Myxedema

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Myxedema (Greek myxa, “slime”; oidema, “swelling”), deficiency disease caused by insufficient or lack of production of hormone by the thyroid gland. Patients with myxedema complain of fatigue, lethargy, sleepiness, poor tolerance to cold, mental sluggishness, a tendency to gain weight, and generalized aches and pains. Their faces often look puffy and waxy. Their skin is dry and coarse; their hair is coarse, dry, and brittle, and it tends to fall out easily. Often patients also lose the outer portion of their eyebrows. These and other symptoms are caused by a low metabolic rate resulting from a deficiency of the thyroid hormone that stimulates metabolism. Myxedema differs from cretinism in that it develops after birth and produces less severe cerebral inadequacy. The disease may occur in several members of a single family. Any condition that decreases the elaboration of thyroid gland hormone may bring on myxedema. The disease is treated by the administration of thyroxine, other thyroid extracts, or a synthetic preparation such as levothyroxine.

Goiter

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Goiter, disease of the thyroid gland, characterized by an enlargement of the gland, visible externally as a swelling on the front of the neck. In simple goiter the basal metabolic rate is somewhat lowered, and in toxic goiter it is elevated.

Iodine deficiency in the body can cause goiter. Treatments include the ingestion of small doses of iodine, or, in extreme cases, the removal of the thyroid gland.

SIMPLE GOITER

This condition is characterized by an enlargement of the entire gland, or of one of its two lobes, caused by a deficiency of iodine in the diet. The disease is especially apt to appear in adolescence. Prevention requires taking small doses of iodine for long periods. Ingestion of iodine during pregnancy prevents development of the disease in the infant as well as in the mother. Public health measures, including the addition of iodine to water supplies and to table salt, have helped to reduce the incidence of simple goiter in certain areas. Iodine is most effective when administered to children who have the disease. Thyroidectomy, or surgical removal of the gland, may be necessary in cases in which the gland has become greatly enlarged.

TOXIC GOITER

This disease, also called exophthalmic goiter, hyperthyroidism, thyrotoxicosis, or Graves' disease, for the Irish physician Robert James Graves, is caused by an excess of thyroxine secretion. The cause of the excessive secretion is obscure. In some cases it may result from excessive stimulation by the pituitary gland. The symptoms of toxic goiter may include a rapid heartbeat, tremor, increased sweating, increased appetite, weight loss, weakness, and fatigue. Some patients have eye problems, such as staring or protrusion. Thiouracil and iodine are sometimes used in the treatment of toxic goiter, as is irradiation of the gland by radioactive iodine.

See also Myxedema.

Disorders of Human Teeth

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The three main diseases of human teeth are tooth decay, also called dental caries; gum disease, or periodontal disease; and problems with tooth alignment, called malocclusions. Human teeth problems are treated or prevented by dentists, professionals who are specially trained to practice dentistry.

Tooth decay affects approximately 90 percent of all children by the time they are 14 years old. Tooth decay begins when bacteria are passed from mothers or caregivers to children between their first and second birthdays. When these bacteria are exposed to sugars commonly found in foods, the bacteria produce harmful acids that attack tooth enamel. Left unchecked, the acid eats holes in the enamel and forms cavities of tooth decay. Most tooth decay forms in the deep grooves on the chewing surfaces of the molars, called pits and fissures. Daily tooth brushing and proper dental care help prevent and reduce tooth decay. Dentists use preventive treatments to reduce the risk of tooth decay; clear plastic coatings painted on the teeth, called dental sealants, and applications of the mineral fluoride, which fortifies tooth enamel, are two such treatments.

Gum disease, or periodontal disease, is a progressive condition that worsens with age. Gum disease occurs when bacteria eat away at gum tissue, causing it to pull away from the teeth. This space between the tooth and gum, called a periodontal pocket, traps even more bacteria. Gum disease develops in two stages. Gingivitis, the early stage, causes red, swollen gums that bleed easily. Gingivitis can be eliminated through good oral hygiene and dental care. If not treated, gingivitis can progress to periodontitis, when bacteria attack the bone supporting the teeth. To treat periodontitis, dentists may have to surgically cut out the infected portion of the gum so the bacteria can be removed.

Malocclusions—teeth that are crowded, crooked, or out of alignment—make it more difficult to clean teeth, which can lead to other oral health problems such as tooth decay and gum disease. Many of these disorders start to appear between the ages of 6 and 12, when permanent teeth begin to erupt. Generally, malocclusions result when the jaw is too small to hold all of the teeth. Malocclusions are often genetic, tending to run in families. In other cases, dental injury or chronic thumb sucking may lead to poorly aligned teeth. Malocclusions are treated by dentists specially trained to correct them, called orthodontists.

Disorders of the Urinary System

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Urologists are physicians who specialize in treating urinary system disorders. One of the most serious disorders urologists treat is renal failure, which slows or stops the filtration of blood, causing toxic waste products to build up in the blood. Acute renal failure, which occurs suddenly, may be caused by bacterial infection, injury, shock, congestive heart failure, drug poisoning, or severe bleeding following surgery. Treatment may include drugs to address the underlying cause or to stimulate proper kidney function, blood transfusions, surgery, or, in some cases, kidney dialysis, in which the blood is mechanically filtered.

Chronic renal failure is a progressive deterioration of kidney function over a long period of time. It can be caused by diseases such as hypertension, diabetes, lupus erythematosus, acquired immunodeficiency syndrome (AIDS), and a form of cancer called myeloma. If diagnosed early the degenerative process can be slowed, but not reversed, by interventions that can range from simply restricting fluid intake and protein consumption (proteins are the main source of waste products) to taking drugs to address the underlying disease that is damaging the kidneys. Some patients may go on to develop end-stage renal failure, a life-threatening condition that requires long-term dialysis or a kidney transplant.

Urinary calculi, commonly known as kidney stones, result from the gradual buildup of crystallized salts and minerals in the urine. Kidney stones can cause intense pain if they obstruct a passageway that carries urine. Usually, the stones pass through and out of the urinary tract on their own. If they fail to pass out of the body, they can be removed surgically or broken up nonsurgically by an ultrasound technique called lithotripsy.

Bacterial infections, most frequently caused by the common intestinal bacterium Escherichia coli, can occur in any part of the urinary system. Antibiotics usually conquer the infection, although recurrent and chronic infections are not uncommon.

Among the many inherited and congenital disorders of the urinary system are polycystic renal diseases, in which numerous cysts form in the kidney, reducing the amount of functioning renal tissue. Kidney dialysis or transplantation usually is necessary to avoid kidney failure and death. Hypospadias is a birth defect in which the male urinary opening is misplaced on the penis; it may be under the head of the penis or as far away as the scrotum. Surgery before the child reaches 24 months can correct the defect, permitting normal urination and, later, sexual intercourse.

Human Nutrition

Human Nutrition is learning how food affects the health and survival of the human body. Human beings require food to grow, reproduce, and maintain good health. Without food, our bodies could not stay warm, build or repair tissue, or maintain a heartbeat. Eating the right foods can help us avoid certain diseases or recover faster when illness occurs. These and other important functions are fueled by chemical substances in our food called nutrients. Nutrients are classified as carbohydrates, proteins, fats, vitamins, minerals, and water.

When we eat a meal, nutrients are released from food through digestion. Digestion begins in the mouth by the action of chewing and the chemical activity of saliva, a watery fluid that contains enzymes, certain proteins that help break down food. Further digestion occurs as food travels through the stomach and the small intestine, where digestive enzymes and acids liquefy food and muscle contractions push it along the digestive tract. Nutrients are absorbed from the inside of the small intestine into the bloodstream and carried to the sites in the body where they are needed. At these sites, several chemical reactions occur that ensure the growth and function of body tissues. The parts of foods that are not absorbed continue to move down the intestinal tract and are eliminated from the body as feces.

Once digested, carbohydrates, proteins, and fats provide the body with the energy it needs to maintain its many functions. Scientists measure this energy in kilocalories, the amount of energy needed to raise 1 kilogram of water 1 degree Celsius. In nutrition discussions, scientists use the term calorie instead of kilocalorie as the standard unit of measure in nutrition.

See: ESSENTIAL NUTRIENTS

Skin Cancer

Skin Cancer, malignancy in the skin, and the most common of all cancers. There are three main types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma. Basal cell carcinoma, the most common type, develops in the basal, or bottom, layer of the epidermis, the top layer of skin. Squamous cell carcinoma, the second most common type, develops in the upper layers of the epidermis.

The third type of skin cancer is melanoma. It develops in the melanocytes, or pigment cells, which are found throughout the basal layer. Melanoma is the most dangerous type of skin cancer and is responsible for about three-quarters of all skin cancer deaths.

Skin cancers can grow in any part of the skin, but approximately 90 percent develop in areas exposed to the sun, especially the face, neck, backs of the hands, and the scalps of bald men. Exposure to direct sunlight, especially during childhood, is the chief risk factor for skin cancer, and the greater the number of blistering sunburns a person has had, the greater the risk of developing skin cancer later in life. People with pale skin are at greatest risk for skin cancer, particularly if their skin burns or freckles easily.

SYMPTOMS AND DIAGNOSIS

Early detection and treatment are the keys to survival, especially for melanoma. Any of several skin changes may signal skin cancer and should be reported to a physician. These include any change in the size, shape, color, or texture of a mole or other darkly pigmented area; any mole that begins to itch or becomes tender; the development of a new mole or other growth, particularly if it feels hard; any mole or other growth that spontaneously or persistently bleeds; a skin ulcer that does not heal; and a black spot under a toenail or fingernail that extends beneath the cuticle. To confirm a diagnosis a physician may perform a biopsy, removing a small piece of the skin to examine under a microscope for the presence of cancerous cells.

TREATMENT

One of several surgical methods is used to remove the cancerous tissue. In some cases, the tissue is destroyed through the application of intense cold (cryosurgery). In advanced cases, surgical removal of the tissue coupled with radiation, chemotherapy, or both may be required.

A class of vitamin-based drugs called retinoids have been shown to reduce the number of basal cell and squamous cell carcinomas. However, the drugs can cause liver abnormalities, bone problems, fetal malformation, and other undesirable side effects.

Potential skin cancer treatment studies now underway include the use of the drugs interleukin-2 and interferon. A vaccine to reduce the recurrence of melanoma has shown promise in early tests.

Appendicitis

Appendicitis, acute inflammation of the vermiform (wormlike) appendix, a blind tube projecting from the cecum,—the beginning of the large intestine. The appendix, located in the lower right side of the abdomen, is an organ with no known function in humans. If the appendix wall ruptures, infection may spread to the abdominal cavity, causing peritonitis. Symptoms of appendicitis include pain and cramps in the area between the right hip bone and the navel, fever, nausea and vomiting, constipation, and diarrhea. The treatment is surgical removal of the appendix (appendectomy). Although the frequency of appendicitis is highest among young adults, the ailment can affect persons of any age.