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Information about the Musculoskeletal and Skin Systems (Page 4 of 4)

Vitamin D deficiency may also affect muscles, since calcium is essential for normal nerve impulse transmission and muscle contraction. Calcium deficiency may result in prolonged muscle spasms and muscle pain.

Exposure to the sun is a double-edged sword. On the one hand, excess exposure has adverse effects on the skin and is associated with increased risks of skin cancer. On the other hand, insufficient exposure to the sun may lead to vitamin D deficiency and its attendant bone and muscle problems. It is possible, however, to both protect against sun-damaged skin and get sufficient exposure to ensure adequate vitamin D synthesis. For example, in summer it takes only 10 to 15 minutes of sunlight on the face and wrists, two to three times a week between 8 a.m. and 4 p.m. to allow the body to make enough vitamin D. Sunscreen, which can block the beneficial effects of sun exposure, should be used to protect the skin at all other times.

Other factors influence vitamin D synthesis, including air pollution, which blocks sunlight; dark pigmentation in the skin; and clothing worn to cover skin. Additionally, vitamin D synthesis may decrease during the winter in geographic locations where the days are shorter, more time is spent indoors, and people dress warmly and cover up well when outdoors.23, 24

6 Diseases and Disorders

There are many diseases and disorders of bone, muscle, and skin. However, it is beyond the scope of this section to discuss them all. We provide here brief introductions to diseases and disorders related to lessons in this module and to several that students may ask about.

6.1 Diseases affecting bone

Achondroplasia. Achondroplasia is a genetic disorder of bone growth that affects males and females of all races and occurs in about 1 of every 25,000 births. People with achondroplasia exhibit abnormal body proportions; their arms and legs are very short while their torso is nearly normal in size. In normally proportioned people, cartilage develops into bone during fetal development and childhood. This process is abnormally slow in the growth plates of long bones in people with achondroplasia, resulting in shorter bones in the arms and legs.

Fractures. A bone can fracture, or break, when the pressure on it becomes too great, and the fracture can occur in several different ways. For instance, the bone may break across its width, lengthwise, at an angle, or spirally. The bone may crack rather than break all the way through or, in the case of extreme force, the bone may actually shatter. The broken bone may not damage surrounding tissue or penetrate the skin. On the other hand, it may damage the skin and surrounding tissue and increase the risk of infection to both the skin and the bone. Additionally, fractures may produce significant blood loss since bones have a rich blood supply.

The underlying causes of fractures are varied. Most common are fractures that result from injury. The injury may be acute, such as a fall, or it may occur more slowly over time, such as that resulting from a repetitive activity (for instance, running) that aggravates a susceptible site. Additionally, diseases (such as osteoporosis and cancer), nutritional deficiencies (such as of calcium and vitamin D), and some medications can make bone more susceptible to fracture.

Osteoarthritis. Osteoarthritis, the most common type of arthritis, affects the cartilage that covers the ends of bones in a joint. In osteoarthritis, also called degenerative joint disease, the cartilage breaks down and causes pain, swelling, and loss of motion. In addition, bone spurs may form and bits of bone or cartilage can break off and float inside the joint space.45

Scientists do not yet know what causes osteoarthritis. Like most diseases, scientists believe that genetic factors are an important contributing factor. Physicians can treat individuals with osteoarthritis using a number of strategies, including pain management, exercise, rest and joint care, weight control, medications, and nontraditional treatment approaches. Individuals who are concerned about the degeneration of joint cartilage sometimes take various nutritional supplements, most notably chondroitin and glucosamine (natural components of cartilage), to help maintain healthy cartilage and thereby reduce the risk or severity of osteoarthritis. Scientific evidence for the efficacy of these products varies.

Treatments for osteoporosis are aimed at altering the imbalance between decreased bone formation and increased resorption.

Osteoporosis. Osteoporosis is a disease in which bone loss occurs accompanied by a decrease in bone strength. Women are four times more likely to have osteoporosis than men. Three factors contribute to osteoporosis:

photo of a doctor marking an x-ray of a torso
Figure 9. Healthy behaviors early in life can help prevent bone disorders such as osteoporosis later in life.

Scientists now believe that the best time for preventing osteoporosis may be during childhood and adolescence, when bones are growing rapidly. In healthy children, adequate intake of calcium and vitamin D and weight-bearing physical activity may be sufficient to prevent osteoporosis.29

Some medications inhibit the formation or activity of osteoclasts.46 Scientists are also investigating therapies that would stimulate bone formation by osteoblasts.51

Osteogenesis imperfecta. Osteogenesis imperfecta is also known as brittle bone disease. It affects an estimated 20,000 to 50,000 individuals in the United States.57 The news media will periodically present a case study of someone with this disease. Because it is usually diagnosed in children, it has, at times, been attributed incorrectly to child abuse. This inherited genetic disease is characterized by bones that break easily. In this disease, collagen is either formed in inadequate amounts or is changed structurally.48

There is no cure for this disease. Treatments focus on preventing or controlling the symptoms, maximizing mobility, and developing optimal bone mass and muscle strength.48 The goal for treatment is to prevent fractures and deformities while allowing the child with the disease to function as independently as possible.

6.2 Diseases and injuries affecting muscle

The ability of muscles to function effectively can be impaired by a number of diseases and injuries. In some diseases, the muscle tissue may not be the primary organ affected but may be impaired as a consequence of a problem at another site in the body.

Amyotrophic lateral sclerosis. Amyotrophic lateral sclerosis (ALS) is also called Lou Gehrig’s disease, and it has received media coverage because of the fame of the baseball player, Lou Gehrig. More recently, the book Tuesdays with Morrie (by Mitch Albom, 1997) told the story of a college professor who was afflicted with the disease. Individuals with ALS lose control of voluntary muscles because the nerves that innervate them are destroyed. As the disease progresses, muscles continue to weaken until they become paralyzed. There is currently no treatment for ALS. Most afflicted people die of respiratory failure because ALS paralyzes the muscles used for breathing.34

Muscular dystrophy. Muscular dystrophy is a group of genetic diseases characterized by progressive muscle weakness and loss of muscle tissue. Diagnosis of a specific form of muscular dystrophy is based on the individual’s symptoms, the age of onset, and the nature of the genetic transmission. The most common types of muscular dystrophy are due to a deficiency in the muscle protein dystrophin.36

Duchenne’s muscular dystrophy is the most severe form of the disease. Initially, it affects the muscles of the pelvis, upper arms, and upper legs. Becker’s muscular dystrophy is milder than Duchenne’s and progresses more slowly. Both Duchenne’s and Becker’s muscular dystrophy afflict boys almost exclusively.37 There is currently no cure for any type of muscular dystrophy. Treatments may include physical therapy, medications, assistive devices, and surgery.

Sprains and strains. Ankle sprains are the most common injury, often occurring during sports or recreational activities.40 A sprain occurs when a ligament, the tissue that connects bones at a joint, stretches or tears. A strain is an injury to either muscle or tendon. The immediate treatment for these injuries is “RICE” (Rest, Ice, Compression, Elevation).

Tetany. Tetany is a condition characterized by muscle spasms (twitching and cramps) brought on when calcium levels in body fluids fall below normal. This can be associated with calcium or vitamin deficiencies, the pathogenic bacterium Clostridium tetani, or with other medical conditions. When calcium levels are below normal, the nervous system becomes more excitable and nerves fire spontaneously. These impulses cause skeletal muscles to contract spasmodically. Tetany can usually be treated with calcium, vitamin D, and diet.

6.3 Disorders of skin

Because skin diseases are so visible to others, affected individuals may feel embarrassed or even ashamed about their conditions.

The psychological effects of skin conditions can be more serious than the conditions themselves. Young children with skin diseases may be subject to teasing, while teenagers, concerned about their physical appearance, may be shunned by their peers. Adults, too, feel the stigma associated with skin disease. They may become more withdrawn and even refuse to seek treatment for their condition, believing (often erroneously) that nothing can be done for them. A recent survey indicated that less than half of the people with a skin disorder seek advice from a doctor, but instead rely on others, such as pharmacists, for information.32 It is likely that there are significant numbers of people who are misinformed about their conditions and may be relying on treatments that have little value.

Some of the more common skin diseases include

Many of these diseases can affect individuals of all races and both genders. For example, acne is a problem for both males and females of all races. Other diseases, however, are more prevalent in some populations than others. For example in the United States, scleroderma has a higher prevalence among certain Native Americans, and keloids occur more frequently in African-American individuals.42

The following discussion focuses on those disorders with particular relevance to young people and those relevant to this module.

photo of a boy’s face with acne
Figure 10. Acne is a common skin disease that can be effectively treated.

Acne. Acne is a skin disorder that results when hormones interact with the skin’s sebaceous glands. These glands produce an oily substance called sebum. Sebum normally reaches the skin surface through an opening of a hair follicle called a pore. During acne, the pore becomes blocked by the hair, sebum, and the cells that line the follicle. This mixture of oil and cells allows the bacteria that normally live on the skin to grow within the plugged pore. Substances produced by the bacteria attract white blood cells and cause inflammation, characterized by redness, swelling, heat, and pain. Eventually, the wall of the follicle breaks down and its contents spill into the surrounding skin, producing a lesion commonly called a pimple. People with acne usually exhibit a variety of skin lesions that may include whiteheads and blackheads. Whiteheads are plugged follicles that remain below the skin surface and produce a white bump. If a plugged follicle reaches the skin surface, it appears black and is called a blackhead.

Treatments for acne include oral and topical medications used alone or in combination. Most of these medications retard or halt bacterial growth and reduce inflammation. Severe acne can be treated effectively using isotretinoin (Accutane). This drug usually clears up acne in 15 to 20 weeks and also helps prevent scarring. It can, however, cause birth defects in the developing fetus of a pregnant woman. Therefore, women who take the drug and are of child-bearing age must use two forms of birth control before, during, and after treatment. Another possible side effect of taking Accutane is mental disorders. Some patients taking Accutane have become depressed or developed other serious mental problems. More recently, isotretinoin has been shown to produce detrimental effects on bone.17

Alopecia. Alopecia refers to the partial or complete loss of hair, and it may result from genetic factors, normal aging, certain medications, or disease. Male-pattern alopecia is very common. Although the condition is genetic and related to the male sex hormones, its precise cause is unknown. Female-pattern alopecia is also common, although it is usually characterized by thinning of the hair in specific regions of the head rather than complete hair loss as in males. Alopecia areata is a disorder affecting 4 million Americans, 60 percent of them under the age of 20. It causes sudden hair loss on the scalp and other body regions because follicles stop producing hair; bald patches can appear overnight. The precise cause of this disorder is unknown, although it is thought to be an autoimmune disorder. While alopecia areata is not life threatening, and while it can disappear as quickly as it appeared, it can be difficult for children to cope with psychologically.

Atopic dermatitis. Atopic dermatitis, often called eczema, is a chronic skin disease that most often afflicts infants and young children, although it can arise in adults as well. Major symptoms of atopic dermatitis include intense itching, rashes in areas characteristic of the disease, repeatedly occurring symptoms, and a personal or family history of atopic disorders such as hay fever, asthma, and eczema. Symptoms can be made worse by exposure to irritants such as wool or synthetic fibers, poorly fitting clothes that chafe the skin, soaps that dry out the skin, and allergens (substances in plants or animals that trigger an immune reaction).

The cause of atopic dermatitis is not known. Evidence suggests that it is a multifactorial disease, meaning that both genetic and environmental factors interact to produce the symptoms. Although stress is known to make the condition worse, it is not a cause of the disorder. Atopic dermatitis is not infectious and cannot be passed from one person to another. The disorder seems to be associated with hay fever and asthma. Many children who outgrow atopic dermatitis later develop hay fever and asthma.

Treatment of atopic dermatitis involves healing the skin and keeping it healthy, preventing the onset of symptoms, and treating the symptoms when they arise. An important aspect of treatment is daily skin care, which involves proper bathing and application of lubricants immediately after bathing. When symptoms occur, they may be treated using corticosteroid creams and ointments. Phototherapy with ultraviolet light, sometimes in conjunction with drugs called psoralens, may control the symptoms. Adults with severe forms of the disease may be treated with immunosuppressive drugs such as cyclosporine.

Skin cancer. Skin cancer (including melanoma and nonmelanoma skin cancer) is the most common cancer, accounting for more than 40 percent of all cancers. About 1.3 million cases of nonmelanoma skin cancer are diagnosed each year in the United States.5 Skin cancer is a disease in which cells of the epidermis lose their ability to control their own growth. These cancer cells form tumors that, if left untreated, can spread to other parts of the body and produce serious, often fatal disease.

Cancer can arise in any of the three types of cells found in the epidermis: round cells called basal cells; flat, scaly surface cells called squamous cells; and melanocytes, which give skin its characteristic color. Basal cell cancer is the most common form. It is usually found in body areas that have been exposed to the sun. It may appear as a small, raised bump with a smooth texture. Another form resembles a scar and is firm to the touch. Basal cell cancers may spread to other tissues around the cancer, but they usually do not spread to other parts of the body. Squamous cell tumors also appear in areas that have been exposed to the sun. They may also appear in areas that have been burned, exposed to chemicals, or subjected to X-ray therapy. Squamous cell tumors often appear as firm, red bumps. They may feel scaly, bleed, or develop a crust. Squamous cell tumors can spread to lymph nodes in the area.

A more serious form of skin cancer is called melanoma (cancer in the melanocytes). Melanoma accounts for about 4 percent of skin cancer cases but causes approximately 79 percent of skin cancer deaths.6 It usually occurs in adults and may appear as a new mole or as a change in an existing mole. Melanoma can spread cancer to other parts of the body. Early diagnosis of melanoma is critical for effective treatment.

Sun exposure is linked to more than 90 percent of nonmelanoma skin cancers.39

Exposure to the sun’s radiation has been identified as the primary risk factor for skin cancer. Shorter-wavelength ultraviolet light called UVB rays cause tanning and burning in humans. A 1 percent increase in UVB-ray exposure may produce a 2 percent increase in skin cancer incidence. Longer wavelength UVA rays penetrate more deeply into the dermis. UVA rays produce an immediate darkening of the skin as it is absorbed by melanin. Exposure to UVA rays can weaken the skin’s inner connective tissue, damage the immune system, and possibly lead to cancer.1 UVA rays can also burn the eyes and result in cataracts. Severe, blistering sunburns, particularly those experienced during childhood or as a teenager, increase an individual’s risk of developing melanoma.7,38 Although proponents of tanning beds argue that they are safe, the mere fact that they expose the skin to ultraviolet radiation means that they contribute to the risk of skin cancer.

photo of a young woman lying in a tanning bed
Figure 11. UV light used in tanning beds carries similar health risks to sunlight.

Rates of skin cancer are also influenced by the degree of skin pigmentation. Rates are highest for those with the lightest-colored skin. Theoretically, all skin cancer is preventable. It has been estimated that most people get about 80 percent of their lifetime sun exposure before the age of 18. Therefore, it is prudent to protect children from needless sun exposure. Those at greatest risk for skin cancer (children and those with light skin) should use protective clothing and sunscreens whenever possible.

Skin cancers are treated by several different methods, depending on the type of cell involved and to what extent the cancer has progressed. The most common approach is to surgically remove the tumor by cutting, burning, or freezing. Another technique is radiation therapy, which uses X-rays to kill cancer cells and shrink tumors. Chemotherapy uses drugs to kill cancer cells and may be applied topically to the skin or given systemically, in which case it enters the bloodstream and can kill cancer cells in other areas of the body. Biological therapies are now being developed that use the body’s immune system to fight the disease.

Vitiligo. Vitiligo is a skin condition resulting from a loss of pigment. Any part of the body may be affected and develop the characteristic white patches of the disorder. Vitiligo affects 1 to 2 percent of the population, and about half of those affected first exhibit the disorder before the age of 20. There appears to be a genetic component to vitiligo, and it is thought to be an autoimmune disorder affecting the pigment-producing cells of the skin. Although the disease can be managed with medications and other treatments, there is no cure for it.

7 Influences

The structure and function of bone, muscle, and skin are subject to many influences. Some influences as well as some of their negative ramifications are presented in the following table.

Bone, Muscle, and Skin Can Be Influenced by Many Things
General Factor Influenced by Possible Outcome

Gender (for instance, hormones)
Behavior (for instance, activity level or nutrition)
Genetic predisposition

Obesity, poor muscle tone, poor bone quality
Susceptibility to disease


Social factors
Cultural factors
Economic factors
Political factors

Concern about appearance
Use of products to enhance appearance (for instance, cosmetics and nutritional supplements)
Risky behaviors (for instance, tattoos, body piercing, smoking, overexposure to sun)


Geography (for instance, elevation, latitude, or rural versus urban setting)

Exposure to UV light
Exposure to chemical pollutants

The factor that has the greatest influence on these body systems is genetics. We have no control over this factor, nor do many of us have control over our exposure to environmental pollutants. However, the key for middle school students is to realize that we do have control over many of the large number of factors that influence our bone, muscle, and skin, through the choices we make. For instance, we choose not only how long we will expose ourselves to the sun, but also what protective measures we will use, such as sunscreens and hats. Within cultural, social, and economic limits, we make decisions about the foods we eat and thus determine our intake of key nutrients, such as protein and calcium. We are influenced by peers and the media and make decisions about risky behaviors, such as smoking. We make decisions about exercise, about what we slap (sometimes slop) on our skin, about what we can do to enhance our appearance—all generally done thinking only about now and without concern for any long-term effects on our bone, muscle, and skin.

This curriculum supplement introduces students to three key body systems. It also provides an opportunity to introduce students to decision making and to realizing that decisions made today have consequences in the future.

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