Kids Research Express

. 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 t

. 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 ad

. 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

. 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 tha

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 absor

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

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.

Peritonitis, inflammation of the membrane that lines the abdominal cavity and the organs contained therein. Peritonitis is most often an acute illness, caused by introduction of infection from a perforation of the bowel such as a ruptured appendix or diverticulum. The disease is also caused by introduction of chemically irritating material such as stomach acid from a perforated ulcer or bile from a rupture of the gall bladder or laceration of the liver. Localized peritonitis most often occurs in the pelvis from an infected fallopian tube or a ruptured ovarian cyst. Occasionally peritonitis may occur when the rupture of an abscess causes pus to spill into the abdominal cavity. This sometimes follows surgery inside the bowel with leaking from the site of closure, or from a stab wound through the abdominal wall. Occasionally peritonitis may occur from inflammation of the peritoneal membrane such as in kidney failure, rheumatic fever , and lupus erythematosus . The principal symptom is se

Eye disorders may be classified according to the part of the eye in which the disorders occur. The most common disease of the eyelids is hordeolum, known commonly as a sty, which is an infection of the follicles of the eyelashes, usually caused by infection by staphylococci. Internal sties that occur inside the eyelid and not on its edge are similar infections of the lubricating Meibomian glands. Abscesses of the eyelids are sometimes the result of penetrating wounds. Several congenital defects of the eyelids occasionally occur, including coloboma, or cleft eyelid, and ptosis, a drooping of the upper lid. Among acquired defects are symblepharon, an adhesion of the inner surface of the eyelid to the eyeball, which is most frequently the result of burns. Entropion, the turning of the eyelid inward toward the cornea, and ectropion, the turning of the eyelid outward, can be caused by scars or by spasmodic muscular contractions resulting from chronic irritation. The eyelids also are subject

Color Blindness, defect of vision affecting the ability to distinguish colors, occurring mostly in males. Color blindness is caused by a defect in the retina or in other nerve portions of the eye. The first detailed report on this condition was written by the British chemist John Dalton, who was himself afflicted with it. Total color blindness, in which all hues are perceived as variations of gray, is known as achromatopsia or monochromatism. This condition is congenital, extremely rare, and affects men and women almost equally. Partial color blindness, called dichromatism, consists generally of the inability to differentiate between the reds and the greens or to perceive either reds or greens; infrequently, the confusion may involve the blues or the yellows. Dichromatism is the most common form of color blindness, affecting about 7 percent of men and less than 1 percent of women. Dichromatism is identified as a sex-linked hereditary characteristic. Color blindness also may occur as a

Trachoma, contagious infection of the eye caused by Chlamydia trachomatis, a bacteria related to the organism that causes psittacosis (disease of birds). Infection is spread by the bite of a host fly. It is a major cause of blindness characterized by hard pustules or granular excrescences on the inner surface of the eyelids, inflammation of the membrane, and subsequent involvement of the cornea. It most commonly occurs among populations living under poor sanitary conditions. The disease begins after an incubation period of five to seven days with inflammation of the eye. Ensuing symptoms are considerable discharge of pus, swelling of the lids, tearing, and increased sensitivity to light. It goes on in a few weeks to chronic swelling, formation of blisters in the eye, and destruction and scarring of the cornea, which eventually causes blindness. In its early stages trachoma responds readily to the topical, and sometimes oral, administration of broad-spectrum antibiotics

Hernia, the protrusion of an organ or part of an organ or other structure through the wall of the cavity that normally contains it. Hernias (incorrectly called ruptures) are qualified by the name of the part that protrudes or the area through which protrusion occurs. Thus, an inguinal hernia, perhaps the most common form, is one that passes through the abdominal wall in the groin area. A diaphragmatic or hiatus hernia is one in which part of the stomach or a loop of the intestine herniates upward through an opening in the diaphragm into the chest cavity. An umbilical hernia is one in which the bowel or the membranous apron overlying it, known as the omentum, protrudes through the abdominal wall under the skin at the navel. Hernias often develop in an area of weakness following unusual stress or strain. An inguinal hernia, for example, may follow the abrupt lifting of a heavy object or a severe bout of coughing. Inguinal hernias are more likely to occur in men than in women because the

Peritoneum, serous membrane in the abdominal cavity. It consists of two layers, a parietal one lining the walls of the cavity and a visceral one closely investing the majority of the abdominal organs, and mooring them firmly in position. Between the two layers there is provision for a space, the peritoneal cavity; in the male this is closed, while in the female there is a direct communication between the sac and the fallopian tubes to enable the ova to reach the cavity of the uterus

Poliomyelitis, infectious viral disease that sometimes results in paralysis. The infection chiefly affects children and young adults and is caused by any one of three related viruses called polioviruses. Doctors diagnose polio by isolating the virus from an infected person using throat cultures, stool samples, or samples of fluids from the brain and spinal cord. Blood tests that indicate the presence of antibodies specific for the virus will also confirm a poliovirus infection. As yet there is no cure for polio—no drug or other medical treatment can halt the destruction of poliovirus in the body. However, several medical treatments can lessen the severity of the disease. Mild cases of polio do not require specific treatment. For the more serious cases of paralytic polio, keeping patients still and quiet can, in some cases, minimize the severity of paralysis. For these patients initial treatment consists of immediate hospitalization and strict bed rest. Simple treatments, including mois

Psychosis, mental illness in which a person loses contact with reality and has difficulty functioning in daily life. Psychotic symptoms can indicate severe mental illnesses, such as schizophrenia and bipolar disorder . Unlike people with less severe psychological problems, psychotic individuals do not usually recognize that their mental functioning is disturbed.

Peritonitis, inflammation of the membrane that lines the abdominal cavity and the organs contained therein. Peritonitis is most often an acute illness, caused by introduction of infection from a perforation of the bowel such as a ruptured appendix or diverticulum. The disease is also caused by introduction of chemically irritating material such as stomach acid from a perforated ulcer or bile from a rupture of the gall bladder or laceration of the liver. Localized peritonitis most often occurs in the pelvis from an infected fallopian tube or a ruptured ovarian cyst. Occasionally peritonitis may occur when the rupture of an abscess causes pus to spill into the abdominal cavity. This sometimes follows surgery inside the bowel with leaking from the site of closure, or from a stab wound through the abdominal wall. Occasionally peritonitis may occur from inflammation of the peritoneal membrane such as in kidney failure, rheumatic fever , and lupus erythematosus . The principal symptom is s

. Pus, thick white or yellowish fluid, found at sites of bacterial infection of the body. Certain white blood cells, called phagocytes, migrate to the area of infection and engulf the invaders. They then kill the ingested bacteria by releasing toxic substances inside the cell. In the process the white blood cells also die, and these cells become constituents of pus. See Abscess ; Carbuncle .

. Fermented milk products, including yogurt and cheese, are formed when bacteria break down lactose to produce lactic acid, which sours the milk. Yogurt is usually made from milk that has been fortified by the addition of nonfat powdered milk to improve its texture and taste. The fortified milk is pasteurized at a very high temperature and homogenized. A culture containing the bacteria Streptococcus thermophilus and Lactobacillus bulgaricus, and sometimes Lactobacillus acidophilus, is then added. The two most popular types of yogurt sold are Swiss-style, with added fruit mixed throughout, and sundae-style, with fruit on the top or bottom. Cultured buttermilk and sour cream, like yogurt, are produced by the breakdown of lactose by bacteria. Cultured buttermilk used to be made from buttermilk, but is now more commonly made from skim milk. Sour cream is made from cream. Both have a tangy, sour taste imparted by lactic acid. Cheese making is a complex process, with each of the more than 40

. In order for a product to be labeled as cream, it must contain 18 percent milk fat or more. Light whipping cream must contain at least 30 percent fat, and 36 percent fat is the minimum fat content for heavy whipping cream. Half-and-half, an equal mixture of both milk and cream, must have at least 10.5 percent fat. The various grades of cream are valued for their smooth, thick texture. They are often used in cooking instead of milk, because they are less likely to form a skin when heated and can be whipped into a stiff foam. When chilled cream is churned gently, the fat globules gather together to form butter, leaving buttermilk as the by-product. Butter contains at least 82.5 percent fat. In the past, before the advent of widespread refrigeration, salt was added to butter to retard bacterial spoilage; now salt is added mainly for flavor. Ice cream, a popular frozen dessert, is made of milk, cream, sugar, and flavoring. The mixture is slowly beaten while chilled until it is partially

. Milk in its natural form, directly from a cow, is called raw milk. It is an extremely versatile product from which a myriad of commercial products are derived. A. Whole Milk, Low-fat Milk, and Skim Milk Since the fat in raw milk is lighter in weight than the rest of the milk, it will naturally rise to form a layer of cream if allowed to stand. Spinning the milk in a large machine, called a centrifuge, accelerates the formation of a cream layer, or the separation of fat, from raw milk. Varying amounts of fat are removed from the raw milk, resulting in different kinds of fresh milk. If the fat content is lowered to 3.25 percent, the milk is sold as whole milk. Low-fat milk typically has 1 percent or 2 percent fat. Skim milk, or nonfat milk, is the liquid that remains after removing all the cream; it contains about half a percent milk fat. About half of the milk produced in the United States is consumed as one of these types of fresh milk; the rest is processed into other products such

Human milk provides distinct advantages over formula or cow milk for human infants. Not only is breast milk’s nutritional composition uniquely designed for the needs of human babies, but it also contains antibodies from the mother’s immune system that help the infant fight off infections and diseases. During the first few days after giving birth, a mother releases colostrum, a yellowish liquid that contains less fat and lactose and more protein and antibodies than regular breast milk. After about three or four days, colostrum is replaced by a bluish-white milk that is higher in fats and carbohydrates, reflecting the energy needs of a growing baby (see Breast-feeding ).

. Most milk is composed of 80 to 90 percent water. The remaining 10 percent consists of an abundance of the major nutrients needed by the body for good health, including fats, carbohydrates, proteins, minerals, and vitamins. Cow milk typically contains about 3.5 to 5 percent fat, which is dispersed throughout the milk in globules. In addition to providing milk’s characteristic taste and texture, fat supplies vitamins A, D, E, and K, as well as certain fatty acids that the body cannot produce on its own. Lactose, a kind of sugar found only in milk, gives milk its sweet taste. Making up about 5 percent of milk’s content, lactose is a carbohydrate that is broken down by the body to supply energy. Infants digest lactose easily, but many adults, especially those of Asian and African ancestry, have lost some of their ability to digest this sugar. When these adults drink milk, they often suffer gastric distress and diarrhea. The most important protein in milk is casein , accounting for 80 per

Milk, highly nutritious, versatile food. People enjoy drinking milk in its natural form and also use it to make a wide range of food products, including cream , butter , yogurt , cheese , and ice cream . Female mammals produce milk to feed their newly born young. Milk is produced in the mother’s mammary glands , which are found, for example, in the breasts of humans or the udders of cows, sheep, or goats. Each species of mammal produces milk with a unique composition designed to meet the specific needs of its infants. For instance, the milk of animals that need to develop a thick layer of insulating fat, such as seals, has a high fat content. The milk of animals that grow rapidly, such as cows, which double their birth weight in 50 days, is rich in protein and minerals. Humans drink the milk produced from a variety of domesticated mammals, including cows, goats, sheep, camels, reindeer, buffaloes, and llama. By far the vast majority of milk used for commercial production and consumptio

. Possibly the commonest skull disease in humans is sinusitis. Sinuses are cavities in the frontal bones, the sphenoid bones, the maxillary bone, and the mastoid processes of the temporal bone that are lined with mucous membrane and that open into the nasal cavity. Sinuses are often infected by bacteria, causing inflammation and producing severe pain. Acute sinusitis is treated with antibiotics; chronic sinusitis is extremely difficult to eradicate. Skull deformity occasionally occurs in the womb or during delivery and is often accompanied by brain damage. The skull is also subject to fracture and to tumors. For skull measurement, see Cephalic Index .

Constipation, difficulty in eliminating bowel movements from the body. Constipation is usually accompanied by the passage of hard, dry stools that may result in a tear in the lining of the lower rectum or anus or, more often, in painfully swollen and itchy veins in the lower rectum or anus, known as hemorrhoids . Tenseness and straining to achieve evacuation tend to worsen such conditions. Constipation is sometimes associated with feelings of sluggishness, headache, and distension of the abdomen. Chronic constipation may be caused by a diet insufficient in roughage or fiber, irregular eating hours, improper use of laxatives, or the voluntary avoidance of bowel movements. Many cases are believed to be caused by emotional disturbances. Constipation can usually be relieved by drinking adequate fluids; eating healthy foods such as fruits , vegetables , and cereals ; and establishing routine evacuation habits. A high-fiber diet is particularly important for people who are taking medications

. Hemorrhoid, small swelling, occurring in or around the rectum or at the anus, caused by enlargement of the superficial veins. A hemorrhoid occasionally prolapses, or protrudes from the anus, causing discomfort by strangulation; to relieve the pain, the prolapsed hemorrhoid must be replaced within the anal sphincter muscle. Hemorrhoids, or piles, sometimes itch or cause pain in the rectum. They often bleed. Symptoms usually occur after defecation, particularly after passing a hard stool. Continued bleeding, even if slight, over a long period may cause anemia . A common ailment among adults, hemorrhoids often are associated with habitual constipation and with pregnancy. Prolonged sitting and mental stress may be contributory factors. The treatment includes palliative measures, such as the use of suppositories, astringent ointments, diet, or medication to keep the stool soft, and hot sitz baths. Pain from thrombosed hemorrhoids may be relieved by spraying with a local anesthetic, open

. Disorders of the circulatory system include any injury or disease that damages the heart, the blood, or the blood vessels. The three most important circulatory diseases are hypertension , arteriosclerosis , and atherosclerosis. Hypertension, or elevated blood pressure, develops when the body’s blood vessels narrow, causing the heart to pump harder than normal to push blood through the narrowed openings. Hypertension that remains untreated may cause heart enlargement and thickening of the heart muscle. Eventually the heart needs more oxygen to function, which can lead to heart failure, brain stroke, or kidney impairment. Some cases of hypertension can be treated by lifestyle changes such as a low-salt diet, maintenance of ideal weight, aerobic exercise, and a diet rich in fruits, vegetables, plant fiber, and the mineral potassium. If blood pressure remains high despite these lifestyle adjustments, medications may be effective in lowering the pressure by relaxing blood vessels and

. The diseases and disorders of the respiratory system can affect any part of the respiratory tract and range from trivial to life-threatening. The nasal passages and pharynx, for example, are targets for the viruses that cause colds . These viruses infiltrate and destroy the cells of the nasal passage membranes. The immune system fights back by increasing blood flow to the area, bringing numerous virus-attacking white blood cells to the scene; this causes the membranes to swell, resulting in the stuffy nose associated with colds. Mucous secretions increase in response to the viral attack, creating the runny nose typical of colds. The infection can spread to the sinuses, the membrane-lined cavities in the head, as well as the lower respiratory tract and the middle ear. The respiratory system is also subject to allergic reactions such as hay fever and asthma , brought about when the immune system is stimulated by pollen, dust, or other irritants. Hay fever is characterized by a runny n

. Endocrine disorders are classified in two ways: disturbances in the production of hormones, and the inability of tissues to respond to hormones. The first type, called production disorders, are divided into hypofunction (insufficient activity) and hyperfunction (excess activity). Hypofunction disorders can have a variety of causes, including malformations in the gland itself. Sometimes one of the enzymes essential for hormone production is missing, or the hormone produced is abnormal. More commonly, hypofunction is caused by disease or injury. Tuberculosis can appear in the adrenal glands, autoimmune diseases can affect the thyroid, and treatments for cancer—such as radiation therapy and chemotherapy—can damage any of the endocrine organs. Hypofunction can also result when target tissue is unable to respond to hormones. In many cases, the cause of a hypofunction disorder is unknown. Hyperfunction can be caused by glandular tumors that secrete hormone without responding to feedback c

. Autoimmunity is the immune response of the body turned against its own cells and tissues. Autoimmune diseases may involve either cell-mediated responses, humoral responses, or both. For example, in Type 1 diabetes , the body makes an immune response against its insulin-producing cells and destroys them, with the result that the body cannot use sugars. In myasthenia gravis , the immune system makes antibodies against the normal molecules that control neuromuscular activity, causing weakness and paralysis . In rheumatic fever , the immune system makes antibodies that bind to the heart’s valves, leading to permanent heart damage. In systemic lupus erythematosus , commonly known as lupus, the body makes antibodies against many different body tissues, resulting in widespread symptoms. The mechanisms of autoimmune diseases are poorly understood, and thus the basis for autoimmunity is unclear. Much research focuses on trying to understand these mechanisms and should eventually result in cur

. Deficiencies in immune function may be either inherited or acquired. Inherited immune deficiencies usually reflect the failure of a gene important to the generation or function of immune system components. Some inherited diseases damage a person’s innate immunity by making macrophages incapable of ingesting or breaking down invading organisms. Individuals affected by these diseases are especially susceptible to opportunistic infections—that is, infections by normally harmless organisms that can flourish in a person whose immune system has been weakened. DiGeorge syndrome is an inherited immune disorder in which a person has no thymus and, therefore, cannot produce mature T lymphocytes. People with this disorder can mount only limited humoral immune responses, and their cell-mediated immune responses are severely limited. The most extreme example of a hereditary immune deficiency is severe combined immunodeficiency (SCID). Individuals with this disease completely lack both T and B lym

. The immune system recognizes and attacks anything different from the substances normally present within an individual, even substances that are only slightly different, such as transplanted tissues and organs (see Medical Transplantation ). When an organ is transplanted, the MHC of the donor organ is recognized as foreign and attacked by the recipient’s immune system. To minimize the chances of transplant rejection, physicians seek transplant donors who share as many MHC genes as possible with the transplant recipient. Even then, most transplant recipients are given drugs to suppress their immune response and prevent rejection of the transplant. If the transplanted tissue contains T lymphocytes from the donor, as in bone marrow transplants, these donor T lymphocytes may recognize the recipient’s tissues as foreign and attack them. Physicians can reduce or prevent this potentially fatal graft-versus-host (GVH) reaction by removing all mature T lymphocytes from the organ or tissue bef

Allergy, sometimes called hypersensitivity, is caused by immune responses to some antigens. Antigens that provoke an allergic response are known as allergens. The two major categories of allergic reaction, rapid and delayed, correspond to the two major types of immune responses. Rapid allergic reactions, such as those to bee venom, pollen or pets, are caused by humoral immune mechanisms. These immediate hypersensitivity reactions result from the production of IgE antibodies when a person is first exposed to an allergen. The IgE antibodies become attached to mast cells—white blood cells containing histamine, the chemical that causes the familiar allergic symptoms of runny nose, watery eyes, and sneezing. Mast cells are particularly abundant in the lungs and intestine. If the antigen-binding sites of mast cells become filled with an allergen, the mast cells release histamine. Allergic reactions that are slow in onset (known as delayed-type hypersensitivity, or DTH), such as those to pois

. Disorders of the immune system can range from the less serious, such as mild allergy, to the life threatening, such as more serious allergy, transplant rejection, immune deficiencies, and autoimmune diseases. A. Allergy B. Transplant Rejection C. Immune Deficiency D. Autoimmune Diseases

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. Both vitamins and minerals are needed by the body in very small amounts to trigger the thousands of chemical reactions necessary to maintain good health. Many of these chemical reactions are linked, with one triggering another. If there is a missing or deficient vitamin or mineral—or link—anywhere in this chain, this process may break down, with potentially devastating health effects. Although similar in supporting critical functions in the human body, vitamins and minerals have key differences. Among their many functions, vitamins enhance the body’s use of carbohydrates, proteins, and fats. They are critical in the formation of blood cells, hormones, nervous system chemicals known as neurotransmitters, and the genetic material deoxyribonucleic acid (DNA). Vitamins are classified into two groups: fat soluble and water soluble. Fat-soluble vitamins, which include vitamins A, D, E, and K, are usually absorbed with the help of foods that contain fat. Fat containing these vitamins is br

. Fats, which provide 9 calories of energy per gram, are the most concentrated of the energy-producing nutrients, so our bodies need only very small amounts. Fats play an important role in building the membranes that surround our cells and in helping blood to clot. Once digested and absorbed, fats help the body absorb certain vitamins. Fat stored in the body cushions vital organs and protects us from extreme cold and heat. Fat consists of fatty acids attached to a substance called glycerol. Dietary fats are classified as saturated, monounsaturated, and polyunsaturated according to the structure of their fatty acids (see Fats and Oils ). Animal fats—from eggs, dairy products, and meats—are high in saturated fats and cholesterol, a chemical substance found in all animal fat. Vegetable fats—found, for example, in avocados, olives, some nuts, and certain vegetable oils—are rich in monounsaturated and polyunsaturated fat. As we will see, high intake of saturated fats can be unhealthy. To un

. Dietary proteins are powerful compounds that build and repair body tissues, from hair and fingernails to muscles. In addition to maintaining the body’s structure, proteins speed up chemical reactions in the body, serve as chemical messengers, fight infection, and transport oxygen from the lungs to the body’s tissues. Although protein provides 4 calories of energy per gram, the body uses protein for energy only if carbohydrate and fat intake is insufficient. When tapped as an energy source, protein is diverted from the many critical functions it performs for our bodies. Proteins are made of smaller units called amino acids. Of the more than 20 amino acids our bodies require, eight (nine in some older adults and young children) cannot be made by the body in sufficient quantities to maintain health. These amino acids are considered essential and must be obtained from food. When we eat food high in proteins, the digestive tract breaks this dietary protein into amino acids. Absorbed into

. Carbohydrates are the human body’s key source of energy, providing 4 calories of energy per gram. When carbohydrates are broken down by the body, the sugar glucose is produced; glucose is critical to help maintain tissue protein, metabolize fat, and fuel the central nervous system. Glucose is absorbed into the bloodstream through the intestinal wall. Some of this glucose goes straight to work in our brain cells and red blood cells, while the rest makes its way to the liver and muscles, where it is stored as glycogen (animal starch), and to fat cells, where it is stored as fat. Glycogen is the body’s auxiliary energy source, tapped and converted back into glucose when we need more energy. Although stored fat can also serve as a backup source of energy, it is never converted into glucose. Fructose and galactose, other sugar products resulting from the breakdown of carbohydrates, go straight to the liver, where they are converted into glucose. Starches and sugars are the major carbohydr

. If the importance of a nutrient is judged by how long we can do without it, water ranks as the most important. A person can survive only eight to ten days without water, whereas it takes weeks or even months to die from a lack of food. Water circulates through our blood and lymphatic system, transporting oxygen and nutrients to cells and removing wastes through urine and sweat. Water also maintains the natural balance between dissolved salts and water inside and outside of cells. Our joints and soft tissues depend on the cushioning that water provides for them. While water has no caloric value and therefore is not an energy source, without it in our diets we could not digest or absorb the foods we eat or eliminate the body’s digestive waste. The human body is 65 percent water, and it takes an average of eight to ten cups to replenish the water our bodies lose each day. How much water a person needs depends largely on the volume of urine and sweat lost daily, and water needs are incre

. Nutrients are classified as essential or nonessential. Nonessential nutrients are manufactured in the body and do not need to be obtained from food. Examples include cholesterol , a fatlike substance present in all animal cells. Essential nutrients must be obtained from food sources, because the body either does not produce them or produces them in amounts too small to maintain growth and health. Essential nutrients include water , carbohydrates , proteins , fats , vitamins, and minerals . An individual needs varying amounts of each essential nutrient, depending upon such factors as gender and age. Specific health conditions, such as pregnancy, breast-feeding, illness, or drug use, make unusual demands on the body and increase its need for nutrients. Dietary guidelines, which take many of these factors into account, provide general guidance in meeting daily nutritional needs.

Cretinism, deficiency disease caused by congenital absence of thyroxine , a hormone secreted by the thyroid gland , and characterized by defective mental and physical development. Cretins have dwarfed bodies, with curvature of the spine and pendulous abdomen. Their limbs are distorted, their features are coarse, and their hair is harsh and scanty. Mental development is retarded throughout life. An adult cretin may reach the intelligence of only a four-year-old child. Research has revealed that when an animal or human infant is born with a deficiency of thyroxine, the neurons (nerve cells) in the brain do not develop the multiple branches that normally form the brain's complex network. Treatment of adult cretins with thyroxine or thyroid extract results in some improvement; early treatment in infancy results in cure of the disease and normal development of the individual, provided the treatment is continued throughout life. Treatment is sometimes begun prenatally, for instance, whe

Hallucinogen, any one of a large number of natural or synthetic psychoactive drugs that produce marked distortions of the senses and changes in perception. Hallucinogens generally alter the way time is perceived, making it appear to slow down. As the name suggests, hallucinogens may produce hallucinations , which are shape- and color-shifts in the appearance of the outside world or, in extreme cases, the replacement of external reality with imaginary beings and landscapes. Hallucinogens may also lead to bizarre and antisocial thoughts as well as to disorientation and confusion. The physiological basis of such experiences is not clear, but evidence suggests that hallucinogens work by inhibiting the availability of serotonin, an important neurotransmitter in the brain. The best-known and most potent hallucinogen is lysergic acid diethylamide (LSD). Other hallucinogens include psilocybin, which comes from certain species of mushrooms , and mescaline, which is derived from a cactus calle

Gonorrhea, infectious sexually transmitted infection of humans, which primarily involves the mucous membranes of the urogenital tract. Characterized by a discharge of pus, it is caused by the gonococcus bacterium, Neisseria gonorrhoeae. The incubation period is two to seven days. SYMPTOMS AND DIAGNOSIS Gonorrhea is much more obvious in males, who develop an acute discharge of pus from the urethra. Scant at the start, it becomes progressively thicker and heavier and causes frequent urination, often with a burning sensation. Should the prostate become infected, the passage of urine is partly obstructed. In females the infection occurs in the urethra, the vagina, or the cervix. Although discharge and irritation of the vaginal mucous membranes may be severe, more often few or no early symptoms appear. Gonorrhea can be diagnosed by examining discharge from the penis or vagina for the presence of bacteria. A urine test can also detect the presence of bacteria and it is a noninvasive way to

Glaucoma, family of eye diseases characterized by increased pressure within the eye and resulting loss of vision. Although the vision loss caused by glaucoma is irreversible, medication or surgery can usually control the pressure within the eye and slow or halt the progression of the disease. If glaucoma is diagnosed in its early stages, it can be treated effectively, and vision can usually be preserved. Glaucoma occurs in two main varieties, known as chronic simple and acute glaucoma. In chronic simple glaucoma, pressure within the eye rises gradually, and vision loss progresses over a period of years. In acute glaucoma, the pressure inside the eye rises suddenly and immediate medical treatment is necessary to preserve vision. Acute glaucoma is also known as narrow-angle or angle-closure glaucoma, because the angle between the cornea (the transparent layer of tissue at the front of the eye) and the iris (the colored part of the eye) becomes smaller than normal. Chronic simple glaucoma

Gene Therapy, experimental medical treatment that manipulates a gene or genes within cells in order to produce proteins that change the function of those cells. Gene therapy originated in efforts to treat and cure some of the more than 9,000 known genetic disorders , most of which lack an effective therapy. The original goal of gene therapy was to substitute a healthy gene for a defective one, or to repair a faulty gene, thereby eliminating symptoms of disease. But researchers have moved beyond inherited genetic disorders to treat other kinds of diseases. Cancer begins in genes and may be caused by an inherited defect or a mutation (permanent alteration to a gene) that causes a cell to malfunction. AIDS is caused by a virus that disrupts the genetic material of immune cells. Other new gene therapy projects are targeted at conditions such as heart disease, diabetes mellitus , arthritis , and Alzheimer's disease , all of which involve genetic susceptibility to illness. Gene therapist

Gastritis, acute or chronic inflammation of the mucosal lining of the stomach . The ailment was first described in 1833 by the American military surgeon William Beaumont, who was able to study the mucosa of a man who had suffered a gunshot wound in the abdomen. The wound healed with an opening in the stomach wall, through which Beaumont was able to observe the patient's digestive process. In gastritis the inflammation may be marked by the erosion of surface cells of the mucosa, formation of granular nodules, and hemorrhage. In chronic gastritis, there is a growth of fibrous tissue on the lining. Weight loss and delayed emptying of the contents of the stomach may accompany the disease. Gastritis may be caused by excessive consumption of alcohol , abnormal secretion of hydrochloric acid in the gastric juices, and various infections ranging from syphilis and tuberculosis to fungus. Psychological stress may also be involved in the development of gastritis.

Gangrene, mass death or necrosis of individual cells or tissues of a living organism. The immediate physiological cause of gangrene is blockage of arterial blood supply. Among the symptoms of gangrene are loss of sensation and function. The affected part, usually a limb, becomes cold, turns progressively darker in color, and finally undergoes decomposition. Gangrene may take two forms, dry gangrene or moist gangrene. Dry, or chronic, gangrene occurs when the arteries are blocked gradually and the tissues are bloodless. It may be a result of arteriosclerosis (see Artery). It may also follow frostbite, injury, or the vascular collapse that often accompanies diabetes. If the dead, bloodless tissue becomes infected by the anaerobic bacterium Clostridium, the condition is called moist, or acute, gangrene. It is also known as gas gangrene because of its putrid-smelling gaseous discharge. The victim's temperature rises sharply, and he or she suffers great pain, acute anemia , and prostr

Blood Transfusion, in medicine, the procedure of introducing the blood of a donor or blood predonated by the recipient (autologous transfusion) into the bloodstream. It is a highly effective form of therapy and has saved the lives of incalculable numbers of people suffering from shock, hemorrhage, or blood diseases. Blood transfusion is employed routinely in cases of surgery, trauma, gastrointestinal bleeding, and in childbirths that involve great loss of blood. Transfusions still tend to cause the development of sensitivity and increase the possibility that the recipient will react to any later transfusions. Transmission of viral hepatitis was a major risk until a method of screening blood for infectivity was developed in the 1960s; some other forms of hepatitis, however, are not detected by this test. In 1985 a test was introduced that screens donated blood for an antigen associated with AIDS, or acquired immunodeficiency syndrome .

Angina Pectoris, symptom of reduced oxygen supply to the heart muscle, usually caused by narrowing or obstruction of the coronary artery. It is marked by a viselike squeezing sensation beneath the breastbone. Pain may radiate from the front of the chest, often into the arm. The attacks usually last several minutes. They may be caused by emotional stress but are more likely to result from physical activities that require an increased supply of blood to the heart. The disease occurs most commonly in middle-aged and older people, particularly those who suffer from arteriosclerosis. Relief is obtained by rest and relaxation. Patients can be treated with drugs that relax and dilate blood vessels or that slow the heart, and surgery can be performed to improve coronary circulation. The attacks themselves cause no damage.

A variety of diseases affect bones. One of the most common bone diseases is osteoporosis , which is characterized by a thinning of bone tissue, causing bones to become weak, brittle, and prone to fractures. Many factors can cause osteoporosis, including menopause, lack of exercise, low calcium intake, smoking, use of steroid drugs, and excessive consumption of alcohol. Dietary deficiencies of calcium, phosphorus, and vitamin D cause rickets , a disease characterized by abnormal bone formation and skeletal deformities. Rickets is most common in children. Dietary deficiencies of these nutrients in adults-or metabolic disorders that cause poor absorption of the nutrients-can result in an abnormal softening of bone, a condition called osteomalacia. Infections of bones called osteomyelitis usually are caused by bacteria, especially Staphylococcus, which enters the body through open wounds and may destroy bone tissues. Tumors, or abnormal growths, occur in bone tissue, though most are benign