reaction /re·ac·tion/ (-ak´shun)
1. opposite action, or counterreaction; the response to stimuli.
2. a phenomenon caused by the action of chemical agents; a chemical process in which one substance is transformed into another substance or other substances.
3. the mental and/or emotional state that develops in any particular situation.
acrosome reaction structural changes and liberation of acrosomal enzymes occurring in spermatozoa in the vicinity of an oocyte, facilitating entry into the oocyte.
alarm reaction the physiologic effects (increase in blood pressure, cardiac output, blood flow to skeletal muscles, rate of glycolysis, and blood glucose concentration; decrease in blood flow to viscera) mediated by sympathetic nervous system discharge and release of adrenal medullary hormones in response to stress, fright, or rage.
allergic reaction hypersensitivity r.
, sometimes specifically a type I hypersensitivity reaction.
anaphylactoid reaction one resembling generalized anaphylaxis but not caused by IgE-mediated allergic reaction.
antibody-mediated hypersensitivity reaction
2. occasionally, any hypersensitivity reaction in which antibodies are the primary mediators, i.e., types I–III.
antigen-antibody reaction the reversible binding of antigen to homologous antibody by the formation of weak bonds between antigenic determinants on antigen molecules and antigen binding sites on immunoglobulin molecules.
a reaction characterized by abnormal apprehension or uneasiness; see also anxiety disorders,
Arias-Stella reaction nuclear and cellular hypertrophy of the endometrial epithelium, associated with ectopic pregnancy.
cross reaction the interaction of an antigen with an antibody formed against a different antigen with which the first antigen shares identical or closely related antigenic determinants.
delayed hypersensitivity reaction
, delayed-type hypersensitivity reaction
that taking 24 to 72 hours to develop and mediated by T lymphocytes rather than by antibodies; usually denoting the subset of type IV hypersensitivity reactions involving cytokine release and macrophage activation, as opposed to direct cytolysis, but sometimes used more broadly, even as a synonym for type IV hypersensitivity r.
(see Gell and Coombs classification,
reaction of degeneration the reaction to electrical stimulation of muscles whose nerves have degenerated, consisting of loss of response to a faradic stimulation in a muscle, and to galvanic and faradic stimulation in the nerve.
foreign body reaction a granulomatous inflammatory reaction evoked by the presence of exogenous material in the tissues, characterized by the formation of foreign body giant cells.
hemiopic pupillary reaction in certain cases of hemianopia, light thrown upon one side of the retina causes the iris to contract, while light thrown upon the other side arouses no response.
one in which the body mounts an exaggerated or inappropriate immune response to a substance perceived as foreign, resulting in local or general tissue damage. Such reactions are usually classified as types I–IV
on the basis of the Gell and Coombs classification
id reaction a secondary skin eruption occurring in sensitized patients as a result of circulation of allergenic products from a primary site of infection.
immediate hypersensitivity reaction 2.
occasionally, any hypersensitivity reaction
mediated by antibodies and developing rapidly, generally in minutes to hours (i.e., types I–III
), as distinguished from those mediated by T lymphocytes and macrophages and requiring days to develop (type IV,
or delayed hypersensitivity r.
Jarisch-Herxheimer reaction a transient immunologic reaction following antibiotic treatment of early and later stages of syphilis and certain other diseases, marked by fever, chills, headache, myalgia, and exacerbation of cutaneous lesions; due to release of toxic or antigenic substances by the infecting microorganisms.
Jones-Mote reaction a mild skin reaction of the delayed (type IV) hypersensitivity type occurring after challenge with protein antigens.
late phase reaction
an IgE-mediated immune reaction occurring 5 to 8 hours after exposure to antigen, after the wheal and flare reactions of immediate hypersensitivity
have diminished, with inflammation peaking around 24 hours, and then subsiding.
lengthening reaction reflex elongation of the extensor muscles which permits flexion of a limb.
leukemoid reaction a peripheral blood picture resembling that of leukemia or indistinguishable from it on the basis of morphologic appearance alone; seen in certain infectious diseases, inflammatory conditions, and intoxications.
Neufeld's reaction swelling of the capsules of pneumococci, seen under the microscope, on mixture with specific immune serum, owing to the binding of antibody with the capsular polysaccharide.
Pirquet reaction appearance of a papule with a red areola 24 to 48 hours after introduction of two small drops of Old tuberculin by slight scarification of the skin; a positive test indicates previous infection.
polymerase chain reaction (PCR) a rapid technique for in vitro amplification of specific DNA or RNA sequences, allowing small quantities of short sequences to be analyzed without cloning.
precipitin reaction the formation of an insoluble precipitate by reaction of antigen and antibody.
redox reaction a reaction oxidizing one substrate while reducing another.
Schultz-Charlton reaction disappearance of scarlet fever rash around the site of an injection of scarlet fever antitoxin.
startle reaction the various psychophysiological phenomena, including involuntary motor and autonomic reactions, evidenced by an individual in reaction to a sudden, unexpected stimulus, as a loud noise.
stress reaction any physiological or psychological reaction to physical, mental, or emotional stress that disturbs the organism's homeostasis.
Weil-Felix reaction agglutination by blood serum of typhus patients of a bacillus of the proteus group from the urine and feces.
wheal and erythema reaction , wheal and flare reaction a cutaneous sensitivity reaction to skin injury or administration of antigen, due to histamine production and marked by edematous elevation and erythematous flare.
1. opposite action or counteraction; the response of a part to stimulation.
2. the phenomena caused by the action of chemical agents; a chemical process in which one substance is transformed into another substance or substances.
one which is self-propagating; a chemical process in which each time a free radical is destroyed a new one is formed.
one in which the free energy released by one chemical reaction drives the other reaction.
photosynthetic reaction which fixes CO2 into sugar and which occurs without exposure to light. Called also Calvin cycle.
reaction of degeneration
the reaction to electrical stimulation of muscles whose nerves have degenerated, consisting of loss of response to a faradic stimulation in a muscle, and to galvanic and faradic stimulation in the nerve.
a reaction, such as an allergic reaction, occurring hours to days after exposure to an inducer.
false negative reaction
an erroneously negative reaction to a test.
false positive reaction
an erroneously positive reaction to a test.
2. formation of a papule and areola without development of a vesicle following smallpox vaccination.
reflex elongation of extensor muscles that permits flexion of a limb.
leukemic reaction, leukemoid reaction
a peripheral blood picture resembling leukemia or indistinguishable from it on the basis of morphological appearance alone, characterized by immature leukocytes in the blood.
reaction pattern analysis
designed to replace archaic, non-specific descriptions of the reactions of the skin to noxious influences; recommended categories are (1) perivascular dermatitis, (2) interface dermatitis, (3) vasculitis, (4) nodular and diffuse dermatitis, (5) intradermal vesicular and pustular dermatitis, (6) subepidermal vesicular and pustular dermatitis, (7) perifolliculitis, folliculitis and furunculosis, (8) fibrosing dermatitis, (9) panniculitis, (10) atrophic dermatosis, (11) mixed reaction patterns.
lack of production of by-products in enzymatic reactions with yields of products being nearly 100%.
development of suppurative peritonitis, localized to the scrotal sac, in the guinea pig after the intraperitoneal injection of material containing Burkholderia mallei.
1. alarm reaction.
2. gross stress reaction.
the time elapsing between the application of a stimulus and the resulting reaction.
a cutaneous sensitivity rection to skin injury or administration of antigen, due to histamine production and marked by edematous elevation and erythematous flare.
van den Bergh test, reaction
a test which differentiates between conjugated and unconjugated bilirubin in serum and assists in the differentiation between biliary or regurgitation hyperbilirubinemia, retention or hemolytic hyperbilirubinemia, or combined hyperbilirubinemia or jaundice. There are many variants of the basic test and the interpretation of them differs markedly between the species.
Patient discussion about reaction
Q. what cause an allergic reaction?
A. Frankly? no ones actually knows for sure. What we do know, is that due to some reason the immune system of certain people, regard several non-harmful substances (e.g. peanuts, antibiotics, bee's venom) as an enemy and learn to react to it.
This tendency to develop abnormal responses to substances other people don't response to is called "atopy". It has a very strong genetic basis (i.e. it runs in families), and also depends on other factors such as the exposure to infections and the pattern of exposure to the allergen (the substance that causes allergy).
It's a very wide subject, far beyond the scope of my answer, so you may read more here:
Q. Is it common to get an allergic reaction in the eye from olive harvest? I've been around olive trees for a few hours and now feel like I have something in my eye but there is nothing there. can it be an allergic reaction? I dont get it from eating olives...
A. but in one eye..? that just doesn't seem likely. but i guess there is no reason not to try both treatments....
Q. I am worried about the allergic reactions I had from the Chinese herbal drug. I am worried about the allergic reactions I had from the Chinese herbal drug that I took for my arthritis…..are these safe?
A. Many people have some type of reaction to either a drug and even a supplement. You can check with your doc to get tested to see what your sensitivities are. Regarding arthritis, no milk, cheese, yogurt, butter, anything with milk for starters, AVOID like the plague! Suagr consumption too will raise hell with it. There is a product that someone I knew took, called, "Cell Guard" which he bought at a health food store or Whole Foods. After a couple of months, he was pain free. Its worth a try! Cell Guard is made with SOD or "superoxide dismutase"More discussions about reaction
Studies have shown that SOD can play a critical role in reducing internal inflammation and lessening pain associated with conditions such as arthritis! Check it out! Let me know how you do!