Difference between revisions of "Bone Response to Damage"

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==Changes to normal structure==
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<big><center>[[Bones|'''BACK TO BONES''']]</center></big>
  
===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 [[Bones Fractures - Pathology|fracture]])
+
 
*Longitudinal bone growth results
+
===Normal structure===
*May be only on one side where periosteum is damaged
+
[[Image:Bone micro structure.jpg|right|thumb|100px|<small><center>Microscopic bone (Courtesy of RVC Histology images)</center></small>]]
**Used by surgeons to treat [[Angular Limb Deformity|angular limb deformities]]
+
 
 +
 
 +
 
 +
 
 +
 
 +
**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 [[Bones - fractures|fracture]])
 +
***Longitudinal bone growth results
 +
***May be only on one side where periosteum is damaged
 +
****Used by surgeons to treat [[Bones - developmental#Angular limb deformity|angular limb deformities]]
 +
*'''Blood vessels'''
 +
 
 +
===Bone development===
 +
 
 +
*Two main types of bone development:
 +
**'''Endochondral ossification''' (cartilage model)
 +
***Long bones mainly - physis and metaphysis
 +
***Mesenchymal cells differentiate into chondroblasts
 +
****Produce scaffold of mineralised cartilage on which osteoblasts deposit bone
 +
***Vascularised
 +
***Developed centres of ossification
 +
****Primary (diaphyseal)
 +
****Secondary (epiphyseal)
 +
**'''Intramembranous ossification'''
 +
***Flat bones mainly (e.g. skull), shaft of long bones
 +
***Mesenchymal cells differentiate into osteoblasts
 +
***No cartilage precursor template
 +
 
  
 
===Physis (Growth plate)===
 
===Physis (Growth plate)===
 +
 +
 +
 +
[[Image:Growth plate.jpg|left|thumb|100px|<small><center>Growth plate (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
 +
[[Image:Growth plate closer.jpg|right|thumb|100px|<small><center>Growth plate magnified(Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
 +
 +
 +
*Originates from the cartilage model that remains only at the junction of the diaphyseal and epiphyseal centres
 +
 +
 +
 +
*Cartilage of metaphyseal growth plate is divided into: (from right to left on the magnified image)
 +
** - Resting (reserve) zone
 +
** - Proliferative zone
 +
** - Hypertrophic zone
 +
 +
 +
  
 
*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal
 
*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal
Line 22: Line 66:
 
*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'''
  
==Test yourself with the Bone and Cartilage Pathology Flashcards==
 
  
[[Bones_and_Cartilage_Flashcards_-_Pathology|Bones and Cartilage Flashcards]]
 
  
  
[[Category:Bones - Pathology|A]]
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===Bone resorption===
 +
 
 +
*Mediated by two [[Parathyroid Pathology#Hormonal Control|hormones]]:
 +
**'''Parathyroid hormone (PTH)'''
 +
***Produced by <u>chief cells in the parathyroid glands</u> in response to <u>decreased</u> serum calcium
 +
***In response, osteoclasts increase in number and resorb mineralised matrix - increase Ca in blood
 +
**'''Calcitonin'''
 +
***Produced by <u>C-cells in the thyroid glands</u> in response to <u>increased</u> serum calcium
 +
***Inhibits osteoclasts
 +
 
 +
===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
 +
 
 +
 
 +
 
 +
<big><center>[[Bones|'''BACK TO BONES''']]</center></big>

Revision as of 10:23, 18 July 2008

BACK TO BONES



Normal structure

Microscopic bone (Courtesy of RVC Histology images)



    • 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
  • Blood vessels

Bone development

  • Two main types of bone development:
    • Endochondral ossification (cartilage model)
      • Long bones mainly - physis and metaphysis
      • Mesenchymal cells differentiate into chondroblasts
        • Produce scaffold of mineralised cartilage on which osteoblasts deposit bone
      • Vascularised
      • Developed centres of ossification
        • Primary (diaphyseal)
        • Secondary (epiphyseal)
    • Intramembranous ossification
      • Flat bones mainly (e.g. skull), shaft of long bones
      • Mesenchymal cells differentiate into osteoblasts
      • No cartilage precursor template


Physis (Growth plate)

Growth plate (Image sourced from Bristol Biomed Image Archive with permission)
Growth plate magnified(Image sourced from Bristol Biomed Image Archive with permission)


  • Originates from the cartilage model that remains only at the junction of the diaphyseal and epiphyseal centres


  • Cartilage of metaphyseal growth plate is divided into: (from right to left on the magnified image)
    • - Resting (reserve) zone
    • - Proliferative zone
    • - Hypertrophic zone



  • 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

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


BACK TO BONES