These bones serve as armor for vital organs and soft tissue, a storehouse for minerals, and a birthplace for blood cells. Together, the bones act in concert with the muscles, ligaments, tendons, and other connective tissue to give humans an amazing range of movement.
Most bone diseases are rare, but a few pose serious health problems.
Osteoporosis, for example, is a progressive loss of bone substance that affects about 25 million Americans, mostly postmenopausal caucasian women. Osteoarthritis, the most common form of arthritis, is widespread among people over 40. Low back pain, which often results from slipped vertebrae or disks, is the second most frequent cause of lost work for adults under 45 years of age. Though solid and seemingly completely formed, bones undergo constant renewal and change. The marrow, or soft center, of certain bones serves as a spawning ground for the many different cells that make up the blood.