anemia Condition in which erythrocytes are reduced in number or vol¬ ume or are deficient in hemoglobin. The patient is usually noticeably pale. Close to 100 varieties exist (including aplastic anemia, pernicious anemia, and sickle-cell anemia), distinguished by cause; erythrocyte size, shape, and hemoglobin content; and symptoms. Anemia may result from blood loss; increased destruction, reduced production, or inhibited formation of red cells; or hormone deficiency. Treatment may involve nutrition, toxin removal, drugs, surgery, or transfusion. See also folic-acid-deficiency ane¬ mia, IRON-DEFICIENCY ANEMIA.
anemometer V.an-s-'ma-ms-tsiA Instrument for measuring the speed of airflow. The most familiar instruments for measuring wind speeds are the revolving cups that drive an electric generator (useful range approxi¬ mately 5-100 knots). For very low airspeeds, a unit in which revolving vanes operate a counter measures the airspeed. For strong, steady wind speeds (in wind tunnels and aboard aircraft in flight), a pitot-tube anemom¬ eter is often used; the pressure difference between the interior of the tube and the surrounding air can be measured and converted to airspeed.
anemone \3-'ne-m3-ne\ Any of about 120 species of perennial plants that make up the genus Anemone , in the buttercup family, many of which are cultivated for their colourful flowers. Though found throughout the world, anemones are most common in woodlands and meadows of the northern temperate zone. Many varieties of the tuberous poppylike anemone A. coronaria are grown for the garden and florist trade. Popular spring-flowering species include A. apennina, A. blanda, and A. pavon- ina. Other species, such as the Japanese anemone (A. hupehensis), are favourite border plants for autumn flowering. The European wood anemone, A. nemorosa , causes blistering of the skin and was once used as an ingredient in medicines. Anemones are also known colloquially as pasqueflowers or windflowers.
anesthesiology X.a-nss-.the-ze-'al-s-jeN Medical specialty dealing with anesthesia and related matters, including resuscitation and pain. Originally concerned only with general anesthesia in the operating room, anesthesiology now includes epidural anesthesia (injection of local anes¬ thetics into the spinal fluid, cutting off feeling below the point of injec¬ tion); artificial respiratory support during operations requiring paralyzing drugs that render patients unable to breathe; clinical management of all unconscious patients; management of pain relief and cardiac and respi¬ ratory resuscitation problems; respiratory therapy; and treatment of fluid, electrolyte, and metabolic disturbances. Progress in anesthesiology has made possible more complex operations and surgery for more critically ill patients. The anesthesiologist’s role has become increasingly impor¬ tant and complex.
anesthetic \,an-es-'thet-ik\ Agent that produces a local or general loss of sensation, including pain, and therefore is useful in surgery and den¬ tistry. General anesthesia induces loss of consciousness, most often using hydrocarbons (e.g., cyclopropane, ethylene); halogenated (see halogen) hydrocarbons (e.g., chloroform, ethyl chloride, trichloroethylene); ethers (e.g., ethyl ether or vinyl ether); or other compounds, such as tribromo- ethanol, nitrous oxide, or barbiturates. Local anesthesia induces loss of sen¬ sation in one area of the body by blocking nerve conduction (see nervous system, neuron), usually with alkaloids such as cocaine or synthetic sub¬ stitutes (e.g., lidocaine). See also anesthesiology.
aneuploidy See ploidy
aneurysm Van-ys-.riz-smV Blood-filled protrusion in the wall of a blood vessel (usually an artery, and particularly the aorta). Disease or injury weakens the wall so that normal blood pressure makes it balloon out. Typically, the two inner layers rupture and the outer layer bulges. In a false aneurysm, all three layers rupture and surrounding tissues hold the blood in place. Symptoms vary with size and location. Aneurysms tend to enlarge over time, and blood-vessel walls weaken with age. Many aneurysms eventually burst, causing serious, even massive, internal bleed-
© 2006 Encyclopaedia Britannica, Inc.
72 I Angora ► Angkor
ing; aortic aneurysm rupture causes severe pain and immediate collapse. Rupture of an aneurysm in the brain is a major cause of strokes. Treat¬ ment can consist of simply tying off a small vessel; more serious aneu¬ rysms require surgery to replace the diseased section of artery with a plastic graft.
Angara \3n-,g3-'ra\ River River, southeast-central Russia. The outlet for Lake Baikal, it is a major tributary of the Yenisey River, which it joins near Yeniseysk. It is about 1,105 mi (1,779 km) long, and with its many rapids, it provides great potential for hydroelectric power. Some existing dams and power stations provide power in the Irkutsk industrial area.
angel Primarily in Western religions, any of numerous benevolent spiri¬ tual beings who mediate between heaven and earth. They often serve as messengers or servants of God or as guardians of an individual or nation. In Zoroastrianism the amesha spenta are arranged in a hierarchy of seven. Judaism and Christianity base their notion of angels on references in the Hebrew scriptures to divine servants and to the heavenly hosts. Two arch¬ angels (Michael and Gabriel) are mentioned in the Old Testament and two others (Raphael and Uriel) in the Apocrypha. Angels are mentioned throughout the Christian scriptures, and Christian tradition identifies nine orders of angels. Islam’s hierarchy of angels descends from the four throne bearers of God to the cherubim who praise God, the four archangels, and lesser angels such as the hafazah (guardian angels). See also cherub; ser¬ aph.
Angel Falls Waterfall, southeastern Venezuela. It lies on the Churun River, a tributary of the Carom, southeast of Ciudad Bolivar. The highest waterfall in the world, the cataract drops 3,212 ft (979 m) and is 500 ft (150 m) wide at its base. It was named for James Angel, an American who crash-landed his plane nearby in 1937.
angelfish Any of various fishes of the order Perciformes. The best- known angelfishes are freshwater cichlids (genus Pterophyllum ) popu¬ lar in home aquariums. These are thin and deep-bodied fishes that usu¬ ally are silver with vertical dark markings but may be solid or par¬ tially black; they may grow to 6 in.
(15 cm) in length. Brightly coloured marine angelfishes are in the family Pomacanthidae. They are found among tropical reefs in the Atlantic and the Indo-Pacific, where they eat algae and marine invertebrates and reach a maximum length of 18 in.
(46 cm).
Angelico Xan-'jel-i-koV Fra orig.
Guido di Pietro (b. c. 1400, Vic- chio, Florence [Italy]—d. Feb. 18,
1455, Rome) Italian painter and Dominican friar active in Florence.
He entered the convent of San Domenico at Fiesole sometime between 1417 and 1425 and began his artistic career by painting illumi¬ nated manuscripts and altarpieces.
He was influenced by Masaccio’s use of architectural perspective.
Among his earliest masterpieces is a large triptych, the Linaiuoli Altar- piece (1433-36), executed for the linen merchants’ guild; it is enclosed in a marble shrine designed by Lorenzo Ghiberti. His most notable works are frescoes at the convent of San Marco, Florence (c. 1440-45), and in the chapel of Pope Nicholas V in the Vatican (c. 1448-49). One of the outstanding fresco painters of the 15th century, he influenced such mas¬ ters as Fra Filippo Lippi; Benozzo Gozzou was among his students.
Angelou Van-ja-JoN, Maya orig. Marguerite Johnson (b. April 4, 1928, St. Louis, Mo., U.S.) U.S. poet. She was raped at age eight and
went through a period of muteness. Her autobiographical works, which explore themes of economic, racial, and sexual oppression, include I Know Why the Caged Bird Sings (1970), The Heart of a Woman (1981), and All God’s Children Need Traveling Shoes (1986). Her poetry collec¬ tions include Just Give Me a Cool Drink of Water fore I Diiie (1971), And Still I Rise (1978), and I Shall Not Be Moved (1990). Her recitation of a poem she wrote for Bill Clinton’s first inauguration (1993) brought her widespread fame. In 2002 she published her sixth volume of mem¬ oirs, A Song Flung Up to Heaven.