 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

 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

 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.

 Compact Bone Low porosity 5-30% bone volume is non-mineralized tissue Withstand greater stress but less strain before fracturing

 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

 The replacement of other tissues with bone

Endochondral and Intramembranous

 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

 Skull, Mandible and Clavicle  Bone develops directly not from cartilage  Develops from the inside out from spongy to dense bone

Epiphyseal and Appositional

 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

 Growth in circumfrence  The inner layer of the periosteum builds concentric layers of bone

Osteoblasts build new bone Osteoclasts reabsorb bone

 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 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

 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

 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

 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.