Websters new world medical dictionary

Fernando Dangond, MD, Neurology • Charles C.P. Davis, MD, PhD, Emergency Medicine • Roxanne Dryden-Edwards, MD, Psychiatry and Mental Health • Jason C. Eck, DO, MS, Orthopaedic Surgery • Steve Ehrlich, MD, Cardiology • Manuel Fernandez, MD, Endocrinology • Robert Ferry, MD, Pediatric Endocrinologist • Michael C. Fishbein, MD, Cardiovascular & Autopsy Pathology • Tse-Ling Fong, MD, Hepatology • Catherine G. Fuller, MD, Allergy & Immunology • Ronald Gehling, MD, Allergy & Immunolgy • Gus Gialamas, MD, Orthopedic Surgery • Gary W. Gibbon, MD, Pulmonary Disease & Allergy • Mitchell J. Gitkind, MD, Gastroenterology • Vay Liang W. Go, MD, Nutrition • Sandra Gonzalez Gompf, MD, FACP, FIDSA, Infectious Disease • Jayson Goo, ATC, MA, CKTI, Human Performance/Corrective Therapy • Daniel L. Gomel, MD, Internal Medicine & Geriatrics • Mark Graber, MD, Family Practice • Harold H. Harsch, MD, Psychiatry • Roza Hayduk, MD, Sleep Medicine • Barbara K. Hecht, PhD • Frederick Hecht, MD, FAAP • Standiford Helm III, MD, Anesthesiologist/Pain Management • Kendall Ho, MD, Emergency Medicine • Debra E. Houry, MD, MPH, Emergency Medicine/Women’s Health • Camille Marie Teres Hylton, MD, Ophthamology • David Kaminstein, MD, Gastroenterology • Kenneth Kaye, MD, Pathology • Jillyen E. Kibby, M.A., CCC-A, Audiology • Harley J. Kornblum, MD, Pediatrics & Neurology • Betty Kovacs, MS, RD, Nutrition • Daniel Lee Kulick, MD, FACC, FSCAI., Internal Medicine & Cardiology • Eric Lee, MD, Gastroenterology • Margaret Lee, DDS, Dentistry • Stacy E. Lee, MD, Allergy & Immunology • Michael Lill, MD, Hematology/Oncology • Arthur H. Loussararian, MD, Inetrnal Medicine & Cardiology • Ralph Maeda, MD, Surgery • Dwight Makoff, MD, Nephrology & Hypertension • Murray Margolis, MD, Internal Medicine • Randy Martin, MD, Pulmonary/Infectious Diseases • James Meaglia, MD, Urology • John Mersch, MD, Pediatrics • Michael Miyamoto, MD, Cardiology • Zab Mohsenifar, MD, Internal Medicine & Pulmonary Diseases • John R. Morris, MD, Orthopedic Surgery • Mim Mulford, MD, Endocrinology • Marty Nettleman, MD, MS, Infectious Disease • Mark Scott Noah, MD, Internal Medicine • Omudhome Ogbru, PharmD, Pharmacy • Peter J. Panzarino, Jr. MD, Psychiatry & Behavioral Medicine • David Adam Perlstein, MD, FAAP, Pediatarics • Dennis Philips, MD, Pediatrics • Donald Pratt, MD, Internal Medicine • Stefan M. Pulst, MD, Neurology • J. Bradley Randleman, MD, Opthamology • Donald Rediker, MD, Cardiology • Alan Rockoff, MD, Dermatology • Emmanuel Saltiel, PharmD FASHP, FCCP, Pharmacy • Stephen J. Sanders, M.A., CCC-A, Audiology • Michael Santoro, MD, Gastroenterology • George Schiffman, MD, Pulmonary • Leslie J. Schoenfield, MD, PhD • Melvin Shiffman, MD, Cosmetic Surgery • Lawrence J. Schwartz, MD, Ophthalmology • Joseph Sciammarella, MD, FACP, FA.CEP, Emergency Medicine • John Sheppard, MD, Ophthalmology and Pharmacology • David Simon, MD, Internal Medicine • Robert Simon, MD, Neurology • Thomas P. Sokol, MD, FACS, FASCRS, Gastroenterology • Mark Sullivan, MD, Urology • Alan Szeftel, MD, Allergy and Immunology/Pulmonary Disease • Bruce Tammelin, MD, Pulmonary Disease • Suzanne Trupin MD, FACOG, Obstetrics and Gynecology • Michael Truong, MD, Endocrinology • Theodore Van Dam, MD, Internal Medicine • John Vierling, MD, Hepatology • Benjamin C. Wedro, MD, FAAEM, Emergency Medicine • Richard Weil, M.Ed., CDE, Exercise Physiology, Diabetes Educator • Maureen Welker, MSN, NPc, CCRN • Edward J. White, MD, General Surgery • Leslie Williams, EdD, Psychology • Joseph Y. Wu, MD, Internal Medicine & Geriatrics • Marilyn A.D. Yee, PharmD, Pharmacy • David Zachary, MD, Family Medicine Introduction lexicographer A writer of dictionaries, a harmless drudge. –Samuel Johnson, 1755 Like the previous editions, this edition has been conceived and developed by the staff of the health information Web site MedicineNet.com, part of the WebMD Health Network. One of the earliest health information sites on the Internet, MedicineNet.com has devoted a number of years to creating an online medical dictionary that now contains a wealth of contemporary medical terms and provides the broad foundation for this book. To create this new edition of Webster’s New World Medical Dictionary, we have reviewed every entry in the previous edition and have rewritten and strengthened many of those entries. In addition, we have selected new entries from our online medical dictionary for incorporation into this third edition. A unique feature of an online medical dictionary is that it can (and does) evolve rapidly to keep pace with the changes in medicine. We have taken advantage of this to update Webster’s New World Medical Dictionary. Like all of the medical content from MedicineNet.com, this dictionary was written and edited by physicians, to be used by anyone and everyone concerned about their own health or the health of those who matter to them. All the medical information found on MedicineNet.com has been developed by a network of physicians. The physicians select the topics and review and edit all written content. These physicians also make use of medical specialists and health writers throughout the US. The “About the Authors” pages provide abbreviated biographies of the editors and specialists who contributed content to the MedicineNet.com online dictionary and this book. Medicine is now advancing with remarkable rapidity on many fronts, and the language of medicine is also continually evolving with remarkable rapidity, commensurate with the changes. Today, there is constant need for communication between and among consumers and providers of health care. There is consequently a need for a high-quality, contemporary medical dictionary. In the current health care environment, patients and their physicians, nurses, and allied health professionals must be able to discuss the ever-changing aspects of health, disease, and biotechnology. An accurate understanding of medical terminology can assist communication and improve care for patients, and it can help to alleviate the concerns of family members and friends. The fact that the content of this dictionary is physician-produced by MedicineNet.com ensures an unusual degree of professional expertise, reliability, and perspective. As a bonus, this edition includes a companion Web site at www.medterms.com/wnw. There you will find content not found in the book such as PDF healthcare guides and audio podcasts. We hope that you will find Webster’s New World Medical Dictionary, Third Edition a valuable addition to your family or office library and a source of both information and illumination in any medical situation. Aa that spans the body cavity, just below the lungs. See also abdominal cavity. A In genetics, adenine, a member of the adeninethymine (A-T) base pair in DNA. abdominal aortic aneurysm See aneurysm, abdominal aortic. a- Prefix indicating the absence or depletion of something: for example, aphagia (not eating) or aphonia (voiceless). The related prefix an- is usually used before a vowel, as in anemia (without blood) and anoxia (without oxygen). abdominal cavity The cavity within the abdomen. This space between the abdominal wall and the spine contains a number of crucial organs, including the lower part of the esophagus, the stomach, small intestine, colon, rectum, liver, gallbladder, pancreas, spleen, kidneys, adrenal glands, ureters, and bladder. See also abdomen. AA 1 Alcoholics Anonymous. 2 Amino acid. AAAS American Association for the Advancement of Science, a professional organization that publishes the weekly journal Science. AAFP 1 American Association of Family Physicians, a professional organization for physicians who treat both children and adults. 2 American Academy of Family Physicians, a professional organization for physicians who treat both children and adults. AAO 1 American Association of Ophthalmology, a professional organization. 2 American Association of Orthodontists, a professional organization. 3 American Academy of Otolaryngology, a professional organization. AAOS American Academy of Orthopaedic Surgeons, a professional organization. See also orthopaedics. AAP 1 American Academy of Pediatrics, a professional organization for physicians who treat infants, children, adolescents, and young adults. 2 American Academy of Pedodontics, a professional organization. 3 American Academy of Periodontology, a professional organization. 4 American Association of Pathologists, a professional organization. ab- Prefix indicating from, away from, or off, as in abduction (movement of a limb away from the midline of the body) and abnormal (away from normal). abdomen The part of the body that contains all the structures between the chest and the pelvis. The abdomen, or belly, is anatomically separated from the chest by the diaphragm, the powerful muscle abdomen, acute See acute abdomen. abdominal aorta The final section of the aorta, the largest artery in the body, which begins at the diaphragm as a continuation of the thoracic aorta and ends by splitting in two, to form the common iliac arteries. The abdominal aorta supplies oxygenated blood to all the abdominal and pelvic organs, as well as to the legs. See also aorta. abdominal guarding Tensing of the abdominal wall muscles to guard inflamed organs within the abdomen from the pain of pressure upon them. Abdominal guarding is detected when the abdomen is pressed and is an indication that inflammation of the inner abdominal (peritoneal) surface may be present due, for example, to appendicitis or diverticulitis. The tensed muscles of the abdominal wall automatically go into spasm to keep the tender underlying tissues from being irritated. abdominal hysterectomy See hysterectomy, abdominal. abdominal muscle One of a large group of muscles in the front of the abdomen that assists in maintaining regular breathing movements, supports the muscles of the spine while lifting, and keeps abdominal organs in place. Abdominal muscles are the target of many exercises, such as sit-ups. Abdominal muscles are informally known as the abs. abdominal pain Pain in the belly. Abdominal pain can be acute or chronic. It may reflect a major problem with one of the organs in the abdomen, such as appendicitis or a perforated intestine, or it may result from a fairly minor problem, such as excess buildup of intestinal gas. abducens nerve See abducent nerve. abducent nerve The sixth cranial nerve, which emerges from the skull to operate the lateral rectus muscle. This muscle draws the eye toward the side of the head. Paralysis of the abducent nerve causes inward turning of the eye. abduction abduction The movement of a limb away from the midline of the body. The opposite of abduction is adduction. abductor muscle See muscle, abductor. ABG Arterial blood gas, a sampling of the blood levels of oxygen and carbon dioxide within the arteries, as opposed to the levels of oxygen and carbon dioxide in veins. Typically, the acidity (pH) is also simultaneously measured. abiotrophy Loss of function, or degeneration for reasons unknown. ablate To remove, from a Latin word meaning “to carry away.” See ablation. 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. abnormal Outside the expected norm, or uncharacteristic of a particular patient. ABO blood group The major human blood group system. The ABO type of a person depends on the presence or absence of two genes, A and B. These genes determine the configuration of the red blood cell surface. A person who has two A genes has red blood cells of type A. A person who has two B genes has red cells of type B. If the person has one A and one B gene, the red cells are type AB. If the person has neither the A nor the B gene, the red cells are type O. It is essential to match the ABO status of both donor and recipient in blood transfusions and organ transplants. abortifacient A medication or substance that causes pregnancy to end prematurely. abortion Premature exit of the products of the fetus, fetal membranes, and placenta from the uterus. Abortion can be a natural process, as in a miscarriage; an induced procedure, using medication or other substances that cause the body to expel the fetus; or a surgical procedure that removes the contents of the uterus. See also dilation and curettage. abortion, habitual The miscarriage of three or more consecutive pregnancies with no intervening pregnancies. Habitual abortion is a form of infertility. Also known as recurrent abortion and multiple abortion. abortion, multiple See abortion, habitual. abortion, recurrent See abortion, habitual. 2 abortion, spontaneous Miscarriage. abortive Tending to cut short the course of a disease, as in abortive polio (polio cut short). abortive polio A minor, abbreviated form of infection with the polio virus. Full recovery occurs in 24 to 72 hours, and the condition does not involve the nervous system or permanent disabilities. See also polio. ABP American Board of Pediatrics, a professional organization for physicians who treat infants, children, adolescents, and young adults. abrasion 1 A wearing away of the upper layer of skin as a result of applied friction force. See also scrape. 2 In dentistry, the wearing away of a tooth surface. abruptio placentae Premature separation (abruption) of the placenta from the wall of the uterus, often in association with high blood pressure or preeclampsia. Abruption is a potentially serious problem both for mother and fetus because the area where it occurs bleeds and the uterus begins to contract. Shock may result. See also placenta; preeclampsia. abs Slang term for the abdominal muscles. abscess A local accumulation of pus anywhere in the body. See also boil; pus. abscess, perianal An abscess next to the anus that causes tenderness, swelling, and pain on defecation. abscess, peritonsillar An abscess behind the tonsils that pushes one of the tonsils toward the uvula (the prominent soft tissue dangling from the back of the palate in the back of the mouth). A peritonsillar abscess is generally very painful and associated with difficulty opening the mouth. If a peritonsillar abscess is untreated, the infection can spread deep into the neck, causing airway obstruction and other life-threatening complications. abscess, skin A confined collection of pus in the skin. The common boil is a type of skin abscess. See also boil. abscission To remove tissue by cutting it away, as in surgery. See also resection. absence of the breast See amastia. absence of the nipple See athelia. 3 absinthe An emerald-green liqueur flavored with extracts of the wormwood plant, licorice, and aromatic flavorings in an alcohol base. Absinthe was manufactured, commercialized, and popularized in France in the late 1700s. It was an extremely addictive drink. Prolonged drinking of absinthe causes convulsions, blindness, hallucinations, and mental deterioration. Absinthe has been banned, but something of its taste is still available in such drinks as Greek ouzo and French pastis. Homemade absinthe may still be illicitly consumed in some areas. absolute CD4 count The number of “helper” Tlymphocytes in a cubic millimeter of blood. The absolute CD4 count is frequently used to monitor the extent of immune suppression in persons with HIV because with HIV, this number declines as the infection progresses. Also known as T4 count. absorption Uptake. For example, intestinal absorption is the uptake of food (or other substances) from the digestive tract. abstinence The voluntary self-denial of food, drink, or sex. Today, abstinence most commonly refers to denial of one’s sexual activity. abuse, child See child abuse. abuse, elder See elder abuse. a.c. Abbreviation of the Latin phrase ante cibum, meaning “before meals.” See also Appendix A, “Prescription Abbreviations.” AC joint See acromioclavicular joint. acanthosis nigricans A skin condition characterized by dark, thickened, velvety patches, especially in the folds of skin in the armpit, groin, and back of the neck. It can occur with endocrine diseases such as Cushing disease and diabetes mellitus, from tumors of the pituitary gland, underlying malignancies, certain drugs, and as a genetic disorder. It is most common in people who have insulin resistance—those whose body is not responding correctly to the insulin that they make in their pancreas. acapnia Lower than normal level of carbon dioxide in the blood. The opposite of acapnia is hypercapnia. accelerated phase of leukemia Chronic myelogenous leukemia that is progressing. In this phase, 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. ACE inhibitor accessory nerve The eleventh cranial nerve, which emerges from the skull and receives an additional (accessory) root from the upper part of the spinal cord. It supplies the sternocleidomastoid and trapezius muscles. accessory neuropathy A disease of the accessory nerve, paralysis of which prevents rotation of the head away from one or both sides and causes the shoulder to droop. Damage can be confined to the accessory nerve, or it may also involve the ninth and tenth cranial nerves, which exit the skull through the same opening. accessory placenta See placenta, accessory. acclimatization to altitude The process of adapting to the decrease in oxygen concentration at a specific altitude. A number of changes must take place for the body to operate with decreased oxygen. These changes include increasing the depth of respiration; increasing the pressure in the pulmonary arteries, forcing blood into portions of the lung that are normally not used at sea level; manufacturing additional oxygen-carrying red blood cells; and manufacturing extra 2, 4-DPG, a substance that facilitates the release of oxygen from hemoglobin to the body tissues. Acclimatization generally takes 1 to 3 days and occurs after any significant altitude change above 1,220 meters (approximately 4,000 feet). Acclimatization is the body’s natural means of correcting altitude sickness and the rate of acclimatization depends on the altitude, rate of ascent, and individual susceptibility. accoucheur A male obstetrician. An accoucheuse is a woman obstetrician, or sometimes a midwife. ACE Angiotensin converting enzyme. ACE converts an angiotensin to its activated form, angiotensin II, enabling it to function. Angiotensin II constricts blood vessels and elevates blood pressure. ACE inhibitor A drug that inhibits ACE. Using an ACE inhibitor relaxes the arteries, not only lowering blood pressure but also improving the pumping efficiency of a failing heart and improving cardiac output in patients with heart failure. ACE inhibitors are therefore used for blood pressure control and congestive heart failure. ACE inhibitors include benazepril (brand name: Lotensin), captopril (brand name: Capoten), lisinopril (brand names: Zestril, Prinivil), quinapril (brand name: Accupril), and ramipril (brand name: Altace). Interestingly, ACE inhibitors were originally developed from the venom of a Brazilian viper snake.