Biology Articles » Anatomy & Physiology » Anatomy, Human » Osteoclasts – the Cells That Break Bone

Osteoclasts – the Cells That Break Bone

In all two hundred and six bones make our skeleton. The bony framework that supports our entire body protects important and delicate organs like the brain, heart and lungs. Some bones like the femur-–the thighbone and humerus–upper arm bone, are rod like. While skull bones are flat like a table.

Whatever the shape, bones are rigid and inflexible. Most people think the bones are like beams and columns in a building; unchanging, solid infrastructural support material. But the bones are dynamic. They are changing, being made and broken, remodeled all the time throughout our life.

The bone is a connective type of tissue and has three types of cells. They are the osteoblasts, osteocytes, and the osteoclasts.

Osteoblasts, form the bone i.e., deposit the mineral calcium and form the organic matrix. They are seen just inside the outermost boundary of the bone and just outside the bone marrow cavity. Osteocytes are seen in all parts of bone in between exterior of the bone marrow and periphery of a bone. They maintain bone as a living tissue. They are the most numerous of the three types of cells in bones. Third type of bone cells is the osteoclasts found in Howship’s lacunae, sort of trenches, they carve out for themselves. They dissolve bone, breaking down calcium and phosphorous, and causing it to be reabsorbed. Bone deposition is the job done by osteoblasts. Bone resorption is done as and when required by osteoclasts. Excess activity of osteoclasts leads to osteoporosis, a disease in which bone develops pores as too much of calcium, the chief mineral in the bone, is removed. Osteoporosis is more common in women after their menopause. This is because the rate of bone loss increases with declining levels of estrogens.

In osteoporosis bone is more porous than average and is therefore more likely to fracture. Unfortunately this condition gives no warning and no symptoms appear in osteopenic bone until the condition worsens and such a bone is broken There are some factors which are not under our control like the genes we have inherited or our gender. There are other factors little known to most people, like the family history (2-3 generations old). But there are factors under our control and we can prevent osteoporosis by: (a) avoiding the use of steroids, tobacco, alcoholic drinks (b) increasing calcium-rich food items in the diet and (c) lifting weights as physical exercise or as a daily chore, about half an hour a day.

If increased activity of osteoclasts is dangerous as it leads to osteoporosis their activity reduced can also be a big problem. It produces a condition called osteopetrosis. In this disorder too much bone is formed leading to extra-dense bone which is more brittle than normal bone and may lead to fractures. Reduced activity of osteoclasts may also fill up bone marrow with bone a fatal condition.

How marvelously intricate is the design of our body! One single type of cell working too hard or too lazily can make difference between life and death.

Written byNarayan Dattatray Wadadekar
Source: Suite101, June 21, 2005