MH 043 Cancellous and Compact Bone

This slide contains two specimens:

Long Bone - partial cross-section from the end of a long bone found in the extremities.
Flat Bone - cross-section of a bone from the skull cap (calvarium).

Examine the partial-cross section of the long bone.

What are the two types of structural arrangements of bones? [+]

Compact bone - dense layer that forms the outside of a bone
Spongy (cancellous) bone – sponge-like meshwork of trabeculae (or spicules) that form the interior of bones

(These terms refer to their macroscopic appearance.)

Why is ther no or very few osteons in spongy bone? [+]

Trabeculae are usually thin enough that nutrients can diffuse through canaliculi connecting osteocytes in lacunae

Name of the organic matter of bone? [+]

Osteoid - unmineralized bone matrix of mostly collagen type I (15 to 20% of bone)

Major inorganic matter of bone? [+]

Calcium phosphates in the form of hydroxyapatite crystals (70 to 80% of bone)

Name of the dense connective tissue that covers the external surface of bone? [+]

Periosteum (except for articular surfaces)

It is poorly perserved in these tissue sections.

Name of its two layers and how do they differ? [+]

Outer fibrous layer - collagen type I fibers and scattered fibroblasts
Inner osteogenic layer – osteoprogenitor cells that can differentiate into osteoblasts

What are Sharpey's fibers? [+]

Collagen fibers that extend from the periosteum into the extracellular matrix of bone that provide a strong anchoring for the periosteum, ligaments, and tendons to bone

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