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A test or experiment, usually conducted under specific conditions. clinical t. a controlled experiment involving a defined set of human subjects, having a clinical event as an outcome measure, and intended to yield scientifically valid information about the efficacy or safety of a drug, vaccine, diagnostic test, surgical procedure, or other form of medical intervention.Four phases of clinical t. are distinguished. Phase I trials usually involve fewer than 100 healthy volunteers who are exposed to a new drug or vaccine. Such studies seek to establish optimal dosage and route of administration and to detect adverse reactions. Phase II trials generally involve 200–500 volunteers randomly assigned to control and study groups. These are pilot efficacy studies, with emphasis on immunogenicity in the case of vaccines, and on relative efficacy and safety in the case of drugs. Phase III trials, often multicenter, involve thousands of volunteers, randomly assigned to control and study groups. The aim is to generate statistically relevant data. Phase IV trials are conducted after a national drug registration authority (in the U.S., the Food and Drug Administration) has approved an agent for distribution or sale. They may explore specific pharmacologic effect, adverse reactions, or long-term effects. randomized controlled t. (RCT) an epidemiologic experiment in which subjects in a population are allocated randomly into groups, called “experimental” or “study” and “control” groups to receive or not receive an experimental therapeutic or preventive regimen, procedure, maneuver, or intervention.

trial and error
The apparently random, haphazard, hit-or-miss exploratory activity which often precedes the acquisition of new information or adjustments; it may be overt, as in a rat running in a maze, or covert (vicarious), as when one thinks of various ways of coping with a situation.

triamcinolone (tri-am-sin′o-lon)
A glucocorticoid with actions and uses similar to those of prednisolone. t. acetonide a potent glucocorticoid for topical treatment of dermatoses. t. diacetate an anti-inflammatory and antiallergic agent for parenteral use.

tri-amelia (tri′a-me′le-a)
Absence of three limbs. [tri- + G. a- priv. + melos, limb]

triamterene (tri-am′ter-en)
A potassium sparing diuretic agent, often used in combination with hydrochlorthiazide.

triangle (tri′ang-gl) [TA]
In anatomy and surgery, a three-sided area with arbitrary or natural boundaries. SEE ALSO: trigonum, region. [L. triangulum, fr. tri-, three, + angulus, angle] anal t. [TA] the posterior portion of the perineal region through which the anal canal opens; bounded by a line through both ischial tuberosities, the sacrotuberous ligaments, and the coccyx. SYN: regio analis [TA] , anal region. anterior t. of neck anterior cervical region. Assézat t. a t. formed by lines connecting the nasion with the alveolar and nasal point; used to indicate prognathism in comparative craniology. auricular t. a t. formed by the base of the auricle and by lines drawn from the true tip of the auricle to the extremities of the base. ausculatory t. [TA] space bounded by the lower border of the trapezius, the latissimus dorsi, and the medial margin of the scapula, where the absence of musculature allows respiratory sounds to be heard clearly with a stethoscope. SYN: trigonum auscultationis [TA] , t. of auscultation&star. t. of auscultation ausculatory t.. axillary t. a triangular area embracing the medial aspect of the arm, the axilla, and the pectoral region which is one of the seats of predilection for the petechial initial rash of smallpox. SEE ALSO: axillary region. Béclard t. area bounded by the posterior border of the hyoglossus muscle, the posterior belly of the digastric, and the greater horn of the hyoid bone. Bonwill t. an equilateral t. formed by lines from the contact points of the lower central incisors, or the medial line of the residual ridge of the mandible, to the condyle on either side and from one condyle to the other. Burger t. a scalene t. representing the frontal plane electrocardiographic leads comparable to, but more accurate than, the Einthoven t.. See Einthoven t.. Burow t. a t. of skin and subcutaneous fat excised so that a flap can be advanced without buckling the adjacent tissue. Calot t. [TA] SYN: cystohepatic t.. cardiohepatic t. SYN: cardiohepatic angle. carotid t. [TA] a space bounded by the superior belly of the omohyoid muscle, anterior border of the sternocleidomastoid, and posterior belly of the digastric; it contains the bifurcation of the common carotid artery. SYN: trigonum caroticum [TA] , fossa carotica, Gerdy hyoid fossa, Malgaigne fossa, Malgaigne t., superior carotid t.. cephalic t. a t. on the cranium formed by lines connecting the metopion, the pogonion, and the occipital point. cervical t. any of the triangles of the neck. clavipectoral t. [TA] area of anterior thoracic region bounded superiorly by the clavicle, inferomedially by the pectoral major (muscle) and superolaterally by the deltoid (muscle); the cephalic vein typically passes from superficial to deep here, and the pectoral branch of the thoracoacromial (arterial) trunk emerges here. SYN: trigonum clavipectorale [TA] , trigonum deltopectorale&star, deltoideopectoral t., deltopectoral t., trigonum deltoideopectorale. Codman t. in radiology, the interface between growing bone tumor and normal bone, presenting as an incomplete t. formed by periosteum. crural t. an area of predilection for the petechial initial rash of smallpox; it occupies the lower abdominal, inguinal, and genital regions and the inner aspects of the thighs, the base of the t. traversing the umbilicus. cystohepatic t. [TA] area bounded by the cystic artery, cystic duct, and (common) hepatic duct—important structures to identify in performing a laparoscopic cholecystectomy. SYN: Calot t. [TA] , trigonum cystohepaticum [TA] . deltoideopectoral t. SYN: clavipectoral t.. deltopectoral t. SYN: clavipectoral t.. digastric t. SYN: submandibular t.. Einthoven t. an imaginary equilateral t. with the heart at its center, its equal sides representing the three standard limb leads of the electrocardiogram. Elaut t. t. formed by the iliac arteries and the promontory of the sacrum. t. of elbow SYN: cubital fossa. facial t. a t. formed by lines connecting the basion, the prosthion, and the nasion. Farabeuf t. the t. formed by the internal jugular and facial veins and the hypoglossal nerve. femoral t. [TA] a triangular space at the upper part of the thigh, bounded by the sartorius and adductor longus muscles and the inguinal ligament, with a floor formed laterally by the iliopsoas muscle and medially by the pectineus muscle; the branches of the femoral nerve are distributed within the femoral t.; it is bisected by the femoral vessels, which enter the adductor canal at the triangles apex. SYN: trigonum femorale [TA] , trigonum femoris&star, fossa scarpae major, Scarpa t., subinguinal t.. t. of fillet SYN: trigone of lateral lemniscus. frontal t. a t. bounded above by the maximum frontal diameter and laterally by lines joining the extremities of this diameter with the glabella. Garland t. a triangular area of relative resonance in the lower back near the spine, found on the same side as a pleural effusion. Gombault t. semilunar fasciculus. Grocco t. a triangular patch of dullness at the base of the chest alongside the spinal column, on the side opposite a pleural effusion. SYN: paravertebral t.. Grynfeltt t. a triangular space bounded above by the end of the last rib and the serratus posterior inferior muscle, anteriorly by the internal oblique, and posteriorly by the quadratus lumborum; lumbar hernia occurs in this space. SYN: Lesshaft t.. Hesselbach t. SYN: inguinal t.. inferior carotid t. SYN: muscular t. (of neck). inferior lumbar t. [TA] an area of the back (posterior abdominal wall) bounded by the edges of the latissimus dorsi and external oblique muscles and the iliac crest; herniations occasionally occur here. SYN: trigonum lumbale inferius [TA] , lumbar t., Petit lumbar t.. inferior occipital t. a t. with its apex at the external occipital protuberance; its base is formed by a line joining the two mastoid processes. infraclavicular t. SYN: infraclavicular fossa. inguinal t. [TA] the triangular area in the lower abdominal wall bounded inferiorly by the inguinal ligament (externally) or iliopubic tract (internally), the border of the rectus abdominis medially and the inferior epigastric vessels (lateral umbilical fold) laterally. It is the site of direct inguinal hernia. SYN: trigonum inguinale [TA] , Hesselbach t., inguinal trigone. interscalene t. SYN: scalene hiatus. Killian t. the triangular-shaped area of the cervical esophagus bordered by the oblique fibers of the inferior constrictor muscle of the pharynx and the transverse fibers of the cricopharyngeus muscle through which Zenker diverticulum occurs. Koch t. a triangular area of the wall of the right atrium of the heart, that marks the approximate situation of the atrioventricular node. Labbé t. an area bounded below by a horizontal line touching the lower edge of the cartilage of the left ninth rib, laterally by the line of the false ribs, and to the right side by the liver; here the stomach is normally in contact with the abdominal wall. Langenbeck t. a t. formed by lines drawn from the anterior superior iliac spine to the surface of the great trochanter and to the surgical neck of the femur; a penetrating wound in this area probably involves the joint. lateral pelvic wall t. [TA] area of lateral wall of pelvis covered by the portion of the obturator internus muscle and fascia superior to the tendinous arch of levator ani (muscle), anterior to the sciatic notch, and inferior to the arcuate line of the ilium. SYN: trigonum parietale laterale pelvis [TA] . Lesser t. the space between the bellies of the digastric muscle and the hypoglossal nerve. Lesshaft t. SYN: Grynfeltt t.. Lieutaud t. SYN: trigone of bladder. lumbar t. SYN: inferior lumbar t.. lumbocostal t. of diaphragm [TA] a triangular area in the diaphragm between its lumbar and costal parts and superior to the lateral arcuate ligament that is devoid of muscle fibers; it is covered by pleura superiorly and by peritoneum inferiorly; when it fails to form congenitally (a closure defect of the fetal pleuroperitoneal hiatus), the consequent foramen of Bochdalek is the most common site of diaphragmatic hernia of abdominal viscera. SYN: trigonum lumbocostale diaphragmatis [TA] , Bochdalek gap, vertebrocostal trigone. lumbocostoabdominal t. an irregular area bounded by the serratus posterior inferior, obliquus externus, obliquus internus, and erector spinae muscles. Macewen t. SYN: suprameatal t.. Malgaigne t. SYN: carotid t.. Marcille t. an area bounded by the medial border of the psoas major, the lateral margin of the vertebral column, and the iliolumbar ligament below; it is crossed by the obturator nerve. muscular t. (of neck) [TA] the t. bounded by the sternocleidomastoid muscle, the superior belly of the omohyoid muscle, and the anterior midline of the neck; the infrahyoid muscles occupy most of it. SYN: trigonum musculare (regionis cervicalis anterioris) [TA] , omotracheal t.&star, trigonum omotracheale&star, inferior carotid t., tracheal t.. occipital t. a t. of the neck bounded by the trapezius, the sternocleidomastoid, and the omohyoid muscles. SEE ALSO: inferior occipital t.. omoclavicular t. [TA] SYN: supraclavicular t.. omotracheal t. muscular t. (of neck). palatal t. a triangular area bounded by the greatest transverse diameter of the palate and by lines converging from its extremities to the alveolar point. SYN: trigonum palati. paravertebral t. SYN: Grocco t.. Petit lumbar t. SYN: inferior lumbar t.. Philippe t. semilunar fasciculus. Pirogoff t. a t. formed by the intermediate tendon of the digastric muscle, the posterior border of the mylohyoid muscle, and the hypoglossal nerve. posterior t. of neck lateral cervical region. pubourethral t. a t. in the perineum bounded by the transversus perinei, the ischiocavernosus, and the bulbocavernosus muscles. Reil t. SYN: trigone of lateral lemniscus. retromolar t. [TA] triangular area posterior to the third mandibular molar tooth. SYN: trigonum retromolare [TA] . sacral t. the surface area over the sacrum. t. of safety the area at the lower left sternal border where the pericardium is not covered by lung (pericardial notch); preferred site for aspiration of pericardial fluid. Scarpa t. SYN: femoral t.. sternocostal t. SYN: trigonum sternocostale. sternocostal t. (of diaphragm) [TA] fibrous (nonmuscular) area of diaphragm between the muscular slips of the sternal part of the diaphragm and the costal part; when it fails to form congenitally, the consequent foramen of Morgagni may allow herniation of abdominal viscera into thorax. SYN: trigonum sternocostale diaphragmatis [TA] . subclavian t. supraclavicular t.. subinguinal t. SYN: femoral t.. submandibular t. [TA] the t. of the neck bounded by the mandible and the two bellies of the digastric muscle; it contains the submandibular gland. SYN: trigonum submandibulare [TA] , digastric t., submaxillary t.. submaxillary t. SYN: submandibular t.. submental t. [TA] a t. bounded by the anterior belly of the digastric muscles, the hyoid bone, and the midline; the mylohyoid muscle forms its floor. SYN: trigonum submentale [TA] . suboccipital t. a deep t. bounded by the obliquus capitis inferior, the obliquus capitis superior, and the rectus capitis posterior major muscles. superior carotid t. SYN: carotid t.. supraclavicular t. [TA] the t. bounded by the clavicle, the omohyoid muscle, and the sternocleidomastoid muscle; it contains the subclavian artery and vein. SYN: omoclavicular t. [TA] , trigonum omoclaviculare [TA] , subclavian t.&star. suprameatal t. [TA] a t. formed by the root of the zygomatic arch, the posterior wall of the bony external acoustic meatus, and an imaginary line connecting the extremities of the first two lines; the suprameatal spine lies in its anterior margins; used as a guide in mastoid operations since it is the lateral wall of the mastoid antrum. SYN: foveola suprameatica [TA] , foveola suprameatalis, Macewen t., mastoid fossa, fossa mastoidea, supramastoid fossa, suprameatal pit. tracheal t. SYN: muscular t. (of neck). Tweed t. a t. defined by facial and dental landmarks on a lateral cephalometric film, using the Frankfort horizontal plane as a base and intended for use as a guide in the evaluation and planning of orthodontic treatment. umbilicomammillary t. a t. with its apex at the umbilicus and its base at the line joining the nipples. urogenital t. [TA] the anterior portion of the perineal region containing the openings of the urethra and vagina in the female and the urethra and root structures of the penis in the male. SYN: regio urogenitalis [TA] , urogenital region. t. of vertebral artery triangular area in the root of the neck bounded laterally by the scalenus anterior and medially by the longus colli (muscles); the two muscles meet at the triangles apex, formed by the anterior (carotid) tubercle of the transverse process of vertebra C6; the vertebral artery arises from the subclavian artery at the base of the t., bisecting the t. as it ascends to the apex to enter the transverse foramen of vertebra C6. vesical t. SYN: trigone of bladder. Ward t. an area of diminished density in the trabecular pattern of the neck of the femur evident by x-ray as well as by direct inspection of a specimen. Weber t. on the sole of the foot, an area indicated by the heads of the first and fifth metatarsal bone and the center of the plantar surface of the heel. Wilde t. SYN: light reflex (3) .

See triangular muscle. [L. triangular]

triangulum (tri-ang′goo-lum)
See triangle. [L.]

Triatoma (tri-a-to′ma)
A genus of insects (subfamily Triatominae, family Reduviidae) that includes important vectors of Trypanosoma cruzi, such as T. dimidiata, T. infestans, and T. maculata.

Triatominae (tri-a-to′mi-ne)
A subfamily of insects (family Reduviidae, suborder Heteroptera) that are vertebrate bloodsuckers and include such important disease vector species as Panstrongylus, Rhodnius, and Triatoma; they are commonly called conenose or kissing bugs.

triazolam (tri-a′zo-lam)
A short-acting benzodiazepine derivative used as a sedative and hypnotic.

triazologuanine (tri′a-zol-o-gwah′nen)
SYN: 8-azaguanine.

tribasic (tri-ba′sik)
Having three titratable hydrogen atoms; denoting an acid with a basicity of 3.

tribasilar (tri-bas′i-lar)
Having three bases.

tribe (trib)
In biologic classification, an occasionally used division between the family and the genus; often the same as the subfamily. [L. tribus]

tribology (tri-bol′o-je)
The study of friction and its effects in biologic systems, especially in regard to articulated surfaces of the skeleton. [G. tribo, to rub, + logos, study]

triboluminescence (trib′o-loo-mi-nes′ens)
Luminosity produced by friction. [G. tribo, to rub, + luminescence]

tribrachia (tri-bra′ke-a)
Condition seen in conjoined twins in which there are only three arms for the two bodies. See conjoined twins, under twin. [tri- + G. brachion, arm]

tribrachius (tri-bra′ke-us)
Conjoined twins exhibiting tribrachia.

tribromsalan (tri-brom′sa-lan)
A disinfectant used in soaps.

tributyrase (tri-bu′ti-ras)
SYN: triacylglycerol lipase.

tributyrin (tri-bu′ti-rin)
A synthetic substrate for lipase assays. SYN: glyceryl tributyrate, tributyrylglycerol.

tributyrinase (tri-bu′ti-ri-nas)
SYN: triacylglycerol lipase.

tributyrylglycerol (tri-bu′ti-ril-glis′er-ol)
SYN: tributyrin.

Acronym for trachoma and inclusion conjunctivitis. See T. agents, under agent.

tricalcium phosphate (tri-kal′se-um)
SYN: tribasic calcium phosphate.

tricephalus (tri-sef′a-lus)
Fetus with three heads. [tri- + G. kephale, head]

triceps (tri′seps)
Three-headed; denoting especially two muscles: t. brachii and t. surae. See muscle. [L. fr. tri-, three, + caput, head]

See tricho-.

trichalgia (trik-al′je-a)
Pain produced by touching the hair; painful hair, as can occur with atypical angina. SYN: trichodynia. [trich- + G. algos, pain]

trichangion (trik-an′je-on)
SYN: telangion. [trich- + G. angeion, vessel]

trichatrophia (trik-a-tro′fe-a)
Atrophy of the hair bulbs, with brittleness, splitting, and falling out of hair. [trich- + G. atrophia, atrophy]

trichauxis (trik-awk′sis)
Excessive growth of hair in length and quantity. [trich- + G. auxis, increase]

See tricho-.

Condition or type of hair. [G. thrix (trich-), hair, + -ia, condition]

trichiasis (tri-ki′a-sis)
A condition in which the hair adjacent to a natural orifice turns inward and causes irritation; e.g., in inversion of an eyelid (entropion), eyelashes irritate the eye. SYN: trichoma, trichomatosis. [trich- + G. -iasis, condition]

trichilemmoma (trik′i-le-mo′ma)
A benign tumor derived from outer root sheath epithelium of a hair follicle, consisting of cells with pale-staining cytoplasm containing glycogen; multiple trichilemmomas are present on the face in Cowden disease. SYN: tricholemmoma. [trichi- + G. lemma, husk, + -oma, tumor]

Trichina (tri-ki′na)
Old name for a genus of nematode worms, correctly called Trichinella.

trichina, pl .trichinae (tri-ki′na, -ne)
A larval worm of the genus Trichinella; the infective form in pork. [Mod. L., fr. G. thrix (trich-), a hair]

Trichinella (trik′i-nel′a)
A nematode genus in the aphasmid group that causes trichinosis in humans and carnivores. [Mod. L. fr. trichina + dim. suffix ella] T. pseudospiralis. nematode species with normal life cycle in small predators; humans are an accidental host. T. spiralis the pork or trichina worm, a species of parasites that cause trichinosis, found in most regions of the world but more frequently in the Northern Hemisphere; transmission occurs as a result of ingesting raw or inadequately cooked meat (especially pork) that contains encysted larvae which develop into adults that survive in the jejunum and ileum for approximately 6 weeks; the female worm is viviparous, and bears approximately 1500 embryonic larvae that are laid deep in the mucosa so that they are picked up in the submucosal capillaries and are transported via the liver to the heart, lungs, and systemic circulation; eventually the larvae break out of the body capillaries, penetrate a muscle fiber, coil, and encyst, thereby inducing the strong sensitization, pain, fever, edema, and eosinophilic reaction characteristic of trichinosis.

trichinelliasis (trik′i-nel-i′a-sis)
SYN: trichinosis.

Trichinellicae (tri-ki-nel′i-ke)
SYN: Trichinelloidea.

Trichinelloidea (trik′i-nel-oy′de-a)
A superfamily of nematodes, including the following roundworms that are parasitic in man: Trichinella spiralis, the trichina worm (family Trichinellidae); Trichuris trichiura, the human whipworm; Capillaria hepatica, the capillary liver worm; and C. philippinensis (family Trichuridae). SYN: Trichinellicae.

trichinellosis (trik′i-nel-o′sis)
SYN: trichinosis.

trichiniasis (trik-i-ni′a-sis)
SYN: trichinosis.

trichiniferous (trik-i-nif′e-rus)
Containing trichina worms.

trichinization (trik′i-ni-za′shun)
Infection with trichina worms.

trichinoscope (trik′i-no-skop)
A magnifying glass used in the examination of meat suspected of being trichinous. [trichina + G. skopeo, to view]

trichinosis (trik-i-no′sis)
The disease resulting from ingestion of raw or inadequately cooked pork (or bear or walrus meat) that contains encysted larvae of the nematode parasite Trichinella spiralis. The initial symptoms of human disease are abdominal pain, cramping, and diarrhea, associated with the development of the parasites in the small intestine. Once the resultant larval parasites migrate and invade muscular tissue, a second set of symptoms is manifest, including facial and periorbital edema, myalgia, fever, pruritus, urticaria, conjunctivitis, and signs of myocarditis. SYN: trichinelliasis, trichinellosis, trichiniasis. [Trichinella (trichina) + G. -osis, condition]

trichinous (trik′i-nus)
Infected with trichina worms.

trichion (trik′e-on)
A cephalometric point at the midpoint of the hairline at the top of the forehead. [G. thrix, hair]

trichite (trik′it)
SYN: trichocyst.

trichloral (tri-klor′al)
SYN: m-chloral.

trichlorfon (tri-klor′fon)
An organophosphorus compound effective against immature and mature stages of Schistosoma haematobium, but ineffective against other species of Schistosoma in humans. SYN: metrifonate.

trichloride (tri-klor′id)
A chloride having three chlorine atoms in the molecule; e.g., PCl3.

trichlormethiazide (tri-klor-me-thi′a-zid)
An orally effective benzothiazide diuretic and antihypertensive agent.

trichlormethine (tri-klor-meth′en)
A nitrogen mustard used in the treatment of leukemia.

trichloroacetic acid (tri-klor′o-a-se′tik)
Used as an astringent antiseptic in 1–5% solution or as an escharotic for venereal and other warts; a widely used protein precipitant.

trichloroethane (tri-klor-o-eth′an)
An industrial solvent with pronounced inhalation anesthetic activity. SYN: methylchloroform.


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