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