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Osseous Tissue

Osseous tissue or bone is the major structural and supportive connective tissue of the body.  The matrix of bone contains abundant collagen fibers and these impart strength, some flex, and resistance to twisting or torsional forces.  Surrounding these "reinforcing rods" of collagen is a cement-like ground substance called hydroxyapatite.  This mineral complex of calcium phosphate salts makes bone highly resistant to compression forces.  Together, collagen fibers and hydroxyapatite make bone one of the strongest and lightest materials known.

Osseous tissue forms the variety of bones that make up the skeletal system.  As such, osseous tissue directly or indirectly contributes to some very important body functions that include:

1. support - for muscles, organs, and soft tissues

2. leverage and movement - the synovial joints

3. protection - for critical organs

4. calcium phosphate storage - mineral balance

5. hemopoiesis - formation of blood cells

Bone or osseous tissue is found in two different forms:

1. compact bone

2. cancellous or spongey bone

Compact Bone

Compact bone is a very dense tissue forming the outer layer of all bones and the thickened shafts or diaphyses of long bones.  In a microscopic view, compact bone always contains numerous osteons or Haversian Systems. Each consists of a central canal through which blood vessels and nerves pass.  Surrounding this canal are multiple concentric lamellae or layers of bone.  Haversian systems are only found in compact bone.   Their specific arrangements within compact bone contribute to the strength of this osseous tissue type.

Cancellous or Spongey Bone

Cancellous or spongey bone is found forming the core of most flat and irregular bones.  It is also very prevalent in the epiphyses(ends) of long bones.  The construction of this osseous tissue type is quite different than that of compact bone.  One key difference is the absence of osteons!  Spongey bone as the name implies is more open and in cross-section offers a compartmentalized appearance not unlike that of a sponge.  Consisting of interconnecting "struts" of bone called trabeculae, spongey bone has abundant spaces typically occupied by bone marrow and adipose tissues.

Here is a view of several osteons in compact bone!

Compare the compact bone to this trabeculum in spongey!  Note the lacunae!

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