Lecture Notes on Bone Structure

1. Introduction to Bone Structure

• Compact Bone
  • Found on the outer surface of all bones.
  • Not solid; mostly spongy bone inside.
  • Composed of compact and spongy bone in varying proportions.
• Spongy Bone
  • Found within bones, surrounded by compact bone.
  • Contains trabeculae and bone marrow.

2. Compact Bone Details

• Osteons
  • Found only in the diaphysis of long bones.
  • Made of concentric lamellae around a central Haversion Canal.
  • Provide structural strength, allowing for movement without bone breakage.
• Functions of Compact Bone (Cortical Bone)
  • Protection: Protects soft tissues like brain, heart, and bone marrow.
  • Anchoring Site: Provides attachment for tendons (muscle to bone) and ligaments (bone to bone).
  • Locomotion: Particularly in long bones, involved in movement.

3. Circumferential Lamellae

• Found on the outermost surface of the bone.
• Consist of rings (lamellae) that provide an attachment site for connective tissue.

4. Osteon Structure

• Long cylindrical structures with a central Haversion Canal.
• Haversion Canal
  • Contains blood vessels, lymph vessels, and neurons.
  • Crucial for nutrition and waste removal of bone cells.
• Collagen Fibers
  • Laid in opposing angles to handle torsion, preventing bone breakage during movement.

5. Spongy Bone Features

• Functions
  • Provides internal support through trabeculae.
  • Houses stem cells due to blood-rich endosteum.
  • Considered bioavailable for minerals like calcium.
• Structure
  • Trabeculae provide support and contain bone marrow.
  • Osteocytes reside in lacunae, not organized in concentric lamellae.

6. Differences Between Compact and Spongy Bone

• Compact Bone
  • Dense, highly organized in osteons with concentric lamellae.
  • Primarily for structural integrity and support.
• Spongy Bone
  • Less dense, contains trabeculae, and is more physiologically active.
  • Provides support, mineral storage, and houses marrow.
  • Contains blood vessels on the surface, not within.

7. Trabeculae Details

• Internal Structure
  • Contains osteocytes but lacks blood vessels.
• External Features
  • Highly vascularized surface with osteoblasts and osteoclasts.
  • Endosteum present, composed of blood vessels and stem cells.

8. Importance of Collagen and Osteons

• Collagen fibers in osteons are key for handling torsion.
• Osteons prevent snapping in long bones during movement.

9. Marrow Characteristics

• Red Marrow
  • Contains actively reproducing hematopoietic stem cells.
  • Found in spongy bone.
• Yellow Marrow
  • Fatty tissue, more prevalent in long bones during adulthood.

10. Additional Notes

• Volkmann's Canals
  • Connect exterior bone surface to interior osteons.
  • Facilitate nutrient and blood supply to bone.
• Bone's Vascularity
  • Highly vascularized with networks of blood vessels for nutrient delivery.

11. Conclusion

• Understanding the detailed structure and function of bone components (compact and spongy) is essential for appreciating the complexity and functionality of the skeletal system.