Like all of the other tissues of your body, your bones are alive. Composed of several types of cells, proteins, blood vessels, nerves and a hard mineral matrix, your bones conduct the processes of living --- collectively termed metabolism. Bone metabolism is regulated by several hormones and influenced by many factors, and it changes throughout your life.
Bone Cells
Bone metabolism is conducted primarily by two types of cells, osteoblasts and osteoclasts. The term "osteo" comes from the Greek word for bone. Osteoblasts --- with a "b" --- are bone builders. Osteoclasts --- with a "c" --- are bone cutters. The activity of your osteoblasts or osteoclasts may dominate at a given point in time, depending on your age, circulating levels of bone-metabolism-controlling hormones, intake of calcium and vitamins, whether you have a bone injury and other factors.
Growth and Modeling
Your osteoblasts are the cells involved in the metabolic processes of bone growth and modeling. New bone forms during these processes, which are highly active during childhood and important in adulthood if you break a bone.
New bone formation begins with the production of a protein-rich, rubbery material, which gains strength as it absorbs calcium, phosphate, magnesium and other minerals. Vitamin and mineral deficiencies can interfere with bone metabolism, leading to impaired growth, healing and strength.
Remodeling
Bone remodeling is an active metabolic bone process throughout your adulthood. As your bones undergo the physical stresses of everyday life, they are remodeled to accommodate the changing ways you use your body; replace old bone; and repair minor injuries. During remodeling, osteoclasts and osteoblasts work together at the same site. While osteoclasts cut away old bone, osteoblasts replace it with new bone. During adulthood, most bones in your body are replaced approximately every 10 years by remodeling.
Osteoporosis
Osteoporosis is a metabolic bone condition of reduced mass and strength, which increases the likelihood of fractures. With osteoporosis, the activity of your osteoclasts outpaces that of your osteoblasts during remodeling, leading to a loss of bone mass. Reduced production of sex hormones associated with advancing age is a major contributing factor to the development of osteoporosis, especially among postmenopausal women. Sex hormones help immature osteoblasts develop and activate. Estrogen also helps to shut down the activity of osteoclasts. The low estrogen levels of postmenopausal women tip the metabolic balance in the bones toward net loss. Physical inactivity, calcium and vitamin D deficiency, smoking and certain medications can further accelerate age-related bone loss in men and women.
Supporting Healthy Bone Metabolism
Eating a diet rich in vitamins D and C, calcium, phosphorus and magnesium is important to supporting healthy bone metabolism. Getting a sufficient amount of calcium from your diet is particularly important because your body will break down bone to release calcium for use by your other tissues if you are not taking in an adequate amount.
Regular exercise is also essential for healthy bone metabolism. Weight-bearing exercise exerts healthy stress on your bones, which induces them to maintain or increase their mass and strength. One of the best ways to fight osteoporosis is to participate in regular, weight-bearing physical activity.
References
- University of Washington; Bone Physiology, Bone Cells; Susan Ott, M.D.; September 2010
- University of Washington; Bone Physiology, Bone Remodeling; Susan Ott, M.D.; September 2010
- FamilyPracticeNotebook.com: Bone Physiology
- "Bone Health and Osteoporosis: A Report of the Surgeon General"; The Basics of Bone in Health and Disease; U.S. Department of Health and Human Services, Office of the Surgeon General; 2004
- "Osteoporosis: Diagnosis, Prevention, Therapy"; Reiner Bartl, M.D. et al.; 2009
- University of Michigan: Biomechanics, Bone Physiology
