Bone Response to Damage

BACK TO BONES

Normal structure

• • Damage to periosteum:
    • Invokes a hyperplastic reaction of the inner layer
    • Is painful
    • Exostoses can remodel or remain
  • Lifting of periosteum causes new bone formation below
  • Circumferential incision (e.g. during fracture)
    • Longitudinal bone growth results
    • May be only on one side where periosteum is damaged
      • Used by surgeons to treat angular limb deformities

Physis (Growth plate)

• Site of many congenital or nutritional bone diseases in the growing animal
• Open in neonates and growing animals
  • Chondrocyte proliferation balances cell maturation and death
• Closes and ossifies at maturity
  • Regulated by androgens
• If growth teporarily stops -> layer of bone seals the growth plate -> moves into metaphysis when growth resumes -> forms Harris lines

Bone resorption

• Mediated by two hormones:
  • Parathyroid hormone (PTH)
    • Produced by chief cells in the parathyroid glands in response to decreased serum calcium
    • In response, osteoclasts increase in number and resorb mineralised matrix - increase Ca in blood
  • Calcitonin
    • Produced by C-cells in the thyroid glands in response to increased serum calcium
    • Inhibits osteoclasts