Osteoporosis Is a Reduction in Bone Mass

Osteoporosis is a major health problem, particularly because older adults are more prone to this disorder and the average age of the population is increasing (see Clinical Fo

Effects of 1,2 5-clihyclroxycholecalciferol ^ttmmU^mm^ [i,25-(OH)2 D3] on calcium and phosphate metabolism.

cus Box 36.1). Osteoporosis involves a reduction in total bone mass with an equal loss of both bone mineral and organic matrix. Several factors are known to contribute directly to osteoporosis. Long-term dietary calcium deficiency can lead to osteoporosis because bone mineral is mobilized to maintain plasma calcium levels. Vitamin C deficiency also can result in a net loss of bone because vitamin C is required for normal collagen synthesis to occur. A defect in matrix production and the inability to produce new bone eventually result in a net loss of bones. For reasons that are not entirely understood, a reduction in the mechanical stress placed on bone can lead to bone loss. Immobilization or disuse of a limb, such as with a cast or paralysis, can result in localized osteoporosis of the affected limb. Space flight can produce a type of disuse osteoporosis resulting from the condition of weightlessness.

Most commonly, osteoporosis is associated with advancing age in both men and women, and it cannot be assigned to any specific definable cause. For several reasons, women are more prone to develop the disease than men. Figure 36.10 shows the average bone mineral content (as grams of calcium) for men and women versus age. Until about the time of puberty, males and females have similar bone mineral content. However, at puberty, males begin to acquire bone mineral at a greater rate, peak bone mass may be approximately 20% greater than that of

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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