| slow-reacting factor of anaphylaxis | Slow-reacting substance of anaphylaxis (SRS-A), a leukotriene of low molecular weight which is released in anaphylactic shock and produces slower and more prolonged contraction of muscle than does histamine; it is active in the presence of antihistamines (but not epinephrine) and seems not to occur preformed in mast cells, but as a result of an antigen-antibody reaction on the granules. Compare: peptidyl leukotrienes. Synonym: slow-reacting factor of anaphylaxis. (05 Mar 2000) |
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| slow-reacting substance | Slow-reacting substance of anaphylaxis (SRS-A), a leukotriene of low molecular weight which is released in anaphylactic shock and produces slower and more prolonged contraction of muscle than does histamine; it is active in the presence of antihistamines (but not epinephrine) and seems not to occur preformed in mast cells, but as a result of an antigen-antibody reaction on the granules. Compare: peptidyl leukotrienes. Synonym: slow-reacting factor of anaphylaxis. (05 Mar 2000) |
| slow reacting substance of anaphylaxis | <immunology> Potent bronchoconstrictor and inflammatory agent released by mast cells, an important mediator of allergic bronchial asthma. A mixture of three leukotrienes (LTC4 mainly, LTD4 and LTE4) (18 Nov 1997) |
| slow scan | <microscopy> A system of video scanning in which the time used to read each line has been increased in comparison to standard video. The bandwidth needed to faithfully transmit or record the signal is reduced in inverse ratio to the scanning time. Slow scan allows the video signal to be transmitted over a telephone line, or line scans to be registered on a chart recorder. (19 Jan 1998) |
| slow virus | 1. <virology> Specifically one of the Lentivirinae 2. Any virus causing a disease that has a very slow onset. Diseases such as sub acute spongiform encephalopathy, Aleutian disease of mink, scrapie, kuru and Creutzfeldt Jacob disease may be caused by slow viruses. See: prion. (18 Nov 1997) |
| slow virus disease | A disease that follows a slow, progressive course spanning months to years, frequently involving the central nervous system, and ultimately leading to death, such as visna and maedi of sheep, caused by viruses of the subfamily Lentivirinae (family Retroviridae), and subacute sclerosing panencephalitis, seemingly caused by the measles virus; spongiform encephalopathies including kuru of man, scrapie of sheep, and transmissible encephalopathy of mink may also be classified under slow virus disease but their respective aetiologic agents have not been adequately characterised. (05 Mar 2000) |
| slow virus diseases | Diseases of viral origin, characterised by incubation periods of months to years, insidious onset of clinical manifestations, and protracted clinical course. Though the disease process is protracted, viral multiplication may not be unusually slow. Conventional viruses produce slow virus diseases such as subacute sclerosing panencephalitis, progressive multifocal leukoencephalopathy (leukoencephalopathy, progressive multifocal), and aids. Diseases produced by unconventional agents were originally considered part of this group. They are now called prion diseases. (12 Dec 1998) |
| acid wave | A temporary increase in the acidity of the urine occurring during fasting. Synonym: acid wave. (05 Mar 2000) |
| alkaline wave | A period of urinary neutrality or even alkalinity after meals due to withdrawal of hydrogen ion for the purpose of secretion of the highly acid gastric juice. Synonym: alkaline wave. (05 Mar 2000) |
| alpha wave | Brain waves in the encephalogram which have a frequency of 8 to 13 per second. They are typical of the normal person awake and in a quiet resting state, and occur principally in the occipital region. (12 Dec 1998) |
| arterial wave | A wave in the jugular phlebogram due to transmission of carotid artery pulsation. B wave, the initial positive deflection in the electroretinogram, possibly arising from the inner nuclear layer of the retina. (05 Mar 2000) |
| A wave | The initial negative deflection in the electroretinogram, presumably reflecting retinal photoreceptor activity, an atrial deflection in an electrocardiogram recorded from within the atrium of the heart, the first positive deflection of the atrial and venous pulses due to atrial systole. (05 Mar 2000) |
| beta wave | <neurology> Brain waves in the electroencephalogram which have a frequency of 18 to 30 per second. They are typical during periods of intense activity of the nervous system, and occur principally in the parietal and frontal regions. (12 Dec 1998) |
| brain wave | Colloquialism for electroencephalogram. (05 Mar 2000) |
| brain wave complex | A specific combination of fast and slow electroencephalographic activity that recurs frequently enough to be identified as a discrete phenomenon. (05 Mar 2000) |