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→Structure of Bone
**Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from stromal fibroblastic system ('''osteoprogenitor cells'''); osteoclasts from haematopoietic system
**Osteoblasts, osteocytes, chondroblasts and chondrocytes are derived from stromal fibroblastic system ('''osteoprogenitor cells'''); osteoclasts from haematopoietic system
==Structure of Bone==
==Organization of Bone==
*Normal progression is from woven bone to lamellar bone, even in pathology, except for [[Bones - hyperplastic and neoplastic#Craniomandibular osteopathy|canine craniomandibular osteopathy]] and [[Bones - metabolic#Hypervitaminosis D|hypervitaminosis D]], where lamellar bone is replaced by woven bone
*'''Cancellous (spongy, or trabecular) bone'''
*'''Woven bone''':
**Forms the hematopoeitic center of epiphyses
**"Random weave" which is only a normal feature in the foetus
**Stacks of parallel or concentrically stacked sheets arranged as rods, plates, and arches
**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)'''
****Sheath covers external surface of long bone, thicker in shaft and thins over epiphyses
****Comprised of thin lamallae in a series of concentric tubes arranged around small central canals (collectively known as an '''osteone''')
****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)'''
****Stacks of parallel or concentrically stacked sheets arranged as rods, plates, and arches
****In vertebrae, flat bones and forms the hematopoeitic center of epiphyses of long bones
****Contains no Haversian systems
*'''Laminar bone'''
**Formed on periosteal surface of diaphysis
**Accommodates 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
*'''Medullary Cavity and Cancellous Interstitium''': bone marrow storage and production
*'''Medullary Cavity and Cancellous Interstitium''': bone marrow storage and production