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Medical Dictionary


ρ, upper case P
  • rho, 17th letter of the Greek alphabet
  • density
  • population correlation coefficient
  • arginine
  • arginyl
  • chemical group, especially an organic chemical group, e.g., thiols have the general formula RSH
  • electrical resistance
  • molar gas constant
  • purine nucleoside
  • radical (usually an alkyl or aryl group, e.g., ROH is an alcohol, RNH2 an amine)
  • radius
  • Réaumur
  • respiration
  • respiratory exchange ratio
  • roentgen
  • rough (bacteriology)
  • stereochemical designation in the Cahn, Ingold, and Prelog system
  • the remainder of a chemical formula
  • calculated unit representing vascular resistance in the cardiovascular system
  • the third product formed in an enzyme-catalyzed reaction
  • racemic, e.g., “r-alanine”
  • radius
  • roentgen
  • correlation coefficient

Symbol for recipe in a prescription. See prescription (2) .

Rf, RF
Symbol denoting movement of a substance in paper chromatography relative to the solvent front ( i.e., retardation factor); equal to the migration distance of a substance divided by the migration distance of the solvent front.

Symbol for radium.

rabbeting (rab′et-ing)
Obsolete term for making congruous stepwise cuts on apposing bone surfaces for stability after impaction. [Fr. raboter, to plane]

Relating to or suffering from rabies. [L. rabidus, raving, mad]

rabies (ra′bez)
Highly fatal infectious disease that may affect all species of warm-blooded animals, including humans; transmitted by the bite of infected animals including dogs, cats, skunks, wolves, foxes, raccoons, and bats, and caused by a neurotropic species of Lyssavirus, a member of the family Rhabdoviridae, in the central nervous system and the salivary glands. The symptoms are characteristic of a profound disturbance of the nervous system, e.g., excitement, aggressiveness, and madness, followed by paralysis and death. Characteristic cytoplasmic inclusion bodies (Negri bodies) found in many of the neurons are an aid to rapid laboratory diagnosis. SYN: hydrophobia. [L. rage, fury, fr. rabio, to rave, to be mad] dumb r. SYN: paralytic r.. furious r. the form or stage of r. in which the animal is markedly hyperactive, characterized by periods of agitation, thrashing, running, snapping, or biting. paralytic r. a form or stage of r. marked by paralytic symptoms. SYN: dumb r..

rabiform (ra′bi-form)
Resembling rabies.

Prefix for racemic.

racefemine (ra-se-fem′en)
Used as a uterine relaxant for relief of postpartum pain.

racemase (ra′se-mas)
An enzyme capable of catalyzing racemization, i.e., inversions of asymmetric groups; when more than one center of asymmetry is present, “epimerase” is used ( e.g., hydroxyproline, ribulose phosphate).

racemate (ra′se-mat)
A racemic compound, or the salt or ester of such a compound. SEE ALSO: racemic.

raceme (ra-sem′)
An optically inactive chemical compound. SEE ALSO: racemic.

racemic (r) (ra-se′mik, -sem′ik)
Denoting a mixture of optically active compounds that is itself optically inactive, being composed of an equal number of dextro- and levorotatory substances, which are separable. Those compounds internally compensated ( i.e., having an internal plane of symmetry) and therefore not separable into d and l (or + and −) forms, are termed “meso.”

racemization (ra′se-mi-za′shun, ras-mi-)
Partial conversion of one enantiomorph into another (as an l-amino acid to the corresponding d-amino acid) so that the specific optical rotation is decreased, or even reduced to zero, in the resulting mixture.

racemose (ras′e-mos)
Branching, with nodular terminations; resembling a bunch of grapes. [L. racemosus, full of clusters]

racephedrine hydrochloride (ras-e-fed′rin)
A sympathomimetic drug with peripheral effects similar to those of epinephrine and with the same actions and uses as ephedrine.

rachi-, rachio-
The spine. [G. rhachis, spine, backbone]

rachial (ra′ke-al)
SYN: spinal.

rachicentesis (ra-ke-sen-te′sis)
SYN: lumbar puncture. [rachi- + G. kentesis, puncture]

rachidial (ra-kid′e-al)
SYN: spinal.

rachidian (ra-kid′e-an)
SYN: spinal.

rachilysis (ra-kil′i-sis)
Forcible correction of lateral curvature of the spine by lateral pressure against the convexity of the curve. [rachi- + G. lysis, a loosening]

See rachi-.

rachiocentesis (ra-ke-o-sen-te′sis)
SYN: lumbar puncture. [rachio- + G. kentesis, puncture]

rachiochysis (ra-ke-ok′i-sis)
A subarachnoid effusion of fluid in the spinal canal. [rachio- + G. chysis, a pouring out]

rachiopagus (ra-ke-op′a-gus)
Conjoined twins united back to back with union of their spinal columns. See conjoined twins, under twin. SYN: rachipagus. [rachio- + G. pagos, something fixed]

rachioplegia (ra′ke-o-ple′je-a)
SYN: spinal paralysis. [rachio- + G. plege, stroke]

rachiotome (ra′ke-o-tom)
A specially devised instrument for dividing the laminae of the vertebrae. SYN: rachitome. [rachio- + G. tome, incision]

rachiotomy (ra-ke-ot′o-me)
SYN: laminotomy. [rachio- + G. tome, incision]

rachipagus (ra-kip′a-gus)
SYN: rachiopagus.

rachis, pl .rachidesrachises (ra′kis, ra′ki-dez, rak-)
SYN: vertebral column. [G. spine, backbone]

rachischisis (ra-kis′ki-sis)
1. Embryologic failure of fusion of vertebral arches and neural tube with consequent exposure of neural tissue at the surface; spina bifida cystica with myelocele or myeloschisis. 2. Spinal dysraphism. [G. rhachis, spine, + schisis, division] r. partialis SYN: merorachischisis. r. totalis SYN: holorachischisis.

rachitic (ra-kit′ic)
Relating to or suffering from rickets (rachitis). SYN: rickety.

rachitis (ra-ki′tis)
SYN: rickets. [G. rhachitis] r. fetalis congenital rickets. SYN: r. intrauterina, r. uterina. r. fetalis annularis congenital enlargement of the epiphyses of the long bones. r. fetalis micromelica a congenital condition in which development of the long bones is deficient. r. intrauterina, r. uterina SYN: r. fetalis. r. tarda SYN: osteomalacia.

rachitism (rak′i-tizm)
A rachitic state or tendency.

rachitogenic (ra-kit-o-jen′ik)
Producing or causing rickets. [rachitis + G. genesis, production]

rachitome (rak′i-tom)
SYN: rachiotome.

1. The unit for the dose absorbed from ionizing radiation, equivalent to 100 ergs per gram of tissue; 100 r. = 1 Gy. 2. Symbol for radian.

radarkymography (ra′dar-ki-mog′ra-fe)
An obsolete procedure involving the video tracking of heart motion by means of image intensification and closed circuit television during fluoroscopy; enabled cardiac motion to be measured by reproducible linear graphic tracing.

radectomy (ra-dek′to-me)
SYN: root amputation. [L. radix, root, + G. ektome, excision]

Edward P., Jr., U.S. physiologist, *1922. See R. nomogram.

radiability (ra′de-a-bil′i-te)
The property of being radiable.

radiable (ra′de-a-bl)
Capable of being penetrated or examined by rays, especially by x-rays.

radiad (ra′de-ad)
In a direction toward the radial side.

radial (ra′de-al)
1. Relating to the radius (bone of the forearm), to any structures named from it, or to the r. or lateral aspect of the upper limb as compared to the ulnar or medial aspect. SYN: radialis [TA] . 2. Relating to any radius. 3. Radiating; diverging in all directions from any given center. [L. radialis, fr. radius, ray, lateral bone of the forearm]

radialis (ra-de-a′lis) [TA]
SYN: radial (1) . [Mod. L.]

radian (rad) (ra′de-an)
A supplementary SI unit of plane angle. [L. radius, ray]

radiant (ra′de-ant)
1. Giving out rays. 2. A point from which light radiates to the eye.

radiate (ra′de-at)
1. To spread out in all directions from a center. 2. To emit radiation. [L. radio, pp. -atus, to shine]

radiatio, pl .radiationes (ra-de-a′she-o, -she-o′nez)
In neuroanatomy, a term applied to any one of the thalamocortical fiber systems that together compose the corona radiata of the cerebral hemisphere's white matter ( e.g., optic radiation, acoustic radiation, etc.). SYN: radiation (3) . [L.] r. acustica [TA] SYN: acoustic radiation. r. corporis callosi [TA] SYN: radiation of corpus callosum. r. inferior thalami [TA] SYN: inferior thalamic peduncle. r. optica [TA] SYN: optic radiation. r. pyramidalis SYN: pyramidal radiation. r. thalami anterior [TA] SYN: anterior thalamic radiation. r. thalami centralis [TA] SYN: central thalamic radiation. r. thalamica posterior [TA] SYN: posterior thalamic radiation.

radiation (ra′de-a′shun)
  • The act or condition of diverging in all directions from a center.
  • The sending forth of light, short radio waves, ultraviolet or x-rays, or any other rays for treatment or diagnosis or for other purpose. Cf.:irradiation, aka radiatio.
  • A ray.
  • Radiant energy or a radiant beam. [L. radiatio, fr. radius, ray, beam]
  • acoustic r.: the fibers that pass from the medial geniculate body to the transverse temporal gyri of the cerebral cortex by way of the sublentiform part of the internal capsule, aka radiatio acustica .
  • afterloading r. :method of administering r. that involves initial placement of local catheters with later installation of the r. source.
  • alpha r. :an emission of a nucleus of high kinetic energy from the nucleus of an atom undergoing radioactive decay or fission.
  • annihilation r. :the r. resulting when a positron from beta positive decay comes to rest. It encounters an electron, and they annihilate each other and convert their rest mass into two 0.51-MeV gamma rays emitted in exactly opposite directions. See pair production.
  • anterior thalamic r.: r. formed by fibers interconnecting, via the anterior limb of the internal capsule, the anterior and medial thalamic nuclei and the cerebral cortex of the frontal lobe (excluding the precentral gyrus bordering on the central sulcus). SYN: radiatio thalami anterior.
  • background r. :irradiation from environmental sources, including the earth's crust, the atmosphere, cosmic rays, and ingested radionuclides.Natural sources account for the largest amount of r. received by most persons each year (average annual dose, 3.00 mSv), with medical and occupational sources providing only a fraction (average less than 0.60 mSv). It is currently believed that radon, a gas produced by radium decay within crystal rock, constitutes the major source of background r. throughout many parts of the U.S. Radon buildup in inadequately ventilated homes may pose a long-term health hazard. The deleterious effects of background r., estimated as causing 1–6% of spontaneous genetic mutations, rise with dose.
  • beta r. :radiant energy from a source of beta rays.
  • central thalamic r.: r. formed by fibers interconnecting, through the posterior limb of the internal capsule, the ventral lateral, ventral posterolateral and posteromedial, lateral dorsal, and lateral posterior nuclei and the precentral gyrus and parietal lobe of the cerebral cortex. SYN: radiatio thalami centralis.
  • Cerenkov r. :light given off by a transparent medium when a high-energy particle speeds through it at a velocity greater than that of light in that medium.
  • characteristic r. ;monochromatic r. that is produced when an electron is ejected from an atom and another takes its place by jumping from another shell; the energy of the emitted photon is the difference between that of the two shell positions. See photoelectric effect. SYN: characteristic emission.
  • r. of corpus callosum: the spreading out of the fibers of the corpus callosum in the centrum semiovale of each cerebral hemisphere. SYN: radiatio corporis callosi.
  • corpuscular r.: r. consisting of streams of subatomic particles such as protons, electrons, neutrons, etc.
  • electromagnetic r:. r. originating in a varying electromagnetic field; e.g., long and short radio waves; light, visible and invisible; x-r. and gamma rays.
  • gamma r. :ionizing electromagnetic r. resulting from nuclear processes, such as radioactive decay or fission.
  • geniculocalcarine r.: optic r..
  • Gratiolet r.: optic r..
  • hemibody r.: a palliative cancer therapy involving r. to one-half of the body. [hemi- + body]
  • heterogeneous r.: r. consisting of different frequencies, various energies, or a variety of particles. SEE ALSO: polychromatic r..
  • homogeneous r.: r. consisting of a narrow band of frequencies, the same energy, or a single type of particle.
  • hyperfractionated r.: smaller fractions of a dose of r. given more frequently than daily.
  • hypofractionated r.: larger fractions of a dose of r. given less frequently than daily.
  • inferior thalamic r.: inferior thalamic peduncle.
  • ionizing r.: corpuscular ( e.g., neutrons, electrons) or electromagnetic ( e.g., gamma) r. of sufficient energy to ionize the irradiated material.
  • K-r.: usually a very penetrating form of x-r. excited by cathode rays (high-speed electrons) impinging upon a metal anode such as tungsten; the energy of the r. is a function of the binding energy of the K-shell electrons of the metal anode.
  • L-r.: an x-r. of slight penetrating power excited by cathode rays (high-speed electrons) impinging on a metal anode; the energy of the r. is a function of the binding energy of the L-shell electrons of the metal anode.
  • monochromatic r.: light rays or ionizing r. of a very narrow band of wavelengths (ideally, of a single wavelength). Cf.:photopeak, characteristic r..
  • neutron r.: an emission of neutrons from the nucleus of an atom by decay or fission.
  • occipitothalamic r.: optic r..
  • optic r.: the massive, fanlike fiber system passing from the lateral geniculate body of the thalamus to the visual cortex (striate or calcarine cortex, area 17 of Brodmann); the fibers follow the retrolenticular and sublenticular limbs of the internal capsule into the corona radiata but they curve back along the lateral wall of the temporal and occipital horns of the lateral ventricle to the striate cortex on the medial surface and pole of the occipital lobe, aka radiatio optica, geniculocalcarine r., geniculocalcarine tract, Gratiolet fibers, Gratiolet r., occipitothalamic r., Wernicke r..
  • polychromatic r.: r. containing gamma rays, under ray of many different energies; in diagnostic radiology, typically bremsstrahlung.
  • posterior thalamic r.: r. formed by fibers interconnecting through the retrolenticular part of the posterior limb of the internal capsule, the pulvinar complex and lateral geniculate nucleus, and the posterior parietal and occipital lobes of the cerebral cortex, aka: radiatio thalamica posterior.
  • primary r.: an incident x-ray beam.
  • pyramidal r.: corticospinal fibers passing from the cortex into the pyramid, aka radiatio pyramidalis.
  • scattered r.: secondary r. emitted from the interaction of x-rays with matter; generally lower in energy, with a directional distribution that depends on the energy of the incident r., aka secondary r..
  • secondary r.: scattered r..
  • Wernicke r.: optic r..
radical (rad′i-kal)
1. In chemistry, a group of elements or atoms usually passing intact from one compound to another, but usually incapable of prolonged existence in a free state ( e.g., methyl, CH3); in chemical formulas, a r. is often distinguished by being enclosed in parentheses or brackets. 2. Thorough or extensive; relating or directed to the extirpation of the root or cause of a morbid process; e.g., a r. operation. 3. Denoting treatment by extreme, drastic, or innovative, as opposed to conservative, measures. 4. SYN: free r.. [L. radix (radic-), root] acid r. a r. formed from an acid by loss of one or more hydrogen ions; e.g., SO4−, NO3−. color r. SYN: chromophore. free r. a r. in its (usually transient) uncombined state; an atom or atom group carrying an unpaired electron and no charge; e.g., hydroxyl and methyl Free radicals may be involved as short-lived, highly active intermediates in various reactions in living tissue, notably in photosynthesis. The free r. nitric oxide, NO, plays an important role in vasodilation. SYN: r. (4) .Free radicals occur naturally within the body as a result of metabolic processes and can also be introduced from without (through smoking, inhaling environmental pollutants, or exposure to UV radiation). They interact readily with nearby molecules and may cause cellular damage, including genetic alterations. It has been theorized that they are involved in plaque formation in atherosclerosis, in cancer, and in degenerative disorders such as Alzheimer dementia and parkinsonism. Natural enzymes such as superoxide dismutase and peroxidase are thought to counteract free radicals, and there is evidence that many nutrients, including vitamins C and E and β-carotene, also exert an antioxidant effect. see also antioxidant. oxygen-derived free radicals an atom or atom group having an unpaired electron on an oxygen atom, typically derived from molecular oxygen. For example, one-electron reduction of O2 produces the superoxide r., O2·; other examples include the hydroperoxyl r. (HOO·), the hydroxyl r. (HO·), and nitric oxide (NO·). These apparently have a role in reprofusion injury.

radices (ra-di′sez)
Plural of radix.

radicle (rad′i-kl)
A rootlet or structure resembling one, as the r. of a vein, a minute veinlet joining with others to form a vein, or the r. of a nerve, a nerve fiber that joins others to form a nerve. [L. radicula, dim. of radix, root]

radicotomy (rad-i-kot′o-me)
SYN: rhizotomy. [L. radix (radic-), root, + G. tome, incision]

See radiculo-.

radicula (ra-dik′u-la)
A spinal nerve root. [L. dim of radix, root]

radiculalgia (ra-dik′u-lal′je-a)
Neuralgia due to irritation of the sensory root of a spinal nerve. [radicul- + G. algos, pain]

radicular (ra-dik′u-lar)
1. Relating to a radicle. 2. Pertaining to the root of a tooth.

radiculectomy (ra-dik′u-lek′to-me)
SYN: rhizotomy. [radicul- + G. ektome, excision]


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