Medical Dictionary

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asteroid (as′te-royd)
Resembling a star. [G. aster, star, + eidos, resemblance]

asthenia (as-the′ne-a)
Weakness or debility. SYN: adynamia (1) . [G. astheneia, weakness, fr. a- priv. + sthenos, strength] neurocirculatory a. an obsolete term for a type of anxiety neurosis formerly encountered often among military personnel during times of war, in which cardiorespiratory symptoms, such as palpitation, rapid pulse, and precordial pain, were prominent.

asthenic (as-then′ik)
1. Relating to asthenia. 2. Denoting a thin, delicate body habitus.

asthenopia (as-the-no′pe-a)
Subjective symptoms of ocular fatigue, discomfort, lacrimation, and headaches arising from use of the eyes. SYN: eyestrain. [G. astheneia, weakness, + ops, eye] accommodative a. a. due to errors of refraction and excessive contraction of the ciliary muscle. muscular a. a. due to imbalance of the extrinsic ocular muscles. nervous a. a. due to functional or organic nervous disease.

asthenopic (as-the-nop′ik)
Relating to or suffering from asthenopia.

asthenospermia (as-the-no-sper′me-a)
SYN: asthenozoospermia. [G. astheneia, weakness, + sperma, seed, semen]

asthenozoospermia (as′the-no-zo-o-sperm′e-a)
Loss or reduction of mobility of the spermatozoa, frequently associated with infertility. SYN: asthenospermia. [G. astheneia, weakness + zoos, living, + sperma, seed, semen, + -ia]

asthma (az′ma)
An inflammatory disease of the lungs characterized by reversible (in most cases) airway obstruction. Originally, a term used to mean “difficult breathing”; now used to denote bronchial a.. SYN: reactive airway disease. [G.] atopic a. bronchial a. due to atopy. bronchial a. an acute or chronic disorder characterized by widespread and largely reversible reduction in the caliber of bronchi and bronchioles, due in varying degrees to smooth muscle spasm, mucosal edema, and excessive mucus in the lumens of airways; cardinal symptoms are dyspnea, wheezing, and cough; attacks or exacerbations may be induced by airborne allergens ( e.g., molds, pollens, animal dander, dust mite and cockroach antigens), inhaled irritants ( e.g., cold air, cigarette smoke, ozone), physical exercise, respiratory infection, psychological stress, or other factors; the signs and symptoms of bronchial a. are caused by the local release of spasmogens and inflammatory mediators (histamines, leukotrienes, prostaglandins) and other substances from mast cells, eosinophils, lymphocytes, neutrophils, and epithelial cells; airway caliber may be abruptly and drastically reduced during a paroxysm or after diagnostic challenge with methacholine or histamine, and may quickly return to normal after administration of a bronchodilator (inhaled β-adrenergic agonist or subcutaneous epinephrine).A. is a common disease, with an incidence of about 5% in the U.S., and a leading cause of disease and disability in persons between 2 and 17 years of age. It is responsible for 14.5 million outpatient visits and 5000 deaths yearly in this country. From 1980 to 1994 the prevalence of a. increased 75%; the greatest increase (160%) occurred in children under age 5. A. first occurring in childhood is more likely to be allergic in origin and to show seasonal variation. Chronic sinusitis and gastroesophageal reflux disease are statistically correlated with a.. A subset of people with allergic a. also have nasal polyps and sensitivity to aspirin and most other nonsteroidal antiinflammatory drugs. Occupational exposure to airborne irritants or allergens is increasingly recognized as a cause of chronic a. in adults. Current views of the pathophysiology of a. emphasize its inflammatory component and the risk of gradual, irreversible airway remodeling due to subepithelial fibrosis in poorly controlled a.. Current recommendations for treatment of chronic or severe a. call for use of antiinflammatory drugs (particularly inhaled corticosteroids). Other treatments include β2-adrenergic bronchodilators (albuterol, terbutaline, salmeterol), xanthines (theophylline, oxtriphylline, dyphylline), mast cell stabilizers (cromolyn, nedocromil), and antileukotrienes (montelukast, zafirlukast, zileuton). Self-monitoring of peak respiratory flow rate with a simple portable device helps patients adjust drug doses for optimum effect. Avoidance of allergens, irritants, and other known triggers is essential to good control. bronchitic a. a. precipitated by bronchitis. SYN: catarrhal a.. cardiac a. an asthmatic attack, the bronchoconstriction being secondary to the pulmonary congestion and edema of left ventricular failure. catarrhal a. SYN: bronchitic a.. cotton-dust a. SYN: byssinosis. dust a. a. aggravated by inhalation of dust, especially seen as occupational disease resulting from cotton dust. extrinsic a. bronchial a. resulting from an allergic reaction to foreign substances, such as inhaled particles, vapors, or gases, or ingested foods, beverages, or drugs. food a. a. caused by allergic reaction to a dietary item. hay a. an asthmatic stage of hay fever. intrinsic a. bronchial a. in which no extrinsic causes can be identified, and which is assumed to be due to an endogenous process, possibly allergic. miller a. a. caused by flour or grain allergens. miner's a. the dyspnea of anthracosis or other pneumoconioses in miners. nervous a. a. precipitated by psychic stress. reflex a. a. occurring as a reflex in disease of the viscera, the nose, or other parts. spasmodic a. a. due to spasm of the bronchioles. steam-fitter's a. a. associated with asbestosis acquired by exposure to asbestos-insulated heating and plumbing components. stripper's a. a. associated with byssinosis. summer a. a. associated with hay fever or allergy to summer vegetation. triad a. syndrome comprising nasal polyps, a., and intolerance to aspirin.

asthmatic (az-mat′ik)
Relating to or suffering from asthma.

asthma-weed
1. SYN: lobelia. 2. SYN: Euphorbia pilulifera.

asthmogenic (az′mo-jen′ik)
Causing asthma.

astigmatic (as′tig-mat′ik)
Relating to or suffering from astigmatism.

astigmatism (a-stig′ma-tizm)
1. A lens or optical system having different refractivity in different meridians. 2. A condition of unequal curvatures along the different meridians in one or more of the refractive surfaces (cornea, anterior or posterior surface of the lens) of the eye, in consequence of which the rays from a luminous point are not focused at a single point on the retina. SYN: astigmia. [G. a- priv. + stigma ( stigmat-), a point] a. against the rule a. when the greater curvature or refractive power is in the horizontal meridian. compound hyperopic a. a. in which all meridians are hyperopic but to different degrees. compound myopic a. a. in which all meridians are myopic but to different degrees. corneal a. a. due to a defect in the curvature of the corneal surface. hyperopic a. that form of a. in which one meridian is hyperopic and the one at a right angle to it is without a refractive error. SYN: simple hyperopic a.. irregular a. a. in which different parts of the same meridian have different degrees of curvature. lenticular a. a. due to defect in the curvature, position, or index of refraction of the lens. mixed a. a. in which one meridian is hyperopic while the one at right angle to it is myopic. myopic a. that form of a. in which one meridian is myopic and the one at right angle to it is without refractive error. SYN: simple myopic a.. a. of oblique pencils an aberration occurring when a bundle of light rays strikes a refracting medium in some other direction than parallel to the axis of the lens. regular a. a. in which the curvature in each meridian is equal throughout its course, and the meridians of greatest and least curvature are at right angles to each other. simple hyperopic a. SYN: hyperopic a.. simple myopic a. SYN: myopic a.. a. with the rule a. when the greater curvature or refractive power is in the vertical meridian.

astigmatometry, astigmometry (a-stig-ma-tom′e-tre, as-tig-mom′e-tre)
Determination of the form and measurement of the degree of astigmatism.

astigmia (a-stig′me-a)
SYN: astigmatism.

astomatous (a-sto′ma-tus)
Without a mouth. SYN: astomous.

astomia (a-sto′me-a)
Congenital absence of a mouth. [G. a- priv. + stoma, mouth]

astomous (a-sto′mus)
SYN: astomatous.

astragalar (as-trag′a-lar)
Relating to the astragalus or talus.

astragalectomy (as-trag-a-lek′to-me)
Removal of the astragalus, or talus. [astragalus, + G. ektome, excision]

astragalocalcanean (as-trag′a-lo-kal-ka′ne-an)
Relating to both the talus (astragalus) and the calcaneus (os calcis).

astragalofibular (as-trag′a-lo-fib′u-lar)
Relating to both the talus (astragalus) and the fibula.

astragaloscaphoid (as-trag′a-lo-scaf′oyd)
SYN: talonavicular.

astragalotibial (as-trag′a-lo-tib′e-al)
Relating to both the talus (astragalus) and the tibia.

Astragalus (as-trag′a-lus)
A genus of plants (family Leguminosae), notably A. mollissimus (locoweed) on the range lands of western North America, capable of taking selenium from the soil and causing poisoning in sheep, cattle, and horses. A. gummifer is a source of tragacanth.

astral (as′tral)
Relating to an astrosphere.

astrapophobia (as′tra-po-fo′be-a)
Morbid fear of lightning. [G. astrape, lightning, + phobos, fear]

astriction (as-trik′shun)
1. Astringent action. 2. Compression to arrest hemorrhage.

astringent (as-trin′jent)
1. Causing contraction or shrinkage of the tissues, arrest of secretion, or control of bleeding. 2. An agent having these effects. [L. astringens]

astroblast (as′tro-blast)
A primitive cell developing into an astrocyte. [G. astron, star, + blastos, germ]

astroblastoma (as′tro-blas-to′ma)
A relatively poorly differentiated glioma composed of young, immature, neoplastic cells of the astrocytic series, frequently arranged radially with short fibrils terminating on small blood vessels. [astro- + G. blastos, germ, + -oma, tumor]

astrocele (as′tro-sel)
SYN: centrosphere. [G. astron, star, + koilia, hollow]

astrocyte (as′tro-sit)
One of the large neuroglia cells of nervous tissue. SEE ALSO: neuroglia. SYN: astroglia cell, astroglia, Cajal cell (2) , Deiters cells (2) , macroglia cell, macroglia, spider cell (1) . [G. astron, star, + kytos, hollow (cell)] Alzheimer type I a. enlarged frequently multinucleated astrocytes, seen in progressive multifocal leukoencephalopathy. Alzheimer type II a. enlarged astrocytes with vesicular nuclei and one or more small basophilic nucleoli, seen in hepatocerebral disease and Wilson disease. fibrillary a., fibrous a. stellate astrocytic cell with long processes found mainly in the white matter of the brain and spinal cord and characterized by having bundles of glial filaments in its cytoplasm; origin of most astrocytomas. gemistocytic a. a round to oval a. cell with abundant cytoplasm containing glial filaments and an eccentric nucleus; may contain two nuclei in the cell; hypertrophy of astrocytes. SYN: gemistocyte, gemistocytic cell, reactive a., reactive cell. protoplasmic a. one form of a., found mainly in gray matter, having few fibrils and numerous branching processes. reactive a. SYN: gemistocytic a..

astrocytoma (as′tro-si-to′ma)
A glioma derived from astrocytes. [G. astron, star, + kytos, cell, + -oma, tumor] anaplastic a. intermediate grade a. characterized by increased cellularity, nuclear pleomorphism, mitoses, and variable vascular endothelial proliferation. cerebellar a. a variant of a. located in the cerebellum occurring mostly in children, consists of two architectural patterns on microscopy including a loose reticular pattern and a more compact often spindled cell pattern. SYN: juvenile cerebellar a.. desmoplastic cerebral a. a rare variant of a. most frequently occurring in infancy, the tumor has a spindled cell appearance. fibrillary a. a. derived from fibrillary astrocytes. gemistocytic a. an a. composed primarily of gemistocytic-type astrocytes. SYN: gemistocytoma. grade I a. solid or cystic a. of low grade; World Health Organization (WHO) designation including pilocytic a. and other low-grade a. variants. grade II a. a. of low grade; World Health Organization (WHO) designation including well-differentiated fibrillary a.. grade III a. a. of intermediate grade; World Health Organization (WHO) designation. SEE ALSO: anaplastic a.. grade IV a. a. of high grade; World Health Organization (WHO) designation. SEE ALSO: glioblastoma multiforme. juvenile cerebellar a. SYN: cerebellar a.. low grade a. a. characterized by an increased cellularity of uneven distribution and mild nuclear pleomorphism. pilocytic a. a slowly growing a. composed histologically of elongated astrocytes; often located in the optic chiasm region of the third ventricle, hypothalamus, or cerebellum, predominantly in younger individuals. SYN: piloid a.. piloid a. SYN: pilocytic a.. protoplasmic a. a neoplasm composed primarily of protoplasmic-type astrocytes. subependymal giant cell a. a rare a., frequently located in the wall of the lateral ventricle, comprised of large glial cells with abundant eosinophilic cytoplasm and intermixed elongated astrocytes, associated with tuberous sclerosis.

astrocytosis (as′tro-si-to′sis)
An increase in the number of astrocytes, frequently observed in an irregular, poorly or moderately well-defined zone adjacent to degenerative lesions ( e.g., encephalomalacia), focal inflammations ( e.g., abscesses), or certain neoplasms in the brain; in some instances, a. may be diffuse in a relatively large region; a. represents a reparative mechanism. a. cerebri SYN: gliomatosis cerebri.

astroependymoma (as′tro-e-pen′di-mo′ma)
A glial neoplasm composed of a mixed population of astrocytic and ependymal cells.

astroglia (as-trog′le-a)
SYN: astrocyte. [G. astron, star, + neuroglia]

astroid (as′troyd)
Star-shaped. [G. astroeides, fr. astron, star, + eidos, resemblance]

astrokinetic (as′tro-ki-net′ik)
Relating to movement of the centrosome and astrosphere of a dividing cell. [G. astron, star, + kinesis, movement]

astrosphere (as′tro-sfer)
A set of radiating microtubules extending outward from the cytocentrum and centrosphere of a dividing cell. SYN: aster, attraction sphere, Lavdovsky nucleoid, paranuclear body. [G. astron, star, + sphaira, ball]

Astrovirus (as-′ro-vi′rus)
A small RNA virus and the only genus in the family Astroviridae; it is associated with diarrhea and is detected in the feces of numerous animals.

Astrup
Poul, Danish clinical chemist, *1915. See micro-A. method.

Astwood
Edwin B., U.S. endocrinologist, 1909–1976. See A. test.

asverin (as′ver-in)
An antitussive.

Asx
Symbol meaning Asp or Asn.

asyllabia (a-si-la′be-a)
Form of alexia in which one recognizes individual letters, but cannot comprehend them when arranged collectively in syllables or words. [G. a- priv. + syllable, syllable]

asylum (a-si′lum)
Old term for an institution for the housing and care of those who by reason of age or mental or bodily infirmities are unable to care for themselves. [L. fr. G. asylon, a sanctuary, fr. a- priv. + syle, right of seizure]

asymbolia (a-sim-bo′le-a)
A form of aphasia in which the significance of signs and symbols is not appreciated. SYN: sight blindness. [G. a- priv. + symbolon, an outward sign]

asymmetric (a) (a-sim-et′rik)
Not symmetric; denoting a lack of symmetry between two or more like parts.

asymmetry (a-sim′e-tre)
1. Lack of symmetry; disproportion between two normally alike parts. 2. Significant difference in amplitude or frequency of EEG activity recorded simultaneously from the two sides of the brain under identical conditions. SYN: dissymmetry.

asymptomatic (a′simp-to-mat′ik)
Without symptoms, or producing no symptoms.

asymptotic (a′simp-tot′ik)
Pertaining to a limiting value, for example of a dependent variable, when the independent variable approaches zero or infinity.

asynclitism (a-sin′kli-tizm)
Absence of synclitism or parallelism; may be used, e.g., to refer to the axis of the presenting part of the child and the pelvic planes in childbirth, to the dental arches, or to the planes of the skull. SYN: obliquity. [G. a- priv. + syn-klino, to incline together] anterior a. SYN: Nägele obliquity. posterior a. SYN: Litzmann obliquity. a. of the skull SYN: plagiocephaly.

asynechia (a-si-nek′e-a)
Discontinuity of structure. [G. a- priv. + synecheia, continuity]

asynergia (a-sin-er′je-a)
SYN: asynergy. [G. a- priv. + syn, with, + ergon, work]

asynergic (a′sin-er′jik)
Characterized by asynergy.

asynergy (a-sin′er-je)
Lack of coordination among various muscle groups during the performance of complex movements, resulting in loss of skill and speed. When severe, results in decomposition of movement, wherein complex motor acts are performed in a series of isolated movements; caused by cerebellar disorders. SYN: asynergia.

asynesia, asynesis (a-si-ne′ze-a, -ne′sis)
Lack of easy comprehension and practical intelligence. [G. a- priv. + synesis, union, understanding]

asystematic (a′sis-te-mat′ik)
Not systematic; not relating to one system or set of organs.

asystole (a-sis′to-le)
Absence of contractions of the heart. SYN: asystolia, cardiac standstill. [G. a- priv, + systole, a contracting]

asystolia (a-sis-to′le-a)
SYN: asystole.

asystolic (a-sis-tol′ik)
1. Relating to asystole. 2. Not systolic.

AT
Abbreviation for the adenine-thymine hydrogen-bonded base pair observed in double-stranded polynucleotides.

At
Symbol for astatine.

ata
Abbreviation for atmosphere absolute.

atabrine hydrochloride (a′te-brin)
SYN: quinacrine hydrochloride.

atactilia (a-tak-til′e-a)
Loss of the sense of touch. [G. a- priv. + L. tactilis, relating to touch, fr. tango, pp. tactus, to touch]

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