| Arias-Stella phenomenon | Focal, unusual, decidual changes in endometrial epithelium, consisting of intraluminal budding, and nuclear enlargement and hyperchromatism with cytoplasmic swelling and vacuolation; may be associated with ectopic or uterine pregnancy. Synonym: Arias-Stella effect, Arias-Stella reaction. (05 Mar 2000) |
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| arm phenomenon | In tetany, spasm both of the extensor muscles of the knee and of the calf muscles when the extended leg is flexed at the hip. Synonym: leg phenomenon, Pool-Schlesinger sign, Schlesinger's sign. In tetany, contraction of the arm muscles following the stretching of the brachial plexus by elevation of the arm above the head with the forearm extended, resembles the contraction resulting from stimulation of the ulnar nerve. Synonym: arm phenomenon. (05 Mar 2000) |
| Arthus phenomenon | A form of immediate hypersensitivity resulting in erythema, oedema, haemorrhage, and necrosis observed in rabbits after injection of antigen to which the animal has already been sensitised and has specific IgG antibodies. The reaction is caused by the inflammation that results from the deposition of antigen-antibody complexes in tissue spaces and in blood vessel walls that activate complement, most of the damage seemingly being due to the polymorphonuclear leukocytes that phagocytise the deposits and release lysosomal enzymes. The phenomenon, described by Arthus, was in rabbits, but similar reactions (Arthus-type reactions) are observed in guinea pigs, rats, and dogs, as well as in humans. See: Arthus reaction. Synonym: Arthus reaction. (05 Mar 2000) |
| Ascher's aqueous influx phenomenon | The filling of the aqueous vein, which normally carries blood and aqueous, with aqueous, when the junction of the aqueous vein and the recipient vein is partially occluded. Synonym: Ascher's aqueous influx phenomenon. (05 Mar 2000) |
| Aschner's phenomenon | A decrease in pulse rate associated with traction on extraocular muscles or compression of the eyeball; especially sensitive in children; may produce asystolic cardiac arrest. Synonym: Aschner's phenomenon, Aschner's reflex, Aschner-Dagnini reflex, oculovagal reflex. (05 Mar 2000) |
| Ashman's phenomenon | Aberrant ventricular conduction of a beat ending a short cycle that is preceded by a longer cycle most commonly during atrial fibrillation. (05 Mar 2000) |
| Aubert's phenomenon | A phenomenon in which a bright perpendicular line appears to incline to one side when the observer turns the head to the opposite side in a dark room. (05 Mar 2000) |
| Austin Flint phenomenon | The murmur of relative mitral stenosis during significant aortic regurgitation owing to narrowing of the mitral orifice by pressure of the aortic regurgitant flow on the anterior mitral leaflet. Synonym: Austin Flint murmur. (05 Mar 2000) |
| autoscopic phenomenon | The encountering of an image of oneself, the image being an illusion, a hallucination, or a vivid fantasy. (05 Mar 2000) |
| Babinski's phenomenon | <clinical sign> Extension of the great toe and abduction of the other toes instead of the normal flexion reflex to plantar stimulation, considered indicative of pyramidal tract involvement ("positive" Babinski). Synonym: Babinski reflex, Babinski's phenomenon, great-toe reflex, paradoxical extensor reflex, toe phenomenon. (05 Mar 2000) |
| Bell's phenomenon | A patient with peripheral facial paralysis cannot close the eyelids of the affected side without at the same time moving the eyeball upward and outward. (05 Mar 2000) |
| Bombay phenomenon | A rare recessive trait at a locus that ordinarily manufactures H substance, the precursor from which the A and B phenotypes are elaborated; the mutant causes failure to produce H substance and no matter what the genotype at the ABO locus, the phenotype is O. The Bombay phenomenon is epistatic to the ABO locus. Origin: Bombay, India, where first reported (05 Mar 2000) |
| Bordet-Gengou phenomenon | The phenomenon of complement fixation; when alexin (complement)-containing serum is added to a mixture of bacteria and specific antibody, the alexin is removed (fixed) and is not available to lyse subsequently added erythrocytes sensitised with specific antibody. See: Gengou phenomenon. (05 Mar 2000) |
| breakaway phenomenon | The occurrence, during high-altitude flight, of a sensation of being totally detached from the earth and from other people. (05 Mar 2000) |
| Brucke-Bartley phenomenon | The sensation of glare in response to successive stimuli at frequencies just below the fusion point. (05 Mar 2000) |