Bone Structure and Function

Overview of Bone Composition

Characteristics:
- Contains few spaces between bone cells and extracellular matrix components.
- Found beneath the periosteum of all bones.
- Makes up the bulk of the diaphysis (shaft of a long bone).
- Provides protection, support, and resists stresses from weight and movement.
Structure:
- Composed of repeating units called osteons.
  - Osteon: Comprises concentric lamellae arranged around a central canal.
    - Concentric Lamellae: Circular plates of mineralized matrix.
    - Central Canal: Houses blood vessels and nerves; runs parallel to bone's long axis.
  - Lacunae: Small spaces housing osteocytes.
    - Osteocytes: Mature bone cells that maintain bone metabolism.
    - Canaliculi: Channels connecting lacunae for osteocyte communication.
- Blood supply and nerve connection via transverse perforating canals (Volkmann's canals).
  - Connect periosteum vessels/nerves with central canal.

Location: Interior of bones, protected by compact bone.
Structure:
- Made of lamellae arranged in an irregular pattern of trabeculae (thin columns).
  - Spaces between trabeculae filled with red/yellow bone marrow.
  - Trabeculae consist of concentric lamellae, osteocytes in lacunae, and canaliculi.
Function:
- Supports and protects red bone marrow.
- Reduces overall weight of the skeleton.
- Oriented along lines of stress to resist stress and transfer force efficiently.

Compact Bone:
- Located where bones are heavily stressed with force from one direction.
- Thickest under high force or weight bearing.
Spongy Bone:
- Located where stressors are applied from multiple directions.
- Less strong but reduces bone weight and supports blood cell production.