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Medical Dictionary


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ricinism (ris′i-nizm)
Poisoning by ingestion of toxic principles from seeds (castor beans) or leaves of the castor oil plant, Ricinus communis.

ricinoleate (ris-i-no′le-at)
A salt of ricinoleic acid.

ricinoleic acid (ris-i-no-le′ik, ri-si-)
An unsaturated hydroxy acid present in castor oil.

Ricinus (ris′i-nus)
A genus of plants (family Euphorbiaceae) with one species, R. communis, the castor oil plant, the source of castor oil; the leaves are said to be a galactagogue. SYN: castor bean. [L.]

rickets (rik′ets)
A disease due to vitamin D deficiency and characterized by overproduction and deficient calcification of osteoid tissue, with associated skeletal deformities, disturbances in growth, hypocalcemia, and sometimes tetany; usually accompanied by irritability, listlessness, and generalized muscular weakness; fractures are frequent. SYN: infantile osteomalacia, juvenile osteomalacia, rachitis. [E. wrick, to twist] acute r. SYN: hemorrhagic r.. adult r. SYN: osteomalacia. celiac r. arrested growth and osseous deformities associated with defective absorption of fat and calcium in celiac disease. familial hypophosphatemic r. SYN: vitamin D-resistant r.. hemorrhagic r. bone changes seen in infantile scurvy, consisting of subperiosteal hemorrhage and deficient osteoid tissue formation; often used to indicate simultaneous occurrence of r. and scurvy. SYN: acute r.. hereditary hypophosphatemic r. with hypercalciuria, an inherited disorder in which there is a defect in renal tubular reabsorption. late r. SYN: osteomalacia. refractory r. r. that does not respond to treatment with usual doses of vitamin D and adequate dietary calcium and phosphorus; most often due to inherited renal tubular disorder, e.g., Fanconi syndrome. renal r. a form of r. occurring in children in association with and apparently caused by renal disease with hyperphosphatemia. SYN: pseudorickets, renal fibrocystic osteosis, renal infantilism, renal osteitis fibrosa. scurvy r. SYN: infantile scurvy. vitamin D-resistant r. a group of metabolic disorders characterized by renal tubular defect in phosphate transport and bone abnormalities resulting in hypophosphatemic r. or osteomalacia; hypocalcemia and tetany are not features. There is an autosomal dominant form [MIM*193100] and an X-linked dominant form [MIM*307800], the latter caused by mutation in the phosphate-regulating gene with homologies to endopeptidases (PHEX) on chromosome Xp. Both forms are not responsive to standard therapeutic doses of vitamin D but they may respond to very large doses of phosphate and/or vitamin D. There is also an autosomal recessive form [MIM*277440] caused by mutation in the vitamin D receptor gene (VDR) on 12q. SYN: familial hypophosphatemic r..

Ricketts
Howard T., U.S. pathologist, 1871–1910. See Rickettsia.

Rickettsia (ri-ket′se-a)
A genus of bacteria (order Rickettsiales) containing small (nonfilterable), often pleomorphic, coccoid to rod-shaped, Gram-negative organisms that usually occur intracytoplasmically in lice, fleas, ticks, and mites but do not grow in cell-free media; pathogenic species infect humans and other animals, causing epidemic typhus, murine, or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox, and other diseases; type species is R. prowazekii. [Howard T. Ricketts] R. africae a species of R. studied principally in Zimbabwe that appears to be carried by the tick Amblyomma hebraeum; a cause of spotted fever. R. akari a bacterial species causing human rickettsialpox; transmitted by the house mouse mite, Liponyssoides sanguineus; a mild febrile disease of 7–10 days is produced with an urban distribution in the northeastern U.S. and in wild or commensal rodents in the countries of the former USSR and Africa. R. australis a bacterial species causing a spotted fever, North Queensland tick typhus, clinically and serologically similar to the disease caused by the agent of rickettsialpox; Ixodes holocyclus and I. tasmani are probable vectors. Small marsupials are suspected reservoirs of this agent, which is found over much of coastal Queensland, especially in secondary scrub and savannah. R. burnetii former name for Coxiella burnetii. R. canis former name for Ehrlichia canis. R. conorii a species of bacteria causing boutonneuse fever in southern Europe, Africa, and the Middle East; transmitted by various ticks, such as the dog tick Rhipicephalis sanguineus. R. honei a bacterial species causing Flinders Island spotted fever in Australia. R. japonica a bacterial species causing Japanese spotted fever. R. mooseri a species similar to R. prowazekii but with less variation in appearance; the resultant endemic typhus is milder and has a somewhat slower onset. R. prowazekii a bacterial species causing epidemic and recrudescent typhus, transmitted by body lice; type species of the genus R.. R. psittaci former name for Chlamydia psittaci. R. rickettsii a bacterial species, the agent of Rocky Mountain spotted fever, South African tick-bite fever, São Paulo exanthematic typhus of Brazil, Tobia fever of Colombia, and spotted fevers of Minas Gerais and Mexico; transmitted by infected ixodid ticks, especially Dermacentor andersoni and D. variabilis. R. sennetsu SYN: Ehrlichia sennetsu. R. sibirica a bacterial species, the agent of Siberian or North Asian tick typhus, transmitted by various ixodid ticks, which also serve as reservoirs, possibly aided by rodents and hares; the disease resembles Rocky Mountain spotted fever. R. slovaca a bacterial species causing a newly recognized rickettsiosis associated with local erythema and possibly meningoencephalitis; transmitted by the tick Dermacentor marginatus. R. tsutsugamushi former name for Orientia tsutsugamushi. R. typhi a bacterial species causing murine or endemic typhus fever, transmitted by the rat flea.

rickettsial (ri-ket′se-al)
Pertaining to or caused by rickettsiae.

rickettsialpox (ri-ket′se-al-poks′)
Infection with Rickettsia akari, which is spread by mites from reservoir in house mice; a benign, self-limited process first recognized in 1946 in the Kew Gardens area of New York City; a few limited outbreaks have been observed elsewhere since then. SYN: Kew Gardens fever, mite-born typhus, vesicular rickettsiosis.

rickettsiosis (ri-ket-se-o′sis)
Infection with rickettsiae. vesicular r. SYN: rickettsialpox.

rickettsiostatic (ri-ket′se-o-stat′ik)
An agent inhibitory to the growth of Rickettsia. [Rickettsia + G. statikos, bringing to a standstill]

rickety (rik′e-te)
SYN: rachitic.

Rickles
Norman H., U.S. oral pathologist, *1920. See R. test.

RID
Abbreviation for radial immunodiffusion.

Riddoch
George, British physician, 1888–1947. See R. phenomenon. SEE ALSO: R. phenomenon.

Rideal
Samuel, English chemist and bacteriologist, 1863–1929. See R.-Walker coefficient, R.-Walker method.

ridge (rij)
1. A (usually rough) linear elevation. SEE ALSO: crest. 2. In dentistry, any linear elevation on the surface of a tooth. 3. The remainder of the alveolar process and its soft tissue covering after the teeth are removed. [A. S. hyrcg, back, spine] alveolar r. SYN: alveolar process of maxilla. apical ectodermal r. the layer of surface ectodermal cells at the apex of the embryonic limb bud; thought to exert an inductive influence on the condensation of underlying mesenchyme and be necessary for continued outgrowth of the limb. basal r. 1. SYN: alveolar process of maxilla. 2. SYN: cingulum of tooth. bicipital ridges SYN: crest of greater tubercle, crest of lesser tubercle. buccocervical r. a convexity within the cervical third of the buccal surface of molars. buccogingival r. a distinct r. on the buccal surface of a deciduous molar tooth, approximately 1.5 mm from the crown-root junction. bulbar r. one of two spiral subendocardial thickenings in the embryonic bulbus cordis; when they fuse, they divide the bulbus into the aorta and pulmonary artery. bulboventricular r. an elevation on the inner surface of the embryonic heart at 4–5 weeks; it indicates the division between the developing ventricles and the bulbus cordis. dental r. the prominent border of a cusp or margin of a tooth. dermal ridges [TA] surface ridges of the epidermis of the palms and soles, where the sweat pores open. SYN: cristae cutis [TA] , epidermal ridges, papillary ridges, skin ridges. epidermal ridges SYN: dermal ridges. epipericardial r. an elevation separating the developing pharyngeal region from the embryonic pericardium. external oblique r. SYN: oblique line of mandible. ganglion r. SYN: neural crest. genital r. SYN: gonadal r.. gluteal r. SYN: gluteal tuberosity. gonadal r. an elevation of thickened mesothelium and underlying mesenchyme on the ventromedial border of the embryonic mesonephros; the primordial germ cells become embedded in it, establishing it as the primordium of the testis or ovary. SYN: genital r.. interpapillary ridges SYN: rete r.. key r. SYN: zygomaxillare. lateral epicondylar r. SYN: lateral supraepicondylar r.. lateral supracondylar r. lateral supraepicondylar r.. lateral supraepicondylar r. [TA] the distal sharp portion of the lateral margin of the humerus. SYN: crista supraepicondylaris lateralis [TA] , crista supracondylaris lateralis&star, lateral supracondylar r.&star, lateral epicondylar crest, lateral epicondylar r., lateral supracondylar crest. linguocervical r. SYN: linguogingival r.. linguogingival r. a r. occurring on the lingual surface, near the cervix, of the incisor and cuspid teeth. SYN: linguocervical r.. Mall ridges rarely used eponym for pulmonary ridges. mammary r. bandlike thickening of ectoderm in the embryo extending on either side from just below the axilla to the inguinal region; in human embryos, the mammary glands arise from primordia in the thoracic part of the r., the balance of the r. disappearing; in some lower mammals that give birth to a litter of young, several milk glands develop along these lines. SYN: mammary fold, milk line, milk r.. marginal r. SYN: marginal crest of tooth. medial epicondylar r. SYN: medial supraepicondylar r.. medial supracondylar r. medial supraepicondylar r.. medial supraepicondylar r. [TA] the distal sharp portion of the medial margin of the humerus. SYN: crista supraepicondylaris medialis [TA] , crista supracondylaris medialis&star, medial supracondylar r.&star, medial epicondylar crest, medial epicondylar r., medial supracondylar crest. mesonephric r. a r. that, in early human embryos, composes the entire urogenital r.; however, later in development a more medial genital r., the potential gonad, is demarcated from it. SEE ALSO: urogenital r.. SYN: mesonephric fold. milk r. SYN: mammary r.. mylohyoid r. SYN: mylohyoid line. nasal r. SYN: agger nasi. oblique r. a r. on the masticatory surface of an upper molar tooth from the mesiolingual to the distobuccal cusp. oblique r. of trapezium SYN: tuberculum of trapezium bone. palatine r. SYN: palatine raphe. papillary ridges SYN: dermal ridges. Passavant r. a prominence on the posterior wall of the nasopharynx formed by contraction of the superior constrictor muscle of the pharynx during swallowing. SYN: Passavant bar, Passavant cushion, Passavant pad. pectoral r. SYN: crest of greater tubercle. pharyngeal r. SYN: posterior fascicle of palatopharyngeus muscle. primitive r. one of the paired ridges on either side of the primitive groove. pronator r. an oblique r. on the anterior surface of the ulna, giving attachment to the pronator quadratus muscle. pterygoid r. of sphenoid bone SYN: infratemporal crest of greater wing of sphenoid. pulmonary ridges a pair of ridges overlying the common cardinal veins and bulging from the lateral body wall into the embryonic celom; so called because they give early indication of where the pleuropericardial folds will develop. residual r. that portion of the processus alveolaris remaining in the edentulous mouth following resorption of the section containing the alveoli. rete r. downward thickening of the epidermis between the dermal papillae; peg is a misnomer because the dermal papillae are cylindric but the epidermal thickening between papillae is not. SYN: interpapillary ridges, rete pegs. skin ridges SYN: dermal ridges. sphenoidal ridges sharp posterior margins of the lesser wings of the sphenoid bone that end medially in the anterior clinoid process; the sphenoidal ridges demarcate the anterior cranial fossa from the lateral part of the middle cranial fossa. superciliary r. SYN: superciliary arch. supplemental r. a r. on the surface of a tooth that is not normally present. supraorbital r. SYN: supraorbital margin. taste r. one of the ridges surrounding the vallate papillae of the tongue. temporal r. SYN: inferior temporal line of parietal bone, superior temporal line of parietal bone. transverse r. [TA] SYN: crista transversalis. transverse palatine r. SYN: transverse palatine fold. transverse ridges of sacrum [TA] one of four ridges that cross the pelvic surface of the sacrum; these mark the positions of the intervertebral disks between the bodies of the five sacral vertebrae in the immature bone. SYN: lineae transversae ossis sacri [TA] . trapezoid r. SYN: trapezoid line. triangular r. [TA] SYN: crista triangularis. urogenital r. one of the paired longitudinal ridges developing in the dorsal body wall of the embryo on either side of the dorsal mesentery; the r. is formed at first by the growing mesonephros and later by the mesonephros and the gonad. SYN: genital fold, wolffian r.. wolffian r. SYN: urogenital r..

Ridley
Humphrey, English anatomist, 1653–1708. See R. circle, R. sinus, circulus venosus ridleyi.

Riedel
Bernhard M.C.L., German surgeon, 1846–1916. See R. disease, R. lobe, R. struma, R. thyroiditis.

Rieder
Hermann, German pathologist, 1858–1932. See R. cells, under cell, R. cell leukemia, R. lymphocyte.

Riegel
Franz, German physician, 1843–1904. See R. pulse.

Rieger
Herwigh, German ophthalmologist. See R. anomaly, R. syndrome.

Riehl
Gustav, Austrian dermatologist, 1855–1943. See R. melanosis.

RIF
Abbreviation for resistance-inducing factor.

rifampicin (rif′am-pi-sin)
SYN: rifampin.

rifampin (rif′am-pin)
A first-line antituberculosis drug; a bactericidal agent used in the treatment of tuberculosis and other infections, that, like all antituberculosis drugs, must not be used alone in the treatment of active tuberculosis; a powerful inducer of hepatic microsomal enzymes. SYN: rifampicin.

rifamycin, rifomycin (rif-a-mi′sin, rif-o-)
A complex antibiotic, isolated from Nocardia mediterranei, that is active against Mycobacterium tuberculosis and Staphylococcus aureus; it is poorly absorbed from the gastrointestinal tract and often causes irritation and severe pain at the sites of injection.

Riga
Antonio, Italian physician, 1832–1919. See R.-Fede disease.

right-eyed (rit-id)
SYN: dextrocular.

right-footed (rit′fut-ed)
SYN: dextropedal.

right-handed (rit′hand-ed)
Denoting the habitual or more skillful use of the right hand for writing and most manual operations. SYN: dextral, dextromanual.

rigidity (ri-jid′i-te)
1. Stiffness or inflexibility. SYN: rigor (1) . 2. In psychiatry and clinical psychology, an aspect of personality characterized by an individual's resistance to change. 3. In neurology, one type of increase in muscle tone at rest; characterized by increased resistance to passive stretch, independent of velocity and symmetric about joints; increases with activation of corresponding muscles in the contralateral limb. Two basic types are cogwheel r. and lead-pipe r.. SEE ALSO: nuchal r.. [L. rigidus, rigid, inflexible] cadaveric r. SYN: rigor mortis. catatonic r. r. associated with catatonic psychotic states in which all muscles exhibit flexibilitas cerea. cerebellar r. increased tone of the extensor muscles, related to injury of the vermis of the cerebellum. clasp-knife r. SYN: clasp-knife spasticity. cogwheel r. a type of r. seen in parkinsonism in which the muscles respond with cogwheel-like jerks to the use of constant force in bending the limb. decerebrate r. a postural change that occurs in some comatose patients, consisting of episodes of opisthotonos, rigid extension of the limbs, internal rotation of the upper extremities, and marked plantar flexion of the feet; produced by a variety of metabolic and structural brain disorders. SYN: decerebrate state. decorticate r. a unilateral or bilateral postural change, consisting of the upper extremities flexed and adducted and the lower extremities in rigid extension; due to structural lesions of the thalamus, internal capsule, or cerebral white matter. SYN: decorticate state. lead-pipe r. the plastic type of r. resembling that of a pipe of lead seen in certain forms of parkinsonism. nuchal r. impaired neck flexion resulting from muscle spasm (not actual r.) of the extensor muscles of the neck; usually attributed to meningeal irritation. ocular r. the resistance offered by the eyeball to a change in intraocular volume; manifested as a change in intraocular pressure. postmortem r. SYN: rigor mortis. scleral r. the resistance of the eye to changes in shape with changes in intraocular pressure.

rigor (rig′er)
1. SYN: rigidity (1) . 2. SYN: chill (2) . [L. stiffness] acid r. coagulation of muscle protein induced by acids. calcium r. arrest of the heart in the fully contracted state as a result of poisoning with calcium. heat r. coagulation of muscle protein induced by heat. r. mortis stiffening of the body, 1–7 hours after death, from hardening of the muscular tissues as a consequence of the coagulation of the myosinogen and paramyosinogen; it disappears after 1–6 days or when decomposition begins. SYN: cadaveric rigidity, postmortem rigidity. myocardial r. mortis SYN: ischemic contracture of the left ventricle.

Riley
Conrad M., U.S. pediatrician, *1913. See R.-Day syndrome.

Riley
Harris D., Jr., 20th century U.S. physician. See Smith-R. syndrome.

riluzole (ril′oo-zol)
A drug used to treat amyotrophic lateral sclerosis; mechanism of action not known.

rim
A margin, border, or edge, usually circular in form. bite r. SYN: occlusion r.. occlusal r. SYN: occlusion r.. occlusion r. occluding surfaces built on temporary or permanent denture bases for the purpose of making maxillomandibular relation records and for arranging teeth. SYN: bite r., occlusal r., record r.. orbital r. SYN: orbital margin. record r. SYN: occlusion r..

rima, gen. and pl. rimae (ri′ma, ri′me) [TA]
A slit or fissure, or narrow elongated opening between two symmetric parts. [L. a slit] r. glottidis [TA] the interval between the true vocal cords. SYN: r. vocalis&star, glottis vera, true glottis. r. oris [TA] SYN: oral fissure. r. palpebrarum [TA] SYN: palpebral fissure. r. pudendi [TA] SYN: pudendal cleft. r. respiratoria SYN: r. vestibuli. r. vestibuli [TA] the interval between the false vocal cords or vestibular folds. SYN: false glottis, glottis spuria, r. respiratoria. r. vocalis r. glottidis. r. vulvae SYN: pudendal cleft.

rimantadine (ri-man′ta-den)
An antiviral agent resembling amantadine in its activity but seemingly with fewer central nervous system adverse reactions.

Rimini test
See under test.

rimose (ri′mos)
Fissured; marked by cracks in all directions, like the crackle of porcelain. [L. rimosus, fr. rima, a fissure]

rimula (rim′u-la)
A minute slit or fissure. [L. dim. of rima]

Rindfleisch
Georg E., German physician, 1836–1908. See R. folds, under fold.

ring (ring) [TA]
1. A circular band surrounding a wide central opening; a r.-shaped or circular structure surrounding an opening or level area. SYN: anulus [TA] . 2. The closed ( i.e., endless) chain of atoms in a cyclic compound; commonly used for “cyclic” or “cycle.” 3. A marginal growth on the upper surface of a broth culture of bacteria, adhering to the sides of the test tube in the form of a circle. SYN: annulus. [A.S. hring] abdominal r. SYN: deep inguinal r.. amnion r. the r. formed by the attachment of the amnion to the umbilical cord at its point of emergence from the umbilicus. annuloplasty r. the dilated annulus is sutured, often to a prosthetic r., thereby reducing it to its normal systolic size. anterior limiting r. SYN: anterior limiting lamina. Balbani r. an extremely large puff at a band of a polytene chromosome. benzene r. the closed-chain arrangement of the carbon and hydrogen atoms in the benzene molecule. SEE ALSO: cyclic compound. Bickel r. SYN: pharyngeal lymphatic r.. Cannon r. SYN: Cannon point. cardiac lymphatic r. SYN: lymph nodes around cardia of stomach, under lymph node. casting r. SYN: refractory flask. choroidal r. a lightly pigmented crescent or r. adjacent to the optic disk. ciliary r. SYN: orbiculus ciliaris. common tendinous r. of extraocular muscles [TA] a fibrous r. that surrounds the optic canal and the medial part of the superior orbital fissure; it gives origin to the four rectus muscles of the eye and is partially fused with the sheath of the optic nerve. SYN: anulus of Zinn, anulus tendineus communis, Zinn ligament, Zinn r., Zinn tendon. conjunctival r. [TA] a narrow r. at the junction of the periphery of the cornea with the conjunctiva. SYN: anulus conjunctivae [TA] . constriction r. 1. true spastic stricture of the uterine cavity resulting when a zone of muscle goes into local tetanic contraction and forms a tight constriction about some part of the fetus; 2. SYN: amnionic band. crural r. SYN: femoral r.. deep inguinal r. [TA] the opening in the transversalis fascia through which the ductus deferens and gonadal vessels (or round ligament in the female) enter the inguinal canal. Located midway between anterior superior iliac spine and pubic tubercle, it is bounded medially by the lateral umbilical fold (inferior epigastric vessels) and inferiorly by the iliopubic tract. Indirect inguinal hernias exit the abdominal cavity via the deep inguinal r. SYN: anulus inguinalis profundus [TA] , abdominal r., anulus abdominalis, internal inguinal r.. external inguinal r. SYN: superficial inguinal r.. femoral r. [TA] the superior opening of the femoral canal, bounded anteriorly by the inguinal ligament, posteriorly by the pectineus muscle, medially by the lacunar ligament, and laterally by the femoral vein. Passageway by which many lymphatics from lower limb pass to abdomen. Accommodates enlargement of femoral vein in Valsalva maneuver. Often occupied by a lymph node (Cloquet) and is the site of femoral hernias. SYN: anulus femoralis [TA] , crural r.. fibrocartilaginous r. of tympanic membrane [TA] the thickened portion of the circumference of the tympanic membrane that is fixed in the tympanic sulcus. SYN: anulus fibrocartilagineus membranae tympani [TA] , Gerlach annular tendon. fibrous r. 1. SYN: (right and left) fibrous rings of heart. 2. SYN: anulus fibrosus of intervertebral disk. fibrous r. of intervertebral disk SYN: anulus fibrosus of intervertebral disk. Fleischer r. an incomplete r. often present at the base of the keratoconus cone; it may be yellow or greenish from deposition of hemosiderin. Fleischer-Strümpell r. SYN: Kayser-Fleischer r.. Flieringa r. a stainless steel r. sutured to the sclera to prevent collapse of the globe in difficult intraocular operations. gestational r. the white r. identified by pulse echosonography that signals an early stage of pregnancy. glaucomatous r. SYN: glaucomatous halo (1) . Graefenberg r. obsolete term for a silver or silkworm gut r. designed for insertion into the uterine cavity as a means of contraception. greater r. of iris SYN: outer border of iris. internal inguinal r. SYN: deep inguinal r.. r. of iris SYN: border of iris. Kayser-Fleischer r. a greenish yellow pigmented r. encircling the cornea just within the corneoscleral margin, seen in hepatolenticular degeneration, due to copper deposited in Descemet membrane. SYN: Fleischer-Strümpell r.. lesser r. of iris SYN: inner border of iris. Liesegang rings colored rings of precipitated silver chromate formed when a drop of concentrated silver nitrate is added to the surface of a gel (such as gelatin, agar, or silica gel) containing potassium dichromate. Lower r. SYN: (right and left) fibrous rings of heart. lymphatic r. of cardiac part of stomach SYN: lymph nodes around cardia of stomach, under lymph node. neonatal r. SYN: neonatal line. pathologic retraction r. a constriction located at the junction of the thinned lower uterine segment with the thick retracted upper uterine segment, resulting from obstructed labor; this is one of the classic signs of threatened rupture of the uterus. pharyngeal lymphatic r. [TA] the broken r. of lymphoid tissue, formed of the lingual, faucial, and pharyngeal tonsils. SYN: anulus lymphoideus pharyngis [TA] , Bickel r., tonsillar r., Waldeyer throat r.. physiologic retraction r. a ridge on the inner uterine surface at the boundary line between the upper and lower uterine segment that occurs in the course of normal labor. polar r. a thickened, electron-dense r. at the anterior end of certain stages of the Apicomplexa; part of the apical complex characteristic of these sporozoans. (right and left) fibrous rings of heart [TA] two fibrous rings that surround atrioventricular orifices of the heart, providing attachment for the atrioventricular valve leaflets and maintaining patency of the orifices. As part of the fibrous skeleton of the heart, the fibrous rings also provide origin and insertion for the myocardium. SYN: anulus fibrosus (1) [TA] , anulus fibrosus dexter/sinister cordis, coronary tendon, fibrous r. (1) , Lower r.. Schatzki r. a contraction r. or incomplete mucosal diaphragm in the lower third of the esophagus, which is occasionally symptomatic. Schwalbe r. SYN: anterior limiting lamina. scleral r. the appearance of the sclera adjacent to the optic disk when the retinal pigment epithelium does not extend to the optic nerve. signet r. the early stage of trophozoite development of the malaria parasite in the red blood cell; the parasite cytoplasm stains blue around its circular margin, and the nucleus stains red in Romanowsky stains, while the central vacuole is clear, giving the ringlike appearance. r. of Soemmerring a mass of lenticular fibers enclosed between the anterior and posterior portion of the lenticular capsule, leaving the pupillary area relatively free. subcutaneous r. SYN: superficial inguinal r.. superficial inguinal r. [TA] the slitlike opening in the aponeurosis of the external oblique muscle of the abdominal wall through which the spermatic cord (round ligament in the female) and inguinal hernias emerge from the inguinal canal. SEE ALSO: aponeurosis of external oblique muscle. SYN: anulus inguinalis superficialis, external inguinal r., subcutaneous r.. tonsillar r. SYN: pharyngeal lymphatic r.. tracheal r. SYN: tracheal cartilages, under cartilage. tympanic r. [TA] in the fetus, a more or less complete bony r. at the medial end of the cartilaginous external acoustic meatus, to which is attached the tympanic membrane. SYN: anulus tympanicus, tympanic bone. umbilical r. [TA] an opening in the linea alba through which pass the umbilical vessels in the fetus; in young embryos it is relatively nearer to the pubis, but gradually ascends to the center of the abdomen; it is closed in the adult, its site being indicated by the umbilicus or navel. SYN: anulus umbilicalis, canalis umbilicalis. vascular r. anomalous arteries (aortic arches) congenitally encircling the trachea and esophagus, at times producing pressure symptoms. Vieussens r. SYN: limbus fossae ovalis. Vossius lenticular r. a r.-shaped opacity found on the anterior lens capsule after contusion of the eye, due to pigment and blood. Waldeyer throat r. SYN: pharyngeal lymphatic r.. Zinn r. SYN: common tendinous r. of extraocular muscles.

Ringer
Sydney, English physiologist, 1835–1910. See R. injection, R. solution, lactated R. injection, Krebs-R. solution, Locke-R. solution, R. lactate.

ring-knife (ring-nif)
A circular or oval ring with internal cutting edge, on the model of the carpenter's spoke-shave, for shaving off tumors in the nasal and other cavities. SYN: spoke-shave.

ringworm (ring′werm)
SYN: tinea. r. of beard SYN: tinea barbae. black-dot r. tinea capitis due most commonly to Trichophyton tonsurans or T. violaceum. r. of body SYN: tinea corporis. crusted r. SYN: favus. r. of foot SYN: tinea pedis. honeycomb r. SYN: favus. r. of nails SYN: onychomycosis. Oriental r. SYN: tinea imbricata. r. of scalp SYN: tinea capitis. scaly r. SYN: tinea imbricata. Tokelau r. SYN: tinea imbricata. [Tokelau Islands in S. Pacific Ocean]

Rinne
Friedrich Heinrich A., German otologist, 1819–1868. See R. test.

Riolan
Jean, French anatomist and botanist, 1577–1657. See R. anastomosis, R. arc, R. arcades, under arcade, R. bones, under bone, R. bouquet, R. muscle.

RIP
Abbreviation for radioimmunoprecipitation.

riparian (ri-par′e-an, ri-)
Relating to a ripa; marginal.

Ripault
Louis H.A., French physician, 1807–1856. See R. sign.

ripening (ri′pen-ing)
Denoting progressive oxidation of dye solutions, as in the r. of hematoxylin solutions to hematein or of methylene blue to azure dyes.

Ripstein
Charles B., 20th century U.S. surgeon. See R. operation.

RISA
Abbreviation for radioiodinated serum albumin.

risk
The probability that an event will occur. attributable r. the rate of a disease or other outcome in exposed individuals that can be attributed to the exposure. competing r. an event that removes a subject from being at r. for an outcome under investigation. empiric r. r. that is based on empiric evidence alone, without any appeal to formal theory or surmise. radiation risks the risks to health posed by exposure to radiation. Sources of exposure are both natural and artificial ( e.g., medical and occupational). See background radiation.Excessive exposure to ionizing radiation is associated with increased r. of malignant diseases, particularly of the skin and blood-forming organs; increased r. of abnormal variation in reproductive cells, with the possibility of abnormality in offspring; and increased r. of fetal abnormality from maternal exposure during early pregnancy. For most people, natural sources account for the bulk of received radiation, with artificial sources adding only a small percentage to the average annual dose. Public perception of the hazards of radiation is often at odds with scientific positions on the subject. Equivocal research results (as in attempts to assess the added cancer r. posed by mammograms) have contributed to public fears. Some studies have concluded that, whether or not public fears of nuclear power plants are justified, the added stress caused by such fears in itself constitutes a threat to health. recurrence r. r. that a disease will occur elsewhere in a pedigree, given that at least one member of the pedigree (the proband) exhibits the disease. relative r. the ratio of the r. of disease among those exposed to a r. factor to the r. among those not exposed.

Risley
Samuel D., U.S. ophthalmologist, 1845–1920. See R. rotary prism.

risorius (ri-sor′e-us)
See r. (muscle). [L. risor, a laughter, fr. rideo, pp. risus, to laugh]

RIST
Abbreviation for radioimmunosorbent test.

ristocetin (ris-to-se′tin)
An antibiotic produced by the fermentation of Amycolatopsis orientalis lurida, comprising two substances; r. A and r. B; it is useful against staphylococcic and enterococcic infections refractory to other antibiotics.




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