Difference between revisions of "Bone Response to Damage"

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==Changes to normal structure==
+
<big><center>[[Bones|'''BACK TO BONES''']]</center></big>
  
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===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
+
===Introduction===
 +
 
 +
*Bone is a hard, highly specialised connective tissue
 +
*Consists of interconnected cells embedded in a calcified, collagenous matrix
 +
*Living, dynamic, responsive tissue, growing and remodelling throughout life
 +
*Pathogenesis of many bone diseases is complex
 +
**May involve genetic defects, diet or infection or a combination of these
 +
*'''Function''':
 +
**Support/protection
 +
**Movement
 +
**Stem cell storage
 +
**Mineral storage
 +
 
 +
 
 +
===Normal structure===
 +
 
 +
*'''Cells'''
 +
**'''Osteoblasts'''
 +
***Mesenchymal cells
 +
***Arise from bone marrow stroma
 +
***Produce bone matrix = '''osteoid''' - uncalcified
 +
***Cell membranes are rich in alkaline phosphatase (ALP)
 +
***Promoted by growth factors
 +
***Plump, cuboidal basophilic cells
 +
**'''Osteocytes'''
 +
***Osteoblasts that have become surrounded by mineralised bone matrix
 +
***Occupy cavities called '''lacunae'''
 +
**'''Osteoclasts'''
 +
***Large, often multinucleated cells
 +
***Acidophilic cytoplasm
 +
***Derived from haematopoietic stem cells
 +
***Responsible for bone resorption (have a brush border for this)
 +
***Sit in bone surface depression - '''Howship's lacuna'''
 +
*'''Matrix''':
 +
**Osteoid
 +
***Type I collagen forms the backbone of the matrix (90%)
 +
***Non-collagenous protein forming amorphous ground substance (10%)
 +
**Mineral
 +
***Crystalline lattice of calcium phosphate and calcium carbonate
 +
***Also contains Mg, Mn, Zn, Cu, Na, F
 +
***Accounts for 65% of bone
 +
 
 +
 +
===Bone organisation===
 +
 
 +
*Patterns of collagen deposition:
 +
**'''Woven bone''':
 +
***"Random weave" which is only a normal feature in the foetus
 +
***Coarse collagen fibres
 +
***Later removed by osteoclasts and replaced by lamellar bone
 +
***In adults it is a sign of a pathological condition (e.g. fracture, inflammation, neoplasia)
 +
**'''Lamellar bone''':
 +
***Orderly layers which are much stronger than woven bone
 +
***Fine collagen fibres in concentric or parallel laminae
 +
***Two main types:
 +
****'''Compact bone''' (cortical)
 +
*****Forms 80% of total bone mass
 +
*****Consists of cells and interstitial substance - 30% ossein (type of collagen) and 70% minerals, especially calcium phosphate
 +
*****Forms the shell of long bone shafts - contain [[Haversian systems]]
 +
****'''Cancellous bone''' (spongy or trabecular)
 +
*****Made up of plates, tubes or bars arranged in lines of stress
 +
*****In vertebrae, flat bones and epiphyses of long bones
 +
*****Contains no Haversian systems
 +
**'''Laminar bone'''
 +
***Formed on periosteal surface of diaphysis
 +
***Accomodates rapid growth of large dogs and farm animals
 +
***Plates of woven bone from within the periosteum
 +
***Concentric plates
 +
***As it forms, it fuses with the bone surface
 +
 
 +
 
 +
===Periosteum and blood supply===
 +
 
 +
*Specialised sheath of connective tissue covering bone except at the articular surfaces
 +
*Inner layer
 +
**Merges with the outer layer of bone
 +
**Contains osteoblasts and osteoprogenitor stem cells in young animals and in adults with fractures or disease
 +
*Damage to the periosteum invokes a hyperplastic reaction of the inner layer
 +
*The blood supply to the mature bone enters via the periosteum
 +
 
 +
*'''Endosteum''' lines the marrow cavity
 +
 
 +
 
 +
===Bone development===
 +
 
 +
*Two main types of bone development:
 +
**'''Endochondral ossification''' (cartilage model)
 +
***Long bones mainly
 +
***Vascularised
 +
***Developed centres of ossification
 +
****Primary (diaphyseal)
 +
****Secondary (epiphyseal)
 +
**'''Intramembranous ossification'''
 +
***Flat bones mainly (e.g. skull)
 +
***Mesenchymal cells differentiate into osteoblasts
 +
***No cartilage precursor template
  
−
Circumferential incision (e.g. during [[Bones Fractures - Pathology|fracture]])
 
−
*Longitudinal bone growth results
 
−
*May be only on one side where periosteum is damaged
 
−
**Used by surgeons to treat [[Angular Limb Deformity|angular limb deformities]]
 
  
 
===Physis (Growth plate)===
 
===Physis (Growth plate)===
  
 +
*Originates from the cartilage model that remains only at the junction of the diaphyseal and epiphyseal centres
 
*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal
 
*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal
 
*'''Open''' in neonates and growing animals
 
*'''Open''' in neonates and growing animals
 
**Chondrocyte proliferation balances cell maturation and death  
 
**Chondrocyte proliferation balances cell maturation and death  
 
*'''Closes and ossifies''' at maturity
 
*'''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'''
 
  
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==Test yourself with the Bone and Cartilage Pathology Flashcards==
 
  
−
[[Bones_and_Cartilage_Flashcards_-_Pathology|Bones and Cartilage Flashcards]]
+
===Bone resorption===
 +
 
 +
*Mediated by two 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
 +
 
  
  
−
[[Category:Bones - Pathology|A]]
+
<big><center>[[Bones|'''BACK TO BONES''']]</center></big>

Revision as of 15:03, 28 September 2007

BACK TO BONES


Introduction

  • Bone is a hard, highly specialised connective tissue
  • Consists of interconnected cells embedded in a calcified, collagenous matrix
  • Living, dynamic, responsive tissue, growing and remodelling throughout life
  • Pathogenesis of many bone diseases is complex
    • May involve genetic defects, diet or infection or a combination of these
  • Function:
    • Support/protection
    • Movement
    • Stem cell storage
    • Mineral storage


Normal structure

  • Cells
    • Osteoblasts
      • Mesenchymal cells
      • Arise from bone marrow stroma
      • Produce bone matrix = osteoid - uncalcified
      • Cell membranes are rich in alkaline phosphatase (ALP)
      • Promoted by growth factors
      • Plump, cuboidal basophilic cells
    • Osteocytes
      • Osteoblasts that have become surrounded by mineralised bone matrix
      • Occupy cavities called lacunae
    • Osteoclasts
      • Large, often multinucleated cells
      • Acidophilic cytoplasm
      • Derived from haematopoietic stem cells
      • Responsible for bone resorption (have a brush border for this)
      • Sit in bone surface depression - Howship's lacuna
  • Matrix:
    • Osteoid
      • Type I collagen forms the backbone of the matrix (90%)
      • Non-collagenous protein forming amorphous ground substance (10%)
    • Mineral
      • Crystalline lattice of calcium phosphate and calcium carbonate
      • Also contains Mg, Mn, Zn, Cu, Na, F
      • Accounts for 65% of bone


Bone organisation

  • Patterns of collagen deposition:
    • Woven bone:
      • "Random weave" which is only a normal feature in the foetus
      • Coarse collagen fibres
      • Later removed by osteoclasts and replaced by lamellar bone
      • In adults it is a sign of a pathological condition (e.g. fracture, inflammation, neoplasia)
    • Lamellar bone:
      • Orderly layers which are much stronger than woven bone
      • Fine collagen fibres in concentric or parallel laminae
      • Two main types:
        • Compact bone (cortical)
          • Forms 80% of total bone mass
          • Consists of cells and interstitial substance - 30% ossein (type of collagen) and 70% minerals, especially calcium phosphate
          • Forms the shell of long bone shafts - contain Haversian systems
        • Cancellous bone (spongy or trabecular)
          • Made up of plates, tubes or bars arranged in lines of stress
          • In vertebrae, flat bones and epiphyses of long bones
          • Contains no Haversian systems
    • Laminar bone
      • Formed on periosteal surface of diaphysis
      • Accomodates rapid growth of large dogs and farm animals
      • Plates of woven bone from within the periosteum
      • Concentric plates
      • As it forms, it fuses with the bone surface


Periosteum and blood supply

  • Specialised sheath of connective tissue covering bone except at the articular surfaces
  • Inner layer
    • Merges with the outer layer of bone
    • Contains osteoblasts and osteoprogenitor stem cells in young animals and in adults with fractures or disease
  • Damage to the periosteum invokes a hyperplastic reaction of the inner layer
  • The blood supply to the mature bone enters via the periosteum
  • Endosteum lines the marrow cavity


Bone development

  • Two main types of bone development:
    • Endochondral ossification (cartilage model)
      • Long bones mainly
      • Vascularised
      • Developed centres of ossification
        • Primary (diaphyseal)
        • Secondary (epiphyseal)
    • Intramembranous ossification
      • Flat bones mainly (e.g. skull)
      • Mesenchymal cells differentiate into osteoblasts
      • No cartilage precursor template


Physis (Growth plate)

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


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
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