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1. Macrostructure of bone

Click the Next button to explore the structure of cortical bone
2. Cross-section of cortical bone



Osteons, densely packed concentric
lamellae, have a central Haversian canal
containing a blood vessel. Around the
outermost lamella is the cement
line, which with no collagen is the weakest
component of compact bone.

The long axes of the osteons are roughly parallel to the long axis of the bone
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The microstructure of a sample of cortical bone obtained
from a 58 year old human, showing the diameter of an osteon.
(R.A.G. Hodgskinson, PhD Thesis, Queen Mary College, London, 1991)

3. Close-up of an osteon



Examining the concentric lamellae,
it is seen that they have alternating
directions of collagen fibrils.
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The fracture surface of cortical bone, showing the diameter of the Haversian canal and the thickness of a single lamella.
(B. Charalambides, PhD Thesis, Queen Mary College, London, 1991)

4. Molecular structure of cortical bone

The hydroxyapatite crystals are
approximately 225nm long and
10nm thick.

They form a very regular arrangement on the collagen fibrils.
The collagen fibrils are themselves
bundles of collagen molecues.

The fibrils often exhibit banding, with
light and dark regions along their
length (See next slide)
5. Structure of collagen and hydroxyapatite

      
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Low resolution electron micrograph of bovine bone (stained with osmium tetroxide), showing the collagen banding within the osteon. The light regions are collagen, and the dark regions are bone mineral
(R.A.G. Hodgskinson, PhD Thesis, Queen Mary College, London, 1991)

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High resolution electron micrograph showing an individual apatite crystal.
(R.A.G. Hodgskinson, PhD Thesis, Queen Mary College, London, 1991)