A: Adenine, one member of the A-T (adenine-thymine) base pair in DNA.

AA: Stands for amino acid, a building block of protein (and Alcoholics Anonymous).

AAA: Many Americans know that the AAA ("triple A") is short for the American Automobile Association. Fewer may be aware that it is also the acronym for the American Association of Anatomists, one of a great multitude of professional societies in the health arena. Only a small selection of these is given as a sampler in this DICTIONARY.

AAAS: American Association for the Advancement of Science. Spoken of as the "triple AS", an organization concerned not only with the biomedical sciences but with all sciences. The AAAS publishes the weekly journal "Science", one of the great scientific periodicals that carries a remarkable range of new information. including, for example, findings from the Apollo mission to Mars as well as reports from the project to map the human genome.

AABB: American Association of Blood Banks.

AACP: American Association of Child Psychiatry.

AAD: American Association of Dermatology.

AAFP: American Association of Family Practice.

AAN: American Association of Neurology.

AAO: Abbreviation for multiple organizations including American Association of Ophthalmology, American Association of Orthodontists, and American Academy of Otolaryngology.

AAOS: American Academy of Orthopaedic Surgery.

AAP: Abbreviation for multiple organizations including American Academy of Pediatrics, American Academy of Pedodontics, and American Academy of Periodontists.

AAPMR: American Academy of Physical Medicine and Rehabilitation.

Abdomen: The part of the body that contains the stomach, small intestine, colon, rectum, liver, spleen, pancreas, kidneys, appendix, gallbladder, and bladder.

Abdominal cavity: The space between the abdominal wall and the spine.

Abdominal hysterectomy: Surgical removal of the uterus through an incision made in the abdominal wall. As opposed to a vaginal hysterectomy.

Abduction: Movement of a limb sideways away from the midline of the body.

Abductor muscle: Any muscle used to pull a body part away from the midline of the body. For example, the abductor leg muscles serve to spread the legs. The opposite of "abductor" is "adductor."

Aberration: A deviation, or irregularity. For example, a mental aberration is a significant deviation from normal mental activity. A chromosome aberration is a an abnormality in chromosome number or structure.

Ablate: To remove, usually by cutting. At surgery a tumor may be ablated.

Ablation: Removal or excision. Ablation is usually carried out surgically. For example, surgical removal of the thyroid gland (a total thyroidectomy) is ablation of the thyroid. The word ablation comes from the Latin ablatum meaning to carry away.

ABO blood groups: The major blood group system. A person can be A, B, AB, or O.

Abortion: In medicine, the premature exit of the products of conception from the uterus. A spontaneous abortion is a miscarriage. The miscarriage of 3 or more consecutive pregnancies is termed habitual abortion.

Abortion, habitual: The miscarriage of 3 or more consecutive pregnancies. Recurrent abortion can be identically defined as 3 or more miscarriages (spontaneous abortions) with no intervening pregnancies. Habitual or recurrent abortion is a form of infertility.

Abortion, multiple: Couples who have had 2 or more miscarriages (spontaneous abortions) have about a 5% chance that one member of the couple is carrying a chromsome translocation responsible for the miscarriages.

Abortion, recurrent: See Abortion, habitual.

Abrasion: 1. An Abrasion or "excoriation" is a wearing away of the upper layer of skin as a result of applied friction force. 2. In dentistry an "abrasion" is the wearing away of the tooth substance.

Abruptio (abruptio placentae): Premature separation of the placenta from the wall of the uterus. Abruption is a potentially serious problem both for the mother and baby.

Abscess: Abscess is a local accumulation of pus anywhere in the body.

Abscess, peritonsillar: A persistent collection of pus behind the tonsil.

Abscess, skin: Medical term for a common boil.

Absolute CD4 count: The number of "helper" T-lymphocytes in a cubic millimeter of blood. With HIV, the absolute CD4 count declines as the infection progresses. The absolute CD4 count is frequently used to monitor the extent of immune suppression in persons with HIV. Also called a T4 count.

Absorption: Uptake. Intestinal absorption is the uptake of food (or other substances) from the digestive tract.

Acapnia: Less than the normal level of carbon dioxide in the blood. The opposite of hypercapnia.

Accelerated phase of leukemia: Refers to chronic myelogenous leukemia that is progressing. The number of immature, abnormal white blood cells in the bone marrow and blood is higher than in the chronic phase, but not as high as in the blast phase.

Accessory placenta: An extra placenta separate from the main placenta. Also called a succenturiate or supernumerary placenta.

Accoucheur: French for a male obstetrician.

Accoucheuse: French for a female obstetrician or midwife.

ACE: Angiotensin converting enzyme. The angiotensins are peptides (smaller than proteins) that act as vasoconstrictors to narrow blood vessels.

ACE inhibitors: Agents that inhibit ACE (angiotensin converting enzyme), thereby acting as vasodilators (really as anti-vasoconstrictors), lightening the stress load on the heart.

Acentric: A chromosome fragment lacking a centromere (the "waist" of the chromosome essential for the division and the retention of the chromosome in the cell).

Acetabulum: The cup-shaped socket of the hip joint.

Acetylsalicylic acid: Aspirin.

Achalasia: A failure of relaxation, especially of the muscle fibers at the junction of the esophagus and stomach.

Achlorhydria: A lack of hydrochloric acid in the digestive juices in the stomach. Hydrochloric acid helps digest food.

Achondroplasia: A genetic disorder of bone growth, the most common cause of short stature with disproportionately short arms and legs.

ACL: See Anterior cruciate ligament.

Acne: Localized skin inflammation as a result of overactivity of the oil glands at the base of hair follicles. When these oil glands become plugged up, the overactive oil glands become red and inflamed. Also called pimples.

Acquired: In medicine, the word "acquired" means "new" or "added." New in the sense that it is not genetic (inherited) and added in the sense that is was not congenital (present at birth) but came along later. For example, AIDS is an acquired, not a genetic form of immune deficiency.

Acquired immunodeficiency disease: Acquired immunodeficiency disease: Disease caused by infection with the human immunodeficiency virus (HIV).

Acquired immunodeficiency syndrome: AIDS.

Acquired mutation: A change in a gene or chromosome that occurs in a single cell after the conception of the individual. That change is then passed along to all cells descended from that cell. Acquired mutations are involved in the development of cancer.

ACOG: American College of Obstetricians and Gynecologists.

Acrocentric: A chromosome with a centromere near one end. Down syndrome (trisomy 21) is due to an extra acrocentic chromosome.

Acrocyanosis: Blueness of the extremities (the hands and feet).

Acrodermatitis enteropathica: An historic model for the therapy of genetic disease. In an era (the 1950s) when inherited disorders were usually seen as hopeless, this progressive hereditary (autosomal recessive) disease of children was found treatable. Acrodermatitis enteropathica is characterized by the simultaneous occurrence of skin inflammation (dermatitis) and diarrhea. The skin on the cheeks, elbows and knees and tissue about the mouth and anus are inflammed. There is also balding of the scalp, eyebrows and lashes, delayed wound healing and recurrent bacterial and fungal infections due to immune deficiency.

The key laboratory finding is an abnormally low blood zinc level reflecting impaired zinc uptake. Treatment with zinc by mouth is curative.

Acrodynia: Pain in the extremities.

Acromegaly: Condition due to the production of too much growth hormone by the pituitary gland. Acromegaly is characterized by large structure of the tongue, forehead, hands, and feet.

Actinic keratosis: A precancerous condition of thick and scaly patches of skin; also called solar or senile keratosis.

Activity, drug: A measure of the physiological response a drug produces in the body. A less active drug produces less response (and visa versa).

Active immunity: Immunity produced by the body in response to stimulation by a disease-causing organism or other agent.

Activities of daily living (ADLs): The things we normally do in daily living including any daily activity we perform for self-care (such as feeding ourselves, bathing, dressing, grooming), work, homemaking, and leisure. The ability or inability to perform ADLs can be used as a very practical measure of ability/disability in many disorders.

Acupuncture: The practice of inserting needles into the body with a therapeutic aim such as to reduce pain or induce anesthesia.

Acute: Of short duration. Rapid and abbreviated in onset in reference to a disease process. (As opposed to chronic.)

Acute leukemia: Cancer of the blood cells (leukemia) that characteristically comes on abruptly and (if not treated) progresses rapidly.

ADA: American Dental Association (and the American Diabetes Association).

Adam's apple: This familiar feature in front of the neck is due to forward protrusion of the largest cartilage of the larynx. It takes its name from the story that a piece of the forbidden fruit stuck in Adam's throat.

ADD (Attention Deficit Disorder): An inability to control behavior due to difficulty in processing neural stimuli.

Addison’s disease: Long-term underfunction of the outer portion of the adrenal gland. In medical terms, chronic insufficiency of the adrenal cortex. This may be due to a number of different insults to the adrenal including physical trauma, hemorrhage, and tuberculosis of the adrenal, and destruction of the cells in the pituitary gland that secrete ACTH (adrenocorticotropic hormone) which normally drives the adrenal. Addison’s disease is characterized by bronzing of the skin, anemia, weakness, and low blood pressure. The U.S. President J.F. Kennedy is said to have had Addison’s disease. Named after the British physician Thomas Addison (1793-1860).

Adduction: Movement of a limb sideways toward the body.

Adductor muscle: Any muscle that pulls inward toward the midline of the body. For example, the adductor muscles of the leg serve to pull the legs together. The opposite of "adductor" is "abductor."

Adenine (A): One member of the base pair A-T (adenine-thymine) in DNA.

Adenocarcinoma: A cancer that develops in the lining or inner surface of an organ. More than 95 percent of prostate cancers are adenocarcinoma.

Adenoidectomy: The surgical removal of the adenoids.

Adenoiditis: Infection of the adenoids.

Adenoids: Masses of lymphoid tissue in the upper part of throat behind the nose.

Adenoids and Tonsils: These celebrated structures in the back of the throat are composed of tissue similar to the lymph nodes or "glands."

Adhesion: The union of two opposing tissue surfaces (often referring to the sides of a wound). Also refers to scar tissue strands that can form in an area of a previous operation, such as within the abdomen after a laparotomy.

Adjuvant: Any substance that enhances the pharmacological effect of a drug or increases the ability of an antigen to stimulate the immune system.

Adjuvant therapyTreatment given in addition to the primary treatment.

ADLs: Activities of daily living.

Adnexa: This Latin word (in the plural) is used in medicine in reference to appendages. For example, in gynecology the adnexa are the "appendages" of the uterus, namely the ovaries, Fallopian tubes and ligaments that hold the uterus in place.

Adrenal glands: A pair of small glands, one located on top of each kidney. The adrenal glands produce hormones that help control heart rate, blood pressure, the way the body uses food, and other vital functions.

Adrenaline: A substance produced by the medulla (inside) of the adrenal gland, adrenaline (the official name in the British Pharmacopoeia) is synonymous with epinephrine. Technically speaking, adrenaline is a sympathomimetic catcholamine. It causes quickening of the heart beat, strengthens the force of the heart’s contraction, opens up the bronchioles in the lungs and has numerous other effects. The secretion of adrenaline by the adrenal is part of the "fight-or-flight" reaction that we have in response to being frightened.

Adult-onset Still’s disease: Although Still’s disease was first described in children, it is known to begin in adults. See: Still’s disease.

Advance directives: See: Advance medical directives.

Advance medical directives: Advance directives preserve the person’s right to accept or reject a course of medical treatment even after that person becomes mentally or physically incapacitated to the point of being unable to communicate those wishes. There ared two basic types of advance directives: (1) a living will, in which the person outlines specific treatment guidelines that are to be followed by health care providers; (2) a health care proxy (also called a power of attorney for healthcare decision making) in which the person designates a trusted individual to make medical decisions in the event that he or she becomes too incapacitated to make such decisions. Advance directive requirements vary greatly from one jurisdiction to another and should therefore be drawn up in consultation with an attorney who is familiar with the laws of the particular jurisdiction. (This entry is based upon material from the National MS Society).

Adverse event: In pharmacology, an adverse event is any unexpected or dangerous reaction to a drug.

Aerophagia: The word "phage" in Greek means "to eat." Aerophagia is literally to eat air. Aerophagia is a common cause of gas in the stomach. Everyone swallows small amounts of air when eating or drinking. However, rapid eating or drinking, chewing gum, smoking, or ill-fitting dentures may cause a significant increase in swallowed air.

Aerosol: A fine spray or mist. An aerosol can be administered by a nebulizer and inhaled.

Aetiology: The study of the causes, for example, of a disease. The word comes from the Greek "aitia", a cause + "logos", a discourse. Today in medicine the word "aetiology " is incorrectly used as a synonym for cause so often that it is fast becoming accepted usage, as in "the aetiology is unknown." Aetiology is the preferred spelling in some countries, including the U.K., whereas "etiology" without an "a" has taken over in the U.S.

Afferent: Carrying away. Afferent comes from the Latin "ad", toward + "ferre", to bear = to carry toward. A vein is an afferent vessel since it carries blood toward from the heart. An afferent nerve carries impulses toward the central nervous system. The opposite of afferent is efferent.

Afferent nerve: A nerve that carries impulses toward the central nervous system.

Afferent vessel: A vessel carrying blood toward the heart. A vein or venule.

African tapeworm: The beef tapeworm (Taenia saginata), the most common of the big tapeworms that parasitizes people, contracted from infected raw or rare beef. Can grow to be 12-25 feet (3.6-7.5 m) long in the human intestine.

AFP: Abbreviation for alpha-fetoprotein

AFO: Ankle-foot orthosis (a brace).

African tick typhus: One of the tick-borne rickettsial diseases of the eastern hemisphere, similar to Rocky Mountain spotted fever, but less severe, with fever, a small ulcer (tache noire) at the site of the tick bite, swollen glands nearby (satellite lymphadenopathy), and a red raised (maculopapular) rash. Also called fièvre boutonneuse.

Afterbirth: The placenta + the fetal membranes that are normally expelled from the uterus after the birth of the baby. Hence, the "afterbirth." The placenta is of course the organ that joins the mother and fetus and permits the provision of oxygen and nutrients to the fetus and the release of carbon dioxide and waste products from the fetus to the mother. As humanity only disposable organ, the placenta is disk-shaped and at full term measures about 7 inches (18 cm) in diameter and a bit less than 2 inches (4 cm) thick. The fetal membranes—the chorion is the outer one and the amnion is the inner one—envelop the embryo and contain the amniotic fluid. The word "afterbirth" entered the English language in the 16th century. The term has also been applied to a child born after the father’s death or last testament.

Agammaglobulinemia: Total (or nearly total) absence of the infection-fighting proteins (immunoglobulins) belonging to the class called gamma globulins. Can be due to certain genetic diseases or to acquired diseases such ad HIV.

Agenesis: Lack of development of something. For example, agenesis of a toe means that toe failed to form.

Agent, antihypertensive: As the name suggests, a drug aimed at reducing high blood pressure (hypertension).

Agent, anti-infective: Something capable of acting against infection, by inhibiting the spread of an infectious agent or by killing the infectious agent outright.

Agent, tocolytic: A medication that can inhibit labor, slow down or halt the contractions of the uterus. Tocolytic agents are widely used today to treat premature labor and permit pregnancy to procede and so let the fetus gain in size and maturity before being born.

AIDS: Disease due to infection with the human immunodeficiency virus (HIV). AIDS is an acronym for Acquired ImmunoDeficiency Syndrome.

Alpha-fetoprotein: A plasma protein, alpha-fetoprotein (AFP) is normally produced by the fetus. The level of AFP in the blood serum of pregnant women provides a screening test for open neural tube defects (anencephaly and spina bifida) and for Down syndrome (and other chromosome abnormalities) in the fetus. The maternal serum AFP (MSAFP) tends to be high with open neural tube defects and low with Down syndrome. AFP is also paradoxically produced by liver tumors (hepatomas) and germ cell tumors (teratocarcinoma and embryonal cell carcinomas) and so can be used to help detect and monitor the treatment of these tumors.

Alpha interferon: The interferons are specialized proteins (lymphokines) produced by the body in response to an infection. these substances interfere with cell infection. There are 3 main classes of interferon, alpha, beta, and gamma.

Alb-: Latin root form for the color white.

Albinism: Partial or total lack of the pigment melanin in the skin, hair and iris. The word albino is Portuguese and comes from the Latin albus for white.

Albino: A person with albinism.

Albuginea: Tough white fibrous tissue. The tunica albuginea of the testis, for example, is the layer of dense whitish inelastic tissue that surrounds the testis.

Albumen: "Albumen" with an "e" is the white of an egg, the part of the egg from which meringes are made. Albus in Latin is white.

Albumin: "Albumin" with an "i" is the main protein in human blood. It is key to the regulation of the osmotic pressure of blood. Chemically, albumin is soluble in water, precipitated by acid, and coagulated by heat.

Alcohol, pregnancy: The consumption of alcohol during pregnancy carries the danger of damaging the fetus.

Aldosterone: Hormone produced by the outer portion (cortex) of the adrenal gland that regulates the balance of water and electrolytes (ions such as potassium and sodium) in the body. Aldosterone encourages the kidney to excrete potassium into the urine and retain sodium, thereby retaining water. Aldosterone is classified as a mineralocorticoid hormone.

Aldosteronism: Overproduction of the hormone aldosterone from the cortex (the outer layer) of the adrenal gland or a tumor containing that type of tissue. Excess aldosterone (pronounced al’-do-ster-one) results in low potassium levels (hypokalemia), underacidity of the body (alkalosis), muscle weakness, excess thirst (polydipsia), excess urination (polyuria), and high blood pressure (hypertension). Also called hyperaldosteronism or Conn’s syndrome.

Allele: An alternative form of a gene.

Allergen: A substance that can allergic reaction. For examples, pollen, dander, mold.

Allergic conjunctivitis: Inflammation of the whites of the eyes (the conjunctivae) with itching and redness of the eyes and tearing, due to allergy.

Allergic reaction: A reaction that occurs when the immune system attacks a usually harmless substance (an allergen) that gains access to the body. The immune system calls upon a protective substance called immunoglobulin E (IgE) to fight these invading allergic substances ( allergens). Even though everyone has some IgE, an allergic person has an unusually large army of these IgE defenders -in fact, too many for their own good. This army of IgE antibodies attacks and engages the invading army of allergic substances of allergens. As is often the case in war, innocent bystanders are affected by this battle. These innocent bystanders are special cells called mast cells. These cells are frequently injured during the warring of the IgE antibodies and the allergic substances. When a mast cell is injured, it releases a variety of strong chemicals including histamine into the tissues and blood that frequently cause allergic reactions. These chemicals are very irritating and cause itching, swelling, and fluid leaking from cells. These allergic chemicals can cause muscle spasm and can lead to lung and throat tightening as is found in asthma and loss of voice.

Allergic rhinitis: Medical term for hay fever, a condition due to allergy that mimicks a chronic cold. (Hay fever is a misnomer since hay is not a usual cause of this problem and there is no fever. Many substances cause the allergic symptoms in hay fever. Allergic rhinitis is the correct term for this allergic reaction. (Rhinitis means "irritation of the nose" and is a derivative of Rhino, meaning "nose.") Symptoms include nasal congestion, a clear runny nose, sneezing, nose and eye itching, and tearing eyes. Post-nasal dripping of clear mucus frequently causes a cough. Loss of smell is common and loss of taste occurs occasionally. Nose bleeding may occur if the condition is severe. Eye itching, redness, and tearing frequently accompany the nasal symptoms.

Allergic rhinitis, perennial: Allergic rhinitis (hayfever) that occurs throughout the year.

Allergic rhinitis, seasonal: Allergic rhinitis (hayfever) which occurs during a specific season.

Allergic salute: The person with allergic rhinitis (hayfever) often rubs his/her nose using the index finger. This is the so-called "allergic salute."

Allergy: A hypersensitivity of the body's immune system in response to exposure to specific substances (antigens), such as pollen, beestings, poison ivy, drugs, or foods. Anaphylactic shock is a severe form of allergy response which is a medical emergency. Symptoms of anaphylactic shock include dizziness, loss of consiousness, labored breathing, swelling of the tongue and breathing tubes, blueness of the skin, low blood pressure, and death.

Allergy skin test: Test done on the skin to identify the allergy substance (allergen) triggering the allergic reaction. A small amount of the suspected allergy substance is placed on the skin. The skin is then gently scratched through the small drop with a special sterile needle. If the skin reddens and, more importantly, swells, then allergy to that substance is probable.

Allergy desensitization: Stimulation of the immune system with gradually increasing doses of the substances to which a person is allergic, the aim being to modify or stop the allergy "war" (by reducing the strength of the IgE and its effect on the mast cells). This form of treatment is very effective for allergies to pollen, mites, cats, and especially stinging insects (eg, bees, hornets, yellowjackets, wasps, velvet ants, fire ants). Allergy immunotherapy usually takes 6 months to a year to become effective and injections ("shots") are usually required for 3-5 years.

Allergy shots: See Allergy desensitization.

Alloerotic: Having to do with sexual excitment toward the same sex. The opposite is heteroerotic.

Alopecia: Baldness. There are many types of alopecia, each with a different cause. Alopecia can be localized to the front and top of the head, such as in male pattern baldness; patchy, such as in alopecia areata; or involve the entire head, such as in alopecia capitis totalis.

Alopecia areata: Patchy baldness (alopecia means baldness and areata means occurring in patches). The problem typically begins with patchy hair loss on the scalp and sometimes progresses to complete baldness and even loss of body hair. Although alopecia areata affects 2.5 million people in the United States alone, little is known about its underlying causes. Stress, the immune system, and several different genes may play a part in causing alopecia areata.

Alpha-1 antitrypsin deficiency: An inherited disease that results in low or no production of an important protein, alpha-1 antitrypsin. The lack of this protein leads to damage of various organs, but mainly to the lung and liver. Symptoms may become apparent at a very early age or in adulthood, manifesting either as shortness of breath or liver related symptoms (jaundice, fatigue, fluid in the abdomen, mental changes, or gastrointestinal bleeding). There are several options for treatment of the lung disease, including replacement of the missing protein. Treatment of the liver disease is a well-timed liver transplant

Alpha error: The statistical error (said to be "of the first kind" or type I) made in testing an hypothesis when it is concluded that a result is positive when it really is not. Alpha error is often referred to as a false positive.

ALS (Amyotropic Lateral Sclerosis): A chronic progressive disease of motor neurons (the nerves that come from the spinal cord to supply electrical energy to the muscles).

Alternative medicine: Healing arts not generally taught in medical schools or typically practiced in hospitals.

Alveoli: Tiny air sacs at the end of the bronchioles.

Alzheimer's disease: A progressive degenerative disease of the brain that leads to dementia. On a cellular level, Alzheimer’s is characterized by unusual helical protein filaments in nerve cells (neurons) of the brain. These odd twisted filaments are called neurofibrillary tangles. On a functional level, there is degeneration of the cortical regions, especially the frontal and temporal lobes, of the brain. The U.S. President Ronald Reagan is said to have Alzheimer’s disease. Named after the German neurologist Alois Alzheimer (1864-1915).

AMA: American Medical Association.

Ambulance: Although you are undoubtedly familiar with the sound of the siren and the sight of the flashing lights of the ambulance, you may not necessarily know that the ambulance began as a walking hospital. The word "ambulance" indeed started off as a walking hospital, "un hôpital ambulant" in French, meaning literally "a walking hospital." The "hôpital ambulant" was devised during the campaigns of Napoleon to bring medical aid directly to his troops in the field. The original "hôpital ambulant" was a mobile unit designed to carry dressings and drugs to the wounded and evacuate the injured from the line of battle. The British, knowing a good idea when they saw it, came up with their own version of the "hôpital ambulant." But they economized by dropping the "hôpital" and corrupted "ambulant" to "ambulance." The French, of course, have for many years railed against the incursions of Anglo-Saxon words into the pure precincts of the French language. Nonetheless, they rejected their own "hôpital ambulant" and embraced the English "ambulance." So, in France today you can no longer see a hospital walking but "ambulances" are very much in evidence.

Ambulant: Means the same as "ambulatory" (able to ambulate, walk about).

Ambulatory: Able to ambulate, to walk about, not bed-ridden or hospitalized.

Ambulatory care: Medical care (including diagnosis, observation, treatment and rehabilitation) provided on an outpatient basis. Ambulatory care is given to persons who are not confined to a hospital but rather are "ambulatory" and, literally, are able to ambulate or walk about. (A well-baby visit is considered ambulatory care even though the baby is not walking).

American Type Culture Collection (ATTC): A key resource for cultured cells, located in Rockville, MD.

AMI: Acute myocardial infarction (a heart attack).

Amine: A chemical compound containing nitrogen. Amines are derived from ammonia. (The name "amine" was derived from the word "ammonia.")

Amino acid: One of the building blocks of protein. The term "amino acids" dates to the middle of the 19th century. The idea that amino acids are "Bausteine" (building stones) came from the Nobel Prize winning German biochemist Albrecht Kossel (1853-1927).

Amnesia: An impairment or lack of memory. Amnesia after a trauma event can be either antegrade (lack of memory related to events occurring after the event) or retrograde (lack of memory related to events occurring before the event).

Amniocentesis: Procedure used in prenatal diagnosis to obtain amniotic fluid which can be used for genetic and other diagnostic tests. Informally called an "amnio."

Amnion: A thin membrane surrounding the fetus during pregnancy. The amnion is the inner of the two fetal membranes (the chorion is the outer one). It contains the amniotic fluid.

Amniotic fluid: The fluid bathing the fetus and serving as a shock absorber.

Amplification: Event producing multiple copies of a gene or any sequence of DNA. Gene amplification plays a role in cancer. Amplification can occur in vivo (in the living individual) or in vitro (literally "in glass", or in a plastic vessel in the laboratory).

Ampulla of Vater: A small projection into the duodenum through which bile and pancreatic secretions flow to mix with food for digestion.

Amputation: Surgery to remove all or part of an arm, leg or digit (finger or toe).

Amyloidosis: Disorder due to deposits of abnormal protein (amyloid) in body tissues.

Amyotrophic lateral sclerosis (ALS): A chronic progressive disease of motor neurons (the nerves that come from the spinal cord to supply electrical energy to the muscles).

ANA: See: Antinuclear antibodies.

Anal fissure: Common tear in the anal canal. One of the common causes of red blood in the stool.

Analgesia is the inability to feel pain.

Anaphylactoid purpura: Also called Henoch-Schonlein purpura (HSP), this is a form of blood vessel inflammation, a vasculitis that affects small arterial vessels in the skin (capillaries) and the kidneys. HSP results in skin rash associated with joint inflammation (arthritis) and cramping pain in the abdomen. HSP frequently follows a bacterial or viral infection of the throat or breathing passages and is an unusual reaction of the body’s immune system to this infection. HSP occurs most commonly in children. HSP is generally a mild illness that resolves spontaneously, but sometimes it can cause serious problems in the kidneys and bowels. Treatment is directed toward the most significant area of involvement. Joint pain can be relieved by antiinflammatory medications, such as aspirin or ibuprofen. Some patients can require cortisone-related medications, such as prednisone, especially those with significant abdominal pain or kidney disease.

Anastomosis: A procedure to connect healthy sections of the colon or rectum after the cancerous portion has been surgically removed.

Anatomy: The study of form.

Anatripsis: The use of friction as a treatment modality for a medical condition. Anatripsis may or may not also involve the application of a medicament.

Androgen: A hormone that promotes the development and maintenance of male sex characteristics.

Anemia is the condition of having less than the normal number of red blood cells or hemoglobin in the blood. The oxygen-transporting units are, therefore, insufficient. Patients can feel tired, fatigue easily, appear pale, develop palpitations, and become short of breath. There are many causes of anemia, including: bleeding, abnormal hemoglobin formation (such as in sickle cell anemia), iron, B12 (pernicious anemia), or folate deficiency, rupture of red blood cells (hemolytic anemia), and bone marrow diseases.

Anemia, Cooley’s: Better known today as thalassemia (or as beta thalassemia or thalassemia major) .The clinical picture of this important type of anemia was first described in 1925 by the pediatrician Thomas Benton Cooley. Another name for the disease is Mediterranean anemia. The name thalassemia was coined by the Nobel Prize winning pathologist George Whipple and the professor of pediatrics Wm Bradford at U. of Rochester because thalassa in Greek means the sea (like the Mediterrranean Sea) + -emia means in the blood so thalassemia means sea in the blood. Thalassemia is not just one disease. It is a complex contingent of genetic (inherited) disorders all of which involve underproduction of hemoglobin, the indispensable molecule in red blood cells that carries oxygen. The globin part of normal adult hemoglobin is made up of 2 alpha and 2 beta polypeptide chains. In beta thalassemia, there is a mutation (change) in both beta globin chains leading to underproduction (or absence) of beta chains, underproduction of hemoglobin, and profound anemia. The gene for beta thalassemia is relatively frequent in people of Mediterranean origin (for example, from Italy and Greece). Children with this disease inherit one gene for it from each parent. The parents are carriers (heterozygotes) with just one thalassemia gene, are said to have thalassemia minor, and are essentially normal. Their children affected with beta thalassemia seem entirely normal at birth because at birth we still have predominantly fetal hemoglobin which does not contain beta chains. The anemia surfaces in the first few months after birth and becomes progressively more severe leading to pallor and easy fatiguability, failure to thrive (grow), bouts of fever (due to infections) and diarrhea. Treatment based on blood transfusions is helpful but not curative. Gene therapy will, it is hoped, be applicable to this disease.

Anemia, iron deficiency: Deficiency of iron results in anemia because iron is necessary to make hemoglobin, the key molecule in red blood cells responsible for the transport of oxygen. In iron deficiency anemia, the red cells are unusually small (microcytic) and pale (hypochromic). Characteristic features of iron deficiency anemia in children include failure to thrive (grow) and increased infections. The treatment of iron deficiency anemia, whether it be in children or adults, is with iron and iron-containing foods. Food sources of iron include meat, poultry, eggs, vegetables and cereals (especially those fortified with iron). According to the National Academy of Sciences, the Recommended Dietary Allowances of iron are 15 milligrams per day for women and 10 milligrams per day for men.

Anemia, Mediterranean: Better known today as thalassemia (or as beta thalassemia or thalassemia major) .The clinical picture of this important type of anemia was first described in 1925 by the pediatrician Thomas Benton Cooley. The name thalassemia was coined by the Nobel Prize winning pathologist George Whipple and the professor of pediatrics Wm Bradford at U. of Rochester because thalassa in Greek means the sea (like the Mediterrranean Sea) + -emia means in the blood so thalassemia means sea in the blood. Thalassemia is not just one disease. It is a complex contingent of genetic (inherited) disorders all of which involve underproduction of hemoglobin, the indispensable molecule in red blood cells that carries oxygen. The globin part of normal adult hemoglobin is made up of 2 alpha and 2 beta polypeptide chains. In beta thalassemia, there is a mutation (change) in both beta globin chains leading to underproduction (or absence) of beta chains, underproduction of hemoglobin, and profound anemia. The gene for beta thalassemia is relatively frequent in people of Mediterranean origin (for example, from Italy and Greece). Children with this disease inherit one gene for it from each parent. The parents are carriers (heterozygotes) with just one thalassemia gene, are said to have thalassemia minor, and are essentially normal. Their children affected with beta thalassemia seem entirely normal at birth because at birth we still have predominantly fetal hemoglobin which does not contain beta chains. The anemia surfaces in the first few months after birth and becomes progressively more severe leading to pallor and easy fatiguability, failure to thrive (grow), bouts of fever (due to infections) and diarrhea. Treatment based on blood transfusions is helpful but not curative. Gene therapy will, it is hoped, be applicable to this disease.

Anemia, refractory: Anemia (a shortage of red blood cells) unresponsive to treatment.

Anencephaly: Absence of the cranial vault and absence of most or all of the cerebral hemispheres of the brain. Anencephaly is a neural tube defect (NTD). It is due to abnormal development during embryonic life of the neural tube, the structure which gives rise to the central nervous system (the brain and spinal cord). Specifically, the upper end of the neural tube fails to close. Anencephaly is a uniformally lethal malformation. The risk of all NTDs including anencephaly can be decreased by the mother eating ample folic acid during pregnancy.

Anesthesia: Loss of feeling or awareness. A local anesthetic causes loss of feeling in a part of the body. A general anesthetic puts the person to sleep.

Anesthetic: A substance that causes lack of feeling or awareness. A local anesthetic causes loss of feeling in a part of the body. A general anesthetic puts the person to sleep.

Aneuploidy: One or a few chromosomes above or below the normal chromosome number. For example, three number 21 chromosomes or trisomy 21 (characteristic of Down syndrome) is a form of aneuploidy.

Aneurysm: A widening or dilatation of blood vessel.

Angina: Angina is chest pain that is due to an inadequate supply of oxygen to the heart muscle.

Angina trachealis: This has nothing whatsoever to do with the ordinary adult angina (angina pectoris) with chest pain of cardiac origin. Angina trachealis is more commonly known as croup, an infection of the larynx, trachea, and the bronchial tubes, largely in children. Caused usually by viruses, less often by bacteria. Symptoms include a cough that sounds like a barking seal and a harsh crowing sound during inhaling. Treatment can include moist air, salt water nose drops, decongestants and cough suppressants, pain medication, fluids, and occasionally antibiotics. The major concern in croup is breathing difficulty as the air passages narrow. Close monitoring of the breathing of a child with croup is important, especially at night. While most children recover from croup without hospitalization, some children can develop life-threatening breathing difficulties. Therefore, close contact with the doctor during this illness is important.

Angioedema: Like hives but affects deeper skin layer.

Angioedema, hereditary: A genetic form of angioedema. (Angioedema is also referred to as Quinke’s disease.) Persons with it are born lacking an inhibitor protein (called C1 esterase inhibitor) that normally prevents activation of a cascade of proteins leading to the swelling of angioedema. Patients can develop recurrent attacks of swollen tissues, pain in the abdomen, and swelling of the voice box (larynx) which can compromise breathing. The diagnosis is suspected with a history of recurrent angioedema. It is confirmed by finding abnormally low levels of C1 esterase inhibitor in the blood. Treatment options include antihistamines and male steroids (androgens) that can also prevent the recurrent attacks. Also called hereditary angioneurotic edema.

Angioid streaks: Tiny breaks in the elastin-filled tissue in the back of the eye (retinae). These abnormalities are visible to the doctor during an examination using a viewing instrument called an ophthalmoscope. Angioid streaks are seen in patients with pseudoxanthoma elasticum (abbreviated PXE), a rare disorder of degeneration of the elastic fibers with tiny areas of calcification in the skin, back of the eyes (retinae), and blood vessels. Angioid streaks can be associated with blindness.

Angiogram: An x-ray of blood vessels, which can be seen because of an injection of a dye that shows up in the x-ray pictures.

Angioneurotic edema, hereditary: A genetic form of angioedema. (Angioedema is also referred to as Quinke’s disease.) Persons with it are born lacking an inhibitor protein (called C1 esterase inhibitor) that normally prevents activation of a cascade of proteins leading to the swelling of angioedema. Patients can develop recurrent attacks of swollen tissues, pain in the abdomen, and swelling of the voice box (larynx) which can compromise breathing. The diagnosis is suspected with a history of recurrent angioedema. It is confirmed by finding abnormally low levels of C1 esterase inhibitor in the blood. Treatment options include antihistamines and male steroids (androgens) that can also prevent the recurrent attacks. Also called hereditary angioedema.

Angioplasty: Procedure with a balloon-tipped catheter to enlarge a narrowing in a coronary artery. Also called Percutaneous Transluminal Coronary Angioplasty (PTCA).

Angiotensin: A family of peptides (smaller than proteins) that act as vasoconstrictors to narrow blood vessels.

Angiotensin converting enzyme: Usually abbreviated ACE.

Anhidrosis: Not sweating. From the Greek an- meaning not + hidros meaning sweat. Inability to sweat may seem a blessing but it is not, since to sweat is to be able to stay cool. Anhidrosis creates a dangerous inability to tolerate heat.

Ankle-foot orthosis (AFO): A brace (usually plastic) worn on the lower leg and foot to support the ankle, hold the foot and ankle in the correct position, and correct foot drop.

Ankle pain: The ankle is a "hinged" joint. The severity of ankle sprains ranges from mild (which can resolve within 24 hours) to severe (which can require surgical repair). Tendinitis of the ankle can be caused by trauma or inflammatory forms of arthritis.

Ankylosing spondylitis: A type of arthritis that causes chronic inflammation of the spine.

Anomaly: Something abnormal. A congenital anomaly is a birth defect.

Anonymous reporting: In public health, anonymous reporting permits the acquisition of certain data such as the proportion of persons with a positive test or with a disease.

Anonymous testing: Testing in which no name is used—there is total anonymity—to identify the person tested. For example, the State of Florida requires that each county have a site for anonymous HIV testing.

Anorexia: A decreased appetite or aversion to food. Anorexia nervosa is a serious psychological disorder characterized by an extreme aversion to food, most often affecting young women.

Anorexia nervosa: A decreased appetite or aversion to food. Anorexia nervosa is a serious psychological disorder characterized by an extreme aversion to food, most often affecting young women.

Anosmia: No sense of smell.

Anoxia: Lack of oxygen.

Anterior cruciate ligament (ACL): One of the ligaments in the knee, the ACL crosses from bottom of the femur (the thigh bone) to the top of the tibia (the main bone in the lower leg). ACL injuries can occur in a number of situations including sports, such as football.

Anthrax: A serious infection, anthrax is not primarily a human disease but rather an infection of animals. Cattle, sheep, horses, mules, and some wild animals are highly susceptible. Humans (and swine) are generally resistant to anthrax. Anthrax can take different forms. With the lung form of the disease. People inhale the anthrax spores and, if untreated, are likely to die. An intestinal form is caused by eating meat contaminated with anthrax. But most human anthrax comes from skin contact with animal products. Cutaneous (skin) anthrax was once well known among people who handled infected animals, like farmers, woolsorters, tanners, brushmakers and carpetmakers in the days when the brushes and carpets were animal products. The hallmark of skin anthrax is a carbuncle, a cluster of boils, that ulcerates in an ugly way. Typically this lesion has a hard black center surrounded by bright red inflammation. This accounts for its name, "anthrax", the Greek word for "coal", a burning coal. Anthrax has become the stuff, unfortunately, of frontpage news as a possible agent of biological warfare.

Anthrax immunization: A series of six shots over six months and booster shots annually, the anthrax vaccine now in use in the USA was first developed in the 1950s and approved by the Food and Drug Administration for general use in 1970. It is produced by the Michigan Biologic Products Institute of Michigan’s Department of Health and is given routinely to veterinarians and others working with livestock. In December, 1997 it was announced that all US military would receive the vaccine, as do the military in the UK and Russia, the reason being concern that anthrax might be used in biologic warfare.

Antibiotics: Drugs that fight infections.

Antibiotic resistance: The ability of bacteria and other microorganisms to withstand an antibiotic to which they were once sensitive (and were once stalled or killed outright). Also called drug resistance.

Antibodies are specialized proteins produced by white blood cells that circulate in the blood seeking and attaching to foreign proteins, microorganisms or toxins in order to neutralize them. They are part of the immune system. (see immune system).

Antibodies, antinuclear (ANA): See: Antinuclear antibodies.

Anticipation: The progressively earlier appearance and increased severity of a disease from generation to generation. The phenomenon of "anticipation" was once thought to be an artifact but a biological basis for it has been discovered in a number of genetic disorders such as myotonic dystrophy and Huntington's disease.

Anti-coagulant agents: Medications, like heparin, used as "blood-thinners" to prevent blood clots and to maintain open blood vesssels.

Anticholinergic: The action of certain medications that inhibit the transmission of parasympathetic nerve impulses and thereby reduce spasms of smooth muscle (such as t6hat, for example, in the bladder). Antinuclear antibodies (ANA): Antibodies directed against the nucleus of a cell. The ANA test is almost always positive (indicative of the presence of antinuclear antibodies) in systemic lupus erythematosus (SLE). It may also be positive in other connective tissue diseases such as rheumatoid arthritis and scleroderma.

Antigen: Something potentially capable of inducing an immune response. Antibodies are elicited by antigens.

Antihistamines: Drugs that combat the histamine released during an allergic reaction by blocking the action of the histamine on the tissue. Antihistamines do not stop the formation of histamine nor do they stop the conflict between the IgE and antigen. Therefore, antihistamines do not stop the allergic reaction but protect tissues from some of its effects. Antihistamines frequently cause mouth dryness and sleepiness. Newer "non sedating" antihistamines are generally thought to be somewhat less effective. Antihistamine side effects that very occasionally occur include urine retention in males and fast heart rate.

Antihypertensive: Something that reduces high blood pressure (hypertension).

Anti-infective: Something capable of acting against infection, by inhibiting the spread of an infectious agent or by killing the infectious agent outright.

Antiphospholipid antibody syndrome: An immune disorder characterized by the presence of abnormal antibodies in the blood associated with certain medical conditions including abnormal blood clotting, migraine headaches, premature miscarriage, and low blood platelet counts (thrombocytopenia).

Anti-platelet agents: Medications that, like aspirin, reduce the tendency of platelets in the blood to clump and clot.

Antiseptic: Something that discourages the growth microorganisms. By contrast, aseptic refers to the absence of microorganisms.

Antitoxin: An antibody from the serum of an animal stimulated with specific antibodies, used to provide passive immunity. For example, if a child gets whooping cough (diphtheria), an antitoxin prepared in horses against diphtheria may be useful in treatment. The antitoxin can only be of short-term value because the antibodies against diphtheria were made by the horse and the child is just the passive recipient of the antibodies.

Antrum: A general term for cavity or chamber which may have specific meaning in reference certain organs or sites in the body. The antrum of the stomach (gastric antrum) is a portion before the outlet which is lined by mucosa which does not produce acid. The paranasal sinuses can be referred to as the frontal antrum, ethmoid antrum, and maxillary antrum.

Ants, fire: Originally from S. America. Among the worst insect pests ever to invade the U.S. Red or yellowish ants of small-to-medium size with a severe sting that burns like fire. They normally feed on small insects but, with denser populations, they eat seeds and seedling plants, damage grain and vegetable crops, invade kitchens, attack newly hatched poultry and the young of ground-nesting wild birds. Fire ants can kill newborn domestic and wild animals. Each colony is composed of a queen, winged males and females and 3 kinds of workers. A nest averages about 25,000 workers, but far larger populations are common. Semipermanent nests are large mounds of excavated soil with openings for ventilation. Since nests may number 50-100 (or more) in a heavily infested field, cultivating becomes difficult (or impossible). Fire ants belong to the genus Solenopsis.

Ants, fire (stings from): Also called thief ants, a scourge, these red or yellow ants of small-to-medium size, originally from South America, have a severe sting that burns like fire and can trigger an allergic reaction. Avoidance and prompt treatment are essential.

Ants, velvet (stings from): Common in most parts of the world including the Southern and Southwestern U.S., velvet ants are not true ants but rather parasitic wasps. Their sting can trigger allergic reactions. Avoidance, prompt treatment and, in selected cases, allergy injection therapy are useful.

Anus: The opening of the rectum to the outside of the body.

Aorta: The great (main) artery from the left ventricle of the heart.

Aortic insufficiency (regurgitation): Sloshing of blood back down from the aorta into the left ventricle due to incompetancy of the aortic valve.

Aortic stenosis: Narrowing (stenosis) of the valve between the left ventricle of the heart and the aorta, impeding the delivery of blood via the aorta to the body.

Aortic valve: Valve at the base of the aorta that prevents backflow of blood from the aorta into the left ventricle of the heart.

AP: AP is a versatile abbreviation. It serves in cardiology to abbreviate angina pectoris (AP) and arterial pressure (AP). In endocrinology, it stands for the anterior pituitary (AP). And in anatomy, AP means anteroposterior, i.e., from front-to-back.

AP, X-ray: An X-ray picture in which the beams pass from front-to-back (anteroposterior). As opposed to a PA (posteroanterior) film in which the rays pass through the body from back-to-front.

Apex: From the Latin meaning summit, the apex is the tip of a pyramidal or rounded structure, like the lung or the heart. The apex of the lung is indeed its tip, its rounded most superior portion. The apex of the heart is likewise its tip, but that is formed by the left ventricle so it is essentially the most inferior portion of the heart.

Apgar: Short for Apgar score.

Apgar score: A practical method to assess a newborn infant, the Apgar score is a number arrived at by scoring the heart rate, respiratory effort, muscle tone, skin color, and response to a catheter in the nostril. Each of these objective signs can receive 0, 1, or 2 points. An Apgar score of 10 means an infant is in the best possible condition. The Apgar score is done routinely 60 seconds after the complete birth of the infant. An infant with a score of 0-3 needs immediate resusitation. The Apgar score is commonly repeated 5 minutes after birth and in the event of a difficult resusitation, the Apgar may be done again at 10, 15, and 20 minutes. An Apgar score of 0-3 at 20 minutes of age is predictive of high morbidity (disease) and mortality. The score is named for the American anesthesiologist Virginia Apgar (1909-1974) at Columbia University in New York who invented the scoring method.

Aphasia: Literally aphasia means no speech. Aphasia can apply to a defect in expression or comprehension.

Aphonia: Inability to speak.

Apical: The adjective for apex, the tip of a pyramidal or rounded structure, like the lung or the heart. For example, an apical lung tumor is a tumor located at the top of the lung.

Aplasia: Failure to develop. If something develops and then wastes away, that is atrophy.

Aplastic anemia: Anemia due to failure of the bone marrow to produce red blood cells.

Apnea: The absence of breathing (respirations).

Appendectomy: Removal of the appendex by surgery.

Appendicitis: Inflammation of the appendix.

Appendix (vermiform appendix): A small outpouching from the beginning of the large intestine. Formally called the vermiform appendix because it is wormlike.

Appendix epididymis: A small cystic projection from the surface of the epididymus which represents a remnant the embryologic mesonephros.

Appendix epiploica: A finger-like projection of fat attached to the colon.

Appendix testis: A small solid projection of tissue on the outer surface of the testis which is a remnant of the embryologic mullerian duct.

Apthous ulcers: These small sensitive painful craters in the mouth are common canker sores. There are many possible causes of apthous ulcers and frequently the cause is unknown.

Aqueduct: A channel for the passage of fluid.

Aqueduct of Sylvius: A canal between two of the cavities (called the third and fourth ventricles) in the brain through which cerebrospinal fluid passes.

Arachnodactyly: Long spider-like fingers and toes.

Arborvirus: Although arbor sounds as if it should have something to do with trees, it doesn’t. It comes from the first 2 letters of "arthropod" + the first 3 letters of "borne." Arborviruses are transmitted (borne) to humans by mosquitoes and ticks (arthropods).

Archaea: A unique group of microorganisms. They are called bacteria (Archaeobacteria) but they are genetically and metabolically different from all other known bacteria. They appear to be living fossils, the survivors of an ancient group of organisms that bridged the gap in evolution between bacteria and the eukaryotes (multicellular organisms). The name Archaea comes from the Greek archaios meaning ancient.

Arcus senilis: A cloudy opaque arc or circle around the edge of the eye, often seen in the eye of the elderly.

Areolus: The diminuitive of the Latin "area" meaning a little space or park. The areolus of the breast is the small darkened area around the nipple.

Armed tapeworm: The pork tapeworm (Taenia solium). Contracted from undercooked or measly pork (pork infected with the larval forms of the tapeworm). Can grow to be 3-6 feet (0.9-1.8 m) long in the human intestine. Also known as the measly tapeworm.

Arrayed library: In genetics, an arrayed library consists of (in technical terms) individual primary recombinant clones which are hosted in phage, cosmid, YAC, or another vector that have been placed in two- dimensional arrays in microtiter dishes (plastic dishes with an orderly array of tiny wells). Each primary clone can be identified by the identity of the plate and the clone location (row and column) on that plate. Arrayed libraries of clones are used for many purposes, including screening for a specific gene or genomic region. The information gathered on individual clones from genetic linkage and physical map studies is then entered into a database and used to construct physical and genetic linkage maps

Arrector pili: A microscopic band of muscle tissue which connects a hair follicle to the dermis. When stimulated, the arrector pili will contract and cause the hair to become more perpendicular to the skin surface (stand on end).

Arrhythmias: Abnormal heart rhythms. The heartbeats may be too slow, too rapid, irregular, or too early. Rapid arrhythmias (greater than 100 beats per minute) are called tachycardias. Slow arrhythmias (slower than 60 beats per minute) are called bradycardias. Irregular heart rhythms are called fibrillations (as in atrial fibrillation). When a single heartbeat occurs earlier than normal, it is called a premature contraction.

Arrhythmias, atrial: Abnormal heart rhythm due to electrical disturbances in the atria (the upper chambers of the heart) or the AV node "relay station", leading to fast heart beats. Examples of atrial arrhythmias includes atrial fibrillation, atrial flutter, and paroxysmal atrial tachycardia (PAT).

Arrhythmias, rapid: Abnormally rapid heart rhythms, medically termed tachycardia.

Arrhythmias, slow: Abnormally slow heart rhythms, medically termed bradycardia.

Arrhythmias, ventricular: Abnormal rapid heart rhythms (arrhythmias) that originate in the lower chambers of the heart (the ventricles). Ventricular arrhythmias include ventricular tachycardia and ventricular fibrillation. Both are life threatening arrhythmias most commonly associated with heart attacks or scarring of the heart muscle from previous heart attack.

Arterial tension: The pressure of the blood within an artery, the arterial pressure. Also called the intra-arterial pressure.

Arteriogram: An x-ray of blood vessels, which can be seen after an injection of a dye that shows up in the x-ray pictures.

Arteriole: A small branch of an artery that leads to a capillary.

Arteriosclerosis: Hardening and thickening of the walls of the arteries.

Arthritis: Inflammation of a joint. When joints are inflamed they can develop stiffness, warmth, swelling, redness and pain. There are over 100 types of arthritis. (see osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, lupus, gout, pseudogout).

Arteritis, cranial: A serious disease characterized by inflammation of the walls of the blood vessels (vasculitis). The vessels affected are the arteries (hence the name "arteritis"). The age of affected patients is usually over 50 years of age. Cranial arteritis is also known as temporal arteritis and as giant cell arteritis. It can lead to blindness and/or stroke. The disease is detected by a biopsy of an artery. It is treated with high dose cortisone-related medications.

Artery: A blood vessel that carries blood away from the heart. Put otherwise, an artery is an efferent vessel (efferent coming from the Latin "ex’, out + "ferre", to bear = to bear out or carry away). Arterial blood is normally full of oxygen. The oxygenated hemoglobin (oxyhemoglobin) makes it look bright red.

Arthralgia: Pain in the joints. The Greek "algos" means "pain."

Arthritis, degenerative: A type of arthritis caused by inflammation, breakdown, and eventual loss of the cartilage of the joints. Also called osteoarthritis.

Arteritis, giant cell: A chronic vascular disease, most often involving the carotid artery system, that can lead to blindness and/or stroke, Giant cell arteritis (also called temporal arteritis) is detected by a biopsy of an artery, and is treated with high dose cortisone.

Arthritis, gout: Joint inflammation caused by uric acid crystal deposits in the joint space An attack is usually extremely painful.The uric acid crystals are deposited in the joint fluid (synovial fluid) and joint lining (synovial lining). Intense joint inflammation occurs as white blood cells engulf the uric acid crystals, causing pain, heat, and redness of the joint tissues. The term "gout" commonly is used to refer to these painful arthritis attacks but gouty arthritis is only one manifeatation of gout.

Arthritis in children: Arthritis is not just a problem for the retired. It can and does affect children in the form of juvenile/pediatric arthritis. >

Arthritis, Lyme: Inflammation of the joints associated with Lyme disease, a bacterial disease spread by ticks.

Arthritis, psoriatic: Joint inflammation associated with psoriasis.

Arthritis, quackery: Like many people with chronic ailments, sufferers from arthritis are potentially vulnerable to proponents of "cure-all" treatments which are promoted as having great benefits, but in reality have no right to such claims.

Arthritis, Reiter's: The combination of inflammation of the joints (arthritis), eyes (conjunctivitis), and GU (genitourinary) &/or GI (gastrointestinal) systems.

Arthritis, rheumatoid: Autoimmune disease that is characterized by chronic inflammation of the joints and can cause inflammation of tissues in other areas of the body (such as the lungs, heart, and eyes).

Arthritis, spondylitis: A form of arthritis causing chronic inflammation of the spine.

Arthritis, systemic-onset chronic rheumatoid : See: Arthritis, systemic-onset juvenile rheumatoid (Still’s disease).

Arthritis, systemic-onset juvenile rheumatoid (Still’s disease): A form of joint disease, arthritis, that presents with systemic (bodywide) signs and symptoms including high intermittent fever, a salmon-colored skin rash, swollen lymph glands, enlargement of the liver and spleen, and inflammation of the lungs (pleuritis) and around the heart (pericarditis) The arthritis itself may not be immediately apparent but in time it surfaces and may persist after the systemic symptoms are long gone. Also known as systemic-onset juvenile chronic arthritis.

Arteritis, temporal: Also called giant cell arteritis or cranial arteritis, this is a serious disease characterized by inflammation of the walls of the blood vessels (vasculitis). The vessels affected by inflammation are the arteries (hence the name "arteritis"). The age of affected patients is usually over 50 years of age. Giant cell arteritis can lead to blindness and/or stroke. It is detected by a biopsy of an artery. It is treated with high dose cortisone.

Arthroscopy is a surgical technique whereby a doctor inserts a tube-like instrument into a joint to inspect, diagnose and repair tissues. It is most commonly performed in patients with diseases of the knees or shoulders.

Articulation: The joining of two structures. From the Latin "articulus," meaning a joint. There are diverse application of the word "articulation" including: (1) in medicine, the place where bones come together, that is the joint; (2) in dentistry, the place where teeth come together, the occlusal surfaces of the teeth; and (3) in speech, the production of intelligible words and sentences, again by joining, but in this case by joining together properly the structures such as the lips, tongue and palate needed to articulate speech.

Artery: An Artery is a blood vessel that carries blood high in oxygen content from the heart throughout the body. It is the part of the circulatory system

Asbestos: A natural material that is made up of tiny fibers. If the fibers are inhaled, they can lodge in the lungs and lead to cancer, such as mesothelioma, or a scarring of the lungs, called asbestosis.

Ascaris: Intestinal roundworms.

Ascites: Abnormal buildup of fluid in the abdomen. Ascites can occur as a result of severe liver disease.

ASD: Acronym for atrial septal defect.

Aseptic: The absence of microorganisms. By contrast, something that just discourages the growth of microorganisms is antiseptic.

Aseptic bursitis: Inflammation of a bursa that is not caused by infection. A bursa is a closed fluid-filled sac that functions as a gliding surface to reduce friction between tissues of the body. When the bursa becomes inflamed, the condition is known as "bursitis." Most commonly this is not an infectious condition (aseptic bursitis).

Aseptic necrosis: Condition in which poor blood supply to an area of bone leads to bone death. Also called avascular necrosis and osteonecrosis.

Asphyxia: Impaired or impeded breathing.

Aspirate: To suck in. A patient may aspirate for example by accidentally drawing material from the stomach into the lungs. A doctor can aspirate a joint.

Aspiration: Removal of a sample of fluid and cells through a needle. Aspiration also refers to the accidental sucking in of food particles or fluids) into the lungs.

Aspiration pneumonia: Inflammation of the lungs due to aspiration (the sucking in of food particles or fluids into the lungs).

Aspirin: A good example of a tradename that entered into the language, Aspirin was once the Bayer trademark for acetylsalicylic acid.

Assistive device: Any device that is designed, made, or adapted to assist a person perform a particular task. For examples, canes, crutches, walkers, wheel chairs, and shower chairs are all assistive devices.

Asthma: Breathing problem due to reversible narrowing of airways (bronchospasm).

Astigmatism: A common kind of impaired vision in which part of an image is not sharp. Due to unequal curvature of the refractive surfaces of the eye.

Ataxia: Wobbliness. Ataxia is incoordination and unsteadiness due to the brain’s failure to regulate the body’s posture and regulate the strength and direction of limb movements. Ataxia is usually a consequence of disease in the brain, specifically in the cerebellum which lies beneath the back part of the cerebrum.

Ataxia, cerebellar: See: Ataxia.

Ataxia-telangiectasia (AT): A genetic disease with a wobbly gait and "red eye" due to widening of small blood vessels in the conjunctiva of the eye. AT carries with it an increased risk of leukemia and lymphoma.

ATCC: American Type Culture Collection ( a key resource for cultured cells, located in Rockville, MD).

Athetosis: Involuntary writhing movements particularly of the arms and hands.

Athlete's foot: A skin infection caused by a fungus called Trichophyton which can thrive and infect the upper layer of the skin when the feet (or other areas of the body) remain moist, warm, and irritated. The fungus can be found on floors and in socks and clothing and can be spread from person to person by contact with these objects. However, without proper growing conditions (a warm, moist environment), the fungus will not infect the skin.

Atresia: Failure of a structure to be tubular. Esophageal atresia is a birth defect in which part of esophagus is not hollow. With anal atresia, there is no hole at the bottom end of the intestine.

Atria: The plural of atrium.

Atrial arrhythmias: See Arrhythmias, atrial.

Atrial fibrillation: Abnormal irregular heart rhythm with chaotic generation of electrical signals in the atria of the heart. Familiarly called atrial fib.

Atrial septal defect (ASD): A hole in the septum, the wall, between the atria, the upper chambers of the heart. Commonly called an ASD. ASDs constitute a major class of heart formation abnormalities present at birth (congenital cardiac malformations). Normally, when clots in veins break off (embolize) , they travel first to the right side of the heart and, then to the lungs where they lodge. The lungs act as a filter to prevent the clots from entering the arterial circulation. However, when there is an ASD, a clot can cross from the right to the left side of the heart, then pass into the arteries as a paradoxical embolism. Once in the arterial circulation, a clot can travel to the brain, block a vessel there, and cause a stroke (cerebrovascular accident). Because of the risk of stroke from paradoxical embolism, it is usually recommended that even small ASDs be closed (repaired).

Atrial septum: The wall between the two upper chambers (the right and left atrium) of the heart.

Atrio-ventricular node: See AV node.

Atrium: An entry chamber. On both sides of the heart, the atrium is the chamber leading to the ventricle.

Atrophy: Wasting away or diminuition. Muscle atrophy is wasting of muscle, decrease in muscle mass.

Attention deficit disorder (ADD): An inability to control behavior due to difficulty in processing neural stimuli.

Attenuated virus: A weakened virus that is no longer virulent. Can be used to make a live virus vaccine.

Audiogram: A test of hearing at a range of sound frequencies.

Audiology: The study of hearing.

Audiometry: The measurement of hearing.

Aura: A premonition. There is often an aura before a migraine or a grand mal seizure. The aura, a symptom of brain malfunction, may consist of flashing lights, a gleam of light, blurred vision, an odor, the feeling of a breeze, numbness, weakness, or difficulty speaking.

Auricle: The ear (actually, the pinna which is the principal projecting part of the ear) or something that is ear shaped like the upper chamber (atrium) of the heart.

Auricular: Of or pertaining to the outer ear. Adjective form of auricle. (Not to be confused with avuncular which refers to an uncle).

Auscultate: To listen to the sounds made by the internal organs of the body for diagnostic purposes. For example, nurses and doctors auscultate the lungs and heart of a patient by using a stethoscope placed on the patient's chest.

Autism: Impaired development in social interaction, communication and behavior.

Autoclave: A chamber for sterilizing with steam under pressure. The original autoclave was essentially a pressure cooker. The steam tightened the lid. The device was called an autoclave (from the Greek auto, self + clavis, key) meaning self-locking.

Autogenous: Self-produced.

Autoimmune diseases are illnesses which occur when the body tissues are attacked by its own immune system. The immune system is a complex organization within the body that is designed normally to "seek and destroy" invaders of the body, particularly infections. Patients with these diseases have unusual antibodies in their blood that target their own body tissues.

Autonomic nervous system: Part of the nervous system once thought functionally independent of the brain. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: (1) the sympathetic nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure; and (2) the parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles.

Autopsy: Postmortem examination. Also called a necropsy.

Autoradiography: A technique using X- ray film to visualize molecules or fragments of molecules that have been radioactively labeled. Autoradiography has many applications in the laboratory. Autoradiography can, for example, be used to analyze the length and number of DNA fragments after they are separated from one another by a method called gel electrophoresis.

Autosome: Any chromosome other than the X and Y sex chromosome People normally have 22 pairs of autosomes (44 autosomes) in each cell.

AV node: Specialized heart tissue which acts as an electrical relay station between the atria and the ventricles. Electrical signals from the SA node and the atria must pass through the AV node to reach the ventricles. (The SA node is the pacemaker of the heart and is situated in the right atrium.)

Avascular necrosis: Condition in which poor blood supply to an area of bone leads to bone death. Also called avascular necrosis and osteonecrosis.

Avulsion: Tearing away. A nerve can be avulsed by an injury, as can part of a bone.

Axilla: Armpit.

Axillary dissection: An axillary dissection means removal of a portion of the lymph nodes under the arm.