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Medical Dictionary


exopeptidase (ek-so-pep′ti-das)
An enzyme that catalyzes the hydrolysis of the terminal amino acid of a peptide chain; e.g., carboxypeptidase. Cf.:endopeptidase.

Exophiala (ek-so-fi′a-la)
A genus of pathogenic fungi having dematiaceous conidiophores with one- or two-celled annelloconidia. They cause mycetoma or phaeohyphomycosis; in cases of mycetoma, black granules develop in subcutaneous abscesses; in cases of phaeohyphomycosis, hyaline or brownish hyphae are found in tissues. [exo + G. phiale, a broad flat vessel] E. jeanselmei a fungal species found in cases of mycetoma or phaeohyphomycosis. E. werneckii a fungal species that causes tinea nigra. SYN: Cladosporium werneckii.

exophoria (ek′so-fo′re-a)
Tendency of the eyes to deviate outward when fusion is suspended. SYN: exodeviation (1) . [exo- + G. phora, a carrying]

exophoric (ek-so-for′ik)
Relating to exophoria.

exophthalmic (ek-sof-thal′mik)
Relating to exophthalmos; marked by prominence of the eyeball.

exophthalmometer (ek-sof-thal-mom′e-ter)
An instrument to measure the distance between the anterior pole of the eye and a fixed reference point, often the zygomatic bone. SYN: orthometer, proptometer, statometer. [exophthalmos + G. metron, measure]

exophthalmos, exophthalmus (ek-sof-thal′mos)
Protrusion of one or both eyeballs; can be congenital and familial, or due to pathology, such as a retroorbital tumor (usually unilateral) or thyroid disease (usually bilateral). SYN: proptosis. [G. ex, out, + ophthalmos, eye] endocrine e. e. associated with thyroid gland disorders. See Graves ophthalmopathy, Graves orbitopathy. malignant e. relentless, progressive protrusion of the eyeballs.

exophyte (ek′so-fit)
An exterior or external plant parasite. [exo- + G. phyton, plant]

exophytic (ek-so-fit′ik)
1. Pertaining to an exophyte. 2. Denoting a neoplasm or lesion that grows outward from an epithelial surface.

exoplasm (ek′so-plazm)
SYN: ectoplasm.

exoserosis (ek′so-se-ro′sis)
Serous exudation from the skin surface, as in eczema or abrasions.

exoskeleton (ek-so-skel′e-ton)
1. Hard parts, such as hair, teeth, nails, feathers, hooves, scales, etc., developed from the epidermis in vertebrates. SYN: dermoskeleton. 2. Outer chitinous envelope of an insect, or the chitinous or calcareous covering of certain Crustacea and other invertebrates.

exospore (ek′so-spor)
An exogenous spore, not encased in a sporangium. [exo- + G. sporos, seed]

exosporium (ek-so-spo′re-um)
The outer envelope of a spore.

exostectomy (ek-sos-tek′to-me)
Removal of an exostosis. SYN: exostosectomy. [exostosis + G. ektome, excision]

exostosectomy (ek-sos-to-sek′to-me)
SYN: exostectomy.

exostosis, pl .exostoses (eks-os-to′sis, -sez)
A cartilage-capped bony projection arising from any bone that develops from cartilage. SEE ALSO: osteochondroma. SYN: hyperostosis (2) , poroma (2) . [exo- + G. osteon, bone, + -osis, condition] e. bursata an e. arising from the joint surface of a bone and covered with cartilage and a synovial sac. e. cartilaginea an ossified chondroma arising from the epiphysis or joint surface of a bone. hereditary multiple exostoses [MIM*133700] a disturbance of enchondral bone growth in which multiple, generally benign osteochondromas of long bones appear during childhood, commonly with shortening of the radius and fibula; the skull is not involved; the ill effects are usually mechanical but malignant change is rare; autosomal dominant inheritance with genetic heterogeneity of which some cases are due to mutation in the e.-1 gene (EXT1) on 8q. SYN: hereditary deforming chondrodystrophy (1) , multiple e., osteochondromatosis. ivory e. a small, rounded, eburnated tumor arising from a bone, usually one of the cranial bones. multiple e. SYN: hereditary multiple exostoses. solitary osteocartilaginous e. SYN: osteochondroma. subungual e. painful osseous outgrowths that elevate the nail of the great toe or fingers in young people.

exoteric (ek-so-tar′ik)
Of external origin; arising outside the organism. [G. exoterikos, outer]

exothermic (ek-so-ther′mik)
1. Denoting a chemical reaction during which heat ( i.e., enthalpy) is emitted. Cf.:endothermic. 2. Relating to the external warmth of the body. [exo- + G. therme, heat]

exotoxic (ek-so-tok′sik)
1. Relating to an exotoxin. 2. Relating to the introduction of an exogenous poison or toxin.

exotoxin (ek-so-tok′sin)
A specific, soluble, antigenic, usually heat labile, injurious substance elaborated by certain Gram-positive or Gram-negative bacteria; it is formed within the cell, but is released into the environment where it is rapidly active in extremely small amounts; most exotoxins are protein in nature (MW 70,000–900,000) and can have the toxic portion of the molecule destroyed by heat, prolonged storage, or chemicals; the nontoxic but antigenic form is a toxoid. SYN: ectotoxin, extracellular toxin.

exotropia (ek-so-tro′pe-a)
That type of strabismus in which the visual axes diverge; may be paralytic or concomitant, monocular or alternating, constant or intermittent. SYN: divergent squint, divergent strabismus, exodeviation (2) , external squint, wall-eye (1) . [exo- + G. trope, turn] A-pattern e. divergent strabismus greater in downward than in upward gaze. basic e. e. in which the strabismus is the same for near and far vision. divergence excess e. e. in which the strabismus is notably greater for far vision than for near vision. divergence insufficiency e. e. in which the strabismus is notably greater for near vision than for far vision. V-pattern e. divergent strabismus greater in upward than in downward gaze. X-pattern e. increasing divergence from primary position in both upward and downward gaze.

expansion (eks-pan′shun)
1. An increase in size as of chest or lungs. 2. The spreading out of any structure, as a tendon. 3. An expanse; a wide area. [L. ex-pando, pp. -pansus, to spread out] clonal e. (klo′nal) production of daughter cells all arising originally from a single cell. extensor e. SYN: extensor digital e.. extensor digital e. a triangular tendinous aponeurosis including the tendon of the extensor digitorum centrally, interosseus tendons on each side, and a lumbrical tendon laterally. It covers the dorsal aspect of the metacarpophalangeal joint and the proximal phalanx. SYN: dorsal hood, extensor aponeurosis, extensor e.. hygroscopic e. 1. e. due to the absorption of moisture; 2. in dental casting, the addition of water to the surface of the casting investment during setting to increase the size of the mold. perceptual e. development of an ability to recognize and interpret sensory stimuli through associations with past similar stimuli; perceptual e. by relaxation of defenses is a goal of psychotherapy. setting e. the dimensional increase that occurs concurrently with the hardening of various materials, such as plaster of Paris. wax e. in dentistry, a method of expanding wax patterns to compensate for the shrinkage of gold during the casting process.

expansiveness (ek-span′siv-nes)
A state of optimism, loquacity, and reactivity.

In probability theory and statistics the true mean or average (of a sample distribution).

expectation of life
The average number of years of life an individual of a given age is expected to live if current mortality rates continue to apply; a statistical abstraction based on existing age-specific death rates. e. at age x the average number of additional years a person aged x would live if current mortality trends continue to apply, based on the age-specific death rates for a given year. e. at birth average number of years of life a newborn baby can be expected to live if current mortality trends continue.

In probability theory and statistics, interchangeable with mean or average; it need not be a probable or even possible value. For instance, the e. number of children in completed families may be 2.53, but that is not a possible size of any actual family.

expectorant (ek-spek′to-rant)
1. Promoting secretion from the mucous membrane of the air passages or facilitating its expulsion. 2. An agent that increases bronchial secretion and facilitates its expulsion. [L. ex, out, + pectus, chest]

expectorate (ek-spek′to-rat)
To spit; to eject saliva, mucus, or other fluid from the mouth.

expectoration (ek-spek-to-ra′shun)
1. Mucus and other fluids formed in the air passages and upper food passages (the mouth), and expelled by coughing. SEE ALSO: sputum (1) . 2. The act of spitting; the expelling from the mouth of saliva, mucus, and other material from the air or upper food passages. SYN: spitting. prune-juice e. SYN: prune-juice sputum.

experience (ek-sper′e-ens)
The feeling of emotions and sensations, as opposed to thinking; involvement in what is happening rather than abstract reflection on an event or interpersonal encounter. [L. experientia, fr. experior, to try] corrective emotional e. reexposure under favorable circumstances to an emotional situation with which one could not cope in the past.

experiment (eks-per′i-ment)
1. A study in which the investigator intentionally alters one or more factors under controlled conditions in order to study the effects of doing so. 2. In nuclear magnetic resonance, the term applied to a pulse sequence. [L. experimentum, fr. experior, to test, try] Carr-Purcell e. in magnetic resonance, the multiple spin echo technique. control e. an e. used to check another, to verify the result, or to demonstrate what would have occurred had the factor under study been omitted. SEE ALSO: control, control animal. delayed reaction e. a method of measuring memory: a stimulus is presented and removed before the organism is permitted to respond to it; the interval during which the stimulus is absent, providing the organism responds correctly, is an indication of the length of memory. double blind e. an e. conducted with neither experimenter nor subjects knowing which e. is the control; prevents bias in recording results. SEE ALSO: double-masked e.. double-masked e. a double-blind study conducted so neither the subject nor the observer knows the identity of the control or variable. factorial experiments an experimental design in which two or more series of treatments are tried in all combinations. hertzian experiments experiments demonstrating that electromagnetic induction is propagated in waves, analogous to waves of light but not affecting the retina. Mariotte e. an e. in which one looks fixedly with one eye (the other being closed), at a black dot on a card, on which is also marked a black cross; as the card is moved to or from the eye, at a certain distance the cross becomes invisible but appears again as the card is moved further; this proves the absence of photoreceptors where the optic nerve enters the eye. pulse-chase e. an e. in which an enzyme, a metabolic pathway, a culture of cells, etc., interacts with a brief addition (pulse) of a labeled compound followed by its removal and replacement (chase) by an excess of unlabeled compound. Scheiner e. a demonstration of accommodation; through two minute holes in a card, separated from each other by less than the diameter of the pupil, one looks at a pin; at a short distance from the eye the pin appears double; as it is moved from the eye a point is found where it appears single, and beyond which it remains single for the emmetropic eye, but for the myopic eye it soon again becomes double.

expiration (eks-pi-ra′shun)
1. SYN: exhalation (1) . 2. A death. [L. expiro or ex-spiro, pp. -atus, to breathe out]

expiratory (ek-spi′ra-to-re)
Relating to expiration.

expire (ek-spir′)
1. SYN: exhale (1) . 2. To die.

explant (eks′plant)
Living tissue transferred from an organism to an artificial medium for culture.

explantation (eks-plan-ta′shun)
The act of transferring an explant.

exploration (eks-plor-a′shun)
An active examination, usually involving a surgical procedure, to ascertain conditions present within a body cavity as an aid in diagnosis. [L. ex-ploro, pp. -ploratus, to explore]

exploratory (eks-plor′a-tor-e)
Relating to, or with a view to, exploration.

explorer (ek′splor′er)
A sharp pointed probe used to investigate natural or restored tooth surfaces in order to detect caries or other defects.

explosion (eks-plo′zhun)
A sudden and violent increase in volume accompanied by noise and release of energy, as from a chemical change, nuclear reaction, or escape of gases or vapors under pressure. [L. explosio, fr. explodo, to drive away by clapping]

expose (eks-poz′)
To perform or undergo exposure. [O. Fr. exposer, fr. L. ex-pono, pp. ex-positum, to set out, e.]

exposure (eks-po′zhoor)
1. A displaying, revealing, exhibiting, or making accessible. 2. In dentistry, loss of hard tooth structure covering the dental pulp due to caries, dental instrumentation, or trauma. 3. Proximity and/or contact with a source of a disease agent in such a manner that effective transmission of the agent or harmful effects of the agent may occur. 4. The amount of a factor to which a group or individual was exposed, in contrast to the dose, the amount that enters or interacts with the organism.

express (eks-pres′)
To press or squeeze out. [L. ex-premo, pp. -pressus, to press out]

expression (eks-presh′un)
1. Squeezing out; expelling by pressure. 2. Mobility of the features giving a particular emotional significance to the face. SYN: facies (3) [TA] . 3. Any act by an individual. 4. Something that manifests something else. 5. The act of allowing information to become manifest. 6. A mathematical function consisting of a combination of constants, variables, other functions, and mathematical operations. differential gene e. gene e. that responds to signals or triggers; a means of gene regulation; E.G., effects of certain hormones on protein biosynthesis. gene e. 1. the detectable effect of a gene. 2. appearance of an inherited trait; for many genetic ( e.g., recessiveness, hypostasis, parastasis) and environmental (the absence of pertinent challenges) reasons, a gene may not be expressed at all. In those circumstances, it will have no impact on Darwinian evolution. integrated rate e. an equation of a chemical or enzyme-catalyzed reaction for the entire progress curve. e. library a collection of plasmid or phage containing a representative sample of cDNA or genomic fragments that are constructed in such a way that they will be transcribed and translated by the host organism (usually bacteria).

expressivity (eks-pres-siv′i-te)
In clinical genetics, the degree of severity in which a gene is manifested.

expulsive (eks-pul′siv)
Tending to expel. [L. ex-pello, pp. -pulsus, to drive out]

exquisite (eks-kwiz′it)
Extremely intense, keen, sharp; said of pain or tenderness in a part. [L. exquiro, pp. exquisitus, to search out]

exsanguinate (ek-sang′gwi-nat)
1. To remove or withdraw the circulating blood; to make bloodless. 2. SYN: exsanguine. [L. ex, out, + sanguis (-guin), blood]

exsanguination (ek-sang′gwi-na′shun)
Removal of blood; making exsanguine.

exsanguine (ek-sang′gwin)
Deprived of blood. SYN: exsanguinate (2) .

exsect (ek-sekt′)
Rarely used term for excise. [L. ex- seco, pp. -sectus, to cut out]

exsection (ek-sek′shun)
Rarely used term for excision.

Exserohilum (eks′er-o-hi′lum)
A genus of fungi; a cause of human phaeohyphomycosis.

exsiccant (ek-sik′ant)
SYN: desiccant.

exsiccate (ek′si-kat)
SYN: desiccate.

exsiccation (ek-si-ka′shun)
1. SYN: desiccation. 2. The removal of water of crystallization. SYN: dehydration (3) . [L. ex sicco, pp. siccatus, to dry up]

exsomatize (ek-so′ma-tiz)
To remove from the body. [G. ex, out of, + soma, body]

exsorption (ek-sorp′shun)
Movement of substances from the blood into the lumen of the gut. [L. ex, out, + sorbeo, to suck]

exstrophy (ek′stro-fe)
Congenital eversion of a hollow organ. SYN: ecstrophe. [G. ex, out, + strophe, a turning] e. of the bladder a congenital gap in the anterior wall of the bladder and the abdominal wall in front of it, the posterior wall of the bladder being exposed. SYN: ectopia vesicae. cloacal e. congenital anomaly with two exstrophied bladder units separated by an exstrophied segment of intestine, which is usually cecum, receiving ileum superiorly and continuing distally to blind ending microcolon. A number of variants of anatomic disarray can occur. SYN: ectopia cloacae.

extend (eks-tend′)
To straighten a limb, to diminish or extinguish the angle formed by flexion; to place the distal segment of a limb in such a position that its axis is continuous with that of the proximal segment. [L. ex- tendo, pp. -tensus, to stretch out]

extension (eks-ten′shun) [TA]
1. The act of bringing the distal portion of a joint in continuity (though only parallel) with the long axis of the proximal portion. 2. A pulling or dragging force exerted on a limb in a distal direction. 3. Obsolete term for traction. [L. extensio, a stretching out] Buck e. SYN: Buck traction. primer e. a technique for determining the 5′-untranslated region of a specific mRNA molecule. Uses an oligonucleotide complementary to the known RNA sequence as a primer for cDNA synthesis via reverse transcriptase. ridge e. an intraoral surgical operation for deepening the labial, buccal, and/or lingual sulci; it is performed to increase the intraoral height of the alveolar ridge in order to assist denture retention. skeletal e. SYN: skeletal traction.

extensor (eks-ten′ser, -sor) [TA]
A muscle the contraction of which causes movement at a joint with the consequence that the limb or body assumes a more straight line, or so that the distance between the parts proximal and distal to the joint is increased or extended; the antagonist of a flexor. See muscle. [L. one who stretches, fr. ex-tendo, to stretch out]

exterior (eks-te′re-or)
Outside; external. [L.]

exteriorize (eks-ter′e-or-iz)
1. To direct a patient's interests, thoughts, or feelings into a channel leading outside the self, to some definite aim or object. 2. To expose an organ temporarily for observation, or permanently for purposes of experiment. 3. Fixation of a segment of bowel with blood supply intact to the outer aspect of the abdominal wall.


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