Osseous Tissue Structure and Composition

Osseous Tissue

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

Bone Matrix

• Composed of 35% organic and 65% inorganic matter
• Inorganic matter (bone mineral) includes hydroxyapatite crystal, calcium, and other ions
• Organic matter includes osteoid, type I collagen, ground substance, and proteins (osteocalcin, osteonectin, and osteopontin)

Osteoblast

• Located on the surface of bone matrix
• Appears as a single layer of cuboidal cells under light microscopy
• Functions to produce the organic components of the matrix (osteoid) and help deposit inorganic components

Osteocyte

• Located in bone with long thin processes
• Maintains bone matrix and communicates with other cells through gap junctions

Osteoclast

• Located in resorption lacunae (or Howship lacunae)
• Appears as a multinuclear large cell with acidophilic cytoplasm under light microscopy
• Functions to dissolve the bone matrix

Periosteum and Endosteum

• Periosteum is a layer of bone-forming cells and connective tissue on the external surface of bone
• Endosteum is a delicate matrix of collagen fibers on the internal surface of cavities

Bone Types

• Gross observation: compact bone and cancellous bone
• Under microscope, both show the same basic histological structure

Lamellar Bone

• Matrix exists as discrete sheets
• Collagen fibers are arranged in lamellae
• Three types of lamellae: osteon (Haversian system), interstitial lamellae, and circumferential lamellae

Osteon (Haversian System)

• A long, cylindrical structure parallel to the long axis of the bone
• Composed of 4-20 Haversian lamellae around a central canal
• Central canal contains blood vessels, nerve fibers, and lymphatic vessels

Interstitial Lamellae

• Located among intact osteons
• Irregular lamellae remaining from osteons

Circumferential Lamellae

• Arranged in concentric circles
• Outer lamellae have 10-40 layers, while inner lamellae have fewer layers