1.95 Structure of Bone Flashcards
What is the function of the Haversion system?
Functions in movement, support, protection, mineral storage
Where does Haversion system derive from?
Mesenchyme
What is the Haversion system?
Mineralised matrix containing crystals of hydroxyapatite Ca10(PO4)6(OH)2
What makes up the inner and outer part of the bone?
Dense outer cortex of compact cortical bone
Inner cavity meshwork of trabecular/spongy bone with spaces between are occupied by marrow
Which vessels enter the femur?
Blood vessels - circumflex and acetabulum branch of obturator archery enter this bone
What is the periosteum?
Periosteum - the muscle tendons directly insert into it and are continuous with it
What are the two phases of bone development?
Woven and Lamellar bone
What is woven bone?
Immature Irregular Collagen fibrils Laid bone first during bone formation Irregular arrangement of collagen fibrils Persists in adults in a few sites: Tooth sockets / cranial suture May be formed in fracture repair - gets laid down initially
What makes up the lamellar bone?
Both compact and trabecular bone are both types o lamellar bone
What is Haversion (lamellar) bone?
• Haversian bone (mature) • Can be arranged as: • Compact bone • Trabecular bone • Covered externally with two layers of periosteum • Outer layer – collagen, blood vessels • Inner layer – osteoprogenitor cells • Covered internally with endosteum Osteoprogenitor cells, reticular fibres
What is a Haversion system?
Osteoblast produce matrix - they trap theselves within the matrix and mature into osteocytes
Channel of canaliculi - communication between lacunae
• Cylindrical subunits
• Arranged around central canal
• Surrounded circumferentially by lamellae
Canaliculi are microscopic canals connecting lacunae
What do osteoblasts do?
Secrete osteoid collagen
What do vesicles deposit during bone mineralisation?
Hydroxyapetite
What forms the mineralisation?
Osteoid + hydroxyapetite + proteoglycans + proteins
Collagen fibres start to arrange themsevles in a regular pattern - the vesicles stick onto these fibres to form this regular pattern
What are the organic and inorganic make up the mineralised bone matrix?
Inorganic and organic components
Organic: osteoid collagen fibres, proteins and proteoglycans
Inorganic: hydroxyapatite
and other molecules
What are the organic components?
• Collagen type I fibres • Proteoglycans • Chondrotin sulfate • Keratan sulfate • Other proteins • Osteopontin Osteocalcin
What osteopontin and osteocalcin?
Bone matrix proteins
Osteocalcin is unique to bone and is secreted by osteoblasts
Bind to hydroxyapatite crystals
Bind osteoblasts to bone matrix
What hydroxyapetite?
Almost identical to calcium phosphate found in geological deposits
Hydroxyapatite forms rod-like crystals approx 40nm x 3nm
Crystals attach along length of osteoid collagen fibres
What is mineralisation?
• Occurs in matrix vesicles
• Hydroxyapatite growth and seeding depends on Ca/PO4 concentration
• Bone only forms where crystal nuclei can form
Normal tissue contains factors (e.g. pyrophosphates) which prevent formation of crystal nuclei
what is hypocalceamia?
Low blood calcium levels
Due to low vitamin D or PTH
Can be treated by vitamin D
