Bone Flashcards
(32 cards)
Two major components of bone
Organic
Inorganic
Collagen
90% organic matrix
Provides tensile strength to bone
Type I
Proteoglycans
Composed of glycosaminoglycan complexes
Inhibit mineralization
Numerous functions ranging from growth factors to binding properties
Partially responsible for compressive strength of bone
Osteocalcin
Produced by osteoblasts, related to regulation of bone density, most abundant non collagen matrix protein
Osteonectin
Secreted by platelets and osteoblasts, organization of mineral within matrix
Osteopontin
Cell binding protein
Inorganic matrix
60% dry weight Almost entirely Ca Hydroxyapatite Provides compressibe strength of bone Responsible for mineralization of bone Primer mineralization occurs in holes and pores
Microstructure - 7 levels
- Isolated crystals and collagen fibrils
- Mineralized collagen fibril
- Mineralized fibril array
- Fibril array patterns
- Single osteon
- Spongy and compact bone
- whole bone
Bone Strcutre
Coritcol = 5-30% porous Cancellous = 30-90% porous, no osteons
Osteon formation - bone growth
- Osteoblasts secrete bone matrix
- Groove with BV is a tunnel
- Periosteum lining tunnel becomes endosteum - secrete bone matrix
- Osteoblasts form new lamellae - new osteon is created
Cortical bone types
lamellar
woven
Lamellar bone type
cortical bone type
Parallel layers of lamellae
Mineralized collagen fibers are parallel within each lamella, direction of fibers may alternate btw adjactent lamalla
Woven bone type
Corticol bone type Quickly formed Poorly organized, fibers are more or less randomly arranged More minrralized than lamellar Weaker than minteralized
Cortical Compact bone
80% skeleton Osteons connected by haversion canals Nutrition via interosseous Slow tunrover - remodeling High stiffness (youngs modulus) High resistance to torsion and bending than cancellous
Woven bone
Immature of pathologic
Collagen is arranged irregularly
Isotropic - mechanical properties ind of orientation so stress applied
Woven bone exists in
Fetal skeleton Fx callus Tooth sockets Bone forming tumors Stages of accelerated bone formation
Trabecular bone
Formed by organization of plate and rod like struts called trabeculae
Trabeculae are about 200 um thick
Cancellous/Trabecular bone - spongy
Less dense More remodeling along lines of stress (wolfe) Much larger SA Higher turnover Lower apaprent modulus (less stiff) More elastic More resistant to compressive forces
Wolffs law
Bone remodels in response to the stresses applied to it
Possibel that remodeling occurs to keep strain (not stess) btw certain upper and lower limits
If strain is too high - bone is laid down along lines of stress to make thicker and denser
If strain is too low - bone is lost making bone less dense - Osteoporosis
Bone growth/.formation
Customize the shape of bones during ggrowth in accordance with mechanical needs
Metaphyseal modeling
Reduces bone diamter during growth
Diaphyseal modeling
Increase bone diameter
- addition of bone to periosteum
- resorption of bone at endosteum
Bone stress/strain
Bone has nonlinear elastic behavior
Moderate plastic region
Bone mechanical characteristics vary according to
geometry load mode applied Direction of load rate of loading Frequency of loading
