BONE STRUCTURE & GROWTH

Anatomy of a Long Bone  Epiphysis – ends  Mostly spongy bone  Diaphysis – shaft  Made of compact bone  Center is medullary cavity  Contains yellow bone marrow (mostly fat) in adults, red marrow in children (makes blood cells).

Bone Tissue – Compact Bone  Made of osteons  Run parallel to bone & support weight  Center is Haversian canal – carries blood vessels & nerves  Volkmann’s canal connects Haversian canals

Bone Tissue – Compact Bone  Lacunae – cavities containing trapped bone cells (osteocytes)  Lamellae – rings around central canal, site of lamellae, reinforced with collagen  Canaliculi – tiny canals connecting lamellae

Bone Tissue – Spongy Bone  Made of needle-like projections called trabeculae  Sandwiched between compact bone  Filled with red bone marrow in some bones

Types of Bone Cells  Osteoblasts – Bone forming cells  Osteocytes – Trapped osteoblasts  Osteoclasts – Bone destroying cells, secrete digestive enzymes for remodeling or calcium needs.

Bone Formation (Ossification) 1. Chondrocytes produce cartilage. 2. Osteoblasts cover cartilage with bone matrix. 3. Cartilage is digested away, opening medullary cavity

Bone Growth  Many bones fuse as we age, replacing cartilage with bone  In long bones, the remaining cartilage is the epiphyseal plate

Bone Remodeling  Bones grow or are remodeled in response to forces acting upon them.

Bone Repair 1. Broken blood vessels form clot (hematoma) 2. Living splint made of collagen & cartilage forms (fibrocartilaginous callus)

Bone Repair 3. Osteoblasts form bony callus of spongy bone 4. Osteoclasts remodel to make permanent patch