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Medical Dictionary


hybaroxia (hi-ba-rok′se-a)
Oxygen therapy with pressures greater than 1 atmosphere or ambient oxygen pressure applied to the entire body in a chamber or room. [G. hyper, above, + baros, pressure, + oxys, acute]

hybenzate (hi-ben′zat)
USAN-approved contraction for o-(4-hydroxybenzoyl)benzoate.

hybrid (hi′brid)
1. An individual (plant or animal) whose parents are different varieties of the same species or belong to different but closely allied species. 2. Fused tissue culture cells, as in a hybridoma. 3. A bond or valence orbital obtained by the linear combination of two or more different atomic orbitals. SYN: crossbreed (1) . [L. hybrida, offspring of a tame sow and a wild boar, fr. G. hybris, violation, wantonness] DNA-RNA h. double-stranded polynucleic acids in which one strand is DNA and the other strand is the complementary RNA; formed during transcription and during multiplication of oncogenic RNA viruses. SV40-adenovirus h. a virion consisting of SV40 genetic material encased in an adenovirus capsid.

hybridism (hi′brid-izm)
The state of being hybrid.

hybridization (hi′brid-i-za′shun)
1. The process of breeding a hybrid. 2. Crossing over between related but nonallelic genes. 3. The specific reassociation of complementary strands of polynucleic acids; e.g., the formation of a DNA-RNA hybrid. 4. The process or act of forming a macromolecular hybrid in which the subunits are obtained from different sources. SYN: crossbreeding. cell h. fusion of two or more dissimilar cells, leading to formation of a synkaryon. cross h. annealing of a DNA probe to an imperfectly matching DNA molecule. DNA h. a technique used to determine the relatedness of microorganisms by the speed and efficiency of the reassociation of single-stranded DNA to form double-stranded DNA when one of the strands originates from one organism and the other strand from another organism; occurs when the base sequences are complementary or nearly so. fluorescence in situ h. SYN: fluorescent in situ h.. fluorescent in situ h. a method used to determine the chromosomal location or expression pattern of genomic DNA or cDNA fragments. The piece of DNA to be mapped (the “probe”) is labeled with a fluorescent dye and hybridized to a chromosome preparation or to a tissue section. The probe anneals to complementary DNA or RNA sequences. Examination of the chromosomes or tissue section under a fluorescence microscope reveals the number, size, and location of the target sequences. SYN: fluorescence in situ h.. nucleic acid h. SYN: anneal (5) . overlap h. SYN: chromosome walking. in situ h. a technique developed in 1969 for annealing nucleic acid probes to cellular DNA for detection by autoradiography. Under proper laboratory conditions, the binding process occurs spontaneously. In situ h. constitutes a key step in DNA fingerprinting. SYN: in situ nucleic acid h.. in situ nucleic acid h. SYN: in situ h.. somatic cell h. production of a heterokaryon.

hybridoma (hi-brid-o′ma)
A tumor of hybrid cells used in the in vitro production of specific monoclonal antibodies; produced by fusion of an established tissue culture line of lymphocyte tumor cells ( e.g., mouse plasmacytoma cells) and specific antibody-producing cells ( e.g., splenocytes from specifically immunized mice); fusions are accomplished by use of polyethylene glycol or other methods. [G. hybris, violation, wantonness, + -oma, tumor]

hyclate (hi′klat)
USAN-approved contraction for monohydrochloride hemiethanolate hemihydrate, HCl&chmpnt;12C2H5OH&chmpnt;12H2O.

hydantoin (hi-dan′to-in)
2,4-Imidazolidinedione;derived from urea or from allantoin; the NH–CH2–CO group is prototypical of α-amino acids. H. derivatives are formed by the reaction of phenylisothiocyanate and a polypeptide. SYN: glycolylurea.

hydantoinate (hi-dan-to′in-at)
A salt of hydantoin.

hydatid (hi′da-tid)
1. SYN: h. cyst. 2. A vesicular structure resembling an Echinococcus cyst. [G. hydatis, a drop of water, a hyatid] Morgagni h. SYN: vesicular appendages of epoophoron, under appendage. nonpedunculated h. SYN: appendix of testis. pedunculated h. SYN: appendix of epididymidis. sessile h. SYN: appendix of testis. stalked h. SYN: vesicular appendages of epoophoron, under appendage.

hydatidiform (hi-da-tid′i-form)
Having the form or appearance of a hydatid.

hydatidocele (hi-da-tid′o-sel)
A cystic mass composed of one or more hydatids formed in the scrotum. [hydatid + G. kele, tumor]

hydatidosis (hi′da-ti-do′sis)
The morbid state caused by the presence of hydatid cysts.

hydatidostomy (hi′da-ti-dos′to-me)
Surgical evacuation of a hydatid cyst. [hydatid + G. stoma, mouth]

Hydatigera taeniaeformis (hi-da-tij′er-a te-ni-e-for′mis)
SYN: Taenia taeniaeformis.

hydatoid (hi′da-toyd)
1. The aqueous humor. 2. The hyaloid membrane. 3. Relating to the aqueous humor. 4. Watery or resembling water. [G. hydor (hydat-), water, + eidos, resemblance]

hydnocarpus oil (hid-no-kar′pus)
SYN: chaulmoogra oil.

See hydro-.

hydracetin (hi-dras′e-tin)
Pure form of acetylphenylhydrazine.

hydradenitis (hi′drad-e-ni′tis)
SYN: hidradenitis.

hydradenoma (hi′drad-e-no′ma)
SYN: hidradenoma.

hydragogue (hi′dra-gog)
Producing a discharge of watery fluid; denoting a class of cathartics that retain fluids in the intestine and aid in the removal of edematous fluids, e.g., saline cathartics. [hydr- + G. agogos, drawing forth]

hydralazine hydrochloride (hi-dral′a-zen)
A vasodilating antihypertensive agent.

hydrallostane (hi-dral′o-stan)
11β,17α,21-Trihydroxy-5β-pregnane-3,20-dione;a metabolite of cortisole, reduced at the 4,5 double bond. SYN: 4,5α-dihydrocortisol.

hydramitrazine tartrate (hi-dra-mi′tra-zen)
An intestinal antispasmodic.

hydramnios, hydramnion (hi-dram′ne-os, -ne-on)
Presence of an excessive amount of amniotic fluid, usually over 2,000 mL. SYN: polyhydramnios. [G. hydor, water, + amnion]

hydranencephaly (hi′dran-en-sef′a-le)
Absence of cereberal hemispheres, which have been replaced by fluid-filled sacs, lined by leptomeninges. The skull and its brain cavities are normal. [hydr- + G. an- priv. + enkephalos, brain]

hydrargyria, hydrargyrism (hi-drar-jir′e-a, hi-drar′jir-izm)
SYN: mercury poisoning. [L. hydrargyrum, mercury]

hydrargyrum (hi-drar′ji-rum)
SYN: mercury. [G. hydrargyros, quicksilver, fr. hydor, water, + argyros, silver]

hydrarthrodial (hi-drar-thro′de-al)
Relating to hydrarthrosis.

hydrarthrosis (hi-drar-thro′sis)
Effusion of a serous fluid into a joint cavity. [hydr- + G. arthron, joint] intermittent h. a disorder characterized by a periodically recurring serous effusion into the cavity of a joint; the articulation may be the seat of a chronic arthritis or may apparently be normal in the intervals of the attacks.

hydrase (hi′dras)
Former name for hydratase.

hydrastine (hi-dras′ten)
An alkaloid of hydrastis; an isoquinoline chemically related to narcotine. As the hydrochloride, was used locally in the treatment of catarrhal inflammation of the mucous membranes, and internally in the treatment of gastric inflammation, as a uterine stimulant, and to check uterine hemorrhage.

hydrastinine (hi-dras′ti-nen)
A semisynthetic alkaloid prepared from hydrastine; the hydrochloride has been used in uterine hemorrhage and as an oxytocic; in large doses, it is a powerful depressant of the entire motor system (motor cortex, nerve, and muscle).

hydrastis (hi-dras′tis)
The dried rhizome of H. canadensis (family Ranunculaceae), a native of the eastern U.S.; formerly used in the treatment of chronic catarrhal states of the mucous membranes and in metrorrhagia. SYN: golden seal, jaundice root, yellow root. [Mod. L. fr. G. hydor (hydro-), water, + drao, to accomplish]

hydratase (hi′dra-tas)
Trivial name applied, together with dehydratase, to certain hydro-lyases (EC 4.2.1.x) catalyzing hydration-dehydration; e.g., fumarate-malate interconversion by fumarate h..

hydrate (hi′drat)
An aqueous solvate (in older terminology, a hydroxide); a compound crystallizing with one or more molecules of water; e.g., CuSO4&chmpnt;5H2O.

hydrated (hi′drat-ed)
Combined with water, forming a hydrate. SYN: hydrous.

hydration (hi-dra′shun)
1. Chemically, the addition of water; differentiated from hydrolysis, where the union with water is accompanied by a splitting of the original molecule and the water molecule. SEE ALSO: solvation. 2. Clinically, the taking in of water; used commonly in the sense of reduced h. or dehydration. 3. The formation of a shell of water molecules around a molecular entity. absolute h. actual water excess as measured by a difference from the normal or from a given water content.

hydrazide (hi′dra-zid)
An organic compound of the general formula RCO–NHNH2; an acyl derivative of hydrazine.

hydrazine (hi′dra-zen)
H2N–NH2, an oily liquid from which phenylhydrazine and similar products are derived. It is very toxic and possibly a carcinogen.

hydrazine yellow
SYN: tartrazine.

hydrazinolysis (hi′dra-zi-nol′i-sis)
Cleavage of chemical bonds by hydrazine; applied in protein and nucleic acid degradations.

hydrazone (hi′dra-zon)
A substance derived from aldehydes and ketones by reaction with hydrazine or a hydrazine derivative to give the grouping R′R&dprime;C&dbond;N&cbond;NHR.

hydremia (hi-dre′me-a)
A condition in which the blood volume is increased as a result of an increase in the water content of plasma, with or without a reduction in the concentration of protein; there is an excess of plasma in proportion to the cellular elements and a corresponding decrease in hematocrit. SYN: dilution anemia, polyplasmia. [hydr- + G. haima, blood]

hydrencephalocele (hi-dren-sef′a-lo-sel)
Protrusion, through a cleft in the skull, of brain substance expanded into a sac containing fluid. SYN: encephalocystocele, hydrocephalocele, hydroencephalocele. [hydr- + G. enkephalos, brain, + kele, tumor]

hydrencephalomeningocele (hi′dren-sef′a-lo-me-ning′go-sel)
Protrusion, through a defect in the skull, of a sac containing meninges, brain substance, and cerebrospinal fluid.

hydrencephalus (hi-dren-sef′a-lus)
Rarely used term for internal hydrocephalus. [hydr- + G. enkephalos, brain]

hydriatric, hydriatic (hi-dre-at′rik, -at′ik)
Relating to the obsolete use of water to treat or cure disease. SYN: hydrotherapeutic. [hydr- + G. iatrikos, relating to medicine]

hydric (hi′drik)
Relating to hydrogen in chemical combination.

hydride (hi′drid)
A negatively charged hydrogen ( i.e., H:−) or a compound of hydrogen in which it assumes a formal negative charge, e.g., sodium borohydride (NaBH4).

hydrindantin (hi-drin-dan′tin)
The reduced form of ninhydrin. It is often used in conjunction with ninhydrin in the detection of amino or imino groups.

hydro-, hydr-
1. Water, watery. 2. Containing or combined with hydrogen. 3. A hydatid. [G. hydor, water]

hydroa (hi-dro′a)
Any vesicular or bullous eruption. SYN: hidroa. [hydro + G. oon, egg] h. aestivale SYN: h. vacciniforme. h. puerorum SYN: h. vacciniforme. h. vacciniforme a recurrent eruption of erythema evolving to umbilicated bullae, occurring on exposure to the sun and affecting chiefly male children with resolution before adult life. In severe cases, hand and face deformities and corneal opacity may develop. SYN: h. aestivale, h. puerorum.

hydroadipsia (hi′dro-a-dip′se-a)
Absence of thirst for water. [hydro- + G. a- priv. + dipsa, thirst]

hydroappendix (hi′dro-a-pen′diks)
Distention of the vermiform appendix with a serous fluid.

hydrobilirubin (hi′dro-bil-i-roo′bin)
A dark brown-red pigment that may be formed when bilirubin is reduced.

hydrobromate (hi-dro-bro′mat)
A salt of hydrobromic acid.

hydrobromic acid (hi-dro-bro′mik)
An aqueous solution of hydrogen bromide (HBr); its salts are bromides.

hydrocalycosis (hi′dro-kal-i-ko′sis)
A usually symptomless anomaly of the renal calix that is dilated from obstruction of the infundibulum; usually discovered incidentally at pyelography or autopsy; may become infected. [hydro- + G. kalyx, cup of a flower]

hydrocarbon (hi-dro-kar′bon)
A compound containing only hydrogen and carbon. Diels h. a phenanthrene derivative obtained by the dehydrogenation of various steroids. saturated h. a h. that contains the greatest possible number of hydrogen atoms, so that the molecule contains neither rings nor multiple bonds.

hydrocele (hi′dro-sel)
A collection of serous fluid in a sacculated cavity; specifically, such a collection in the space of the tunica vaginalis testis, or in a separate pocket along the spermatic cord. [hydro- + G. kele, hernia] cervical h. a cyst formed by secretion into a persistent duct or fissure of the neck; when it involves lymph channels, it is usually a lymphangioma. SYN: h. colli. h. colli SYN: cervical h.. communicating h. associated with patent processus vaginalis. congenital h. a collection of fluid in the patent processus vaginalis leading from the abdominal cavity to the investing sac of the testis. cord h. isolated h. of spermatic cord. SYN: funicular h.. Dupuytren h. bilocular h. in which the sac fills the scrotum and also extends into the abdominal cavity beneath the peritoneum. h. feminae accumulation of serous fluid in the labium majus or in Nuck canal. SYN: Nuck h.. filarial h. h. due to microfilaria (chiefly of Wuchereria bancrofti) in the tunica vaginalis. funicular h. SYN: cord h.. noncommunicating h. cord or scrotal h. without communication to peritoneal cavity because processus vaginalis is not patent. Nuck h. SYN: h. feminae. h. spinalis SYN: spina bifida.

hydrocelectomy (hi′dro-se-lek′to-me)
Excision of a hydrocele by drainage of its fluids and, sometimes partial excision of tunical vaginalis. [hydrocele + G. ektome, excision]

hydrocephalic (hi′dro-se-fal′ik)
Relating to or suffering from hydrocephalus.

hydrocephalocele (hi-dro-sef′a-lo-sel)
SYN: hydrencephalocele.

hydrocephaloid (hi-dro-sef′a-loyd)
1. Resembling hydrocephalus. 2. A condition in infants suffering from diarrhea or other debilitating disease, in which there are dehydration and general symptoms resembling those of hydrocephalus without, however, any abnormal accumulation of cerebrospinal fluid.

hydrocephalus (hi-dro-sef′a-lus)
A condition marked by an excessive accumulation of cerebrospinal fluid resulting in dilation of the cerebral ventricles and raised intracranial pressure; may also result in enlargement of the cranium and atrophy of the brain. SYN: hydrocephaly. [hydro- + G. kephale, head] communicating h. type of h. in which there is an abnormality in cerebrospinal fluid absorption; there is no obstruction to cerebrospinal fluid flow in the ventricular system or where the cerebrospinal fluid passes into the spinal canal. congenital h. h. due to a developmental defect of the brain. SYN: primary h.. double compartment h. independent supra- and infratentorial h. usually due to a veil occlusion of the aqueduct of Sylvius. external h. 1. accumulation of fluid in the subarachnoid spaces of the brain; 2. accumulation of fluid in the subdural space owing to a persistent communication between the subarachnoid and subdural spaces. h. ex vacuo h. due to loss or atrophy of brain tissue; less commonly associated with raised intracranial pressure. internal h. h. in which the accumulation of fluid is confined to the ventricles. noncommunicating h. SYN: obstructive h.. normal pressure h. a type of h. developing usually in older people, due to failure of cerebrospinal fluid to be absorbed by the pacchionian granulations, and characterized clinically by progressive dementia, unsteady gait, urinary incontinence, and usually, a normal spinal fluid pressure. SYN: occult h.. obstructive h. h. secondary to a block in cerebrospinal fluid flow in the ventricular system or between the ventricular system and spinal canal. SYN: noncommunicating h.. occult h. SYN: normal pressure h.. otitic h. a form of h. associated with otitis media and thrombosis of one or both sigmoid sinuses of the dura, characterized by marked increase in cerebrospinal fluid pressure. postmeningitic h. ventricular dilation following meningitis and secondary to obstruction of cerebrospinal fluid pathways. posttraumatic h. ventricular dilation following injury, due either to impaired circulation and/or absorption of cerebrospinal fluid or due to loss of brain substance (h. ex vacuo). primary h. SYN: congenital h.. secondary h. an accumulation of fluid in the cranial cavity, due to meningitis or obstruction to the venous flow. thrombotic h. increase in cerebrospinal fluid and of intracranial pressure following thrombosis of the cerebral veins or sinuses; caused by septic infection, dehydration, tuberculosis, typhoid, leukemia, and other conditions. toxic h. thrombotic h. associated with some general infection or toxic state.

hydrocephaly (hi-dro-sef′a-le)
SYN: hydrocephalus.

hydrochloric acid (hi-dro-klor′ik)
HCl;the acid of gastric juice. The commercial product is used as an escharotic; the gas and the concentrated solution are strong irritants. SYN: muriatic acid. diluted h. a preparation that contains, in each 100 mL, 10 g of HCl; used internally for achlorhydria.

hydrochloride (hi-dro-klor′id)
A compound formed by the addition of a hydrochloric acid molecule to a basic moiety on the substance; e.g., guanine h., glycine h..


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