Copy of `Dorland's Medical Dictionary`

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Dorland's Medical Dictionary Category: Health and Medicine > Medical Dictionary Date & country: 31/12/2010, USA Words: 39128

haversian system
a haversian canal and its concentrically arranged lamellae, constituting the basic unit of structure in compact bone (osteon).

Haw River syndrome
(haw) an autosomal dominant neurodegenerative disorder characterized by ataxia, chorea, seizures, and dementia, with onset usually between ages 15 to 30 years, and death within 15 to 25 years. It is a triplet repeat disorder caused by expansion of the CAG triplet repeat in the DPRLA gene encoding the atrophin-1 protein,...

Hawkins sign
in fractures of the talar neck, a radiolucent zone beneath the subchondral plate of the head of the talus, indicative of disuse osteoporosis; its absence reflects increased risk of talar avascular necrosis.

hay fever
an atopic allergy characterized by sneezing, itching and watery eyes, nasal discharge, and a burning sensation of the palate and throat. It is a localized anaphylactic reaction to an extrinsic allergen, usually pollen or the spores of molds. When the allergen comes in contact with cell-bound immunoglobulin E in the tissue...

Hay-Wells syndrome
(ha´ welz´) an autosomal dominant syndrome of ectodermal dysplasia, cleft lip and palate, and ankyloblepharon filiforme adnatum; it is also characterized by hypodontia, palmar and plantar keratoderma, partial anhidrosis, sparse wiry hair, and sometimes otologic defects. Called also AEC syndrome and ankyloblepharon...

Hayem-Widal syndrome
(ah-yah´ ve-dahl´) former name for hemolytic anemia.

hazards of immobility
complications that are associated with a limited or absolute lack of movement by the patient; various members of the health care team may collaborate to assist the patient in avoiding these problems. See also disuse atrophy.

HB
hepatitis B.

Hb
hemoglobin.

HBcAg
hepatitis B core antigen.

HBeAg
hepatitis B e antigen.

HBIG
hepatitis B immune globulin.

HBO
hyperbaric oxygenation.

HBsAg
hepatitis B surface antigen.

HBV
hepatitis B virus.

HCFA
Health Care Financing Administration, former name for the Centers for Medicare and Medicade Services (CMS).

HCG
hCG human chorionic gonadotropin.

HD
hemodialysis.

HDL
high-density lipoprotein.

HDL-C
high-density-lipoprotein cholesterol; see cholesterol.

He
helium.

head
(hed) the anterior or superior part of a structure or organism. in vertebrates, the part of the body containing the brain and the organs of special sense. Called also caput. articular head an eminence on a bone by which it articulates with another bone. head i...

head fold
a fold of blastoderm at the cephalic end of the developing embryo.

Head zones
areas of cutaneous sensitiveness associated with diseases of the viscera; called also zoness of hyperalgesia.

headache
(hed´āk″) pain in the head; see also migraine. One of the most common ailments of humans, it is a symptom rather than a disorder in itself; it accompanies many diseases and conditions, including emotional distress. Although recurring headache may be an early sign of serious organic disease, relatively f...

Heaf test
a type of intracutaneous tuberculin test; needle points of a multiple-puncture apparatus are dipped into 1 to 2 drops of tuberculin PPD, then placed on the forearm and made to penetrate the skin to a depth of 1 mm, depositing tuberculin in the outer layer of the skin. In three to seven days, a positive reaction is palpabl...

healed yellow atrophy
macronodular cirrhosis.

healing
(hēl´ing) the process of returning to health; the restoration of structure and function of injured or diseased tissues. The healing processes include blood clotting, tissue mending, scarring, and bone healing. See also wound healing. the process of helping someone return to health. ...

healing ridge
a hardened ridge that normally forms deep to the skin along the length of a healing wound.

health
(helth) a relative state in which one is able to function well physically, mentally, socially, and spiritually in order to express the full range of one's unique potentialities within the environment in which one is living. Current views of health and illness recognize health as more than the absence of disease. R...

health care
see health care system.

health care system
an organized plan of health services. The term usually is used to refer to the system or program by which health care is made available to the population and financed by government, private enterprise, or both.

health maintenance organization
(HMO) any of a variety of health care delivery systems with structures ranging from group practice through independent practice models or independent practice associations (IPAs). They provide alternatives to the fee-for-service private practice of medicine and other allied health professions. The primary goal is ...

hearing
(hēr´ing) the sense by which sounds are perceived, or the capacity to perceive sound; sound waves must be converted into nerve impulses that can be interpreted by the brain. The organ of hearing is the ear, which is divided into three sections, the outer, middle, and inner ear, each with its own role in hearing. Called a...

hearing aid
an instrument to amplify sounds for those with hearing loss. There are two types of electronic hearing aids: the air conduction type, which is worn in the external acoustic meatus, and the bone conduction type, which is worn in back of the ear over the mastoid process. Persons with conductive hearing loss can often use one of the bet...

hearing loss
(hēr´ing los´) lack or loss of all or a major part of the sense of hearing; there are two main types, conductive and sensorineural. Called also deafness.

heart
(hahrt) a hollow muscular organ to the left of the midline of the chest that serves as a pump controlling blood flow in the pulmonary and systemic circulation. The septum, a thick muscular wall, divides the heart into right and left halves, each with an upper chamber called the atrium and a lower chamber called the ventricle....

heart block
impairment of conduction in heart excitation; often applied specifically to atrioventricular block. See types listed at block. When isolated impulses from the atria fail to reach the ventricles, heartbeats are missed and the block is called incomplete. When no impulses reach the ventricles from the atria the heart block is called com...

heart disease
any organic, mechanical, or functional abnormality of the heart, its structures, or the coronary arteries.

heart disease cells
heart failure cells iron-containing, rust-colored macrophages found in the pulmonary alveoli and sputum in congestive heart failure.

heart failure
inability of the heart to maintain cardiac output sufficient to meet the body's needs; it most often results from myocardial failure affecting the right or left ventricle.

heart murmur
any sound in the heart region other than normal heart sounds; common causes include movement of blood through narrowed or stenotic heart valves and blood leaking through a valve that does not close properly. In many cases a murmur may be of the innocent or functional type, with no heart disease at all, so that it causes no trou...

heart rate
the number of contractions of the cardiac ventricles per unit of time (usually per minute).

heart reflex
Abrams heart reflex.

heart sounds
sounds heard on the surface of the chest in the heart region, which can be amplified by a stethoscope in order to be heard more distinctly. They are caused by vibrations generated during the normal cardiac cycle and may be produced by muscular action, valvular actions, motion of the heart, or blood passing through the heart. The firs...

heart valve prosthesis
prosthetic heart valve.

heart valves
cardiac valves.

heart-hand syndrome
Holt-Oram syndrome.

heart-lung machine
a mechanical device that temporarily takes over the functions of the heart and lungs; it is used as an aid in some surgeries, especially cardiovascular surgery. The “heart” of the machine is a pump that draws blood from the patient's vessels before it reaches the heart. The blood is routed through a “lun...

heartbeat
(hahrt´bēt) the cycle of contraction of the heart muscle; it begins with an electrical impulse in the sinoatrial node, which serves as the normal pacemaker for the heart.

heartburn
(hahrt´bәrn) a burning sensation in the esophagus, or below the sternum in the region of the heart, one of the common symptoms of indigestion. This often occurs when there is distention of a part of the esophagus, particularly the lower part, such as with gastroesophageal reflux (regurgitation by the stomach of part of ...

heat
(hēt) energy that raises the temperature of a body or substance. Heat is associated with molecular motion, and is generated in various ways, including combustion, friction, chemical action, and radiation. The total absence of heat is absolute zero, at which all molecular activity ceases. a rise in tem...

heat capacity
the amount of heat required to raise the temperature of a specific quantity of a substance by one degree Celsius.

heat cataract
posterior subcapsular opacity caused by chronic exposure to infrared radiation.

heat cradle
electric cradle.

heat exhaustion
an effect of excessive exposure to heat, seen among workers in hot places such as furnace rooms and foundries and sometimes in persons having prolonged exposure to the sun's heat. Symptoms include dizziness, headache, nausea, and sometimes delirium or collapse. The body temperature is near normal, in contrast to heat stro...

heat shock protein
any of a group of prokaryotic and eukaryotic proteins first identified as being synthesized in response to hyperthermia, hypoxia, or other stresses and believed to enable cells to recover from these stresses, perhaps by enabling recovery of gene expression.

heat unit
the amount of heat energy that is produced by one kVp (kilovolt peak) and one mA (milliampere) for one second with single phase, full wave rectified radiographic equipment.

heat urticaria
cholinergic urticaria produced by application of heat to the skin or by exposure to high environmental temperature; it may be associated with cramps, weakness, flushing, salivation, and collapse.

heat-regulating centers
thermoregulatory centers.

heavy chain diseases
a group of rare monoclonal gammopathies characterized by neoplastic proliferation of plasma cells and precursors that secrete immunoglobulin heavy chains. They are often accompanied by enlargement of the liver and spleen, lymphadenopathy, and soft tissue tumors. There are three varieties, each characterized by a specific heavy chain:...

heavy metal
one with a high specific gravity, usually defined to be above 5.0.

heavy metal nephropathy
the kidney damage resulting from any of various forms of heavy metal poisoning, usually in the form of tubulointerstitial nephritis. The most common metals involved are cadmium, lead, and mercury.

heavy metal poisoning
poisoning with any of the heavy metals, particularly antimony, arsenic, cadmium, lead, mercury, thallium, or zinc.

hebephrenic schizoprenia
disorganized schizophrenia.

Heberden disease
(he´bәr-dәn) rheumatism of the smaller joints, accompanied by nodules in or about the distal interphalangeal joints. angina pectoris.

Heberden nodes
Heberden sign nodular protrusions on the phalanges at the distal interphalangeal joints of the fingers in osteoarthritis. Similar nodes on the proximal joints are called Bouchard nodes.

hebetic
(hә-bet´ik) pubertal.

hebetude
(heb´ә-tldbomacd) mental dullness; apathy.

Hebra disease
(ha´brah) erythema multiforme minus; see erythema multiforme.

hecatomeral cells
cells of gray matter of the spinal cord whose axis cylinder processes divide and send one branch into the white substance of the same side of the cord and another into the anterolateral columns of the other side.

hecatomeric
(hek″ә-to-mer´ik) having processes that divide in two, one going to each side of the spinal cord; said of certain neurons.

Hecht pneumonia
giant cell pneumonia.

Hecht syndrome
(hekt) Hecht-Beals syndrome (hekt´ bēlz´) Hecht-Beals-Wilson syndrome (hekt´ bēlz´ wil´sәn) trismus-pseudocamptodactyly syndrome.

Heck disease
(hek) focal epithelial hyperplasia.

Heckathorn disease
(hek´ә-thorn) a rare variant of hemophilia A in which the levels of coagulation factor VIII fluctuate; inherited as an X-linked recessive trait.

hectic fever
a fever that recurs each day, with profound sweating, chills, and facial flushing.

hedonism
(he´don-iz-әm) pleasure-seeking behavior. the ethical doctrine that regards pleasure and happiness as the highest good. in psychology, the theory that the attainment of pleasure and the avoidance of pain are the prime motivators of human behavior. adj., hedon´ic., adj.

heel
(hēl) the hindmost part of the foot; called also calx. the hindmost portion of an elongated structure, or something else comparable to the heel of the foot. Thomas heel a shoe correction consisting of a heel about 0.5 inch (1 cm) longer and slightly higher on the inside...

heel bone
calcaneus.

heel-knee test
heel-shin test (for coordinated movements of the lower limbs) the patient, lying supine, is asked to touch the knee on one side with the opposite heel and then to pass the heel slowly down the front of the shin to the ankle. Called also heel-to-knee or heel-to-shin test.

heel-tap reflex
heel-tap test a reflex occurring in disease of the pyramidal tract, consisting of fanning and plantar flexion of the toes produced by a sharp tap on the heel.

heel-to-knee test
heel-to-shin test heel-knee test.

Heerfordt syndrome
(hār´fort) a manifestation of sarcoidosis, marked by chronic inflammation of the parotid gland and uvea, with chronic iridocyclitis, unilateral facial paralysis, lassitude, and an elevated but subfebrile temperature. Called also uveoparotid fever.

Hegar sign
(ha´gahr) compressibility and softening of the lower segment of the uterus, a probable sign of pregnancy; the segment just above the cervix becomes so soft that when compressed between two fingers its wall cannot be felt or feels extremely thin.

Heidenhain syndrome
(hi´dәn-hīn) a rapidly progressive degenerative disease manifested by cortical blindness, presenile dementia, dysarthria, ataxia, athetoid movements, and generalized rigidity.

height
(hīt) the vertical measurement of something. height of contour the measurement of a tooth from the lingual to the vestibular surface at its greatest bulge.

Heim-Kreysig sign
a depression of the intercostal spaces occurring along with the cardiac systole in adherent pericarditis.

Heimlich maneuver
(hīm´lik) a method of dislodging food or other material from the throat of a choking victim: the rescuer wraps arms around the victim at the belt line and allows victim's upper torso to hang forward; rescuer makes a fist with one hand and grasps it with the other; with both hands placed against the victim's a...

Heine operation
cyclodialysis in glaucoma.

Heine-Medin disease
(hi´nĕ ma´din) the major illness of poliomyelitis.

Heineke-Mikulicz operation
Heineke-Mikulicz pyloroplasty enlargement of a pyloric stricture by incising the pylorus longitudinally and suturing the incision transversely.

Heinz bodies
Heinz-Ehrlich bodies coccoid inclusion bodies resulting from oxidative injury to and precipitation of hemoglobin, seen in the presence of abnormal hemoglobins such as Hb H, Hb Köln, etc. and in erythrocytes with enzyme deficiencies. Refractile in fresh blood smears, they are not visible when stained with Romanowsky dyes bu...

Heinz body anemias
a group of hemolytic anemias of diverse etiology with the common morphologic characteristic of having Heinz bodies within affected erythrocytes.

HeLa cells
cells of the first continuously cultured carcinoma strain, descended from a human cervical carcinoma; used in the study of life processes, including viruses, at the cell level.

Helbing sign
medialward curving of the Achilles tendon as viewed from behind; seen in flatfoot.

helcoid
(hel´koid) like an ulcer.

helical
(hel´ĭ-kәl) spiral (def. 2).

helicine
(hel´ĭ-sēn) spiral (def. 2).

helicine arteries
small arteries that for their entire length have a band of thickened intima on one side, in which longitudinal muscle fibers are embedded. They follow a convoluted or curled course and open directly into cavernous sinuses instead of capillaries; they play a dominant role in erection of erectile tissue.