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Medical Dictionary


dispersoid (dis-per′soyd)
A colloidal solution in which the dispersed phase can be concentrated by centrifugation. SYN: dispersion colloid, molecular dispersed solution.

dispireme (di-spi′rem)
The double chromatin skein in the telophase of mitosis. [G. di-, twice, + speirema, coil, convolution]

displaceability (dis-plas-a-bil′i-te)
The capability of, or susceptibility to, displacement. tissue d. the property of tissue that permits it to be moved from an initial or relaxed position or form. SYN: compression of tissue.

displacement (dis-plas′ment)
1. Removal from the normal location or position. 2. The adding to a fluid (particularly a gas) in an open vessel one of greater density whereby the first is expelled. 3. In chemistry, a change in which one element, radical, or molecule is replaced by another, or in which one element exchanges electric charges with another by reduction or oxidation. 4. In psychiatry, the transfer of impulses from one expression to another, as from fighting to talking. affect d. a shift of feeling from the object originally arousing it to some associated object. mesial d. SYN: mesioversion. tissue d. the change in the form or position of tissues as a result of pressure.


disproportion (dis-pro-por′shun)
Lack of proportion or symmetry. cephalopelvic d. a condition in which the fetal head is too large to traverse the maternal pelvis.

Josef, German anatomist, 1852–1912. See D. space.

dissect (di-sekt′, di-)
1. To cut apart or separate the tissues of the body for study. 2. In an operation, to separate the different structures along natural lines by dividing the connective tissue framework. [L. dis-seco, pp. -sectus, to cut asunder]

dissection (di-sek′shun, di-)
The act of dissecting. SYN: anatomy (3) [TA] , necrotomy (1) . aortic d. a pathologic process, characterized by splitting of the media layer of the aorta, which leads to formation of a dissecting aneurysm. Classified according to location as follows: type I involves the ascending aorta, transverse arch, and distal aorta; type II is confined to the ascending aorta; type III extends distally in the descending aorta usually from a starting point just distal to the left subclaviar artery. functional neck d. operation to remove metastases to the lymph nodes of the neck; differs from a radical neck d. by preserving any of the following structures: the sternocleidomastoid muscle, the spinal accessory nerve, and the internal jugular vein. SYN: limited neck d.. limited neck d. SYN: functional neck d.. radical neck d. an operation for the removal of metastases to the lymph nodes of the neck in which all of the tissue is removed between the superficial and the deep cervical fascia from the mandible to the clavicle. SEE ALSO: functional neck d..

dissector (dis-ek′ter)
1. One who dissects. 2. A written guide for dissection. 3. Instrument for dissecting.

disseminated (di-sem′i-na-ted)
Widely scattered throughout an organ, tissue, or the body. [L. dissemino, pp. -atus, to scatter seed, fr. semen (-min-), seed]

dissepiment (di-sep′i-ment)
A separating tissue, partition, or septum. [L. dis- sepio, pp. -septus, to divide by a fence]

dissimilation (di-sim-i-la′shun)
1. SYN: disassimilation. 2. SYN: catabolism.

dissimulation (di-sim-u-la′shun)
Concealment of the truth about a situation, especially about a state of health or during a mental status examination, as by a malingerer or someone with a factitious disorder. [L. dissimulatio, fr. dissimulo, to feign, fr. dis, apart, + simillis, same]

dissociation (di-so-se-a′shun, -she-a′shun)
1. Separation, or a dissolution of relations. SYN: disassociation. 2. The change of a complex chemical compound into a simpler one by any lytic reaction, by ionization, by heterolysis, or by homolysis. 3. An unconscious separation of a group of mental processes from the rest, resulting in an independent functioning of these processes and a loss of the usual associations; for example, a separation of affect from cognition. See multiple personality. 4. A state used as an essential part of a technique for healing in psychology and psychotherapy, for instance in hypnotherapy or the neurolinguistic programming technique of time-line therapy. SEE ALSO: Time-Line therapy. 5. The translocation between a large chromosome and a small supernumerary one. 6. Separation of the nuclear components of a heterokaryotic dikaryon. [L. dis-socio, pp. -atus, to disjoin, separate, fr. socius, partner, ally] albuminocytologic d. increased protein in the cerebrospinal fluid without increase in cell count, characteristic of the Guillain-Barré syndrome; it is also associated with spinal block and with intracranial neoplasia, and is seen in the last phases of poliomyelitis. atrial d. mutually independent beating of the two atria or of parts of the atria. atrioventricular d. (AVD) , AV d. 1. any situation in which atria and ventricles are activated and contract independently, as in complete AV block; 2. more specifically, the d. between atria and ventricles that results from slowing of the atrial pacemaker or acceleration of the ventricular pacemaker at nearly equal (rarely equal) rates, each depolarizing its own chamber, thus interfering with depolarization by the other (interference-d.). complete atrioventricular d., complete AV d. aV d. not interrupted by ventricular captures. SYN: complete AV block (2) , third degree AV block. electromechanical d. persistence of electrical activity in the heart without associated mechanical contraction; often a sign of cardiac rupture. SYN: pulseless electrical activity. incomplete atrioventricular d., incomplete AV d. aV d. interrupted by ventricular captures. interference d. the simultaneous operation of two separate cardiac pacemaking foci that are unassociated because of interference (a normal physiologic phenomenon) due to rendering their respective territories refractory to each other. Usually atrioventricular d. is indicated, the rates being quite close to each other with the atrial rate slightly slower than that of the pacemaker in control of the ventricles. Capture is in either direction, usually the ventricle by the atrium, in incomplete d.. h SYN: d. by interference. d. by interference SYN: interference d.. isorhythmic d. AV d. characterized by equal or closely similar atrial and ventricular rates. light-near d. SYN: pupillary light-near d.. longitudinal d. d. between parallel chambers of the heart, as between one atrium and the other or between one ventricle and the other, in contrast to d. between atria and ventricles. pupillary light-near d. pupillary light-near d.. sleep d. SYN: sleep paralysis. syringomyelic d. loss of pain and temperature sensation with relative retention of tactile sensation, related to a cavity in the central portion of the cord interrupting the decussation of nerve fibers. tabetic d. loss of proprioceptive sensation with retained pain and temperature sensation due to involvement of the posterior columns of the spinal cord. visual-kinetic d. the neurolinguistic programming process of removing a synesthesia from a person's internal experience. SEE ALSO: neurolinguistic programming.

dissolve (di-zolv′)
To change or cause to change from a solid to a dispersed form by immersion in a fluid of suitable properties. [L. dis-solvo, pp. -solutus, to loose asunder, to d.]

dissonance (di′so-nans)
In social psychology and attitude theory, an aversive state which arises when an individual is minimally aware of inconsistency or conflict within himself. See cognitive d. theory. [L. dissonus, discordant, confused] cognitive d. a motivational state studied by social and clinical psychologists which exists when a person's attitudes, perceptions, and related cognitive state are inconsistent with each other, e.g., hating blacks but admiring Martin Luther King.

dissymmetry (di-sim′e-tre)
SYN: asymmetry. [dis- + symmetry]

distad (dis′tad)
Toward the periphery; in a distal direction.

distal (dis′tal) [TA]
1. Situated away from the center of the body, or from the point of origin; specifically applied to the extremity or distant part of a limb or organ. 2. In dentistry, away from the median sagittal plane of the face, following the curvature of the dental arch. SYN: distalis [TA] . [L. distalis]

distalis (dis-ta′lis) [TA]
SYN: distal.

distance (dis′tans)
The measure of space between two objects. [L. distantia, fr. di-sto, to stand apart, be distant] focal d. the d. from the center of a lens to its focus. infinite d. the limit of distant vision, the rays entering the eyes from an object at that point being practically parallel. SYN: infinity. interarch d. 1. the vertical d. between the maxillary and mandibular arches under conditions of vertical dimensions which must be specified; 2. the vertical d. between maxillary and mandibular ridges. SYN: interalveolar space, interridge d.. interocclusal d. 1. the vertical d. between the opposing occlusal surfaces, assuming rest relation unless otherwise designated; SYN: interocclusal rest space (1) . 2. SYN: freeway space. interridge d. SYN: interarch d.. large interarch d. a large d. between the maxillary and mandibular arches; may also imply an excessive vertical dimension. SYN: open bite (1) . pupillary d. the d. between the center of each pupil; the major reference points in measuring for fitting of spectacle frames and lenses. reduced interarch d. an occluding vertical dimension which results in an excessive interocclusal d. when the mandible is in rest position, and in a reduced interridge d. when the teeth are in contact. small interarch d. a small d. between the maxillary and mandibular arches. SYN: close bite. sociometric d. some measurable degree of mutual or social perception, acceptance, and understanding; hypothetically, greater sociometric d. is associated with more inaccuracy in evaluating a relationship ( e.g., it is easier to understand and deal with a native than a foreigner).

distensibility (dis-ten-si-bil′i-te)
The capability of being distended or stretched. [L. dis- tendo, to stretch apart]

distention, distension (dis-ten′shun)
The act or state of being distended or stretched. SEE ALSO: dilation. [L. dis-tendo, to stretch apart]

distichiasis (dis′ti-ki′a-sis)
A congenital, abnormal, accessory row of eyelashes. [G. di- double, + stichos, row]

distill (dis-til′)
To extract a substance by distillation.

distillate (dis′ti-lat)
The product of distillation.

distillation (dis-ti-la′shun)
Volatilization of a liquid by heat and subsequent condensation of the vapor; a means of separating the volatile from the nonvolatile, or the more volatile from the less volatile, part of a liquid mixture. [L. de-(di-)stillo, pp. -atus, to drop down] destructive d. SYN: dry d.. dry d. submission of an organic substance to heat in a closed vessel so that oxygen is absent and combustion prevented, with the objective of effecting its decomposition with release of volatile constituents and the formation of new substances. SYN: destructive d.. fractional d. d. of a compound liquid at varying degrees of heat whereby the components of different boiling points are collected separately. molecular d. d. in high vacuum, intended to make possible use of low temperatures to minimize damage to thermally labile molecules that would be decomposed by boiling at higher temperatures.

distobuccal (dis-to-buk′kal)
Relating to the distal and buccal surfaces of a tooth; denoting the angle formed by their junction.

distobucco-occlusal (dis′to-buk′o-o-kloo′sal)
Relating to the distal, buccal, and occlusal surfaces of a bicuspid or molar tooth; denoting especially the angle formed by the junction of these surfaces.

distobuccopulpal (dis′to-buk′o-pul′pal)
Relating to the point (trihedral) angle formed by the junction of a distal, buccal, and pulpal wall of a cavity.

distocervical (dis-to-ser′vi-kal)
Relating to the line angle formed by the junction of the distal and cervical (gingival) walls of a class V cavity.

distoclusal (dis-to-kloo′sal)
1. Relating to or characterized by distoclusion. 2. Denoting a compound cavity or restoration involving the distal and occlusal surfaces of a tooth. 3. Denoting the line angle formed by the distal and occlusal walls of a class V cavity. SYN: disto-occlusal.

distoclusion (dis-to-kloo′zhun)
A malocclusion in which the mandibular arch articulates with the maxillary arch in a position distal to normal; in Angle classification, a Class II malocclusion. SYN: distal occlusion (2) .

distogingival (dis-to-jin′ji-val)
Relating to the junction of the distal surface with the gingival line of a tooth.

distoincisal (dis′to-in-si′zal)
Relating to the line (dihedral) angle formed by the junction of the distal and incisal walls of a class V cavity in an anterior tooth.

distolabial (dis-to-la′be-al)
Relating to the distal and labial surfaces of a tooth; denoting the angle formed by their junction.

distolabiopulpal (dis′to-la′be-o-pul′pal)
Relating to the point (trihedral) angle formed by the junction of distal, labial and pulpal walls of the incisal part of a class IV (mesioincisal) cavity.

distolingual (dis-to-ling′gwal)
Relating to the distal and lingual surfaces of a tooth; denoting the angle formed by their junction.

distolinguo-occlusal (dis′to-ling′gwo-o-kloo′zal)
Relating to the distal, lingual, and occlusal surfaces of a bicuspid or molar tooth; denoting especially the angle formed by the junction of these surfaces.

Distoma (dis′to-ma)
Obsolete term for various digenetic flukes, now referred to other genera; e.g., Fasciola, Fasciolopsis, Paragonimus, Opisthorchis, Clonorchis, Dicrocoelium, Heterophyes, and Schistosoma. SYN: Distomum. [G. di-, two, + stoma, mouth]

distomiasis, distomatosis (dis′to-mi′a-sis, -ma-to′sis)
Presence in any of the organs or tissues of digenetic flukes formerly classified as Distoma or Distomum; in general, infection by any parasitic trematode or fluke. hemic d. SYN: schistosomiasis. pulmonary d. SYN: paragonimiasis.

distomolar (dis-to-mo′lar)
A supernumerary tooth located in the region posterior to the third molar tooth.

Distomum (dis′to-mum)
SYN: Distoma.

disto-occlusal (dis′to-o-kloo′sal)
SYN: distoclusal.

disto-occlusion (dis′to-o-kloo′zhun)
SYN: distal occlusion (1) .

distoplacement (dis′to-plas-ment)
SYN: distoversion.

distopulpal (dis-to-pul′pal)
Relating to the line (dihedral) angle formed by the junction of the distal and pulpal walls of a cavity.

distortion (dis-tor′shun)
1. In psychiatry, a defense mechanism that helps to repress or disguise unacceptable thoughts. 2. In dental impressions, the permanent deformation of the impression material after the registration of an imprint. 3. A twisting out of normal shape or form. 4. In ophthalmology, unequal magnification over a field of view. [L. distortio, fr. dis-torqueo, to wrench apart] barrel d. irregular image produced when peripheral magnification is greater than axial magnification. See Petzval surface. parataxic d. an attitude toward another person based on a distorted evaluation, usually because of too close an identification of that person with emotionally significant figures in the patient's past life. pincushion d. irregular image produced when axial magnification is greater than peripheral magnification. See Petzval surface.

distoversion (dis′to-ver-zhun)
Malposition of a tooth distal to normal, in a posterior direction following the curvature of the dental arch. SYN: distoplacement.

distractibility (dis-trak-ti-bil′i-te)
A disorder of attention in which the mind is easily diverted by inconsequential occurrences; seen in mania and attention deficit disorder.

distraction (dis-trak′shun)
1. Difficulty or impossibility of concentration or fixation of the mind. 2. A force applied to a body part to separate bony fragments or joint surfaces. [L. dis-traho, pp. -tractus, to pull in different directions]

distress (dis-tres′)
Mental or physical suffering or anguish. [L. distringo, to draw asunder] fetal d. SYN: nonreassuring fetal status.

distribution (dis-tri-bu′shun)
1. The passage of the branches of arteries or nerves to the tissues and organs. 2. The area in which the branches of an artery or a nerve terminate, or the area supplied by such an artery or nerve. 3. The relative numbers of individuals in each of various categories or populations such as in different age, sex, or occupational samples. See frequency d.. 4. Partition. 5. The pattern of occurrence of a substance within or between cells, tissues, organisms, or taxa. [L. distribuo, pp. -tributus, to distribute, fr. tribus, a tribe] Bernoulli d. the probability d. associated with two mutually exclusive and exhaustive outcomes, e.g., death or survival. binomial d. 1. a probability d. associated with two mutually exclusive outcomes, e.g., presence or absence of a clinical sign. 2. the possible array of the number of successes in the outcomes from a fixed number, n, of independent Bernoulli trials; the probabilities associated with each constitute a binomial process of order n. chi-square d. (ki) a variable is said to have a chi-square d. with K degrees of freedom if it is distributed like the sum of the squares of K independent random variables, each of which has a normal (gaussian) d. with mean zero and variance one. The chi square d. is the basis for many variations of the chi-square(d) test, perhaps the most widely used test for statistical significance in biology and medicine. countercurrent d. a method of separation of two or more substances by repeated d. between two immiscible liquid phases that move past each other in opposite directions; a form of liquid-liquid chromatography. dermatomal d. SYN: dermatome (3) . epidemiological d. histogram. exponential d. the time until failure of a process at constant hazard. f d. the d. of the ratio of two independent quantities each of which is distributed like a variance in normally distributed samples. So named in honor of the English statistician and geneticist R.A. Fisher. frequency d. a statistical description of raw data in terms of the number or frequency of items characterized by each of a series or range of values of a continuous variable. gaussian d. SYN: normal d.. lognormal d. if a variable y is such that x = log y, it is said to have a lognormal d.; this is a skew d.. multinomial d. probability d. associated with the classification of each of a sample of individuals into one of several mutually exclusive and exhaustive categories. normal d. a specific bell-shaped frequency d. commonly assumed by statisticians to represent the infinite population of measurements from which a sample has been drawn; characterized by two parameters, the mean (x) and the standard deviation (σ), in the equation: SYN: gaussian curve, gaussian d.. Poisson d. 1. a discontinuous d. important in statistical work and defined by the equation p (x) = e -μμx/ x!, where e is the base of natural logarithms, x is the sequence of integers, μ is the mean, and x! represents the factorial of x. 2. a d. function used to describe the occurrence of rare events, or the sampling d. of isolated counts in a continuum of time or space. skew d. an asymmetrical frequency d.; in biology and medicine it is usually a lognormal d.. t d. the d. of the quotient of independent random variables, the numerator of which is a standardized normal variate and the denominator the positive square root of the quotient of a chi-square distributed variate and its number of degrees of freedom.

districhiasis (dis-tri-ki′a-sis)
Growth of two hairs in a single follicle. [G. dis, double, + thrix (trich-), hair]

distrix (dis′triks)
Splitting of the hairs at their ends. [G. dis, twice, + thrix, hair]

SYN: dystrophin.

disturbance (dis-ter′bans)
Deviation from, interruption of, or interference with a normal state. emotional d., mental d. mental illness, behavior disorder.

disulfamide (di-sul′fa-mid)
A diuretic.

disulfate (di-sul′fat)
A molecule containing two sulfates.

disulfide (di-sul′fid)
1. A molecule containing two atoms of sulfur to one of the reference element, e.g., CS2, carbon d.. 2. A compound containing the –S–S– group, e.g., cystine. asymmetric d. SYN: mixed d.. mixed d. d. which is not symmetric on both sides of the &cbond;S&cbond;S&cbond; linkage; e.g., the d. formed between coenzyme A and glutathione or between cysteine and coenzyme A or glutathione. SYN: asymmetric d.. symmetric d. d. that is symmetric on both sides of the &cbond;S&cbond;S&cbond; linkage; i.e., d. formed from identical thiol-containing compounds; e.g., cystine, glutathione d..

disulfiram (di-sul′fi-ram)
An antioxidant that interferes with the normal metabolic degradation of alcohol in the body, resulting in increased acetaldehyde concentrations in blood and tissues. Used in the treatment of chronic alcoholism; when a small quantity of alcohol is consumed an unpleasant reaction results. Also used as a chelator in copper and nickel poisoning. SYN: tetraethylthiuram disulfide.

Abbreviation for diiodotyrosine.

diterpenes (di-ter′penz)
Hydrocarbons or their derivatives containing four isoprene units, hence containing 20 carbon atoms and four branched methyl groups; e.g., vitamin A, retinene, aconitine.

dithiazanine iodide (di-thi-az′a-nen)
A broad spectrum anthelmintic, effective against Strongyloides.

dithiothreitol (di-the′o-thre-tol)
A donor of thiol groups used in biochemical and pharmacological studies. SYN: Cleland reagent.


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