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| − | <big><center>[[Bones|'''BACK TO BONES''']]</center></big>
| + | ==Changes to normal structure== |
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| | + | ===Damage to Periosteum=== |
| | + | *Invokes a hyperplastic reaction of the inner layer |
| | + | *Is painful |
| | + | *Exostoses can remodel or remain |
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| − | ===Introduction===
| + | Lifting of periosteum causes new bone formation below |
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| − | *Bone is a hard, highly specialised connective tissue
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| − | *Consists of interconnected cells embedded in a calcified, collagenous matrix
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| − | *Living, dynamic, responsive tissue, growing and remodelling throughout life
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| − | *Pathogenesis of many bone diseases is complex
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| − | **May involve genetic defects, diet or infection or a combination of these
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| − | *'''Function''':
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| − | **Support/protection
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| − | **Movement
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| − | **Stem cell storage
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| − | **Mineral storage
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| − | ===Normal structure===
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| − | [[Image:Bone micro structure.jpg|right|thumb|100px|<small><center>Mibroscopic bone (Courtesy of RVC Histology images)</center></small>]]
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| − | *'''Cells'''
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| − | **'''Osteoblasts'''
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| − | ***Mesenchymal cells
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| − | ***Arise from bone marrow stroma
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| − | ***Histologically:
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| − | ****Plump and cuboidal when active
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| − | ****Basophilic cytoplasm
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| − | ****When inactive - less cytoplasm -> flattened
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| − | ***Produce bone matrix = '''osteoid''' - uncalcified
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| − | ****Homogeneous substance
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| − | ****Stains light pink with H&E
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| − | ***Cell membranes are rich in alkaline phosphatase (ALP)
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| − | ****Possibly involved in pumping calcium across membranes
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| − | ***Promoted by growth factors
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| − | ***Have receptors for PTH
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| − | **'''Osteocytes'''
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| − | ***Osteoblasts that have become surrounded by mineralised bone matrix
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| − | ***Occupy cavities called '''lacunae'''
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| − | **'''Osteoclasts'''
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| − | ***Large, often multinucleated cells
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| − | ***Acidophilic cytoplasm
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| − | ***Derived from haematopoietic stem cells
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| − | ***Responsible for bone resorption (have a brush border for this)
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| − | ***Sit in bone surface depression - '''Howship's lacuna'''
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| − | *'''Matrix''':
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| − | **Osteoid
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| − | ***Type I collagen forms the backbone of the matrix (90%)
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| − | ***Non-collagenous protein forming amorphous ground substance (10%)
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| − | **Mineral
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| − | ***Crystalline lattice of calcium phosphate and calcium carbonate
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| − | ***Also contains Mg, Mn, Zn, Cu, Na, F
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| − | ***Accounts for 65% of bone
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| − | ===Bone organisation===
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| − | | |
| − | *Patterns of collagen deposition:
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| − | **'''Woven bone''':
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| − | ***"Random weave" which is only a normal feature in the foetus
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| − | ***Coarse collagen fibres
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| − | ***Later removed by osteoclasts and replaced by lamellar bone
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| − | ***In adults it is a sign of a pathological condition (e.g. fracture, inflammation, neoplasia)
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| − | **'''Lamellar bone''':
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| − | ***Orderly layers which are much stronger than woven bone
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| − | ***Fine collagen fibres in concentric or parallel laminae
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| − | ***Two main types:
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| − | ****'''Compact bone (cortical)'''
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| − | *****Forms 80% of total bone mass
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| − | *****Consists of cells and interstitial substance - 30% ossein (type of collagen) and 70% minerals, especially calcium phosphate
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| − | *****Forms the shell of long bone shafts - contain [[Haversian systems]]
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| − | ****'''Cancellous bone (spongy or trabecular)'''
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| − | *****Made up of plates, tubes or bars arranged in lines of stress
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| − | *****In vertebrae, flat bones and epiphyses of long bones
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| − | *****Contains no Haversian systems
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| − | **'''Laminar bone'''
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| − | ***Formed on periosteal surface of diaphysis
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| − | ***Accomodates rapid growth of large dogs and farm animals
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| − | ***Plates of woven bone from within the periosteum
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| − | ***Concentric plates
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| − | ***As it forms, it fuses with the bone surface
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| − | ===Periosteum and blood supply===
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| − | *Specialised sheath of connective tissue covering bone except at the articular surfaces
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| − | *Inner layer
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| − | **Merges with the outer layer of bone
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| − | **Contains osteoblasts and osteoprogenitor stem cells in young animals and in adults with fractures or disease
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| − | *Damage to the periosteum invokes a hyperplastic reaction of the inner layer
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| − | *The blood supply to the mature bone enters via the periosteum
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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:
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| − | **'''Endochondral ossification''' (cartilage model)
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| − | ***Long bones mainly - physis and metaphysis
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| − | ***Mesenchymal cells differentiate into chondroblasts
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| − | ****Produce scaffold of mineralised cartilage on which osteoblasts deposit bone
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| − | ***Vascularised
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| − | ***Developed centres of ossification
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| − | ****Primary (diaphyseal)
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| − | ****Secondary (epiphyseal)
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| − | **'''Intramembranous ossification'''
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| − | ***Flat bones mainly (e.g. skull), shaft of long bones
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| − | ***Mesenchymal cells differentiate into osteoblasts
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| − | ***No cartilage precursor template
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| | + | 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]] |
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| | ===Physis (Growth plate)=== | | ===Physis (Growth plate)=== |
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| − | *Originates from the cartilage model that remains only at the junction of the diaphyseal and epiphyseal centres
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| | *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== |
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| − | ===Bone resorption===
| + | [[Bones_and_Cartilage_Flashcards_-_Pathology|Bones and Cartilage Flashcards]] |
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| − | *Mediated by two hormones:
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| − | **'''Parathyroid hormone (PTH)'''
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| − | ***Produced by <u>chief cells in the parathyroid glands</u> in response to <u>decreased</u> serum calcium
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| − | ***In response, osteoclasts increase in number and resorb mineralised matrix - increase Ca in blood
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| − | **'''Calcitonin'''
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| − | ***Produced by <u>C-cells in the thyroid glands</u> in response to <u>increased</u> serum calcium
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| − | ***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
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| − | *Mechanical forces generate bioelectrical potentials (piezoelectricity)
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| − | **These potentials strengthen bone
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| − | **Inactivity reduces the potentials -> bone loss
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| − | *In neonates:
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| − | **Bone growth predominates
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| − | **Modelling is important
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| − | *In adults:
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| − | **Formation of bone is balanced by resorption - remodelling
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| − | **Continues throughout life under the influence of hormones and mechanical pressure
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| − | **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>
| + | [[Category:Bones - Pathology|A]] |