Difference between revisions of "Bone Response to Damage"
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===Physis (Growth plate)=== | ===Physis (Growth plate)=== | ||
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*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal | *Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal | ||
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**Regulated by androgens | **Regulated by androgens | ||
*If growth teporarily stops -> layer of bone seals the growth plate -> moves into metaphysis when growth resumes -> forms '''Harris lines''' | *If growth teporarily stops -> layer of bone seals the growth plate -> moves into metaphysis when growth resumes -> forms '''Harris lines''' | ||
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===Bone resorption=== | ===Bone resorption=== | ||
Revision as of 10:28, 18 July 2008
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
- Damage to periosteum:
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
- Parathyroid hormone (PTH)
Bone dynamics
- Bone growth and maintenance of normal structure are directly related to mechanical forces
- Mechanical forces generate bioelectrical potentials (piezoelectricity)
- These potentials strengthen bone
- Inactivity reduces the potentials -> bone loss
- In neonates:
- Bone growth predominates
- Modelling is important
- In adults:
- Formation of bone is balanced by resorption - remodelling
- Continues throughout life under the influence of hormones and mechanical pressure
- Bone resorption may exceed formation in pathological states (hormonal, trauma, nutritional) or in old age and disuse