Osseous Tissue Structure

Osseous Tissue

• A specialized connective tissue composed of cells and bone matrix (calcified extracellular material)

Bone Matrix

• Composed of 35% organic matter and 65% inorganic matter
• Inorganic matter: hydroxyapatite crystal, calcium hydroxyapatite, bicarbonate, citrate, magnesium, potassium, and sodium ions
• Organic matter: osteoid (non-calcified bone matrix) consisting of type I collagen, ground substance (GAGs, proteoglycans, and glycoproteins), osteocalcin, osteonectin, and osteopontin

Osteoblast

• Location: on the surface of bone matrix
• Structure: single layer of cuboidal cells
• Outcome: osteocytes and bone lining cells
• Function: produce organic components of the matrix (osteoid) and help with deposition of inorganic components

Osteocyte

• Structure: long thin processes, located in bone lacuna and bone canaliculus
• Function: maintain bone matrix

Osteoclast

• Location: resorption lacunae (or Howship lacunae)
• Structure: multinuclear large cell, 30-100µm, acidophilic cytoplasm
• Origin: fusion of bone marrow-derived monocytes
• Function: dissolve bone matrix

Periosteum and Endosteum

• Periosteum: outer layer and inner layer on the external surface of bone
• Endosteum: delicate matrix of collagen fibers on the internal surface of cavities

Bone Types

• Gross observation: compact bone and cancellous bone
• Under microscope: both show same basic histological structure (lamellar bone)

Lamellar Bone

• Matrix existing as discrete sheets
• Collagen fibers arranged in lamellae
• Typical organization:
  • Osteon (Haversian system)
  • Interstitial lamellae
  • Circumferential lamellae

Osteon (Haversian System)

• Long, cylindrical structure parallel to the long axis of the bone
• 4-20 Haversian lamellae around a central canal
• Outer boundary: the cement line wraps
• Communicated by transverse or oblique Volkmann’s canal

Interstitial Lamellae

• Among the intact osteons
• Irregular lamellae
• Remaining lamellae of osteons