Difference between revisions of "Bone Response to Damage"

Revision as of 15:03, 28 September 2007

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

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

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

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 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

@@ Line 50: / Line 50: @@
 **'''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)
@@ Line 62: / Line 65: @@
 *****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