of bone matrix?▸
  • Mainly provides compressive strength
  • Calcium hydroxyapatite Ca10(PO4)6(OH)2
  • Osteocalcium phosphate
Q10Which bone matrix markers can be detected in urine and what do they indicate?▸
  • Urine hydroxyproline: osteoblast turnover marker
  • Urine osteocalcin: bone maturation
← Bone cell lineage and osteoblastsCalcium metabolism and metabolic bone di →