Compact bone is a highly structured, dense type of bone found where maximum strength is required.  The osteons of compact bone are the elements that determine this strength via their arrangment along lines of stress.  Think of osteons as reinforcing columns, all arranged in the same direction, like a stack of pencils.  Compact bone in cross-section, the typical view in most textbooks, looks like this with osteons also cut in cross-section.

concentric lamellae.  Other lamellae, isolated and not associated with a central canal are remnants of older osteons called interstitial lamellae.  Bone is a very dynamic tissue, constantly being restructured as older osteons are replaced by new.  The interstitial lamellae are evidence of this restructuring.

As you can see, there are many lacunae(the small dark spots) where mature bone cells or osteocytes are found.  Bone forming cells or osteoblasts are never found in lacunae but rather along the edges of bone where new lamellae form.  When an osteoblast is completely surrounded by the forming hydroxyapatite, it becomes an osteocyte.  A third type of bone cell to remember is the osteoclast, also found along the edges of bone.  Osteoclasts are active where bone or calcified cartilage is being resorbed resorbed and restructured.  The osteoclast is a large, multinucleate cell with microvilli.  Microvilli increase surface area on the membrane and this in turn increases efficiency of secretion/absorption.

Now, lets review some aspects of bone!

• Here is a closer look at an osteon of compact bone.  Notice the concentric lamellae with lacunae!
• Now, let's enlarge a single lacuna where an osteocyte is found.  See canaliculi?
• Along edges of bone where appositional growth occurs you find osteoblasts.  When these are surrounded by bone they become osteocytes.
• Also along edges of bone are larger, multinucleate osteoclasts that resorb bone to release minerals and aid in restructuring of bone.  Can you see the pocket where bone has been removed?

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