Specialized Cells in the Skeletal System

The human skeleton is composed mainly of a substance called bone, and there are primarily four types of cells that make up bone. These are the osteoprogenitor cells, osteoblasts, osteoclasts and osteocytes. Their names all start with the prefix "osteo," which is the Greek word for "bone."

Skeleton (Image: George Doyle/Stockbyte/Getty Images)

Osteoprogenitor Cells

These are immature cells that are primarily located in the bone marrow and periosteum (membrane that lines the surface of all bones). They mature into the osteoblasts, another type of bone cell.

Osteoblast Cells

These are the bone cells that are primarily responsible for bone formation. They only have one nucleus and are derived from osteoprogenitor cells. They function by secreting a substance called osteoid, which is also known as the bone matrix. This substance is then mineralized with substances like calcium and phosphate, which forms the substance we know as bone. When a group of osteoblasts is finished forming bone, they flatten out and line the surface of the bone. Henceforth they are known as "lining cells," and their job is to regulate the passage of minerals, such as calcium, in and out of the bone. They also function by secreting proteins that regulate the osteoclast cells.

Osteoclast Cells

These are the cells that are primarily responsible for dissolving bone tissue, also known as resorption. They do not arise from osteoprogenitor cells; instead, white blood cells that normally have immune system function (monocytes) fuse together to create the osteoclasts. As a result, they are quite large, with multiple nuclei, and are located in the endosteum (membrane that lines the inner cavity of the bone where bone marrow resides).


These can be recognized by their typical star-shaped appearance, and are mature osteoblasts that do not secrete the osteoid bone matrix, but are surrounded by it. They have long branches that reach out from the cell body and communicate with neighboring osteocytes, and play an important role in maintaining calcium levels in body fluids. They do this by regulating the process of bone formation and/or resorption; since the bone is the body's primary reservoir of calcium, they end up controlling the release/storage of calcium in the bloodstream.

Load Comments

Copyright © 2019 Leaf Group Ltd. Use of this web site constitutes acceptance of the LIVESTRONG.COM Terms of Use , Privacy Policy and Copyright Policy . The material appearing on LIVESTRONG.COM is for educational use only. It should not be used as a substitute for professional medical advice, diagnosis or treatment. LIVESTRONG is a registered trademark of the LIVESTRONG Foundation. The LIVESTRONG Foundation and LIVESTRONG.COM do not endorse any of the products or services that are advertised on the web site. Moreover, we do not select every advertiser or advertisement that appears on the web site-many of the advertisements are served by third party advertising companies.