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Medical Dictionary - Dictionary of Medicine and Human Biology

Medical Dictionary


heartburn (hart′bern)
SYN: pyrosis.

SYN: Dirofilaria immitis.

heat (q) (het)
1. A high temperature; the sensation produced by proximity to fire or an incandescent object, as opposed to cold. 2. The kinetic energy of atoms and molecules, as well as rotation and vibration. 3. SYN: estrus. 4. SYN: enthalpy. [A.S. haete] atomic h. the amount of h. required to raise an atom from 0° to 1°C; approximately the same for all elements (about 25 kJ/g-atom). h. of combustion the quantity of h. liberated per gram-molecular weight when a substance undergoes complete oxidation. h. of compression h. produced when a gas is compressed. conductive h. h. transmitted by direct contact, as by an electric pad or hot-water bottle. convective h. h. conveyed by a warm medium, such as air or water, in motion from its source. conversive h. h. produced in a body by the absorption of waves that are not in themselves hot, such as the sun's rays or infrared radiation. h. of crystallization the quantity of h. liberated or absorbed per mol when a substance passes into the crystalline state. h. of dissociation the h. (expressed in calories or joules) expended in the dissociation of 1 mol of a substance into specified products. h. of evaporation the h. absorbed in the evaporation of water, sweat or other liquid; for water it amounts to 540 cal/g at 100°C. SYN: h. of vaporization. h. of formation the h. (expressed in calories or joules) absorbed or liberated during the (hypothetical) reaction in which a mole of a compound is formed from the necessary elements, in elemental form. initial h. the first burst of h. produced after the beginning of a muscle twitch, described by A. V. Hill. latent h. the amount of h. that a substance may absorb without an increase in temperature, as in conversion from solid to liquid state (ice to water at 0°C), or from liquid to gaseous state (water to steam at 100°C). Cf.:sensible h.. molecular h. the product of the specific h. of a body multiplied by its molecular weight. prickly h. SYN: miliaria rubra. radiant h. h. given off from any body in the form of infrared waves. sensible h. the amount of h. that, when absorbed by a substance, causes a rise in temperature. Cf.:latent h.. h. of solution the quantity of h. absorbed or evolved when a solid is dissolved in a liquid. specific h. the amount of h. required to raise any substance through 1°C of temperature, compared with that raising the same volume of water 1°C. h. of vaporization SYN: h. of evaporation.

heat-labile (het′la′bl)
Destroyed or altered by heat.

heat-stable (het′sta′bl)
SYN: thermostabile.

heatstroke (het′strok)
A severe and often fatal illness produced by exposure to excessively high temperatures, especially when accompanied by marked exertion; characterized by headache, vertigo, confusion, hot dry skin, and a slight rise in body temperature; in severe cases, very high fever, vascular collapse, and coma develop. SYN: heat apoplexy (1) , heat hyperpyrexia, malignant hyperpyrexia, thermic fever.

Hebeloma (heb-e-lo′ma)
A genus of mushrooms that is a source of gastrointestinal toxins.

hebephrenia (he-be-fre′ne-a, heb′e-)
A syndrome characterized by shallow and inappropriate affect, giggling, and silly, regressive behavior and mannerisms; a subtype of schizophrenia now renamed disorganized schizophrenia. [G. hebe, puberty, + phren, the mind]

hebephrenic (he-be-fren′ik, heb-e-)
Relating to or characterized by hebephrenia.

William, English physician, 1710–1801. See H. angina, H. nodes, under node, Rougnon-H. disease.

hebetic (he-bet′ik)
Pertaining to youth. [G. hebetikos, youthful, fr. hebe, youth]

hebetude (heb′e-tood)
SYN: moria (1) . [L. hebetudo, fr. hebeo, to be dull]

hebiatrics (he-be-at′riks)
SYN: adolescent medicine. [G. hebe, youth, + iatrikos, relating to medicine]

Ferdinand von, Austrian dermatologist, 1816–1880. See H. prurigo.

hecateromeric (hek′a-ter-o-mer′ik)
Denoting a spinal neuron whose axon divides and gives off processes to both sides of the cord; usually the same as a heteromeric neuron. SYN: hecatomeral, hecatomeric. [G. hekateros, each of two, + meros, part]

hecatomeral, hecatomeric (hek′a-tom′er-al, hek′a-to-mer′ik)
SYN: hecateromeric.

Victor, early 20th century Austrian pathologist. See H. pneumonia.

John W., U.S. dentist, *1923. See H. disease.

hectic (hek′tik)
Denoting a daily afternoon rise of temperature, accompanied by a flush on the cheeks, occurring in active tuberculosis and other infections; use of the term is based on the appearance of the temperature chart. [G. hektikos, habitual, h., consumptive, fr. hexis, habit]

hecto- (h)
Prefix used in the SI and metric system to signify multiples of one hundred (102). [G. hekaton, one hundred]

hectogram (hek′to-gram)
One hundred grams, the equivalent of 1543.7 grains.

hectoliter (hek′to-le-ter)
One hundred liters, the equivalent of 105.7 quarts or 26.4 American (22 imperial) gallons.

hedeoma (he-de-o′ma)
See pennyroyal.

hederiform (hed′er-i-form)
Ivy-shaped; a term used for certain sensory endings in the skin. [L. hedera, ivy, + forma, shape]

hedonophobia (he′do-no-fo′be-a)
Morbid fear of pleasure. [G. hedone, delight, + phobos, fear]

Gustav, Swedish endodontist. See H. file.

heel (hel) [TA]
1. Proximal portion of the plantar surface of the foot. 2. SYN: calx (2) . 3. SYN: distal end. [A.S. hela] black h. SYN: calcaneal petechiae. cracked h. SYN: keratoderma plantare sulcatum. painful h. a condition in which bearing weight on the h. causes pain of varying severity. SYN: calcaneodynia. prominent h. a condition marked by a tender swelling on the os calcis due to a thickening of the periosteum or fibrous tissue covering the back of the os calcis.

Christian Frederick, Danish ophthalmologist, *1871. See H. disease.

Alfred, German gynecologist, 1830–1914. See H. dilators, under dilator, H. sign.

Robert M.P., Swiss physician, 1907–1970. See H. anomaly, H. syndrome, May-H. anomaly.

Otto, British chemist, 1853–1924. See H. number.

Rudolph P.H., German histologist and physiologist, 1834–1897. See H. crescents, under crescent, H. demilunes, under demilune, H. law, H. azan stain, H. iron hematoxylin stain, H. pouch, Biondi-H. stain.

height (h) (hit)
Vertical measurement. anterior facial h. (AFH) in cephalometrics, the linear measurement from the nasion to the menton. h. of contour the line encircling a tooth or other structure at its greatest bulge or diameter. It relates to a selected path of insertion of a dental appliance or device. cusp h. 1. the shortest distance between the tip of a cusp and its base plane; 2. the shortest distance between the deepest part of the central fossa of a posterior tooth and a line connecting the points of the cusps of the tooth. facial h. the linear dimension in the midline from the hairline to the menton. nasal h. the distance between the nasion and the lower border of the nasal aperture. orbital h. the distance between the midpoints of the upper and lower margins of the orbit.

Karl, Dutch physician, 1869–1914. See H. thigh.

Ernst L., German physician, 1747–1834. See H.-Kreysig sign.

Henry J., U.S. thoracic surgeon, *1920. See H. maneuver.

Leopold, German ophthalmologist, 1870–1940.

Walter, German surgeon, 1834–1901. See H.-Mikulicz pyloroplasty.

Robert, German pathologist, 1865–1924. See H. body anemia, H. bodies, under body, H. body test, H.-Ehrlich body, H. body anemia.

Lorenz, German anatomist, 1683–1758. See H. diverticulum, H. valve.

HeLa (he′la)
Referring to cells of the first continuously cultured (human cervical) carcinoma strain. [Henrietta Lacks (d. 1951), whose cervical carcinoma was the source of the cell line]

helcomenia (hel-ko-me′ne-a)
Occurrence of ulcers at the time of a menstruation. [G. helkos, ulcer, + emmenos, monthly]

Hans, German anatomist, 1866–1942. See H. bundle, H. decussation.

helianthine (he-li-an′thin)
SYN: methyl orange.

helical (hel′i-kal)
1. Relating to a helix. SYN: helicine (2) . 2. SYN: helicoid. [G. helix, a coil]

helices (hel′i-sez)
Plural of helix.

helicine (hel′i-sen)
1. Coiled. 2. SYN: helical (1) . [G. helix, a coil]

Helicobacter (hel′i-ko-bak′ter)
A genus of helical, curved, or straight microaerophilic bacteria with rounded ends and multiple sheathed flagella (unipolar or bipolar and lateral) with terminal bulbs. Form nonpigmented, translucent colonies, 1–2 mm in diameter. Catalase and oxidase positive. Found in gastric mucosa of primates, including human beings and ferrets. Some species are associated with gastric and peptic ulcers and predispose to gastric carcinoma. The type species is H. pylori. H. cinaedi a bacterial species associated with cases of proctitis and colitis in homosexual men. H. fennelliae a bacterial species reported associated with proctitis and colitis in homosexual men. H. heilmannii species observed in gastric mucosa. This agent has a low prevalence (less than 1% in patients), has not been cultured in vitro, and is of unknown pathogenic significance. H. pylori a bacterial species that produces urease and causes gastritis and is involved in most cases of peptic ulcer disease of the stomach and duodenum; infection with this organism also plays an etiologic role (probably along with dietary cofactors) in dysplasia and metaplasia of gastric mucosa, distal gastric adenocarcinoma, and non-Hodgkin lymphoma of the stomach. SYN: Campylobacter pylori.The organism was first observed in 1982 by Robin Warren and Barry J. Marshall at Royal Perth Hospital in Western Australia in biopsy specimens from patients with chronic gastritis. Originally believed to be a species of Campylobacter, the organism was reclassified as H. pylori in 1989. H. pylori, a curved or spiral, flagellated Gram-negative bacillus, colonizes the gastric mucosa, attaching itself to the surface of mucus-secreting columnar cells. The ability of the organism to survive in an acid medium is due to its production of urease, which converts urea to ammonia and alkalizes the film of mucus in which it resides. Infection with H. pylori is common worldwide, and the incidence of infection increases with age, reaching about 50% among persons aged 60. Transmission is believed to be from person to person by the fecal-oral route. Familial clustering of infection and a higher incidence among blacks and Hispanics have been attributed to social rather than genetic factors. Once infection occurs, it typically remains for life unless treated with antibiotics. Newly acquired infection results in extensive damage to parietal cells, with acute gastritis accompanied by impairment of acid production, which may be transitory. Most people infected have no symptoms (possibly because some strains of H. pylori do not produce cytotoxins) but about 1% of H. pylori–infected adults each year develop peptic ulcer. The risk of progression to peptic ulcer disease is increased by cigarette smoking and long-term use of nonsteroidal antiinflammatory agents. About 70% of all people with gastric ulcers and 90% of those with duodenal ulcers are found to be infected with H. pylori. In the U.S., about 500,000 new cases of peptic ulcer disease occur each year. The disease is responsible for 3–4 million physician visits and approximately 16,000 deaths annually. H. pylori infection has not been associated with nonulcer dyspepsia or inflammatory disorders of the digestive tract other than peptic ulceration. However, the incidence of both gastric adenocarcinoma and gastric lymphoma is higher in infected persons. In addition, the organism has been implicated in some cases of cholecystitis and autoimmune thyroiditis, and some studies have suggested that gastric infection with H. pylori may be a factor, by an unknown mechanism, in some cases of sudden infant death syndrome (SIDS). Diagnosis of H. pylori infection can be confirmed by identification of the organism in stained sections of gastric biopsy material, by culture from biopsy material, by testing biopsy material for urease activity, by identification of bacterial antigen in stool, by finding IgG antibody to the organism in the serum (the method of choice to confirm infection in a previously untreated patient), or by detection of urease activity with various biochemical tests. The urea breath test is more useful than serologic testing to confirm eradication of H. pylori after a course of treatment, since IgG antibody may remain elevated for more than 1 year after eradication. Eradication of the organism with antibiotic therapy does not yield faster healing of a peptic ulcer than treatment with antisecretory agents, but it greatly reduces the likelihood of ulcer recurrence. Recommended regimens for eradication of H. pylori include combinations of bismuth subsalicylate with 2 antibiotics (metronidazole or clarithomycin and tetracycline or amoxicillin). Acquired resistance of H. pylori to the macrolide and imidazole antibiotics is a growing problem. It is estimated that about 30% of strains of the organism in the U.S. are resistant to metronidazole and that almost 10% are resistant to macrolides. A major factor in the emergence of resistant strains appears to be an inadequate or failed first course of treatment. Active vaccination by oral administration of an enzymatically inactive recombinant subunit of H. pylori urease combined with a mucosal adjuvant (labile toxin of Escherichia coli) has elicited microbiologic and clinical cure of H. pylori infection in animal studies and limited human trials.

helicoid (hel′i-koyd)
Resembling a helix. SYN: helical (2) . [G. helix, a coil, + eidos, resemblance]

helicopodia (hel′i-ko-po′de-a)
SYN: helicopod gait. [G. helix, a coil, + pous, foot]

helicotrema (hel′i-ko-tre′ma) [TA]
A semilunar opening at the apex of the cochlea through which the scala vestibuli and the scala tympani of the cochlea communicate with one another. SYN: Breschet hiatus, Scarpa hiatus. [G. helix, a spiral, + trema, a hole]

Louis T., French gynecologist, 1804–1867. See H. bundle.

heliencephalitis (he-le-en-sef-a-li′tis)
Inflammation of the brain following sunstroke. [G. helios, sun, + enkephalos, brain, + -itis, inflammation]

The sun. [G. helios]

helioaerotherapy (he′le-o-ar-o-thar′a-pe)
Treatment of disease by exposure to sunshine and fresh air.

heliopathy (he-le-op′a-the)
Injury from exposure to sunlight. [helio- + G. pathos, suffering]

heliophobia (he′le-o-fo′be-a)
Morbid fear of exposure to the sun's rays. [helio- + G. phobos, fear]

heliosis (he-le-o′sis)
SYN: sunstroke. [helio- + G. -osis, condition]

heliotaxis (he-le-o-tak′sis)
A form of phototaxis, and perhaps of thermotaxis, in which there is a tendency to growth or movement toward (positive h.) or away from (negative h.) the sun or the sunlight. SYN: heliotropism. [helio- + G. taxis, orderly arrangement]

heliotropism (he-le-ot′ro-pizm)
SYN: heliotaxis. [helio- + G. trope, a turning]

Heliozoea (he′le-o-zo′e-a)
A class of protozoans (subphylum Sarcodina) distinguished by stiff radiating axopodia on all sides, usually naked, though some have a skeleton of siliceous scales and spines, but without a central capsule. They are mostly fresh water dwellers, and colonial forms are common. [helio- + G. zoon, animal]

helium (He) (he′le-um)
A gaseous element present in minute amounts in the atmosphere (0.000524% of dry volume); atomic no. 2, atomic wt. 4.002602; used as a diluent of medicinal gases; used as a diluent of oxygen principally in nonmedical applications, and in its liquid form as the coolant for super-conducting magnets (as in magnetic resonance imaging). [G. helios, the sun]

The rare stable isotope of helium (1.37 parts per million of ordinary helium); produced by the beta decay of tritium.

The common helium isotope, making up 99.999% of natural helium; it is emitted in the form of alpha rays (which are helium nuclei), from a variety of radionuclides.

helix, pl .helices (he′liks, hel′i-sez) [TA]
1. [NA] The margin of the auricle; a folded rim of cartilage forming the upper part of the anterior, the superior, and the greater part of the posterior edges of the auricle. 2. A line in the shape of a coil (or a spring, or the threads on a bolt), each point being equidistant from a straight line that is the axis of the cylinder in which each point of the h. lies; often, mistakenly, applied to a spiral. [L. fr. G. h., a coil] 310 h. a type of right-handed h. found in small pieces in a number of proteins; has three amino acid residues per turn. 3.613 h. SYN: α h.. α h. the helical (commonly right-handed) form present in many proteins, deduced by Pauling and Corey from x-ray diffraction studies of proteins such as α-keratin; the h. is stabilized by hydrogen bonds between, e.g., R2C&dbond;O and HNR2′ groups (symbolized by the center dot in R2CO&chmpnt;HNR2′) of different eupeptide bonds. In a true α h., there are 3.6 amino acid residues per turn of the h. and a rise of 1.5 Å per residue. SYN: 3.613 h., Pauling-Corey h.. collagen h. an extended left-handed h. resulting from the high levels of glycine, l-proline, and l-hydroxyproline present in the collagens. There are 3.3 amino acids per turn of the h.. Three of those left-handed helices form a triple superhelix that is right-handed. DNA h. SYN: Watson-Crick h.. double h. SYN: Watson-Crick h.. π h. a rare right-handed h. found only in small portions of certain proteins. Stabilized by similar hydrogen bonds as in an α h.; there are 4.3 amino acid residues per turn of this h.. Pauling-Corey h. SYN: α h.. triple h. the superhelix formed (right-handed) from three individual collagen helices (each being left-handed). twin h. SYN: Watson-Crick h.. Watson-Crick h. the helical structure assumed by two strands of deoxyribonucleic acid, held together throughout their length by hydrogen bonds between bases on opposite strands, referred to as Watson-Crick base pairing. See base pair. SYN: DNA h., double h., twin h..

hellebore (hel′e-bor)
A plant of the genus Helleborus, especially H. niger (black h.). SEE ALSO: Veratrum album, Veratrum viride. [G. helleboros] false h. SYN: adonis.


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