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Medical Dictionary


hexon (heks′on)
One of a group of six protein units (hexamer unit) on the triangular face of an icosohedral capsomere on certain viruses. [hex- + -on]

hexonic acid (heks-on′ik)
The aldonic acid obtained on the oxidation of the aldehyde group of an aldohexose to a carboxylic acid ( e.g., gluconic acid from glucose).

hexosamine (hek′so-sam′en)
The amine derivative (NH2 replacing OH) of a hexose; e.g., glucosamine.

hexosaminidase (hek′so-sa-min′i-das)
General term for enzymes cleaving N-acetylhexose ( e.g., N-acetylglucosamine) residues from gangliosidelike oligosaccharides. At least four specific enzymes carrying out this type of reaction are known: α-N-acetyl-d-galactosaminidase, α-N-acetyl-d-glucosaminidase, β-N-acetyl-d-h., and β-N-acetyl-d-galactosaminidase, each being specific for the configuration and type of sugar included in the name. h. A a hydrolytic enzyme that acts on ganglioside GM2, producing N-acetyl-d-galactosamine and ganglioside GM3; a deficiency of this enzyme is associated with Tay-Sachs disease. h. B a hydrolytic enzyme that acts on ganglioside GM1, producing ganglioside GM1 and galactose, as well as on globoside, producing N-acetylgalactosamine and trihexosylceramide; a deficiency of this enzyme is associated with Sandhoff disease.

hexosans (hek′so-sanz)
Polysaccharides with the general formula (C6H10O5)x that, on hydrolysis, yield hexoses; included are glucosans (glucans), mannans, galactans, and fructosans (fructans). SYN: polyhexoses.

hexose (hek′sos)
A monosaccharide containing six carbon atoms in the molecule (C6H12O6); d-glucose is the principal h. in nature.

hexosebisphosphatase, hexosediphosphatase (hek′sos-bis-fos′fa-tas, -di-)
SYN: fructose 1,6-bisphosphate.

hexose phosphatase (hek′sos fos′fa-taz)
An enzyme catalyzing the hydrolysis of a hexose phosphate to a hexose ( e.g., glucose-6-phosphatase).

hexosephosphate isomerase (hek-sos-fos′fat)
SYN: glucose-phosphate isomerase.

hexose-1-phosphate uridylyltransferase
SYN: UDPglucose-hexose-1-phosphate uridylyltransferase.

hexulose (hek′su-los)
SYN: ketohexose.

hexuronic acid (hek-sur-on′ik)
The uronic acid of a hexose.

hexyl (hek′sil)
The radical of hexane, CH3(CH2)4CH2&cbond;.

hexylresorcinol (hek′sil-re-sor′si-nol)
A broad spectrum anthelmintic and antiseptic.

William, English surgeon, 1736–1819. See H. amputation, H. hernia, H. ligament.

W.T., U.S. scientist, *1902. See H.-Pudenz valve.

Symbol for hafnium.

Symbol for mercury (hydrargyrum).

Abbreviation for human granulocytic ehrlichiosis.

Abbreviation for hyperglycemic-glycogenolytic factor.

Abbreviation for human growth hormone. See somatotropin.

Abbreviation for hypoxanthine guanine phosphoribosyltransferase.

Abbreviation for high-grade squamous intraepithelial lesion.

Abbreviation for hepatitis G virus.

Abbreviation for human herpesvirus.

hiatal (hi-a′tal)
Relating to a hiatus.

hiatus (hi-a′tus) [TA]
An aperture, opening, or foramen. [L. an aperture, fr. hio, pp. h., to yawn] adductor h. [TA] the aperture in the aponeurotic insertion of the adductor magnus that transmits the femoral artery and vein from the adductor canal to the popliteal space. SYN: h. adductorius [TA] , femoral opening, h. tendineus, tendinous opening. h. adductorius [TA] SYN: adductor h.. aortic h. [TA] the opening in the diaphragm bounded by the two crura, the vertebral column, and the median arcuate ligament, through which pass the aorta and thoracic duct. SYN: h. aorticus [TA] , aortic foramen, aortic opening. h. aorticus [TA] SYN: aortic h.. Breschet h. SYN: helicotrema. h. canalis facialis SYN: h. for greater petrosal nerve. h. canalis nervi petrosi majoris [TA] SYN: h. for greater petrosal nerve. h. canalis nervi petrosi minoris [TA] SYN: h. for lesser petrosal nerve. esophageal h. [TA] the opening in the right crus of the diaphragm, between the central tendon and the h. aorticus, through which pass the esophagus and the two vagus nerves. SYN: h. esophageus [TA] , esophageal opening. h. esophageus [TA] SYN: esophageal h.. h. ethmoidalis SYN: semilunar h.. h. of facial canal SYN: h. for greater petrosal nerve. fallopian h. SYN: h. for greater petrosal nerve. h. for greater petrosal nerve [TA] the opening on the anterior aspect of the petrous part of the temporal bone that leads to the facial canal and gives passage to the greater petrosal nerve. SYN: h. canalis nervi petrosi majoris [TA] , fallopian h., Ferrein foramen, h. canalis facialis, h. of facial canal. h. for lesser petrosal nerve [TA] the small opening in the petrous bone lateral to the h. for greater petrosal nerve that gives passage to the lesser petrosal nerve. SYN: h. canalis nervi petrosi minoris [TA] , Arnold canal, canalis nervi petrosi superficialis minoris. h. maxillaris [TA] SYN: maxillary h.. maxillary h. [TA] the large opening into the maxillary sinus on the nasal surface of the maxilla. SYN: h. maxillaris [TA] . pleuropericardial h. an opening connecting the pleural and pericardial cavities; usually the result of incomplete development of the pleuropericardial fold of the embryo. pleuroperitoneal h. an opening through the diaphragm, connecting pleural and peritoneal cavities, usually the result of defective development of the pleuroperitoneal membrane in the embryo; if the defect is extensive there may be herniation of digestive organs into the pleural cavity. SEE ALSO: diaphragmatic hernia. SYN: Bochdalek foramen. sacral h. [TA] a normally occurring gap at the lower end of the sacrum, exposing the vertebral canal, due to failure of the laminae of the last sacral segment to coalesce. It is closed by the sacrococcygeal ligament, and provides cannular access to the sacral epidural space for administration of anesthetics (caudal nerve blocks). SYN: h. sacralis [TA] . h. sacralis [TA] SYN: sacral h.. saphenous h. SYN: saphenous opening. h. saphenus [TA] SYN: saphenous opening. scalene h. triangular gap bounded by the scalenus anterior and scalenus medius muscles and the first rib to which the muscles attach; the h. provides passage for the subclavian artery and the roots of the brachial plexus. Compression of the structures passing through the h. by any means is manifest as “thoracic outlet syndrome.” SYN: interscalene triangle. Scarpa h. SYN: helicotrema. semilunar h. [TA] a deep, narrow groove in the lateral wall of the middle meatus of the nasal cavity, into which the maxillary sinus, the frontonasal duct, and the middle ethmoid cells open. SYN: h. semilunaris [TA] , h. ethmoidalis. h. semilunaris [TA] SYN: semilunar h.. h. subarcuatus SYN: subarcuate fossa. h. tendineus SYN: adductor h.. h. totalis sacralis developmental clefting in all sacral vertebrae; may also involve adjacent lumbar vertebrae.

hibernation (hi-ber-na′shun)
A torpid condition in which certain animals pass the cold months. True hibernators, such as woodchucks, ground squirrels, dormice, and some others, have body temperatures reduced to near the freezing point, with a very slow heartbeat, low metabolism, and infrequent respirations. Partial hibernators, such as bears, skunks, and raccoons, have reduced physiologic activity during the cold months, but they are not comatose. Cf.:estivation. SYN: winter sleep. [L. hibernus, relating to winter]

hibernoma (hi′ber-no′ma)
A rare type of benign neoplasm in humans, consisting of brown fat that resembles the fat in certain hibernating animals; individual tumor cells contain multiple lipid droplets. SEE ALSO: brown fat. [L. hibernus, pertaining to winter, + G. -oma, tumor] interscapular h. SYN: brown fat.

hiccup, hiccough (hik′up)
A diaphragmatic spasm causing a sudden inhalation that is interrupted by a spasmodic closure of the glottis, producing a noise. SYN: singultus. epidemic h. a persistent h. occurring as a complication of influenza.

Robert o., 20th century U.S. pediatric surgeon. See H. catheter.

See Braxton H..

Abbreviation for dimethyl iminodiacetic acid.

See hidro-.

hidradenitis (hi-drad′e-ni′tis)
Inflammation of the sweat glands. SYN: hydradenitis. [G. hidros, sweat, + aden, gland, + -itis, inflammation] h. suppurativa chronic suppurative folliculitis of apocrine sweat-gland–bearing skin of the perianal, axillary, and genital areas or under the breasts, developing after puberty and producing abscesses or sinuses with scarring. neutrophilic eccrine h. an inflammatory condition occuring in patients receiving chemotherapy, with deep eccrine gland neutrophil infiltration.

hidradenoma (hi-drad-e-no′ma)
A benign neoplasm derived from epithelial cells of sweat glands. SYN: hydradenoma. [G. hidros, sweat, + aden, gland, + -oma, tumor] clear cell h. a tumor derived from eccrine sweat glands, composed of glycogen-rich clear cells. SYN: eccrine acrospiroma, nodular h.. nodular h. SYN: clear cell h.. papillary h. a solitary benign tumor occurring in women usually in the labia majora, cystic and papillary, and composed of epithelium resembling that of apocrine glands. SYN: apocrine adenoma, h. papilliferum. h. papilliferum SYN: papillary h..

hidro-, hidr-
Sweat, sweat glands. Cf.:sudor-. [G. hidros]

hidroa (hi-dro′a)
SYN: hydroa.

hidrocystoma (hi′dro-sis-to′ma)
A cystic form of hidradenoma, usually apocrine. SYN: hydrocystoma (2) , syringocystoma. [hidro- + G. kystis, bladder, + -oma, tumor] apocrine h. SYN: sudoriferous cyst.

hidromeiosis (hi′dro-mi-o′sis)
A decline in the rate of sweating during exposure to heat, especially that from warm baths. [hidro- + G. meiosis, a lessening]

hidropoiesis (hi′dro-poy-e′sis, hid′ro-)
The formation of sweat. [hidro- + G. poiesis, formation]

hidroschesis (hi-dros′ke-sis, hid-ros′)
Suppression of sweating. [hidro- + G. schesis, a checking]

hidrosis (hi-dro′sis, hi-)
The production and excretion of sweat. [G. hidros, sweat, + -osis, condition]

hidrotic (hi-drot′ik, hi-)
Relating to or causing hidrosis.

hierarchy (hi′er-ar-ke, hi-rar′ke)
1. Any system of persons or things ranked one above the other. 2. In psychology and psychiatry, an organization of habits or concepts in which simpler components are combined to form increasingly complex integrations. [G. hierarchia, rule or power of the high priest] dominance h. a social situation in which one organism dominates all below it, the next all below it, and so on down to the organism dominated by all; e.g., the pecking order in apes, seals, barnyard hens, and other species. Maslow h. a ranking of needs which humans presumably fills successively in the order of lowest to highest: physiological needs, love and belonging, self-esteem, and self-actualization. response h. alternative reactions or modes of adjustment to a given situation arranged in the probable order of prior effectiveness; e.g., a mother attempting to discipline an unruly child may first request, cajole, then plead, scold, and finally punish; her behaviors can be ordered along a response h. for further monitoring of effectiveness. h. of terms in radiology, the semantic concept of using different terms to describe anatomic or pathologic structures versus the resultant diagnostic images.

hierophobia (hi′er-o-fo′be-a)
Morbid fear of religious or sacred objects. [G. hieros, holy, + phobos, fear]

hierotherapy (hi′er-o-thar′a-pe)
Treatment of disease by prayer and religious practices. [G. hieros, holy, + therapeia, therapy]

Ototaka. Japanese physician. See Chédiak-H. disease, Chédiak-Steinbrinck-H. anomaly, Chédiak-Steinbrinck-H. syndrome.

Nathaniel, British anatomist, 1613–1685. See antrum of H., H. body.

Higoumenakia sign
See under sign.

hila (hi′la)
Plural of hilum.

hilar (hi′lar)
Pertaining to a hilum.

hilitis (hi-li′tis)
Inflammation of the lining membrane of any hilus.

Archibald V., English biophysicist and Nobel laureate, 1886–1977. See H. equation, H. plot, initial heat.

Austin Bradford, British medical statistician, 1897–1991. See H.'s criteria of evidence, under criterion.

Harold A., 20th century U.S. radiologist. See H.-Sachs lesion.

Sir Leonard Erskine, English physiologist, 1866-1952. See H. sign, H. phenomenon.

Lucius D., U.S. thoracic surgeon, *1921. See H. operation.

Robert, British plant physiologist, *1899. See H. reaction.

David S., U.S. obstetrician-gynecologist, 1873–1942. See H.-Müller maneuver.

hillock (hil′lok)
In anatomy, any small elevation or prominence. axon h. the conical area of origin of the axon from the nerve cell body; it contains parallel arrays of microtubules and is devoid of Nissl substance. SYN: implantation cone. facial h. SYN: facial colliculus. seminal h. SYN: seminal colliculus.

John, English surgeon, 1804–1878. See H. law, H. white line, H. method, H. sac.

hilum, pl .hila (hi′lum, hi′la) [TA]
1. The part of an organ where the nerves and vessels enter and leave. SYN: porta (1) . 2. A depression or slit resembling the h. in the olivary nucleus of the brain. [L. a small bit or trifle] h. of dentate nucleus [TA] the mouth of the flasklike dentate nucleus of the cerebellum, directed inward, and giving exit to many of the fibers which compose the superior cerebellar peduncle or brachium conjunctivum. SYN: h. nuclei dentati [TA] . h. of inferior olivary nucleus [TA] the medially oriented opening in the folded cell layer composing the inferior olivary nucleus through which the efferent fibers of the nucleus make their exit. SYN: h. nuclei olivaris inferioris [TA] . h. of kidney [TA] the depression on the medial border of the kidney through which pass the segmental renal vessels and renal nerves and where the apex of the renal pelvis occurs. SYN: h. renalis [TA] , porta renis. h. lienis splenic h.. h. of lung [TA] a wedge-shaped depression on the mediastinal surface of each lung, where the bronchus, blood vessels, nerves, and lymphatics enter or leave the viscus. SYN: h. pulmonis [TA] , porta pulmonis. h. of lymph node [TA] the depressed area of the surface of a lymph node through which the efferent lymphatics emerge from the medulla and through which blood vessels enter and leave the node. SYN: h. nodi lymphatici [TA] . h. nodi lymphatici [TA] SYN: h. of lymph node. h. nuclei dentati [TA] SYN: h. of dentate nucleus. h. nuclei olivaris inferioris [TA] SYN: h. of inferior olivary nucleus. h. ovarii SYN: h. of ovary. h. of ovary the depression along the mesovarian margin, at the insertion of the mesovarium, where vessels and nerves enter or leave the ovary. SYN: h. ovarii. h. pulmonis [TA] SYN: h. of lung. h. renalis [TA] SYN: h. of kidney. h. of spleen SYN: splenic h.. splenic h. [TA] a fissure on the gastric surface of the spleen, giving passage to the splenic vessels and nerves. SYN: h. splenicum [TA] , h. lienis&star, h. of spleen, porta lienis. h. splenicum [TA] SYN: splenic h..

hilus (hi′lus)
Former incorrect designation for hilum. [an Eng. variant of L. hilum]


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