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Bone Growth and Development. Bone Composition & Structure. Material Constituents: Calcium carbonate and Calcium phosphate 60-70% bone weight Adds stiffness Primary determinant for compressive strength. Collagen Adds flexibility Contributes to tensile strength. Long Bone Structure.
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Bone Composition & Structure • Material Constituents: • Calcium carbonate and Calcium phosphate • 60-70% bone weight • Adds stiffness • Primary determinant for compressive strength. • Collagen • Adds flexibility • Contributes to tensile strength
Long Bone Structure • Diaphysis: shaft • Periosteum: fibrous connective tissue covering shaft • Epiphyses: the ends • Articular cartilage: hyaline cartilage covering epiphysis • Epiphyseal line & plate: the growth plate or the line left over in adult bones • Medullary Cavity: cavity in bone that contains marrow
The Haversian System • Haversian Canal: Central Canal • surrounded by concentric layers of calcified matrix called lamellae. • Osteocytes are found between concentric lamellae and connected to each other, and the central canal by canals called canaliculi. • This network permits the exchange of nutrients and metabolic waste.
Cortical Bone • Compact Bone • Low porosity • 5-30% bone volume is non-mineralized tissue • Withstand greater stress but less strain before fracturing
Trabecular Bone • Spongy Bone • High porosity • 30 - >90% bone volume is non-mineralized tissue • Trabeculae filled with marrow and fat • Withstand more strain (but less stress) before fracturing
Ossification The replacement of other tissues with bone
Two Major Types of Ossification Endochondral and Intramembranous
Endochondral Ossification Most Bones of the Skeleton Bone develops from cartilage Blood vessels infiltrate cartilage, forming bone Primary ossification begins at the center of the diaphysis Secondary centers form later at the epiphyses
Intramembranous Ossification • Skull, Mandible and Clavicle • Bone develops directly • not from cartilage • Develops from the inside out • from spongy to dense bone
Types of Bone Growth Epiphyseal and Appositional
Epiphyseal Growth Virtually all growth in length occurs at the growth plates Growth plates fuse after puberty,as rate of ossification exceedes the growth of cartilage. Once the growth plate is entirely ossified (fused) there can be no further growth in bone length This limits the size of adults
Appositional Growth Growth in circumfrence The inner layer of the periosteum builds concentric layers of bone
Combined Activity of Osteoclasts and Osteoblasts Determine Bone Density Osteoblasts build new bone Osteoclasts reabsorb bone
Bone Response to Stress • Wolf’s Law • Indicates that bone strength increases and decreases as the functional forces on the bone increase and decrease. • Bone Modeling and Remodeling • Mechanical loading causes strain • Bone Modeling • If Strain > modeling threshold, then bone modeling occurs.
Bone Response to Stress • Bone mineral density generally parallels body weight • Body weight provides most constant mechanical stress • Determined by stresses that produce strain on skeleton • Think: weight gain or loss and its effect on bone density
Bone Hypertrophy • An increase in bone mass due to predominance of osteoblast activity. • Seen in response to regular physical activity • Ex: tennis players have muscular and bone hypertrophy in playing arm. • The greater the habitual load, the more mineralization of the bone. • Also relates to amount of impact of activity/sport
Bone Atrophy • A decrease in bone mass resulting form a predominance of osteoclast activity • Accomplished via remodeling • Decreases in: • Bone calcium • Bone weight and strength • Seen in bed-ridden patients, sedentary elderly, and astronauts
Summary • Bone is an important living tissue that is continuously being remodeled. • Bone Strength and Resistance to fracture depend on its material composition and organizational structure. • Bones continually change in density.
