Mader: Understanding ② The McG ysiology, Fifth Edition Clinical Connections Additional readings engage the students by creating a richer understanding of the concepts presented and provide a real life connection to anatomy and physiology Medical Focus Readings Medical focus encourage students to explore clinical examples that they may see through heir health care career or within thei What's ney What's New Readings ffer fascinating information on treatments now experimental but promise to be particularly helpful in the future Effects of Aging Effects of Aging presents some of the age- related physical and Education is not preparation for life; education is life itself. John DMader: Understanding Human Anatomy & Physiology, Fifth Edition Front Matter Preface © The McGraw−Hill Companies, 2004 Clinical Connections Additional readings engage the students by creating a richer understanding of the concepts presented and provide a real life connection to anatomy and physiology. 88 Part II Support, Movement, and Protection Osteoporosis Osteoporosis is a condition in which the bones are weakened due to a decrease in the bone mass that makes up the skeleton. Throughout life, bones are continuously remodeled. While a child is growing, the rate of bone formation is greater than the rate of bone breakdown. The skeletal mass continues to increase until ages 20 to 30. After that, the rates of formation and break￾down of bone mass are equal until ages 40 to 50. Then, reabsorp￾tion begins to exceed formation, and the total bone mass slowly decreases. Over time, men are apt to lose 25% and women 35% of their bone mass. But we have to consider that men tend to have denser bones than women anyway, and their testosterone (male sex hor￾mone) level generally does not begin to decline significantly until after age 65. In contrast, the estrogen (female sex hormone) level in women begins to decline at about age 45. Because sex hor￾mones play an important role in maintaining bone strength, this difference means that women are more likely than men to suffer fractures, involving especially the hip, vertebrae, long bones, and pelvis. Although osteoporosis may at times be the result of various disease processes, it is essentially a disease of aging. Everyone can take measures to avoid having osteoporosis when they get older. Adequate dietary calcium throughout life is an im￾portant protection against osteoporosis. The U.S. National Insti￾tutes of Health recommend a calcium intake of 1,200–1,500 mg per day during puberty. Males and females require 1,000 mg per day until age 65 and 1,500 mg per day after age 65, because the intestinal tract has fewer vitamin D receptors in the elderly. A small daily amount of vitamin D is also necessary to absorb calcium from the digestive tract. Exposure to sunlight is required to allow skin to synthesize vitamin D. If you reside on or north of a “line” drawn from Boston to Milwaukee, to Minneapolis, to Boise, chances are, you’re not getting enough vitamin D during the win￾ter months. Therefore, you should avail yourself of the vitamin D in fortified foods such as low-fat milk and cereal. Postmenopausal women should have an evaluation of their bone density. Presently, bone density is measured by a method called dual energy X-ray absorptiometry (DEXA). This test mea￾sures bone density based on the absorption of photons generated by an X-ray tube. Soon, a blood and urine test may be able to detect the biochemical markers of bone loss, making it possible for physicians to screen all older women and at-risk men for osteoporosis. If the bones are thin, it is worthwhile to take measures to gain bone density because even a slight increase can significantly re￾duce fracture risk. Regular, moderate, weight-bearing exercise such as walking or jogging is a good way to maintain bone strength (Fig. 6A). A combination of exercise and drug treatment, as recommended by a physician, may yield the best results. A wide variety of prescribed drugs that have different modes of action are available. Hormone therapy includes black cohosh, which is a phytoestrogen (estrogen made by a plant as opposed to an animal). Calcitonin is a naturally occurring hormone whose main site of action is the skeleton where it inhibits the action of osteoclasts, the cells that break down bone. Promising new drugs include slow-release fluoride therapy and certain growth hor￾mones. These medications stimulate the formation of new bone. a. b. osteoporosis normal bone Figure 6A Preventing osteoporosis. a. Exercise can help prevent osteoporosis, but when playing golf, you should carry your own clubs and walk instead of using a golf cart. b. Normal bone growth compared to bone from a person with osteoporosis. Chapter 6 The Skeletal System 107 Coaxing the Chondrocytes for Knee Repair To the young, otherwise healthy, 30-something athlete on the physician’s exam table, the diagnosis must seem completely un￾fair. Perhaps he’s a former football player, or she’s a trained dancer. Whatever the sport or activity, the patient is slender and fit, but knee pain and swelling are this athlete’s constant compan￾ions. Examination of the knee shows the result of decades of use and abuse while performing a sport: The hyaline cartilage, also called articular cartilage, of the knee joint has degenerated. Hya￾line cartilage (see page 84) is the "Teflon coating" for the bones of freely movable joints such as the knee. Hyaline cartilage allows easy, frictionless movement between the bones of the joint. Once repeated use has worn it away, hyaline cartilage does not grow back naturally. Exposed bone ends can grind against one another, resulting in pain, swelling, and restricted movements that can cripple the athlete. In severe cases, total knee replacement with a prosthetic joint is the athlete’s only option (Fig. 6B). Now the technique of tissue culture (growing cells outside of the patient’s body in a special medium) can help young athletes with cartilage injuries regenerate their own hyaline cartilage. In an autologous chondrocyte implantation (ACI) surgery, a piece of healthy hyaline cartilage from the patient’s knee is first removed surgically. This piece of cartilage, about the size of a pencil eraser, is typically taken from an undamaged area at the top edge of the knee. The chondrocytes, living cells of hyaline cartilage, are grown outside the body in tissue culture medium. Millions of the pa￾tient’s own cells can be grown to create a "patch" of living carti￾lage. Growing these cells takes two to three weeks. Once the chon￾drocytes have grown, a pocket is created over the damaged area using the patient’s own periosteum, the connective tissue that sur￾rounds the bone (see page 84). The periosteum pocket will hold the hyaline cartilage cells in place. The cells are injected into the pocket and left to grow. As with all injuries to the knee, once the cartilage cells are firmly established, the patient still faces a lengthy rehabilitation. The patient must use crutches or a cane for three to four months to protect the joint. Physical therapy will stimulate cartilage growth without overstressing the area being repaired. In six months, the athlete can return to light-impact training and jogging. Full work￾outs can be resumed in about one year after surgery. However, most patients regain full mobility and a pain-free life after ACI sur￾gery and do not have to undergo total knee replacement. ACI surgery can’t be used for the elderly or for overweight pa￾tients with osteoarthritis. Muscle or bone defects in the knee joint must be corrected before the surgery can be attempted. As with all surgeries, there is a risk for postoperative complications, such as bleeding or infection. However, ACI may offer young athletes the chance to restore essential hyaline cartilage and regain a healthy, functional knee joint. polyethylene polyethylene pelvis femur femur a. tibia b. Figure 6B Artificial joints in which polyethylene replaces articular cartilage. a. Knee. b. Hip. 6.5 Effects of Aging Both cartilage and bone tend to deteriorate as a person ages. The chemical nature of cartilage changes, and the bluish color typical of young cartilage changes to an opaque, yellowish color. The chondrocytes die, and reabsorption occurs as the cartilage undergoes calcification, becoming hard and brittle. Calcification interferes with the ready diffusion of nutrients and waste products through the matrix. The articular cartilage may no longer function properly, and the symptoms of arthri￾tis can appear. There are three common types of arthritis: (1) Osteoarthritis is accompanied by deterioration of the ar￾ticular cartilage. (2) In rheumatoid arthritis, the synovial membrane becomes inflamed and grows thicker cartilage, possibly due to an autoimmune reaction. (3) Gout, or gouty arthritis, is caused by an excessive buildup of uric acid (a metabolic waste) in the blood. Rather than being excreted in the urine, the acid is deposited as crystals in the joints, where it causes inflammation and pain. Osteoporosis, discussed in the Medical Focus on page 88, is present when weak and thin bones cause aches and pains. Such bones tend to fracture easily. Effects of Aging presents some of the age-related physical and functional changes that occur in the body. What’s New Readings offer fascinating information on treatments that are now experimental but promise to be particularly helpful in the future. Medical Focus Readings encourage students to explore clinical examples that they may see throughout their health care career or within their own family. “Education is not preparation for life; education is life itself.” – John Dewey xvii