The absence of menstrual periods is called amenorrhea. Primary amenorrhea is the failure to start having a period by the age of 16. Secondary amenorrhea is more common and refers to either the temporary or permanent ending of periods in a woman who has menstruated normally in the past. Many women miss a period occasionally. Amenorrhea occurs if a woman misses three or more periods in a row. The ab…
Amino acid disorder screening checks for inherited disorders in amino acid metabolism. Tests are most commonly done on newborns. Two tests are available, one using a blood sample and the other a urine sample. Amino acid disorder screening is done in newborns, and sometimes children and adults, to detect inborn errors in metabolism of amino acids. Twenty of the 100 known amino acids are the main bu…
Aminoglycosides are a group of antibiotics that are used to treat certain bacterial infections. This group of antibiotics includes at least eight drugs: amikacin, gentamicin, kanamycin, neomycin, netilmicin, paromomycin, streptomycin, and tobramycin. All of these drugs have the same basic chemical structure. Aminoglycosides are primarily used to combat infections due to aerobic, Gram-negative bact…
Amnesia refers to the loss of memory. Memory loss may result from two-sided (bilateral) damage to parts of Memory loss may result from bilateral damage to the limbic system of the brain responsible for memory storage, processing, and recall. (Illustration by Electronic Illustrators Group). the brain vital for memory storage, processing, or recall (the limbic system, including the hippocampu…
Amniocentesis is a procedure used to diagnose fetal defects in the early second trimester of pregnancy. A sample of the amniotic fluid, which surrounds a fetus in the womb, is collected through a pregnant woman's abdomen using a needle and syringe. Tests performed on fetal cells found in the sample can reveal the presence of many types of genetic disorders, thus allowing doctors and prospec…
Amputation is the intentional surgical removal of a limb or body part. It is performed to remove diseased tissue or relieve pain. Arms, legs, hands, feet, fingers, and toes can all be amputated. Most amputations involve small body parts such as a finger, rather than an entire limb. About 65, 000 amputations are performed in the United States each year. Amputation is performed for the following rea…
Amylase is a digestive enzyme made primarily by the pancreas and salivary glands. Enzymes are substances made and used by the body to trigger specific chemical reactions. The primary function of the enzyme amylase is to break down starches in food so that they can be used by the body. Amylase testing is usually done to determine the cause of sudden abdominal pain. Amylase testing is performed to d…
Amyloidosis is a progressive, incurable, metabolic disease characterized by abnormal deposits of protein in one or more organs or body systems. Amyloid proteins are manufactured by malfunctioning bone marrow. Amyloidosis, which occurs when accumulated amyloid deposits impair normal body function, can cause organ failure or death. It is a rare disease, occurring in about eight of every 1, 000, 000 …
Amyotrophic lateral sclerosis (ALS) is a disease that breaks down tissues in the nervous system (a neurodegenerative disease) of unknown cause that affects the nerves responsible for movement. It is also known as motor neuron disease and Lou Gehrig's disease, after the baseball player whose career it ended. ALS is a disease of the motor neurons, those nerve cells reaching from the brain to …
An anaerobic infection is an infection caused by bacteria (called anaerobes) which cannot grow in the presence of oxygen. Anaerobic bacteria can infect deep wounds, deep tissues, and internal organs where there is little oxygen. These infections are characterized by abscess formation, foul-smelling pus, and tissue destruction. Anaerobic means "life without air." Anaerobic bacteria gr…
The anus is either not present or it is in the wrong place. There are basically two kinds of anal atresia. In boys with high anal atresia, there may be a channel (fistula) connecting the large intestine to either the urethra (which delivers urine from the bladder) or the bladder itself. In girls, the channel may connect with the vagina. Sixty percent of children with high anal atresia have other d…
Anal cancer is an uncommon form of cancer affecting the anus. The anus is the inch-and-a-half-long end portion of the large intestine, which opens to allow solid wastes to exit the body. Other parts of the large intestine include the colon and the rectum. Different cancers can develop in different parts of the anus, part of which is inside the body and part of which is outside. Sometimes abnormal …
Anal warts, also known as condyloma acuminata, are small warts that can occur in the rectum. Initially appear as tiny blemishes that can be as small as the head of a pin or grow into larger cauliflower-like protuberances. They can be yellow, pink, or light brown in color, and only rarely are painful or uncomfortable. In fact, infected individuals often are unaware that they exist. Most cases are c…
Analgesics are medicines that relieve pain. Analgesics are those drugs whose primary purpose is pain relief. The primary classes of analgesics are the narcotics, including additional agents that are chemically based on the morphine molecule but have minimal abuse potential; nonsteroidal anti-inflammatory drugs (NSAIDs) including the salicylates; and acetaminophen. Other drugs, notably the tricycli…
Opioid analgesics, also known as narcotic analgesics, are pain relievers that act on the central nervous system. Like all narcotics, they may become habit-forming if used over long periods. Opioid analgesics are used to relieve pain from a variety of conditions. Some are used before or during surgery (including dental surgery) both to relieve pain and to make anesthetics work more effectively. The…
Anaphylaxis is a rapidly progressing, life-threatening allergic reaction. Anaphylaxis is a type of allergic reaction, in which the immune system responds to otherwise harmless substances from the environment. Unlike other allergic reactions, however, anaphylaxis can kill. Reaction may begin within minutes or even seconds of exposure, and rapidly progress to cause airway constriction, skin and inte…
Anemia is a condition characterized by abnormally low levels of healthy red blood cells or hemoglobin (the component of red blood cells that delivers oxygen to tissues throughout the body). The tissues of the human body need a regular supply of oxygen to stay healthy. Red blood cells, which contain hemoglobin that allows them to deliver oxygen throughout the body, live for only about 120 days. Whe…
General anesthesia is the induction of a state of unconsciousness with the absence of pain sensation over the entire body, through the administration of anesthetic drugs. It is used during certain medical and surgical procedures. General anesthesia has many purposes including: Anesthesia performed with general anesthetics occurs in four stages which may or may not be observable because they can oc…
Local or regional anesthesia involves the injection or application of an anesthetic drug to a specific area of the body, as opposed to the entire body and brain as occurs during general anesthesia. Local anesthetics are used to prevent patients from feeling pain during medical, surgical, or dental procedures. Over-the-counter local anesthetics are also available to provide temporary relief from pa…
Aneurysmectomy is a surgical procedure performed to repair a weak area in the aorta. The aorta is the largest artery in the body and the main blood vessel leading away from the heart. The purpose of aneurysmectomy is to repair an aortic aneurysm that is likely to rupture if left in place. Aneurysmectomy is indicated for an aortic aneurysm that grows to at least 2 in (5 cm) or for an aortic aneurys…
Angina is pain, "discomfort," or pressure localized in the chest that is caused by an insufficient supply of blood (ischemia) to the heart muscle. It is also sometimes characterized by a feeling of choking, suffocation, or crushing heaviness. This condition is also called angina pectoris. Often described as a muscle spasm and choking sensation, the term "angina" is used…
Angiography is the x-ray study of the blood vessels. An angiogram uses a radiopaque substance, or dye, to make the blood vessels visible under x ray. Arteriography is a type of angiography that involves the study of the arteries. Angiography is used to detect abnormalities or blockages in the blood vessels (called occlusions) throughout the circulatory system and in some organs. The procedure is c…
Angioplasty is a term describing a procedure used to widen vessels narrowed by stenoses or occlusions. There are various types of these procedures and their names are associated with the type of vessel entry and equipment used. For example, percutaneous transluminal angioplasty (PTA) describes entry through the skin (percutaneous) and navigates to the area of the vessel of interest through the sam…
Angiotensin-converting enzyme inhibitors (also called ACE inhibitors) are medicines that block the conversion of the chemical angiotensin I to a substance that increases salt and water retention in the body. ACE inhibitors are used in the treatment of high blood pressure. They may be used alone or in combination with other medicines for high blood pressure. They work by preventing a chemical in th…
This test measures blood levels of angiotensin-converting enzyme (ACE), also known as Serum Angiotensin-Converting Enzyme (SASE). The primary function of ACE is to help regulate arterial pressure by converting angiotensin I to angiotensin II. The ACE test is used primarily to detect and monitor the clinical course of sarcoidosis (a disease that affects many organs, especially the lungs), to differ…
The most common problem following an animal bite is simple infection. The saliva of dogs and cats is known to contain a wide variety of bacteria. According to one recent study, bacteria or other pathogens show up in about 85 percent of bites. When an animal bites, it can then transmit pathogens into the wound. These microorganisms may grow within the wound and cause an infection. The consequences …
Ankylosing spondylitis (AS) refers to inflammation of the joints in the spine. AS is also known as rheumatoid spondylitis or Marie-Strümpell disease (among other names). A form of arthritis, AS is characterized by chronic inflammation, causing pain and stiffness of the back, progressing to the chest and neck. Eventually, the whole back may become curved and inflexible if the bones fuse (thi…
Anorectal disorders are a group of medical disorders that occur at the junction of the anal canal and the rectum. The anal canal, also called the anus, is the opening at the bottom end of the digestive tract and is a combination of external skin and tissue from the digestive tract. It has many sensory nerves and is sensitive to pain. The rectum is the last section of the digestive tract and has a …
Anorexia nervosa is an eating disorder characterized by unrealistic fear of weight gain, self-starvation, and conspicuous distortion of body image. The name comes from two Latin words that mean nervous inability to eat. In females who have begun to menstruate, anorexia nervosa is usually marked by amenorrhea, or skipping at least three menstrual periods in a row. The fourth edition of the Diagnost…
An anoscopy is an examination of the rectum in which a small tube is inserted into the anus to screen, diagnose, and evaluate problems of the anus and anal canal. This test may be ordered for the evaluation of perianal or anal pain, hemorrhoids, rectal prolapse, digital rectal examination that shows a mass, perianal abscess and condyloma (a wart-like growth). An anascopy may be performed to check …
The term anosmia means lack of the sense of smell. It may also refer to a decreased sense of smell. Ageusia, a companion word, refers to a lack of taste sensation. Patients who actually have anosmia may complain wrongly of ageusia, although they retain the ability to distinguish salt, sweet, sour, and bitter—humans' only taste sensations. Of the five senses, smell ranks fourth in imp…
Anoxia is a condition characterized by an absence of oxygen supply to an organ or a tissue. Anoxia results when oxygen is not being delivered to a part of the body. If the condition does not involve total oxygen deprivation, it is often called hypoxia, although the two terms have been used interchangeably. A related condition, anoxemia, occurs when the blood circulates but contains a below normal …
Antacids are medicines that neutralize stomach acid. Antacids are used to relieve acid indigestion, upset stomach, sour stomach, and heartburn. Additional components of some formulations include dimethicone, toreduce gas pains (flatulence) and alginic acid, which, in combination with antacids, may help manage GERD (gastro-esophageal reflux disease). Antacids should not be confused with gastric aci…
Antenatal testing includes any diagnostic procedures performed before the birth of a baby. These tests and exams are essential for protecting the health of a pregnant woman and her developing child. Some tests, such as amniocentisis, carry a small risk of a miscarriage or other complications that could harm the mother or baby. Women who become pregnant undergo a wide variety of tests throughout th…
Antepartum testing consists of a variety of tests performed late in pregnancy to verify fetal well-being, as judged by the baby's heart rate and other characteristics. Antepartum tests include the nonstress test (NST), biophysical profile, and contraction stress test (CST). Antepartum testing is performed after 32 weeks of pregnancy so that the couple and the doctor can be warned of any pro…
Anthrax is a bacterial infection caused by Bacillus anthracis that primarily affects livestock but that can occasionally spread to humans, affecting either the skin, intestines, or lungs. In humans, the infection can often be treated, but it is almost always fatal in animals. Anthrax is most often found in the agricultural areas of South and Central America, southern and eastern Europe, Asia, Afri…
Antiacne drugs are medicines that help clear up pimples, blackheads, whiteheads, and more severe forms of acne. Different types of antiacne drugs are used for different purposes. For example, lotions, soaps, gels, and creams containing benzoyl peroxide or tretinoin may be used to clear up mild to moderately severe acne. Isotretinoin (Accutane) is prescribed only for very severe, disfiguring acne. …
Antiangina drugs are medicines that relieve the symptoms of angina pectoris (severe chest pain). The dull, tight chest pain of angina occurs when the heart's muscular wall is not getting enough oxygen. By relaxing the blood vessels, antiangina drugs reduce the heart's work load and increase the amount of oxygen-rich blood that reaches the heart. These drugs come in different forms, a…
Antianxiety drugs are medicines that calm and relax people with excessive anxiety, nervousness, or tension, or for short term control of social phobia disorder or specific phobia disorder. Antianxiety agents, or anxiolytics, may be used to treat mild transient bouts of anxiety as well as more pronounced episodes of social phobia and specific phobia. Clinically significant anxiety is marked by seve…
Antiarrhythmic drugs are medicines that correct irregular heartbeats and slow down hearts that beat too fast. Normally, the heart beats at a steady, even pace. The pace is controlled by electrical signals that begin in one part of the heart and quickly spread through the whole heart. If something goes wrong with this control system, the result may be an irregular heartbeat, or an arrhythmia. Antia…
Antiasthmatic drugs are medicines that treat or prevent asthma attacks. For people with asthma, the simple act of breathing can be a struggle. Their airways become inflamed and blocked with mucus during asthma attacks, narrowing the opening through which air passes. This is not such a problem when the person breathes in, because the airways naturally expand when a person takes a breath. The real p…
Antibiotic-associated colitis is an inflammation of the intestines that sometimes occurs following antibiotic treatment and is caused by toxins produced by the bacterium Clostridium difficile. Antibiotic-associated colitis, also called antibioticassociated enterocolitis, can occur following antibiotic treatment. The bacteria Clostridia difficile are normally found in the intestines of 5% of health…
Antibiotics may be informally defined as the sub-group of anti-infectives that are derived from bacterial sources and are used to treat bacterial infections. Other classes of drugs, most notably the sulfonamides, may be effective antibacterials. Similarly, some antibiotics may have secondary uses, such as the use of demeclocycline (Declomycin, a tetracycline derivative) to treat the syndrome of in…
Ophthalmic antibiotics are medicines that kill bacteria that cause eye infections. Ophthalmic antibiotics are applied to the eye, or under the eyelid, to treat eye infections caused by bacteria. The medicine described here, tobramycin (Tobrex), comes in the form of eye drops or ointment. It is available only with a physician's prescription. The dosages given here are typical doses. Physicia…
Topical antibiotics are medicines applied to the skin to kill bacteria. Topical antibiotics help prevent infections caused by bacteria that get into minor cuts, scrapes, and burns. Treating minor wounds with antibiotics allows quicker healing. If the wounds are left untreated, the bacteria will multiply, causing pain, redness, swelling, itching, and oozing. Untreated infections can eventually spre…
Anticancer, or antineoplastic, drugs are used to treat malignancies, cancerous growths. Drug therapy may be used alone, or in combination with other treatments such as surgery or radiation therapy. Anticancer drugs are used to control the growth of cancerous cells. Cancer is commonly defined as the uncontrolled growth of cells, with loss of differentiation and commonly, with metastasis, spread of …
Anticoagulants are drugs used to prevent clot formation or to prevent a clot that has formed from enlarging. They inhibit clot formation by blocking the action of clotting factors or platelets. Anticoagulant drugs fall into three categories: inhibitors of clotting factor synthesis, inhibitors of thrombin and antiplatelet drugs. Anticoagulant drugs reduce the ability of the blood to form clots. Alt…
Anticonvulsant drugs are medicines used to prevent or treat convulsions (seizures). Anticonvulsant drugs are used to control seizures in people with epilepsy. Epilepsy is not a single disease—it is a set of symptoms that may have different causes in different people. The common thread is an imbalance in the brain's electrical activity. This imbalance causes seizures that may affect p…
Antidepressant drugs are medicines that relieve symptoms of depressive disorders. Depressive disorders may be either unipolar (depression alone) or bipolar (depression alternating with periods of extreme excitation). The formal diagnosis requires a cluster of symptoms, lasting at least two weeks. These symptoms include, but are not limited to mood changes, insomnia or hypersomnia, and diminished i…
Tricyclic antidepressants are medicines that relieve mental depression. Since their discovery in the 1950s, tricyclic antidepressants have been used to treat mental depression. Like other antidepressant drugs, they reduce symptoms such as extreme sadness, hopelessness, and lack of energy. Some tricyclic antidepressants are also used to treat bulimia, cocaine withdrawal, panic disorder, obsessive-c…
Antidiabetic drugs are medicines that help control blood sugar levels in people with diabetes mellitus (sugar diabetes). Diabetes may be divided into type I and type II, formerly termed juvenile onset or insulin-dependent, and maturity onset or non insulin-dependent. Type I is caused by a deficiency of insulin production, while type II is characterized by insulin resistance. Treatment of type I di…
Antidiarrheal drugs are medicines that relieve diarrhea. Antidiarrheal drugs help control diarrhea and some of the symptoms that go along with it. An average, healthy person has anywhere from three bowel movements a day to three a week, depending on that person's diet. Normally the stool (the material that is passed in a bowel movement) has a texture something like clay. With diarrhea, bowe…
Antidiuretic hormone (ADH) test, also called the Vasopressin test, is a test for the antidiuretic hormone, which is released from the pituitary gland and acts on the kidneys to increase their reabsorption of water into the blood. An ADH test is used to aid in the diagnosis of diabetes insipidus or the syndrome of inappropriate ADH called SIADH. Certain drugs can either increase or decrease ADH lev…
Systemic antifungal drugs are medicines taken by mouth or by injection to treat deep infections caused by a fungus. Systemic antifungal drugs are used to treat infections in various parts of the body that are caused by a fungus. A fungus is an organism that can be either onecelled or filamentous. Unlike a plant, which makes its own food, or an animal, which eats plants or other animals, a fungus s…
Topical antifungal drugs are medicines applied to the skin to treat skin infections caused by a fungus. Dermatologic fungal infections are usually described by their location on the body: tinea pedis (infection of the foot), tinea unguium (infection of the nails), tinia capitis (infection of the scalp.) Three types of fungus are involved in most skin infections: Trichophyton, Epidermophyton, and M…
Antigas agents are medicines that relieve the uncomfortable symptoms of too much gas in the stomach and intestines. Excess gas can build up in the stomach and intestines for a number of reasons. Eating high-fiber foods, such as beans, grains, and vegetables is one cause. Some people unconsciously swallow air when they eat, drink, chew gum, or smoke cigarettes, which can lead to uncomfortable amoun…
These drugs are used to treat gastroesophageal reflux, the backward flow of stomach contents into the esophagus. The drug discussed here, cisapride (Propulsid), is used to treat nighttime heartburn resulting from gastroesophageal reflux disease (GERD). In this condition, food and stomach juices flow backward from the stomach into the esophagus, the part of the digestive tract through which food pa…
Antihelminthic drugs are used to treat parasitic infestations. Parasitic infestations are caused by protozoa or worms gaining entry into the body. Most of these organisms cause infections by being ingested in the form of eggs or larvae, usually present on contaminated food or clothing, while others gain entry through skin abrasions. Common parasitic infestations include amebiasis, malaria, giardia…
Antihemorrhoid drugs are medicines that reduce the swelling and relieve the discomfort of hemorrhoids (swellings in the area around the anus). Hemorrhoids are bulges in the veins that supply blood to the skin and membranes of the area around the anus. They may form for various reasons. Frequent heavy lifting, sitting for long periods, or straining to have bowel movements may put stress on anal tis…
Antihistamines are drugs that block the action of histamine (a compound released in allergic inflammatory reactions) at the H1 receptor sites, responsible for immediate hypersensitivity reactions such as sneezing and itching. Members of this class of drugs may also be used for their side effects, including sedation and antiemesis (prevention of nausea and vomiting). Antihistamines provide their pr…
