USMLE

Compact Bone

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Musculoskeletal
  1. Osteoblasts
  2. Osteoclasts
  3. Osteocytes
  4. Spongy Bone
  5. Compact Bone
  6. Bone Structure
  7. Cartilage
  8. Joints
  9. Type 1 vs. Type 2 Muscle Fibers

Summary

Compact bone is the dense, protective outer layer of bone that surrounds the spongy bone. Compact bone is organized into repeating units called Haversian Systems, or osteons, which are further divided into two portions. First, there is the outer lamellae, which is made of concentric circles of bone with spaces in between them called lacunae. Second, we have the Haversian canals running through the center of the rings of bone, which contain blood vessels to exchange nutrients and waste. Finally, the Vokmann’s canals connect different Haversian systems.

Key Points

  • Compact Bone
    • Harder, denser layer
    • Outer layer of bone
    • Organized into Haversian systems 
      • Each Haversian system (or osteon) is composed of 2 parts
        • Lamellae 
          • Concentric rings of bone produced by osteoblasts 
          • Lacunae are spaces between lamellar layers
            • Osteocytes trapped inside maintain bone
            • Canaliculi connect lacunae
              • Allow for communication and nutrient exchange between osteocytes
        • Haversian Canals
          • Open spaces at center of lamellae
          • Contain blood/lymph vessels
          • Interconnected to each other by Volkmann’s canals