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Medical Dictionary


  • upsilon, 20th letter of the Greek alphabet
  • kinematic viscosity.
  • pyrimidine nucleosid
  • tyrosine
  • yttrium
Y chromosome
a sex chromosome that is characteristic of male cells in species in which the male typically has two unlike sex chromosomes

Abbreviation for yeast artificial chromosomes, under chromosome.

Abbreviation for yttrium-aluminum-garnet.

yang (yang)
See yin-y..

yanggona (yang′go-na)

yaqona (ya′kona)
A Fijian drink made from the powdered root of Piper methysticum (family Piperaceae); excessive drinking of it causes a state of hyperexcitability and a loss of power in the legs; chronic intoxication induces roughening of the skin and a state of debility. SEE ALSO: methysticum. SYN: kava (2) , yanggona. [Fijian name]

yaw (yau)
An individual lesion of the eruption of yaws. mother y. a large granulomatous lesion, considered to be the primary inoculation lesion in yaws, most commonly present on the hand, leg, or foot. SYN: buba madre, frambesioma, protopianoma.

yawn (yaun)
1. To gape. 2. An involuntary opening of the mouth, usually accompanied by inspiration; it may be a sign of drowsiness or of vital depression, as after hemorrhage, but is often caused by suggestion. [A.S. ganian]

The act of producing a yawn. SYN: oscitation.

yaws (yawz)
An infectious tropical disease caused by Treponema pertenue and characterized by the development of crusted granulomatous ulcers on the extremities; may involve bone, but, unlike syphilis, does not produce central nervous system or cardiovascular pathology. SEE ALSO: nonvenereal syphilis. SYN: boubas, frambesia tropica, granuloma tropicum, mycosis framboesioides, pian, zymotic papilloma. [of Caribbean origin; similar to Calinago yaya, the disease] bosch y. SYN: pian bois. bush y. SYN: pian bois. foot y. y. of the feet with keratoderma of the palms and soles and ulcer formation.

Symbol for ytterbium.

years of potential life lost (YPLL) measure of the relative impact of various diseases and lethal forces on society, computed by estimating the years that people would have lived if they had not died prematurely from injury, cancer, heart disease, or other causes.

yeast (yest)
  • A general term denoting true fungi of the family Saccharomycetaceae that are widely distributed in substrates that contain sugars (such as fruits), and in soil, animal excreta, the vegetative parts of plants, etc. Because of their ability to ferment carbohydrates, some yeasts are important to the brewing and baking industries. [A.S. gyst]
  • brewers' y.: y. produced by Saccharomyces cerevisiae; a by-product from the brewing of beer.
  • compressed y.: the moist living cells of Saccharomyces cerevisiae combined with a starchy or absorbent base.
  • cultivated y.: a form of y. propagated by culture and used in breadmaking, brewing, etc.
  • dried y.: the dry cells of a suitable strain of Saccharomyces cerevisiae; brewers' dried y., debittered brewers' dried y., or primary dried y. are the sources of dried y.; it contains not less than 45% of protein, and in 1 g not less than 0.3 mg of nicotinic acid, 0.04 mg riboflavin, and 0.12 mg thiamin hydrochloride; used as a dietary supplement.
  • primary dried y.: a source of dried y.; obtained from suitable strains of Saccharomyces cerevisiae grown in media other than those required for the production of beer.
  • wild y.: any of the uncultivated forms of yeasts, useless as ferments and sometimes pathogenic.
yellow (yel′o)
A color occupying a position in the spectrum between green and orange. For individual y. dyes see specific name. [A.S. geolu] corralin y. the sodium salt of rosolic acid. indicator y. a compound formed in the bleaching of rhodopsin by light; it is chrome y. at pH 3.3–4.0 and pale y. at pH 9.0–10.0. tumeric y. SYN: curcumin. visual y. SYN: all-trans-retinal.

yellow root
SYN: hydrastis.

yerba santa (yer′ba san′ta)
SYN: eriodictyon. [Sp. sacred herb]

Yersinia (yer-sin′e-a)

  • A genus of motile and nonmotile, non-spore-forming bacteria (family Enterobacteriaceae) containing Gram-negative, unencapsulated, ovoid to rod-shaped cells; Y. are nonmotile at 37°C, but some species are motile at temperatures below 30°C; motile cells are peritrichous; citrate is not used as a sole source of carbon; these organisms are parasitic on humans and other animals; the type species is Y. pestis. [A. J. E. Yersin, Swiss bacteriologist, 1862–1943]
  • Y. enterocolitica: a bacterial species that causes yersiniosis in humans; it is found in the feces and lymph nodes of sick and healthy animals, including humans, in material likely to be contaminated with feces, and in the cadavers of cattle, rabbits, hares, dogs, guinea pigs, horses, monkeys, pigs, and sheep; it replicates at refrigerator temperatures and has been associated with contamination of blood and blood products.
  • Y. frederiksenii: reclassified from Y. enterocolitica; rare cause of enterocolitis in humans.
  • Y. intermedia: reclassified from Y. enterocolitica; rare cause of enterocolitis in humans.
  • Y. kristensenii: reclassified from Y. enterocolitica; pathogenicity uncertain.
  • Y. pestis: a bacterial species causing plague in humans, rodents, and many other mammalian species and transmitted from rat to rat and from rat to humans by the rat flea, Xenopsylla; it is the type species of the genus Y.. SYN: Kitasato bacillus, Pasteurella pestis, plague bacillus.
  • Y. pseudotuberculosis: a bacterial species causing pseudotuberculosis in birds, rodents, and, rarely, in humans. SYN: Pasteurella pseudotuberculosis.
yersiniosis (yer-sin-e-o′sis)
A common human infectious disease caused by Yersinia enterocolitica and marked by diarrhea, enteritis, pseudoappendicitis, ileitis, erythema nodosum, and sometimes septicemia or acute arthritis. pseudotubercular y. SYN: pseudotuberculosis.

yield (yeld)
The amount or quantity produced or returned, often measured as a percentage of the starting material; e.g., a y. in an enzyme preparation is equal to the units of enzyme activity recovered at the end of the preparation divided by the total units observed in the starting material. quantum y. (φ) the number of molecules transformed ( E.G., via a reaction) per quantum of light absorbed; the inverse of the quantum requirement. SYN: quantum efficiency.

yin-yang (yin′yang)
In ancient Chinese thought, the concept of two complementary and opposing influences, Yin and Yang, underlying and controlling all nature, the aim of Chinese medicine being to produce proper balance between them. Used in modern terms to characterize any dualistic, reciprocal control system in which one influence tends to promote things that the opposing influence tends to inhibit, and vice versa; e.g., the y. hypothesis of biologic control in which cyclic GMP and cyclic AMP are supposed to act in this dualistic, reciprocal way in controlling cellular functions.

Chemical suffix signifying that the substance is a radical by loss of an H atom ( e.g., alkyl, methyl, phenyl) or OH group ( e.g., acyl, acetyl, carbamoyl).

Chemical suffix denoting a bivalent hydrocarbon radical ( e.g., methylene, –CH2–) or possessing a double bond ( e.g., ethylene, CH2&dbond;CH2).

ylides (il′idz)
A class of compounds in which a positively charged negative element from group V or VI of the periodic table ( E.G., N, O, S, P) is bonded to a carbon atom having an unshared pair of electrons; y. have been observed in a number of enzyme-catalyzed reactions.

The state of a genetic factor (gene) being borne on the Y chromosome. This idea is analogous with X-linkage, but since the Y chromosome does not fully take part in chiasma formation and recombination, it is not amenable to analysis by conventional linkage methods. Little is known about its content. There is a gene for the H-Y antigen, and indirect arguments suggest that there is a principle that determines the formation of the testis and masculinization of the fetus but its localization, though narrowing the limits, remains elusive.

yogurt, yoghurt (yo′gert)
Fermented, partially evaporated, whole milk prepared by maintaining it at 50°C for 12 hours after the addition of a mixed culture of Lactobacillus bulgaricus, L. acidophilus, and Streptococcus lactis; used as a food. [Turkish]

yohimbine (yo-him′ben)
An alkaloid, the active principle of yohimbé, the bark of Corynanthe yohimbi (family Rubiaceae); it produces a competitive blockade, of limited duration, of adrenergic α-receptors; has also been used for its alleged aphrodisiac properties.

yoke (yok) [TA]
SYN: jugum (1) . [A.S. geoc] alveolar yokes [TA] one of the eminences on the outer surface of the alveolar process of the maxilla or mandible, formed by the roots of the incisor teeth. SYN: juga alveolaria [TA] . sphenoidal y. jugum sphenoidale.

yolk (yok, yolk)
1. One of the types of nutritive material stored in the ovum for the nutrition of the embryo; y. is particularly abundant and conspicuous in the eggs of birds. SYN: vitellus. 2. Fatty material found in the wool of sheep; when extracted and purified, it becomes lanolin. [A.S. geolca; geolu, yellow] white y. y. consisting of much finer particles than those of yellow y.; thin layers of it lie between the zones of yellow y. and form the latebra. yellow y. the chief constituent of the y. in a bird's egg; it consists of relatively coarse particles of stored food materials and is laid down in concentric zones with interposed thin layers of white y..

Yorke autolytic reaction
See under reaction.

William John, 20th century Australian biochemist. See Harden-Y. ester.

Thomas, English physician and physicist, 1773–1829. See Y. modulus, Y. rule, Y.-Helmholtz theory of color vision.

Hugh H., U.S. urologist, 1870–1945. See Y. prostatic tractor.

Abbreviation for years of potential life lost, under year.

ypsiliform (ip′si-li-form)
SYN: hypsiloid. [G. ypsilon, upsilon, the letter u or y, + L. forma, form]

ytterbium (Yb) (i-ter′be-um)
A metallic element of the lanthanide group; atomic no. 70, atomic wt. 173.04. 169Yb, with a half-life of 32.03 days, has been used in cisternography and in brain scans. [Ytterby, village in Sweden]

yttrium (Y) (it′re-um)
A metallic element, atomic no. 39, atomic wt. 88.90585. [Ytterby, village in Sweden]

An artificial radioactive isotope with a physical half-life of 2.67 days, which decays with the emission of a 2.282 MeV β particle; used as an implant in pituitary ablation.

Paul, French physician and chemist, 1848–1913. See Y. test.


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