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Bone Response to Damage (view source)
Revision as of 11:45, 12 November 2007
, 11:45, 12 November 2007→Normal structure
[[Image:Bone micro structure.jpg|right|thumb|100px|<small><center>Microscopic bone (Courtesy of RVC Histology images)</center></small>]]
[[Image:Bone micro structure.jpg|right|thumb|100px|<small><center>Microscopic bone (Courtesy of RVC Histology images)</center></small>]]
====Cells====
*Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from stromal fibroblastic system ('''osteoprogenitor cells); osteoclasts from haematopoietic system
*Ischaemia and hypoxia favour development of cartilage
*High oxygen tension and good blood supply favour bone development
*'''Osteoblasts'''
**Mesenchymal cells
**Arise from bone marrow stroma
**Histologically:
***Plump and cuboidal when active
***Basophilic cytoplasm
***When inactive - less cytoplasm -> flattened
**Produce bone matrix = '''osteoid''' - uncalcified
***Homogeneous substance
***Stains light pink with H&E
**Cell membranes are rich in alkaline phosphatase (ALP)
***Possibly involved in pumping calcium across membranes
**Promoted by growth factors
**Have receptors for [[Bones - normal#Bone resorption|PTH]]
***They contract in response -> space for osteoclasts to attach
*'''Osteocytes'''
**Osteoblasts that have become surrounded by mineralised bone matrix
**Occupy cavities called '''lacunae'''
**Contact osteoblasts and each other with cytoplasmic processes
***Reach through canaliculi in mineralised bone matrix
**Regulate composition of bone fluid
*'''Osteoclasts'''
**Histologically:
***Large, often multinucleated cells
***Acidophilic cytoplasm
**Derived from haematopoietic stem cells
**Responsible for bone resorption
***Firstly dissolve mineral followed by collagen
***Use brush border for this
**Sit in bone surface depression - '''Howship's lacuna'''
**Do <u>not</u> have receptors for PTH
**Have receptors for [[Bones - normal#Bone resorption|calcitonin]]
***Involute their brush border in response
***Detach from bone surface
*'''Matrix''':
**Respond to vitamin D by increasing their numbers and activity (parathyroid independent)
====Matrix====
**Mineral
*'''Osteoid'''
**Type I collagen forms the backbone of the matrix (90%)
***Molecules in staggered rows
**Non-collagenous protein forming amorphous ground substance (10%)
***Mainly glycoproteins and proteoglycans
*'''Mineral'''
**Crystalline lattice of calcium phosphate and calcium carbonate
**Also contains Mg, Mn, Zn, Cu, Na, F
**Accounts for 65% of bone
===Bone organisation===
===Bone organisation===