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−<big><center>[[Bones|'''BACK TO BONES''']]</center></big>+ +===Normal structure===+[[Image:Bone micro structure.jpg|right|thumb|100px|<small><center>Microscopic bone (Courtesy of RVC Histology images)</center></small>]]+ +
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−===Bone organisation===
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−*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
−*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
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−===Periosteum and blood supply===
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−*'''Periosteum'''
−**Specialised sheath of connective tissue covering bone except at the articular surfaces
−**Loosely attached except at tendon insertions and boney prominences (associated with major blood vessels penetrating bone)
−**Histologically:
−***Outer layer - fibrous for support
−***Inner layer - osteogenic
−****Contains osteoblasts and osteoprogenitor stem cells in young animals and in adults with fractures or disease
−**Rich supply of nerves and lymph vessels
−**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'''
−**Nutrient, metaphyseal, periosteal arteries
−**Normal flow of blood from medulla to periosteum due to higher pressures in medulla
−**Young animals have greater blood supply
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−*'''Endosteum''' lines the marrow cavity
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−===Bone development===
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−*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
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[[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
−===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
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−===Bone dynamics===
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−*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
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−*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
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−<big><center>[[Bones|'''BACK TO BONES''']]</center></big>
==Changes to normal structure==
+===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
−*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)===
−*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal
*Site of many '''congenital''' or '''nutritional''' bone diseases in the growing animal
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*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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