When asked to visualize the word “bones,” many people tend to picture a dry, rattling skeleton – perhaps topped off with a grinning skull. But this cartoonish image can’t do justice to the amazingly complex living organs that form your body’s scaffolding. From supporting muscles and protecting vital organs to producing blood cells, your bones perform a variety of functions, all essential to sustaining life.
Composition of Bones
Your bones are made of up of living material – blood vessels, nerves, and bone cells – as well as non-living material, including minerals and collagen. The outer layer, or periosteum, is a dense, collagen-rich surface which provides attachment points for tendons and muscles.
The periosteum also contains specialized bone cells called osteoblasts, which grow and repair the outside of the bone. In addition, the periosteum contains blood vessels which nourish the bone’s inner cells. Under the periosteum lies a layer of compact bone, composed primarily of collagen and calcium salts. It is the bonding of collagen fibers with calcium salts that gives bones their tensile and compressional strength.
The compact bone layer also contains osteoclasts, a type of bone cell responsible for reabsorbing and reshaping bone. Deep inside the compact bone is the cancellous, or spongy, bone. It is here that the bone marrow is found. Bright red in childhood, the marrow decreases in amount and turns increasingly yellow after puberty. The rounded protuberance at the ends of the bones, known as the epiphysis, are composed of mostly cancellous bone.
How strong ARE bones? The National Space Biomedical Research Institute notes that our bone’s calcium salts are physically similar to marble.
Functions of Bones
Your skeleton, a sturdy but lightweight network of 206 different bones connected to each other by ligaments, is divided into two sections.
- The axial skeleton, which runs down the center of your body, includes the cranium, the ribcage, and the spinal column.
- The appendicular skeleton, which connects bones to the axial skeleton and allows for support and movement, consists of your upper and lower limbs as well as your pelvic and shoulder girdles.
In addition to forming a framework, bones serve as production factories and storehouses. Red marrow produces red blood cells along with infection-fighting white blood cells. Yellow bone marrow, found in bones after puberty, stores iron, as well as energy in the form of lipids, or fats. Bones also store and release calcium, essential to to the proper working of nerves and muscles. Finally, bones release a hormone that helps to regulate blood sugar and distribute fats.
Bone Disease: Osteoporosis and Osteopenia
Osteoporosis, a condition in which decreasing density leaves bones brittle and vulnerable to fracture, is the most common bone disease. Although it can affect men, postmenopausal women are most at risk. According to the National Institutes of Health, roughly 50 percent of all women over age 50 will suffer a fracture of the hip, wrist, or spine. Additional risk factors include being Caucasian or Asian, being small-boned, and having a family history of the condition.
Osteoporosis develops when the production of new bone does not keep pace with the loss of old bone. Anything that interferes with the body’s absorption of calcium can raise the risk of osteoporosis. Using nicotine, being sedentary, taking steroids, undergoing weight loss surgery, and drinking more than two alcoholic drinks a day are all associated with osteoporosis – as are lifelong low calcium intake and the presence of eating disorders, particularly anorexia.
Symptoms include decreasing height over time, stooped posture, and back pain, which can be caused by an undiagnosed broken or collapsed vertebra. Experiencing a fracture under conditions in which you would not ordinarily expect to break a bone is another indication of osteoporosis.
In osteopenia, the bones have begun to thin, but are not yet brittle enough to qualify as osteoporosis. Both conditions can be diagnosed with a painless bone density test, which compares your bone density with that of young adults of your same race and sex, as well as that of people in your age group who share your race and sex. According to Harvard Health, a T-score between -1.0 and -2.5 indicates osteopenia; a T-score lower than -2.5 signifies osteoporosis.
Osteoporosis is usually treated with a group of medications called biphosphonates. These include alendronate, sold under the brand name Fosamax, and ibandronate, sold as Boniva. These treatments are often given in quarterly injections to avoid digestive side effects.
Because the likelihood of developing osteoporosis depends on the amount of bone mass accumulated in youth, experts stress the lifelong importance of ingesting sufficient calcium. Dr. Robert Sheeler, M.D., Medical Editor of the Mayo Clinic Health Letter, advises taking 1500 milligrams of calcium citrate a day, split into three doses, along with 800 to 1000 I.U. of vitamin D to increase calcium absorption.
You can also up your calcium intake through diet. A cup of plain, low-fat yogurt contains a whopping 450 mg of calcium. A 3-oz. serving of sardines has a respectable 325 mg. Other calcium-rich foods are calcium-fortified soy milk, oil roasted almonds, canned sockeye salmon, and cooked rhubarb. Sheeler also recommends at least 35 minutes of weight-bearing exercise per day. Walking, running, playing basketball or racquetball, dancing, jumping rope and rollerblading can all build bone mass and increase density.
The Bottom Line
Although your bones are designed to last a lifetime, certain genetic and lifestyle factors can influence their density and strength. Fortunately, there are some simple steps you can take to promote healthy bones. To be on the safe side, check with your doctor before taking vitamin supplements and starting a new exercise program.