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Medical Dictionary - Dictionary of Medicine and Human Biology


Medical Dictionary


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X
  • Kienböck unit
  • halogen atom
  • power of magnification
  • reactance
  • unspecified amino acid the basic or monoploid number of chromosomes of a polyploid series : the number contained in a single genome
  • xanthosine
X chromosome
a sex chromosome that usually occurs paired in each female cell and single in each male cell in species in which the male typically has two unlike sex chromosomes

Xaa
unspecified amino acid

Xan
xanthine

xanth-
See xantho-.

xanthelasma (zan-the-laz′ma)
SYN: x. palpebrarum. [xanth- + G. elasma, a beaten metal plate] generalized x. xanthoma planum of the neck, trunk, extremities, and eyelids in patients with normal plasma lipid levels. x. palpebrarum soft, yellow-orange plaques on the eyelids or medial canthus, the most common form of xanthoma; may be associated with low-density lipoproteins, especially in younger adults. SYN: x., xanthoma palpebrarum.

xanthematin (zan-them′a-tin)
A yellow substance derived from hematin by treating with nitric acid.

xanthemia (zan-the′me-a)
SYN: carotenemia. [xanth- + G. haima, blood]

xanthene (zan′then)
1. The basic structure of many natural products, drugs, dyes ( e.g., fluorescein, pyronin, eosins), indicators, pesticides, antibiotics, etc. 2. A class of molecules based upon x. (1).

xanthic (zan′thik)
1. Yellow or yellowish in color. 2. Relating to xanthine.

xanthidylic acid (zan′thi-dil-ik)
SYN: xanthosine 5′-monophosphate.

xanthine (Xan) (zan′then)
2,6-Dioxopurine; 2,6-(1H,3H)-purinedione;oxidation product of guanine and hypoxanthine, precursor of uric acid; occurs in many organs and in the urine, occasionally forming urinary calculi; elevated in molybdenum cofactor deficiency and in xanthinuria. x. dehydrogenase an oxidoreductase oxidizing x. to urate with NAD+ as the oxidant; lower activity in individuals with a deficiency of molybdenum cofactor. x. nucleotide SYN: xanthosine 5′-monophosphate. x. oxidase a flavoprotein containing molybdenum; an oxidoreductase catalyzing the reaction of x., O2, and H2O to produce urate and superoxide; also oxidizes hypoxanthine, some other purines and pterins, and aldehydes. A lower activity is observed in molybdenum cofactor deficiency. SYN: hypoxanthine oxidase, Schardinger enzyme. x. ribonucleoside SYN: xanthosine.

xanthinol niacinate, xanthinol nicotinate (zan′thi-nol)
A peripheral vasodilator.

xanthinuria (zan-thi-noo′re-a)
1. Excretion of abnormally large amounts of xanthine in the urine. 2. A disorder [MIM*278300], characterized by urinary excretion of xanthine in place of uric acid, hypouricemia, and occasionally the formation of renal xanthine stones. There are two types: type I is due to xanthine dehydrogenase deficiency (XDH), and type II is due to deficiencies of both xanthine dehydrogenase and aldehyde oxidase. Autosomal recessive inheritance, caused by mutation in the XDH gene on chromosome 2p in some cases. SYN: xanthiuria, xanthuria. [xanthine + G. ouron, urine]

xanthism (zan′thizm) [MIM*278400]
A pigmentary anomaly of blacks, characterized by red or yellow-red hair color, copper-red skin, and often by dilution of iris pigment; autosomal recessive inheritance caused by mutation in the tyrosinase-related protein 1gene (TYRP1) on chromosome 9. SYN: rufous albinism. [G. xanthos, yellowish]

xanthiuria (zan-the-u′re-a)
SYN: xanthinuria.

xantho-, xanth-
Yellow, yellowish. [G. xanthos]

xanthoastrocytoma (zan′thro-as′tro-si-to- ma)
SYN: pleomorphic x.. [xantho + astrocytoma] pleomorphic x. a rare variant of astrocytoma usually presenting early in life with seizures. The tumor is superficially located and composed of pleomorphic glial cells, lipidized astrocytes, and perivascular lymphocytes. SYN: x..

xanthochromatic (zan′tho-kro-mat′ik)
Yellow-colored. SYN: xanthochromic.

xanthochromia (zan-tho-kro′me-a)
The occurrence of patches of yellow color in the skin, resembling xanthoma, but without the nodules or plates. SYN: xanthoderma (1) , yellow disease, yellow skin (1) . [xantho- + G. chroma, color]

xanthochromic (zan-tho-kro′mik)
SYN: xanthochromatic.

xanthoderma (zan-tho-der′ma)
1. SYN: xanthochromia. 2. Any yellow coloration of the skin. SYN: yellow skin (2) . [xantho- + G. derma, skin]

xanthodont (zan′tho-dont)
One who has yellow teeth. [xantho- + G. odous, tooth]

xanthogranuloma (zan′tho-gran′u-lo′ma)
A peculiar infiltration of retroperitoneal tissue by lipid macrophages, occurring most commonly in women. juvenile x. single or multiple reddish to yellow papules or nodules, usually found in young children, consisting of dermal infiltration by histiocytes and Touton giant cells, with increasing fibrosis. SYN: nevoxanthoendothelioma. necrobiotic x. a cutaneous and subcutaneous x. with focal necrosis, presenting as multiple large, sometimes ulcerated, red to yellow granulomatous nodules with giant cells (often around the eyes) associated with paraproteinemia (usually monoclonal gammopathy).

xanthogranulomatous (zan′tho-gran′u-lo′ma-tus)
Relating to, of the nature of, or affected by xanthogranuloma.

xanthoma (zan-tho′ma)

  • a yellow nodule or plaque, especially of the skin, composed of lipid-laden histiocytes. [xantho- + G. -oma, tumor]
  • x. diabeticorum: eruptive x. associated with severe diabetes.
  • x. disseminatum: a rare benign normolipemic disorder of adults with coalescent cutaneous xanthomas composed of non-X histiocytes on flexural surfaces, often with mild diabetes insipidus.
  • eruptive x.: the sudden appearance of groups of 1–4-mm waxy yellow or yellowish-brown papules with an erythematous halo, especially over extensors of the elbows and knees, and on the back and buttocks of patients with severe hyperlipemia, often familial or, more rarely, in severe diabetes.
  • fibrous x.: fibroxanthoma.
  • x. multiplex: xanthomatosis.
  • x. palpebrarum: xanthelasma palpebrarum.
  • x. planum: a form marked by the occurrence of yellow, flat bands or minimally palpable rectangular plates in the corium, either normolipemic or associated with type IIa or III hyperlipoproteinemia.
  • tendinous x.: x. involving tendons, ligaments, and fascia, forming deep, smooth, sometimes painful nodules beneath normal-appearing freely movable skin of the extremities; associated with abnormal lipid metabolism, commonly familial increased β lipoproteins, or obstructive liver disease.
  • x. tuberosum: xanthomatosis associated with familial type II, and occasionally type III, hyperlipoproteinemia. SYN: x. tuberosum simplex.
  • x. tuberosum simplex: x. tuberosum.
  • verrucous x.: histocytosis Y; a papilloma of the oral mucosa and skin in which squamous cell epithelium covers connective tissue papillae filled with large foamy histiocytes. SYN: histiocytosis Y.
xanthomatosis (zan-tho-ma-to′sis)
  • Widespread xanthomas, especially on the elbows and knees, that sometimes affect mucous membranes and are sometimes associated with metabolic disturbances. SYN: lipid granulomatosis, lipoid granulomatosis, xanthoma multiplex.
  • biliary x.: x. with hypercholesterolemia, resulting from biliary cirrhosis, aka Rayer disease.
  • x. bulbi: ulcerative fatty degeneration of the cornea after injury.
  • cerebrotendinous x.: [MIM*213700] a metabolic disorder associated with deposition of cholestanol and cholesterol in the brain and other tissues; plasma cholestanol level is high but plasma cholesterol level is normal; characterized by progressive cerebellar ataxia beginning after puberty, cataracts, spinal cord involvement, premature atherosclerosis, and tendinous or tuberous xanthomata; due to a defect in hepatic mitochondrial sterol 27-hydroxylase in bile acid biosynthesis; autosomal recessive inheritance, caused by mutation in the gene involved in cytochrome P-450 in the C27 position (CYP27) on chromosome 2q.
  • chronic idiopathic x.: vague or indefinite term for inherited abnormalities of lipid metabolism leading to xanthoma formation ( e.g., primary familial x.).
  • familial hypercholesteremic x.: See type II familial hyperlipoproteinemia.
  • generalized plane x.: widespread x. associated with multiple myeloma, familial hyperlipoproteinemia, or less commonly with primary biliary cirrhosis or no underlying disease.
  • normal cholesteremic x.: Hand-Schüller-Christian disease.
  • Wolman x.: cholesterol ester storage disease.
Xanthomonas (zan-tho-mo′as)
Genus of the family Pseudomonadaceae; aerobic, Gram-negative, chemoorganotrophic, straight bacilli that exhibit motility by flagella. Type species is X. campestris. X. maltophilia a species found primarily in clinical specimens but also in water, milk, and frozen food; frequent cause of infections in hospitalized and immunocompromised humans, it is resistant to many commonly used antibiotics; formerly called Pseudomonas maltophilia. See Stenotrophomonas maltophilia.

xanthophyll (zan′tho-fil)
Oxygenated derivative of carotene; a yellow plant pigment, occurring also in egg yolk and corpus luteum. SYN: lutein (2) , luteol, luteole.

xanthoproteic (zan-tho-pro′te-ik)
Relating to xanthoprotein.

xanthoproteic acid
A noncrystallizable yellow substance derived from proteins upon treatment with nitric acid.

xanthoprotein (zan-tho-pro′ten)
The yellow product formed upon treating protein with hot nitric acid, probably from nitration of phenyl groups.

xanthopsia (zan-thop′se-a)
A condition in which objects appear yellow; may occur in picric acid and santonin poisoning, in jaundice, and in digitalis intoxication. SYN: yellow vision. [xantho- + G. opsis, vision]

xanthopuccine (zan-tho-puk′sen)
SYN: canadine.

xanthosine (X, Xao) (zan′tho-sen, -sin)
9-β-d-Ribosylxanthine;the deamination product of guanosine (O replacing –NH2). SYN: xanthine ribonucleoside. x. 5′-monophosphate (XMP) the monophosphoric ester of x.; an intermediate in GMP biosynthesis. SYN: xanthidylic acid, xanthine nucleotide, xanthylic acid. x. 5′-triphosphate (XTP) x. with a triphosphoric acid esterified at its 5′ position.

xanthosis (zan-tho′sis)
A yellowish discoloration of degenerating tissues, especially seen in malignant neoplasms. [xantho- + G. -osis, condition]

xanthous (zan′thus)
Yellowish; yellow-colored. [G. xanthos, yellow]

xanthurenic acid (zan-thoo-ren′ik)
The sulfur-yellow crystals form a red compound with Millon reagent, or an intensely green one with ferrous sulfate; excreted in the urine of pyridoxine-deficient animals after the ingestion of tryptophan, and of rats fed almost exclusively with fibrin.

xanthuria (zan-thoo′re-a)
SYN: xanthinuria.

xanthyl (zan′thil)
A radical consisting of xanthine minus a hydrogen atom.

xanthylic (zan-thil′ik)
Relating to xanthine.

xanthylic acid
SYN: xanthosine 5′-monophosphate.

Xao
Symbol for xanthosine.

Xe
Symbol for xenon.

133Xe
Symbol for xenon-133.

xemilofiban (zem-il-of′i-ban)
A novel antiplatelet agent that blocks the binding of fibrinogen to specific membrane GPIIb/IIIa integrin receptors and thus prevents platelet aggregation induced by any known platelet agonist.

xeno-
Strange; foreign material; parasite. See hetero-, allo-. [G. xenos, guest, host, stranger, foreign]

xenobiotic (zen′o-bi-ot′ik)
1. A pharmacologically, endocrinologically, or toxicologically active substance not endogenously produced and therefore foreign to an organism. 2. Pertaining to association of two animal species, usually insects, in the absence of a dependency relationship, as opposed to parasitism. [xeno- + G. bios, life + -ic]

xenodiagnosis (zen′o-di-ag-no′sis)
1. A method of diagnosing acute or early Trypanosoma cruzi infection (Chagas disease) in humans. Infection-free (laboratory-reared) triatomine bugs are fed on the tissue of the suspected person and the trypanosome is identified by microscopic examination of the intestinal contents of the bug after a suitable incubation period. 2. A similar method of biologic diagnosis based upon experimental exposure of a parasite-free normal host capable of allowing the organism in question to multiply, enabling it to be more easily and reliably detected.

xenogeneic (zen′o-je-ne′ik)
Heterologous, with respect to tissue grafts, especially when donor and recipient belong to widely separated species. SYN: xenogenic (2) , xenogenous (2) . [xeno- + G. -gen, producing]

xenogenic (zen-o-jen′ik)
1. Originating outside of the organism, or from a foreign substance that has been introduced into the organism. SYN: xenogenous (1) . 2. SYN: xenogeneic. [xeno- + G. -gen, producing]

xenogenous (ze-noj′e-nus)
1. SYN: xenogenic (1) . 2. SYN: xenogeneic.

xenograft (zen′o-graft)
A graft transferred from an animal of one species to one of another species. SYN: heterograft, heterologous graft, heteroplastic graft, xenogeneic graft.

xenon (Xe) (ze′non)
A gaseous element, atomic no. 54, atomic wt. 131.29; present in minute proportion (0.087 ppm) in the dry atmosphere; produces general anesthesia in concentrations of 70 vol.%. [G. xenos, a stranger]

xenon-133 (133Xe)
A radioisotope of xenon with a gamma emission at 81 keV and a physical half-life of 5.243 days; used in the study of pulmonary function and organ blood flow.

xenoparasite (zen-o-par′a-sit)
An ecoparasite that becomes pathogenic in consequence of weakened resistance on the part of its host.

xenophobia (zen-o-fo′be-a)
Morbid fear of strangers. [xeno- + G. phobos, fear]

xenophonia (zen-o-fo′ne-a)
A speech defect marked by an alteration in accent and intonation. [xeno- + G. phone, voice]

Xenopsylla (zen-op-sil′a)
The rat flea; a genus of fleas parasitic on the rat and involved in the transmission of bubonic plague. The species X. cheopis serves as a potent vector of Yersinia pestis, largely because its gut becomes “blocked” by a mass of Y. pestis cells that prevents the flea from feeding normally, so that it is inclined to attack humans and other hosts; it is an important source of infection in traditional epidemic areas such as India. X. astia and X. braziliensis are also efficient vectors of plague. [xeno- + G. psylla, flea]

xenyl (zen′il)
A radical consisting of biphenyl minus a hydrogen atom.

xeransis (ze-ran′sis)
A gradual loss of moisture in the tissues. [G. x., fr. xeros, dry]

xerantic (ze-ran′tik)
Denoting xeransis.

xerasia (ze-ra′ze-a)
A condition of the hair characterized by dryness and brittleness. [G. x., fr. xeros, dry]

xero-
Dry. [G. xeros]

xerochilia (zer-o-ki′le-a)
Dryness of lips. [xero- + G. cheilos, lip]

xeroderma (zer′o-der′ma)
  • A mild form of ichthyosis characterized by excessive dryness of the skin due to slight increase of the horny layer and diminished water content of the stratum corneum from decreased perspiration, wind, or low humidity; seen with aging, atopic dermatitis, vitamin A deficiency, etc. [xero- + G. derma, skin]
  • x. pigmentosum: [MIM*278700] an eruption of exposed skin occurring in childhood and characterized by photosensitivity with severe sunburn in infancy and the development of numerous pigmented spots resembling freckles, larger atrophic lesions eventually resulting in glossy white thinning of the skin surrounded by telangiectases, and multiple solar keratoses that undergo malignant change at an early age; results from several rare autosomal recessive complementation groups in which DNA repair processes are defective, so that they are more liable to chromosome breaks and cancerous change when exposed to ultraviolet light. Severe ophthalmic and neurologic abnormalities are also found. SEE ALSO: De Sanctis-Cacchione syndrome.
xerogram (ze′ro-gram)
SYN: xeroradiograph.

xerography (zer-og′ra-fe)
SYN: xeroradiography.




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