The Structure Of Bone

When thinking of living tissue in the human body bone is not the first to come to mind. Bone is often forgotten about and placed in an area of stagnant minerals and fibers. This is highly untrue, however. Bone is the primary tissue of the skeletal system and even has its own classification within supportive connective tissue.

Bone or Osseous tissue is defined as either compact or spongy. Compact bone, otherwise known as cortical bone, is a dense tissue that is completely filled in except for lacunae. Lacunae are small holes within compact bone that allow blood vessels to run in and out of the tissue to provide nutrients and transport material. Compact bone is usually the bone that covers the outer surface and gives the bone its solid and smooth look. Spongy bone, otherwise known as cancellous bone, is the internal tissue of compact bone. It is identified by having a network of material resembling a web or sponge. The purpose of this tissue is to provide flexibility and reduce the density of bones to absorb and reduce stress during use.

The picture shown above is what compact bone looks like under the microscope. The circular pattern of cells and matrices are called osteons. Osteons are the defining characteristic of mature bone and form during remodeling. The dark oval circles that are within the osteons are called osteocytes. Osteocytes are the main cell of the bone and account for 90-95% of cells in the bone. They are responsible for bone remodeling, bone deposition, and resorption. Finally, the center of the osteon is called the central canal. These are holes within the compact bone that are innervated with blood vessels. They function to provide nutrients as well as transport calcium and other ions when needed from the bones to other parts of the body.

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