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Medical Dictionary


Symbol for:
  • hecto-
  • height
  • hour, used in writing prescriptions
  • Planck constant
  • h = h/2π.
  • The Fraunhofer line at λ 3968 due to calcium
  • Hauch
  • henry, unit of electrical inductance
  • height
  • heroin
  • histidine
  • histone
  • histamine
  • horizontal
  • Holzknecht unit
  • hydrogen
  • hyperopia
  • hyperopic
  • magnetic field strength
  • enthalpy, heat content, in the equation for free energy
  • fluence
  • magnetic field strength.
Hydrogen ion, the proton.

H antigen
Any of various antigens associated with the flagella of motile bacteria and used in serological identification of various bacteria — also called flagellar antigen.

H band
A relatively pale band in the middle of the A band of striated muscle.

A diffusible substance that is thought to be released in the allergic reaction of skin and in the responses of tissue to inflammation and that is held to be similar to histamine or possibly to be histamine itself.

H zone
A narrow and less dense zone of myosin filaments bisecting the A band in striated muscle. H-Y antigen
Amale histocompatibility antigen determined by genes on the Y chromosome.

Symbol for hydrogen-1.

Symbol for hydrogen-2.

Symbol for hydrogen-3.

9H-fluorene (flor′en)
Parent compound of 2-acetylaminofluorene; occurs in coal tar.

Abbreviation for hepatitis-associated antigen.

Otto, Swiss ophthalmologist, 1850–1931.

Haase rule
See under rule.

habena, pl .habenae (ha-be′na, -be′ne)
1. A frenum or restricting fibrous band. 2. A restraining bandage. 3. SYN: habenula (2) . [L. strap]

habenal, habenar (hab′e-nal, ha-be′nar)
Relating to a habena.

habenula, pl .habenulae (ha-ben′u-la, -le)
  • frenulum.
  • In neuroanatomy, the term originally denoted the stalk of the pineal gland (pineal h.; pedunculus of pineal body), but gradually came to refer to a neighboring group of nerve cells with which the pineal gland was believed to be associated, the habenular nucleus. Currently, the TA term refers exclusively to this circumscript cell mass in the caudal and dorsal aspect of the dorsal thalamus, embedded in the posterior end of the medullary stria from which it receives most of its afferent fibers. By way of the retroflex fasciculus (habenulointerpeduncular tract) it projects to the interpeduncular nucleus and other paramedian cell groups of the midbrain tegmentum. Despite its proximity to the pineal stalk, no habenulopineal fiber connection is known to exist. It is a part of the epithalamus.
  • SYN: habena
  • h. of cecum extension of the mesocolic tenia, dorsal or ventral to the terminal ileum.
  • Haller h. rarely used term for the cordlike remains of the vaginal process of the peritoneum. SYN: Scarpa h.. habenulae perforatae SYN: foramina nervosa, under foramen.
  • pineal h. the peduncle or stalk of the pineal gland.
  • Scarpa h. SYN: Haller h..
  • h. urethralis one of two fine, whitish lines running from the meatus urethrae to the clitoris in girls and young women; the vestiges of the anterior part of the corpus spongiosum.
habenular (ha-ben′u-lar)
Relating to a habenula, especially the stalk of the pineal body.

Henry, British dermatologist, 1900–1962. See H. syndrome.

R., German dermatologist, 1884–1941. See Mucha-H. disease.

1. An act, behavioral response, practice, or custom established in one's repertoire by frequent repetition of the same act. SEE ALSO: addiction. 2. A basic variable in the study of conditioning and learning used to designate a new response learned either by association or by being followed by a reward or reinforced event. See conditioning, learning. [L. habeo, pp. habitus, to have]

habituation (ha-bit-choo-a′shun)
1. The process of forming a habit, referring generally to psychological dependence on the continued use of a drug to maintain a sense of well-being, which can result in drug addiction. 2. The method by which the nervous system reduces or inhibits responsiveness during repeated stimulation.

habitus (hab′i-tus)
The physical characteristics of a person. [L. habit] fetal h. relationship of one fetal part to another. SYN: fetal attitude. gracile h. small stature, frail, underweight appearance.

Habronema (ha-bro-ne′ma)
  • A genus of parasitic spiruroid nematode worms of the family Spiruridae that develop in flies of the genera Musca and Stomoxys inhabiting the stomach of horses or the proventriculus of various birds. The larvae develop in housefly and stable fly maggots living in manure, become infective when the fly larvae pupate, and are carried by adult flies to open wounds on horses, where they are left and cause cutaneous habronemiasis; reinfection of the horse's stomach by H. occurs by accidental ingestion of infected flies or from licking wounds in which infective larvae are found. [G. habros, graceful, delicate, + nema, a thread]
  • H. majus: one of two species (the other being H. microstoma) similar in appearance, hosts, distribution, and life cycle to H. muscae; the intermediate host is the stable fly, Stomoxys calcitrans.
  • H. megastoma: a species that causes tumors in gastric mucosa containing large numbers of the small nematodes; the larvae cause cutaneous habronemiasis; the intermediate host is the common housefly, Musca domestica.
  • H. microstoma: H. majus.
  • H. muscae: a species that occurs in the stomach of the horse, mule, ass, or zebra; the intermediate host is the common housefly, Musca domestica, or related flies.
hacking (hak′ing)
A chopping stroke made with the edge of the hand in massage.

Geoffrey, British physician, 1889–1968. See Clarke-H. syndrome.

Hadrurus (ha-droo′rus)
A genus of scorpions found in the southwestern U.S., characterized by numerous setae on the stinger; the commonest species is H. arizonensis, the olive hairy scorpion. SEE ALSO: Scorpionida. [G. hadros, thick, stout, + ouro, tail]

Ernst H.P.A., German naturalist, 1834–1919. See H. gastrea theory, H. law.

See hem-.

Haemadipsa ceylonica (he-ma-dip′sa sa-lon′i-ka)
A species of land leech found in Sri Lanka; it attaches itself to the skin of animals or humans. Its bite is painful, and numerous bites may cause anemia. [G. haima, blood, + dipsa, thirst]

Haemamoeba (he-ma-me′ba)
Old term for ameboid protozoa now classified in the suborder Haemosporina, blood parasites that include the genus Plasmodium. [G. haima, blood, + amoibe, change]

Haemaphysalis (he-ma-fi′sa-lis)
  • A genus of small, eyeless, inornate ticks. As larvae and nymphs, they are found chiefly on small mammals and birds; as adults, they are found on larger mammals and some birds. They are important as vectors of protozoa and viruses, (e.g., Kyasanur Forest disease virus). [G. haima, blood, + physaleos, full of wind]
  • H. cinnabarina: a tick that occurs chiefly in the dry district of British Columbia; this species can cause tick paralysis in both humans and animals. [G. kinnabarinos, like cinnabar, vermilion]
  • H. concinna: common rodent tick species of the area formerly known as the U.S.S.R. that is a vector and reservoir of tick typhus.
  • H. leachi: a species of Africa, Asia, and Australia that occurs on domestic and wild carnivores, on small rodents, and occasionally on cattle; it transmits canine babesiosis and boutonneuse fever.
  • H. spinigera: a tropical forest species in India that is a vector of Kyasanur Forest disease; various rodents and insectivores serve as hosts of immature ticks of this species, which carry an arbovirus of the Russian spring-summer B group complex; monkeys act as reservoirs of human infection.
Haematopinus (he′ma-to-pi′nus)
An important genus of sucking lice (family Haematopinidae) affecting swine and other domestic and wild animals; it is normally nonpathogenic. H. asini affects horses, mules, and asses; H. eurysternus and H. quadripertusus, cattle; and H. suis, swine. [G. haima, blood, + L. pinus, pine tree]

Haemococcidium (he′mo-kok-sid′e-um)
Old name for Plasmodium species. [G. haima, blood, + kokkos, berry]

Haemodipsus ventricosus (he-mo-dip′sus ven-tri-ko′sus)
The rabbit louse, a transmitter of Francisella tularensis. [G. haima, blood, + dipsos, thirst; L. venter (ventr-), belly]

Haemogregarina (he′mo-greg-a-ri′na)
A sporozoan coccidian genus (order Eucoccidiida, family Haemogregarinidae) that parasitizes the blood cells of cold-blooded animals and the digestive system of invertebrate primary hosts in an obligatory two-host cycle. [G. haima, blood, + L. grex, a flock]

Haemonchus (he-mong′kus)
An economically important genus of nematode parasites (family Trichostrongylidae) occurring in the abomasum of ruminant animals and causing severe anemia, especially in younger or previously unexposed animals. Some significant species are Haemonchus placei (in cattle, sheep, and goats), Haemonchus similis (in cattle and sheep), and Haemonchus contortus, the stomach, barberpole, or twisted wire worm of cattle, sheep, goats, and other ruminants, of which a few cases have been reported from humans; accidental parasite of humans. [G. haima, blood, + onchos, spear]

Haemophilus (he-mof′i-lus)
  • A genus of aerobic to facultatively anaerobic, nonmotile bacteria (family Brucellaceae) containing minute, Gram-negative, rod-shaped cells that sometimes form threads and are pleomorphic. These organisms are strictly parasitic, growing best, or only, on media containing blood. They may or may not be pathogenic. They occur in various lesions and secretions, as well as in normal respiratory tracts, of vertebrates. The type species is H. influenzae. [G. haima, blood, + philos, fond]
  • H. actinomycetemcomitans: Actinobacillus actinomycetemcomitans.
  • H. aegyptius: a bacterial species that causes acute or subacute infectious conjunctivitis in warm climates. SYN: Koch-Weeks bacillus.
  • H. aphrophilus: a bacterial species found in the blood and, rarely, on the heart valve as a cause of endocarditis.
  • H. ducreyi: a bacterial species that causes the sexually transmitted soft chancre (chancroid). SYN: Ducrey bacillus.
  • H. haemolyticus: a bacterial species that is usually nonpathogenic but which, on rare occasions, causes subacute endocarditis.
  • H. influenzae: a bacterial species found in the respiratory tract that causes acute respiratory infections, including pneumonia, acute conjunctivitis, otitis, and purulent meningitis in children (rarely in adults in whom it contributes to sinusitis and chronic bronchitis). Originally considered to be the cause of influenza, it is the type species of the genus H.. SYN: influenza bacillus, Weeks bacillus.
  • H. influenzae Type b: the most virulent serotype (there are six, a–f, based on antigenic typing of the polysaccharide capsule); species responsible for meningitis and respiratory infections in young children.
  • nontypeable H. influenzae: bacterial species that is a major pathogen in acute otitis media.
  • H. parahaemolyticus: a bacterial species found in the upper respiratory tract and associated frequently with pharyngitis; occasionally causes subacute endocarditis.
  • H. parainfluenzae: a bacterial species that is usually nonpathogenic but which occasionally causes subacute endocarditis.
  • H. paratropicalis: a relatively nonpathogenic bacterial species that has been associated with human infection, including cases of endocarditis.
  • H. segnis: a usually saprophytic bacterial species that occasionally causes endocarditis, meningitis, and other infections in humans.
Haemoproteus (he′mo-pro′te-us)
A genus of sporozoa (suborder Haemosporina) parasitic in birds and reptiles, combined with Leucocytozoon, Hepatocystis, and other genera in the family Haemoproteidae. Schizogony occurs in endothelial cells of blood vessels, especially in the lungs of the host, while halter-shaped gametocytes are found in the red blood cells. Infection is transmitted by pupiparous Diptera, such as louse flies (Hippoboscidae) and by bloodsucking midges (Culicoides) [G. haima, blood, + Proteus, a sea god who had the power of assuming different shapes]

Haemosporina (he′mo-spo-ri′na)
A suborder of coccidia (class Sporozoea) that lack syzygy, with separate development of macrogamete and microgamont, the latter producing eight flagellated microgametes; heteroxenous with merogany in vertebrates and sporogony in bloodsucking insects; includes the genera Haemoproteus, Leucocytozoon, and Plasmodium. [G. haima, blood, + sporos, seed]

William M., U.S. epidemiologist/statistician, 1910–1998. See Mantel-H. test.

Waldemar M.W., Russian physician, 1860–1930. See H. vaccine.

Hafnia (haf′ne-ah)
Genus in the family Enterobacteriaceae; found in human feces, a rare cause of nosocomial infection; associated with diarrheal disease of undefined mechanism. There is a single species, H. alvei.

hafnium (Hf) (haf′ne-um)
A rare chemical element, atomic no. 72, atomic wt. 178.49. [L. Hafnia, Copenhagen]

Hans Christian, Danish physician, *1888. See NPH insulin.

Werner, German surgeon, 1831–1894. See H. needle.

Surname of person in whom deficiency of H. factor was first observed.

hagiotherapy (hag′e-o-thar′a-pe)
Treatment of the sick by contact with relics of the saints, visits to shrines, and other religious observances. [G. hagios, sacred]

S.E. Patrik, Swedish orthopedist, 1870–1937. See H. deformity, H. disease.

Christian F.S., German physician and founder of homeopathy, 1755–1843. See hahnemannian.

hahnemannian (hah-ne-mahn′e-an)
Relating to homeopathy as taught by Hahnemann.

Hahn oxine reagent
See under reagent.

Wilhelm von, Austrian mineralogist, 1795–1871. See H. brushes, under brush.

Hugh E., U.S. dermatologist, *1909. See H.-H. disease.

W. Howard, U.S. dermatologist, 1898–1967. See H.-H. disease.

hair (ˈha(ə)r, ˈhe(ə)r)
  • One of the fine, keratinized filamentous epidermal growths arising from the skin of the body of mammals except the palms, soles, and flexor surfaces of the joints; the full length and texture of h. varies markedly in different body sites.
  • pilus
  • One of the fine, hairlike processes of the auditory cells of the labyrinth, and of other sensory cells, called auditory h., sensory h., etc.
  • thrix . [A.S. haer]
  • auditory hairs: cilia on the free surface of the auditory cells.
  • axillary hairs: h. of the armpit, aka hircus.
  • bamboo h.: h. with regularly spaced nodules along the shaft caused by intermittent fractures with invagination of the distal h. into the proximal portion, with intervening lengths of normal h., giving the appearance of bamboo; seen in Netherton syndrome; autosomal recessive trait. SYN: trichorrhexis invaginata.
  • bayonet h.: a spindle-shaped developmental defect occurring at the tapered end of the h..
  • beaded h.: monilethrix.
  • burrowing hairs: ingrown hairs.
  • club h.: a h. in resting state, prior to shedding, in which the bulb has become a club-shaped mass.
  • downy h." fine, soft, lightly pigmented fetal h. with minute shafts and large papillae; it appears toward the end of the third month of gestation, aka lanugo, primary h., lanugo h..
  • exclamation point h.: the type of dystrophic anagen h. found at margins of patches of alopecia areata; the bulb is absent.
  • Frey hairs: short hairs of varying degrees of stiffness, set at right angles into the end of a light wooden handle; used for assessing sensation.
  • hairs of head: a h. of the scalp of the head, aka scalp h..
  • ingrown hairs: hairs that grow at more acute angles than is normal, and in all directions; they incompletely clear the follicle, turn back in, and cause pseudofolliculitis. SYN: burrowing hairs.
  • kinky h.: tightly curled or bent h.. See kinky-h. disease.
  • lanugo h.: downy h..
  • moniliform h.: monilethrix.
  • nettling hairs: sharp-pointed barbed hairs of certain caterpillars which cause a dermatitis when brought in contact with the skin.
  • primary h.: downy h..
  • pubic h.: one of the pubic hairs; the h. of the pubic region just above the external genitals, aka pubes.
  • ringed h.: a rare condition in which the h. shows alternate pigmented and bright segments, the latter due to air cavities within the cortex. SYN: pili annulati.
  • scalp h.: hairs of head.
  • Schridde cancer hairs: thick lusterless hairs scattered in the beard and the temporal region, said to occur in cancerous patients but found also in persons with other cachectic conditions.
  • spun glass h.: uncombable h. syndrome.
  • stellate h.: h. split in several strands at the free end.
  • taste hairs: hairlike projections of gustatory cells of taste buds; electron micrographs show them to be clusters of microvilli.
  • terminal h.: a mature pigmented, coarse h..
  • hairs of tragus: hairs growing from the tragus of the auricle.
  • twisted hairs SYN: pili torti, under pilus.
  • vellus h.: colorless, soft, fine postnatal to adult h..
  • hairs of vestibule of nose: one of the hairs growing at the nares, or vestibule of the nose, aka vibrissa.
  • woolly h.: tightly coiled h., oval in cross-section, with the texture of wool.
hair ball
  • A slender threadlike outgrowth of the epidermis of an animal; especially : one of the usually pigmented filaments that form the characteristic coat of a mammal.
  • The hairy covering of an animal or a body part; especially : the coating of hairs on a human head.
hai bulb
The bulbous expansion at the base of a hair from which the hair shaft develops.

hairpin ( har′pin)
1. The structure formed by a polynucleic acid by base-pairing between neighboring complementary sequences of a single strand of either DNA or RNA. 2. The structure seen in a prostaglandin where two segments of the molecule fold back on one another.

hairworm (har′werm)
See Trichostrongylus, Gordius.

hairy (har′e)
1. Of or resembling hair. 2. Covered with hair. SEE ALSO: hirsutism. SYN: pilar, pilary, pilose.

halation (ha-la′shun)
Blurring of the visual image by glare.

halazone (hal′a-zon)
A chloramine used for the sterilization of drinking water.

William A., U.S. physician, *1915. See Stryker-H. syndrome.

Ludwig, German physician, 1876–1949. See H.-Prowazek bodies, under body.

John B.S., English biochemist and geneticist, 1892–1964. See H. relationship.

John S., Scottish physiologist at Oxford, 1860–1936. See H. apparatus, H. effect, H. transformation, H. tube, H.-Priestley sample.

Hale colloidal iron stain
See under stain.

Stephen, English physiologist, 1677–1761. See H. piesimeter.

half-hapten (haf-hap′ten)
A substance that elicits an antigen-antibody reaction, but no precipitation.

half-life (haf′lif)
The period in which the radioactivity or number of atoms of a radioactive substance decreases by half; similarly applied to any substance, such as a drug in serum, whose quantity decreases exponentially with time. Cf.:half-time. biologic half-life the time required for one-half of an amount of a substance to be lost through biologic processes. effective half-life the time required for the body burden of an administered quantity of radioactivity to decrease by half through a combination of radioactive decay and biologic elimination. physical half-life the time required for half the atoms of a radionuclide to undergo disintegration.

half-moon (haf′moon)
SYN: lunule of nail. red half-moon irregular red discoloration of the usually pale demilune at the base of the fingernail; may be seen in congestive failure, malignant disease, or liver disease, but not specific for any of these.

half-time (haf′tim)
The time, in a first-order chemical (or enzymic) reaction, for half of the substance (substrate) to be converted or to disappear. Cf.:half-life.

halfway house (haf′wa hows)
A facility for individuals who no longer require the complete facilities of a hospital or institution but are not yet prepared to return to independent living.

halibut liver oil (hal′i-but)
The fixed oil obtained from the fresh or suitably preserved livers of halibut species of the genus Hippoglossus (family Pleuronectidae); a supplementary source of vitamins A and D.

halide (hal′id)
A salt of a halogen.


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