Medical Dictionary

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atloid (at′loyd)
SYN: atlantal.

atlo-occipital (at′lo-ok-sip′i-tal)
SYN: atlanto-occipital.

atm
Symbol for standard atmosphere.

atmo-
Prefix denoting steam or vapor; or derived by action of steam or vapor. [G. atmos, steam, vapor]

atmolysis (at-mol′i-sis)
Separation of mixed gases by passing them through a porous diaphragm, the lighter gases diffusing through at a faster rate. [atmo- + G. lysis, dissolution]

atmometer (at-mom′e-ter)
An instrument for measuring the rate of evaporation. [atmo- + G. metron, measure]

atmos
Obsolete abbreviation for a unit of pressure; replaced by atm. [abbreviation of atmosphere]

atmosphere (at′mos-fer)
1. Any gas surrounding a given body; a gaseous medium. 2. A unit of air pressure equal to 101.325 kPa. SEE ALSO: standard a., torr. [atmo- + G. sphaira, sphere] a. absolute (ata) a unit of absolute pressure (also known as barometric pressure) expressed in atm. ICAO standard a. the standard a. adopted by the International Civil Aviation Organization, used for calibrating altimeters and for expressing hypobaric chamber pressures in terms of equivalent altitude; it ignores many deviations found in nature. standard a. (atm) 1. the pressure of the a. at mean sea level at 273.15 K, equivalent to 1,013,250 dynes/cm2 or 101,325 Pa (N/m2 in the SI system); 2. a standardized expression of the relation of barometric pressure, temperature, and other atmospheric variables as a function of altitude above sea level.

atmospherization (at′mo-sfer-i-za′shun)
Conversion of venous into arterial blood.

Atmungsferment (aht′mungz-fer-ment)
1. A system of cytochromes and their oxidases that participate in respiratory processes. 2. Often, specifically, cytochrome oxidase. SYN: Warburg respiratory enzyme. [Ger.]

atom (at′om)
Once considered the ultimate particle of an element, believed to be as indivisible as its name indicates. Discovery of radioactivity demonstrated the existence of subatomic particles, notably protons, neutrons, and electrons, the first two comprising most of the mass of the atomic nucleus. We now know that subatomic particles are further classified into hadrons, leptons, and quarks. [G. atomos, indivisible, uncut] activated a. an a. possessing more than normal energy as a result of input of energy. SEE ALSO: excited state. SYN: excited a.. Bohr a. a concept or model of the a. in which the negatively charged electrons move in circular or elliptical orbits around the positively charged nucleus, energy being emitted or absorbed when electrons change from one orbit to another. excited a. SYN: activated a.. ionized a. an a. that possesses an electrostatic charge as a result of loss or gain of electrons; e.g., H+, Ca2+, Cl−, O2−. labeled a. a radioactive a., or a stable but rare one, which by its presence in a molecule helps localization or measurement of that molecule. SYN: tagged a.. nuclear a. a concept or model of the a. characterized by the presence of a small, massive nucleus at its center. quaternary carbon a. an a. of carbon to which four other carbon atoms are attached. radioactive a. an a. with an unstable nucleus, which emits particulate or electromagnetic radiation (radioactive emission) to achieve greater stability. See radionuclide, half-life, Becquerel. recoil a. the remainder of an a. from which a nuclear particle has been emitted or ejected at high velocity; the remainder recoils with a velocity inversely proportional to its mass. stripped a. an a. minus all its electrons; a nucleus. tagged a. SYN: labeled a..

atomic (a-tom′ik)
Relating to an atom.

atomism (at′om-izm)
The approach to the study of a psychological phenomenon through analysis of the elementary parts of which it is assumed to be composed. Cf.:holism.

atomistic (at-om-is′tik)
Pertaining to atomism or a. psychology.

atomization (at-om-i-za′-shun)
Spray production; reduction of a fluid to small droplets.

atomizer (at′om-i-zer)
A device used to reduce liquid medication to fine particles in the form of a spray or aerosol; useful in delivering medication to the lungs, nose, and throat. SEE ALSO: nebulizer, vaporizer. [G. atomos, indivisible particle]

atonia (a-to′ne-a)
SYN: atony. [G. languor]

atonic (a-ton′ik)
Relaxed; without normal tone or tension.

atonicity (at-o-nis′i-te)
SYN: atony.

atony (at′o-ne)
Relaxation, flaccidity, or lack of tone or tension. SYN: atonia, atonicity. [G. atonia, languor] postpartum a. a. of the uterine walls after childbirth. SYN: metratonia. uterine a. failure of the myometrium to contract after delivery of the placenta; associated with excessive bleeding from the placental implantation site.

atopen (at′o-pen)
An old term to denote the excitant causing any form of atopy.

atopic (a-top′ik)
1. Relating to or marked by atopy. 2. Allergic. [G. atopos, out of place; strange]

Atopobium (at-o-po′be-um)
An obligatorily anaerobic genus of Gram-positive, non–spore-bearing bacteria that appear as cocci and coccobacilli, sometimes in short chains. The type species is A. parvulus, a slow-growing organism forming tiny colonies on standard media formerly called Peptostreptococcus parvulus and Streptococcus parvulus.

atopognosia, atopognosis (a-top-og-no′ze-a, -og-no′sis)
Sensory inattention; inability to locate a sensation properly. Usually caused by a contralateral parietal lobe lesion. [G. a- priv. + topos, place, + gnosis, knowledge]

atopy (at′o-pe)
A genetically determined state of hypersensitivity to environmental allergens. Type I allergic reaction is associated with the IgE antibody and a group of diseases, principally asthma, hay fever, and atopic dermatitis. [G. atopia, strangeness, fr. a- priv. + topos, a place]

atoxic (a-tok′sik)
Not toxic.

ATP
Abbreviation for adenosine 5′-triphosphate.

ATPase
Abbreviation for adenosine triphosphatase.

ATP citrate lyase
See ATP citrate (pro-3S)-lyase.

ATPD
Symbol indicating that a gas volume has been expressed as if it had been dried at the ambient temperature and pressure.

ATP-diphosphatase
SYN: apyrase.

ATPS
Symbol indicating that a gas volume has been expressed as if it were saturated with water vapor at the ambient temperature and barometric pressure; the condition of an expired gas equilibrated in a spirometer.

ATP sulfurylase
SYN: sulfate adenylyltransferase.

atractosylidic acid (a-trak′to-sil-id′ik)
SYN: atractyligenin.

atractylic acid (a-trak′til-ik)
A highly poisonous steroid glycoside from Atractylis gummifera L. (Compositae), having a strychnine-like action that produces convulsions of a hypoglycemic nature; the aglycon, atractyliginin, is combined with glucose and isovaleric acid, and is the toxic principle. A. interferes with oxidative reactions, the citric acid cycle, and nerve conduction.

atractyligenin (a-trak′til-i-jen′in)
The steroid aglycon and toxic principle of atractylic acid. SYN: atractosylidic acid, atractylin.

atractylin (a-trak′til-in)
SYN: atractyligenin.

atracurium besylate (a-tra-kur′e-um)
A nondepolarizing neuromuscular relaxant of intermediate duration of action; used as an adjunct to general anesthesia; a curare-like agent.

atrepsy (a-trep′se)
SYN: athrepsia (2) . [G. a- priv. + trepho, to nourish]

atresia (a-tre′ze-a)
Congenital absence of a normal opening or normally patent lumen. SYN: clausura. [G. a- priv. + tresis, a hole] anal a., a. ani congenital absence of an anal opening due to the presence of a membranous septum (persistence of the cloacal membrane) or to complete absence of the anal canal. SYN: imperforate anus, proctatresia. aortic a. congenital absence of the valvular orifice into the aorta. biliary a. a. of the major bile ducts, causing cholestasis and jaundice, which does not become apparent until several days after birth; periportal fibrosis develops and leads to cirrhosis, with proliferation of small bile ducts unless these are also atretic; giant cell transformation of hepatic cells also occurs. Cf.:neonatal hepatitis. bronchial a. severe focal narrowing or obliteration of a segmental, subsegmental, or lobar bronchus, usually associated with distal air trapping and bronchial mucoid impaction distal to the obstruction. choanal a. a. due to congenital failure of one or both choanae to open owing to the failure of the bucconasal membrane to involute. It results in nasal obstruction and creates an emergency in newborns since they are obligatory nasal breathers. esophageal a. congenital failure of the full esophageal lumen to develop; often associated with tracheoesophageal fistula. a. folliculi a normal process affecting the primordial ovarian follicles in which death of the ovum results in cystic degeneration followed by cicatricial closure. intestinal a. an obliteration of the lumen of the small intestine, with the ileum involved in 50% of cases and the jejunum and duodenum next in frequency; most frequent cause of intestinal obstruction in the newborn; etiology may be related to a failure of recanalization during early development or to some impairment of blood supply during intrauterine life. a. iridis congenital absence of the pupillary opening. SYN: atretopsia. laryngeal a. congenital failure of the laryngeal opening to develop, resulting in partial or total obstruction at or just above or below the glottis. pulmonary a. congenital absence of the pulmonary valve orifice. pulmonary artery a. absence of one, usually the right, pulmonary artery. tricuspid a. congenital lack of the tricuspid orifice. vaginal a. congenital or acquired imperforation or occlusion of the vagina, or adhesion of the walls of the vagina. SYN: colpatresia.

atresic (a-tre′zik)
SYN: atretic.

atretic (a-tret′ik)
Relating to atresia. SYN: atresic, imperforate.

atreto-
Lack of an opening. [G. atretos, imperforate fr. a-, not + tretos, perforated, fr. tetraino, titremi, to bore through, to pierce.]

atretoblepharia (a-tre′to-ble-far′e-a)
SYN: symblepharon. [atreto- + G. blepharon, eyelid]

atretocystia (a-tre′to-sis′te-a)
Obsolete term for congenital or acquired absence of an opening of a bladder. [atreto- + G. kystis, bladder]

atretogastria (a-tre′to-gas′tre-a)
Congenital absence of an opening of the stomach. [atreto- + G. gaster, stomach]

atretopsia (a-tre-top′se-a)
SYN: atresia iridis. [atreto- + G. ops, eye]

atria (a′tre-a) [TA]
Plural of atrium.

atrial (a′tre-al)
Relating to an atrium.

atrichia (a-trik′e-a)
Absence of hair, congenital or acquired. SYN: atrichosis. [G. a- priv. + thrix (trich-), hair]

atrichosis (at-ri-ko′sis)
SYN: atrichia.

atrio-
The atrium; atrial. [L. atrium, an entrance hall]

atriomegaly (a′tre-o-meg′a-le)
Enlargement of the atrium. [atrio- + G. megas, great]

atrionector (a-tre-o-nek′ter, -tor)
SYN: sinuatrial node. [atrio- + L. necto, to join]

atriopeptin (a′tre-o-pep′tin)
SYN: atrial natriuretic peptide. [atrio- + peptide + suffix -in, material]

atrioseptoplasty (a′tre-o-sep′to-plas-te)
Surgical repair of an atrial septal defect. [atrio- + L. septum, partition, + G. plastos, formed]

atrioseptostomy (a′tre-o-sep-tos′to-me)
SYN: atrial septostomy. [atrio- + L. septum, partition, + G. stoma, mouth] balloon a. tearing or enlarging the foramen ovale by pulling a balloon-bearing catheter across the atrial septum for the purpose of augmenting interatrial mixing of blood in the treatment of cyanotic congenital heart disease.

atriotomy (a-tre-ot′o-me)
Surgical opening of an atrium. [atrio- + G. tome, incision]

atrioventricular (AV) (a′tre-o-ven-trik′u-lar)
Relating to both the atria and the ventricles of the heart, especially to the ordinary, orthograde transmission of conduction or blood flow.

atriplicism (a-trip′li-sizm)
An intoxication caused by the ingestion of certain species of Atriplex, eaten as greens in China; it is marked by pain and swelling of the fingers, spreading to the forearm; bullae and ulcers form, and the fingers may become gangrenous. [L. atriplex (-plic-), the orach, a vegetable]

atrium, pl .atria (a′tre-um, a′tre-a)
1. [TA] A chamber or cavity to which are connected several chambers or passageways. 2. SYN: a. of heart. 3. That part of the tympanic cavity that lies immediately deep to the eardrum. 4. SYN: a. of middle nasal meatus. 5. In the lung, a subdivision of the alveolar duct from which alveolar sacs open. [L. entrance hall] accessory a. SYN: cor triatriatum. a. cordis [TA] SYN: a. of heart. a. cordis dextrum [TA] SYN: right a. of heart. a. cordis sinistrum [TA] SYN: left a. of heart. a. dextrum cordis SYN: right a. of heart. a. glottidis SYN: vestibule of larynx. a. of heart [TA] the upper chamber of each half of the heart. SYN: a. cordis [TA] , a. (2) . a. of lateral ventricle [TA] portion of lateral ventricle of brain common to the frontal, occipital, and temporal horns. SYN: a. ventriculi lateralis [TA] , a. ventriculus lateralis [TA] . a. of lateral ventricle [TA] that portion of the lateral ventricle where the body (or central part), posterior horn, and temporal horn converge; it contains the choroid enlargement. left a. of heart [TA] a. of the left side of the heart which receives the blood from the pulmonary veins. SYN: a. cordis sinistrum [TA] , a. pulmonale, a. sinistrum cordis. a. meatus medii SYN: a. of middle nasal meatus. a. meatus medii nasalis [TA] SYN: a. of middle nasal meatus. a. of middle nasal meatus [TA] the anterior expanded portion of the middle meatus of the nose, just above the vestibule. SYN: a. meatus medii nasalis [TA] , a. meatus medii, a. (4) , nasal a.. nasal a. SYN: a. of middle nasal meatus. a. pulmonale SYN: left a. of heart. right a. of heart [TA] right a., the a. of the right side of the heart that receives the blood from the venae cavae and coronary sinus. SYN: a. cordis dextrum [TA] , a. dextrum cordis. a. sinistrum cordis SYN: left a. of heart. a. ventriculi lateralis [TA] SYN: a. of lateral ventricle. a. ventriculus lateralis [TA] SYN: a. of lateral ventricle.

Atropa (at′ro-pa)
A genus of plants (family Solanaceae) of which A. belladonna is typical. See belladonna. [G. Atropos, one of the Fates cutting the thread of life, because of the lethal effects of the plant]

atrophia (a-tro′fe-a)
SYN: atrophy. [G. fr. a- priv. + trophe, nourishment] a. cutis SYN: atrophoderma. a. maculosa varioliformis cutis SYN: anetoderma. a. pilorum propria a general term that includes fragilitas crinium, trichorrhexis nodosa, monilethrix, and atrophy of the hair.

atrophic (a-trof′ik)
Denoting atrophy.

atrophie blanche (a′tro-fi blahnsh′)
Small smooth ivory-white areas with hyperpigmented borders and telangiectasis, developing into atrophic stellate scars; seen especially on the legs and ankles of middle-aged women, and associated with livedo reticularis and dermal hyalinizing vasculitis. [Fr.]

atrophied (at′ro-fed)
Characterized by atrophy.

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