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Medical Dictionary


piposulfan (pi-po-sul′fan)
An antineoplastic agent.

pipradrol hydrochloride (pip′ra-drol)
A central nervous system stimulant.

piprinhydrinate (pip-rin-hi′dri-nat)
An antihistaminic and antiemetic.

pipsyl (Ips) (pip′sil)
p-Iodophenylsulfonyl, the radical of p. chloride that combines with the amino groups of amino acids and proteins.

pirbuterol (pir-bu′ter-ol)
A selective β2-adrenergic bronchodilator used to treat bronchospasm in asthma or chronic obstructive lung disease.

Pirenella (pir-e-nel′a)
A genus of marine and brackish water operculate (prosobranch) snails. P. conica is the initial intermediate host of Heterophyes heterophyes, the fish-borne fluke of humans and fish-eating birds and mammals along the Mediterranean and Red Sea coasts.

pirenzepine (pi-ren′ze-pen)
An anticholinergic agent exhibiting relative specificity for suppression of gastric hydrochloric acid secretion; relatively free of anticholinergic side effects; used in the treatment of ulcer disease.

piretanide (pi-ret′a-nid)
High ceiling loop diuretic similar to bumetanide and furosemide; used as a diuretic in hypertension and congestive heart failure.

piribedil (pi-rib′e-dil)
An agent that stimulates dopamine receptors in the brain and also exerts a peripheral vasodilator effect.

George A., Scottish radiologist, 1864–1929. See P. bone.

piriform (pir′i-form, pi′re-)
Pear-shaped. SYN: pyriform. [L. pirum, pear, + forma, form]

Nikolai I., Russian surgeon, 1810–1881. See P. amputation, P. angle, P. triangle.

piromen (pir′o-men, pi′ro-)
A sterile, nonprotein, nonanaphylactogenic extract of Pseudomonas aeruginosa and Proteus vulgaris. The active components are bacterial polysaccharides of low toxicity; used in the treatment of certain allergic, dermatologic, and ophthalmic disorders. SYN: pyromen.

Piroplasma (pir′o-plaz′ma, pi′ro-)
Former name for Babesia. [L. pirum, pear, + G. plasma, a thing formed]

Piroplasmida (pi′ro-plaz-mi′da)
An order of sporozoan protozoa (subclass Piroplasmia, class Sporozoea) consisting of the families Habesiidae, Theileriidae, and Dactylosomatidae; includes heteroxenous tick-borne blood parasites of vertebrates with reduced apical complex, lacking spores, and with asexual reproduction by binary fission or schizogony.

piroplasmosis (pir′o-plas-mo′sis)
SYN: babesiosis.

piroxicam olamine (pir-oks′i-kam)
A long-acting nonsteroidal anti-inflammatory agent with analgesic and antipyretic actions.

pirprofen (pir-pro′fen)
An anti-inflammatory agent used in the treatment of rheumatoid arthritis.

Pirquet von Cesenatico
Clemens P., Austrian physician, 1874–1929. See Pirquet reaction, Pirquet test.

Pisces (pis′ez, pi′sez)
A superclass of vertebrates, generally known as fish; the term is sometimes confined to the bony fishes. [L. pl. of piscis, a fish]

pisiform (pis′i-form) [TA]
Pea-shaped or pea-sized. [L. pisum, pea, + forma, appearance]

1. SYN: fovea. 2. One of the pinhead-sized depressed scars following the pustule of acne, chickenpox, or smallpox (pockmark). 3. A sharp-pointed depression in the enamel surface of a tooth, due to faulty or incomplete calcification or formed at the confluent point of two or more lobes of enamel. 4. To indent, as by pressure of the finger on the edematous skin; to become indented, said of the edematous tissues when pressure is applied with the fingertip. [L. puteus] anal p. SYN: proctodeum (1) . articular p. of head of radius SYN: articular facet of radial head. p. of atlas for dens SYN: facet (of atlas) for dens. auditory pits SYN: otic pits. buccal p. a structural depression found on the buccal enamel of molars. central p. SYN: central retinal fovea. coated p. specialized depressions on the cell surface involved in receptor-mediated endocytosis; the visible proteinaceous layer on the cytosolic side of the depression provides the coated appearance. commisural pits similar to lip pits but found at the labial commisures. costal p. of transverse process SYN: transverse costal facet. gastric p. [TA] one of the numerous small pits in the mucous membrane of the stomach that are the mouths of the gastric glands. SYN: foveola gastrica [TA] . granular pits SYN: granular foveolae, under foveola. p. of head of femur SYN: fovea for ligament of head of femur. inferior articular p. of atlas SYN: inferior articular surface of atlas. inferior costal p. SYN: inferior costal facet. iris pits colobomas affecting the stroma of the iris with pigment epithelium intact. lens pits the paired depressions formed in the superficial ectoderm of the embryonic head as the lens placodes sink in toward the optic cup; the external openings of the pits are closed as the lens vesicles are formed. lip pits malformations of the lip seen in unilateral or bilateral depressions or fistulae. May be hereditary or associated with cleft lip and/or palate. Mantoux p. shallow 2–3-mm depressions of the palms and soles in basal cell nevus syndrome. nail pits small punctate depressions on the surface of the nail plate due to defective nail formation; seen in psoriasis and other disorders. SEE ALSO: geographic stippling of nails. nasal pits the paired depressions formed when the nasal placodes come to lie below the general external contour of the developing face as a result of the rapid growth of the adjacent nasal elevations; the pits are the primordia of the rostral portions of the nasal chambers. SYN: olfactory pits. oblong p. of arytenoid cartilage SYN: oblong fovea of arytenoid cartilage. olfactory pits SYN: nasal pits. optic p. a congenital anomaly characterized by a focal depression of the temporal optic nerve head. otic pits paired depression, one on either side of the head of the embryo, marking the location of the future auditory vesicles. SYN: auditory pits. preauricular p. SYN: preauricular sinus. primitive p. the depression in the primitive node that serves to connect the notochordal canal with the surface ectoderm. pterygoid p. SYN: pterygoid fovea. p. of stomach SYN: epigastric fossa. sublingual p. SYN: sublingual fossa. superior articular p. of atlas SYN: superior articular surface of atlas. superior costal p. SYN: superior costal facet. suprameatal p. SYN: suprameatal triangle. triangular p. of arytenoid cartilage SYN: triangular fovea of arytenoid cartilage. trochlear p. SYN: trochlear fovea.

A nuclear binding transcriptional factor found in many cells in normal human pituitary glands and expressed in a large percentage of pituitary adenomas, in particular those positive for growth hormone, or thyrotropin.

Abbreviation for phenylisothiocyanate.

pitch (pich)
A resinous substance obtained from tar after the volatile substances have been expelled by boiling. SYN: pix. [L. pix] Burgundy p. a resinous exudation from the spruce fir or Norway spruce, Picea excelsa; has been used as a counterirritant in the form of a plaster. SYN: white p.. liquid p. SYN: pine tar. white p. SYN: Burgundy p..

pitchblende (pich′blend)
A mineral of pitchlike appearance, chiefly uranium dioxide, the main source of uranium and elements, such as radium, produced as a result of the radioactive breakdown of that element. SYN: uraninite.

1. The center of a hair. 2. The spinal cord and medulla oblongata. 3. To pierce the medulla of an animal with a sharp instrument introduced at the base of the skull. [A.S. pitha]

pithecoid (pith′e-koyd)
Resembling an ape. [G. pithekos, ape, + eidos, resemblance]

pithode (pith′od)
The nuclear spindle in karyokinesis. [G. pithodes, like a jar, fr. pithos, earthenware wine-jar, + eidos, resemblance]

Henri, French engineer, 1695–1771. See P. tube.

Jean A., French physician, 1848–1927. See P. area, P. sign.

Pitressin (pi-tres′in)
SYN: vasopressin.

In dentistry, the formation of well defined, relatively deep depressions in a surface, usually used in describing defects in surfaces (often golds, solder joints, or amalgam). It may arise from a variety of causes, although the clinical occurrence is often associated with corrosion. SEE ALSO: p. edema, nail pits, under pit.

pituicyte (pi-too′i-sit)
The primary cell of the posterior lobe of the pituitary gland, a fusiform cell closely related to neuroglia. [pituitary + G. kytos, cell]

pituicytoma (pi-too′i-si-to′ma)
A rare gliogenous neoplasm derived from pituicytes, occurring in the posterior lobe of the pituitary gland and characterized by cells with relatively small, round or oval nuclei and long branching processes that form a complex network of cytoplasmic material, in which numerous small droplets of fat may be demonstrated. [pituicyte + G. -oma, tumor]

pituita (pi-too′i-ta)
A thick nasal secretion. SYN: glairy mucus. [L. phlegm or thick mucous secretion]

pituitarism (pi-too′i-tar-izm)
Pituitary dysfunction. See hyperpituitarism, hypopituitarism.

pituitarium (pi-too-i-ta′re-um)
SYN: pituitary. [Mod. L.]

pituitary (pi-too′i-tar-e)
Relating to the p. gland (hypophysis). SYN: pituitarium. [L. pituita, a phlegm] anterior p. the dried, partially defatted, and powdered anterior lobe of the p. gland of cattle, sheep, or swine; now rarely used therapeutically. desiccated p. SYN: posterior p.. pharyngeal p. the embryonic remnant of the oral end of Rathke pouch that is cut off from the adenohypophysis by the developing sphenoid bone; composed chiefly of chromophobes and, under normal conditions, considered physiologically inactive. See p. gland. posterior p. the cleaned, dried, and powdered posterior lobe obtained from the p. body of domestic animals used for food by humans; an oxytocic, vasoconstrictor, antidiuretic, and stimulant of intestinal motility. SYN: desiccated p., hypophysis sicca.

pituitous (pi-too′i-tus)
Relating to pituita.

pityriasis (pit-i-ri′a-sis)
A dermatosis marked by branny desquamation. [G. fr. pityron, bran, dandruff] p. alba patchy hypopigmentation of the skin resulting from mild dermatitis. p. alba atrophicans a scaling condition of the skin followed by atrophy. p. capitis SYN: dandruff. p. circinata SYN: p. rosea. p. lichenoides a self-limited skin disorder of children and adults, usually divided into p. lichenoides et varioliformis acuta and p. lichenoides chronica. SYN: parapsoriasis guttata. p. lichenoides et varioliformis acuta (PLEVA) an acute dermatitis affecting children and young adults that runs a relatively mild course and is self-limited, although persistence of lesions and recurrence of attacks are not uncommon; vesicles, papules, and crusted lesions eventually produce smallpox-like scars. SYN: Mucha-Habermann disease, parapsoriasis lichenoides et varioliformis acuta, parapsoriasis varioliformis. p. linguae SYN: geographic tongue. p. maculata SYN: p. rosea. p. nigra SYN: tinea nigra. p. rosea a self-limited eruption of macules or papules involving the trunk and, less frequently, extremities, scalp, and face; the lesions are usually oval and follow the crease lines of the skin; occurs most commonly in children and young adults and is frequently preceded by a single larger scaling lesion known as the herald patch. SYN: p. circinata, p. maculata. p. rubra pilaris an uncommon chronic pruritic eruption of the hair follicles, which become firm, red, surmounted with a horny plug, and often confluent to form scaly plaques; it is most conspicuously noted on the dorsa of the fingers and on the elbows and knees and is associated with erythema, thickening of the palms and soles, and opaque thickening of the nails. p. versicolor SYN: tinea versicolor.

pityriasis lichenoides chronica (lik′en-noyd′dez kron′ik-a)
An eruption, lasting up to a few years, of reddish-brown papules with central scaling; it clears without scarring. [lichenoides Mod. L., fr. G. leichen, lichen, a lichen-like eruption, + eidos, resemblance chronica Mod. L. chronic, fr. G. chronikos, pertaining to time; fr. chronos, time]

pityroid (pit′i-royd)
SYN: furfuraceous. [G. pityrodes, branlike, fr. pityron, bran, + eidos, resemblance]

Pityrosporum (pit-i-ros′po-rum, pit′i-ro-spo′rum)
A genus of fungi of disputed pathogenicity found in dandruff and seborrheic dermatitis. [G. pityron, bran, + sporos, seed] P. orbiculare SYN: Malassezia furfur. P. ovale SYN: Malassezia furfur.

pivalate (piv′a-lat)
USAN-approved contraction for trimethylacetate, (CH3)3C–CO2−.

pivot (piv′ot)
A post upon which something hinges or turns. adjustable occlusal p. an occlusal p. that may be adjusted vertically by means of a screw or by other means. occlusal p. an elevation contrived on the occlusal surface, usually in the molar region, designed to act as a fulcrum and to induce sagittal mandibular rotation.

pix, gen. picis (piks, pi′sis)
SYN: pitch. [L]

pixel (pik′sel)
A contraction for picture element, a two-dimensional representation of a volume element (voxel) in the display of the CT or MR image, usually 512 × 512 or 256 × 256 pixels, respectively.

Abbreviation for pyruvate kinase.

The negative decadic logarithm of the ionization constant (Ka) of an acid; equal to the pH value at which equal concentrations of the acid and conjugate base forms of a substance (often a buffer) are present.

Abbreviation for picokatal.

Abbreviation for phenylketonuria.

Abbreviation for peak kilovoltage, the nominal voltage setting of an x-ray machine.

Abbreviation for placental lactogen.

placebo (pla-se′bo)
1. An inert substance given as a medicine for its suggestive effect. 2. An inert compound identical in appearance to material being tested in experimental research, which may or may not be known to the physician and/or patient, administered to distinguish between drug action and suggestive effect of the material under study. SYN: active p.. [L. I will please, future of placeo] active p. SYN: p..

placenta (pla-sen′ta)
Organ of metabolic interchange between fetus and mother. It has a portion of embryonic origin, derived from a highly developed area of the outermost embryonic membrane (chorion frondosum), and a maternal portion formed by a modification of the part of the uterine mucosa (decidua basalis) in which the chorionic vesicle is implanted. Within the p., the chorionic villi, with their contained capillaries carrying blood of the embryonic circulation, are exposed to maternal blood in the intervillous spaces in which the villi lie; no direct mixing of fetal and maternal blood occurs, but the intervening tissue (the placental membrane) is sufficiently thin to permit the absorption of nutritive materials, oxygen, and some harmful substances, like viruses, into the fetal blood and the release of carbon dioxide and nitrogenous waste from it. At term, the human p. is disk shaped, about 4 cm in thickness and 18 cm in diameter, and averages about 16 to 17 the weight of the fetus; its fetal surface is smooth, being formed by the adherent amnion, with the umbilical cord normally attached near its center; the maternal surface of a detached p. is rough because of the torn decidual tissue adhering to the chorion and shows lobular elevations called cotyledons or lobes. [L. a cake] accessory p. a mass of placental tissue distinct from the main p.. SYN: succenturiate p., supernumerary p.. p. accreta the abnormal adherence of the chorionic villi to the myometrium, associated with partial or complete absence of the decidua basalis and, in particular, the stratum spongiosum. SEE ALSO: p. percreta. p. accreta vera the term applied when villi are juxtaposed to the myometrium. adherent p. a p. that fails to separate cleanly from the uterus after delivery. anular p. a p. in the form of a band encircling the interior of the uterus. SYN: ring-shaped p., zonary p.. battledore p. a p. in which the umbilical cord is attached at the border; so called because of the fancied resemblance to the racquet (racket) used in battledore, a precursor to badminton. bidiscoidal p. a p. with two separate disc-shaped portions attached to opposite walls of the uterus, normal for certain monkeys and shrews, and occasionally found in humans. p. biloba a p. duplex in which the two parts are separated by a constriction. SYN: p. bipartita. p. bipartita SYN: p. biloba. central p. previa SYN: p. previa centralis. chorioallantoic p. a p. (such as that of primates) in which the chorion is formed by the fusion of the allantoic mesoderm and vessels to the inner face of the serosa. chorioamnionic p. a form of placentation in which the amnion is fused to the inside of the chorion, thus permitting interchange of water and electrolytes between mother and fetus. p. circumvallata a cup-shaped p. with raised edges, having a thick, round, white, opaque ring around its periphery; a portion of the decidua separates the margin of the p. from its chorionic plate; the remainder of the chorionic surface is normal in appearance, but the fetal vessels are limited in their course across the p. by the ring. SEE ALSO: p. marginata, p. reflexa. cotyledonary p. a p. in which the substance is divided into lobes or cotyledons. deciduate p. a p. in which the maternal decidua is cast off with the fetal p.. dichorionic diamnionic p. twin p.. p. diffusa SYN: p. membranacea. p. dimidiata SYN: p. duplex. disperse p. a p. in which the umbilical arteries divide dichotomously before entering the placental substance. Duncan p. a separated p. that appears at the vulva with the chorionic surface outward. p. duplex a p. consisting of two parts, almost entirely detached, being united only at the point of attachment of the cord. See p. biloba. SYN: p. dimidiata. endotheliochorial p. a p. in which the chorionic tissue penetrates to the endothelium of the maternal blood vessels. endothelio-endothelial p. a p. in which the endothelium of the maternal vessels comes in direct contact with the endothelium of the fetal vessels to form the placental barrier. epitheliochorial p. a p. in which the chorion is merely in contact with, and does not erode, the endometrium. p. extrachorales a p. in which the chorionic plate is limited by a thin membranous fold at the edge. p. fenestrata a p. in which there are areas of thinning, sometimes extending to entire absence of placental tissue. fetal p., p. fetalis the chorionic portion of the p., containing the fetal blood vessels, from which the umbilical cord develops; specifically, in humans, it develops from the chorion frondosum. SYN: pars fetalis placentae. hemochorial p. the type of p., as in humans and some rodents, in which maternal blood is in direct contact with the chorion. hemoendothelial p. the type of p., as in rabbits, in which the trophoblast becomes so attenuated that, by light microscopy, maternal blood appears to be separated from fetal blood only by the endothelium of the chorionic capillaries. horseshoe p. an exaggerated p. reniformis curved in the form of a horseshoe; present in some twin pregnancies. incarcerated p. SYN: retained p.. p. increta a form of p. accreta in which the chorionic villi invade the myometrium. labyrinthine p. a p. in which maternal blood circulates through channels within the fetal syncytiotrophoblast. p. marginata a p. with raised edges, less pronounced than the p. circumvallata. SEE ALSO: p. reflexa. maternal p. SYN: pars uterina placentae. p. membranacea an abnormally thin p. covering an unusually large area of the uterine lining. SYN: p. diffusa. monochorionic diamnionic p. twin p.. monochorionic monoamnionic p. twin p.. p. multiloba a p. having more than three lobes separated from each other by simple constrictions, the fetus being single. SYN: p. multipartita. p. multipartita SYN: p. multiloba. nondeciduous p. a p. in which the fetal p. is cast off, leaving the uterine mucosa intact ( e.g., an epitheliochorial p.). p. panduraformis a form of p. dimidiata with the two halves placed side by side in a shape suggestive of a lutelike musical instrument (pandura). p. percreta the term applied when the villi have invaded the full thickness of myometrium to or through the serosa of the uterus, causing incomplete or complete uterine rupture, respectively. SEE ALSO: p. accreta. p. previa the condition in which the p. is implanted in the lower segment of the uterus, extending to the margin of the internal os of the cervix or partially or completely obstructing the os. SYN: placental presentation. p. previa centralis p. previa in which the p. entirely covers the internal os of the cervix. SYN: central p. previa, total p. previa. p. previa marginalis p. previa in which the p. comes to the margin of, but does not occlude, the internal os of the cervix. p. previa partialis p. previa in which the internal os of the cervix is partially covered by placental tissue. p. reflexa an anomaly of the p. in which the margin is thickened so as to appear turned back upon itself. SEE ALSO: p. circumvallata, p. marginata. p. reniformis a kidney-shaped p.. retained p. incomplete separation of the p. and its failure to be expelled at the usual time after delivery of the child. SYN: incarcerated p.. ring-shaped p. SYN: anular p.. Schultze p. a p. that appears at the vulva with the glistening fetal surface (amnion) presenting. p. spuria a mass of placental tissue that has no vascular connection with the main p.. succenturiate p. SYN: accessory p.. supernumerary p. SYN: accessory p.. total p. previa SYN: p. previa centralis. p. triloba SYN: p. tripartita. p. tripartita a p. consisting of three parts almost entirely separate, being joined together only by the blood vessels of the umbilical cord; the fetus is single. SYN: p. triloba, p. triplex. p. triplex SYN: p. tripartita. twin p. the p.(s) of a twin pregnancy; if dizygotic, the placentas may be separate or fused, the latter retaining two amnionic and two chorionic sacs (dichorionic diamnionic p.); if monozygotic, the p. may be a monochorionic monoamnionic p. or monochorionic diamnionic p., depending on the stage at which twinning took place; if twinning occurs early, there may be a fused p. with two chorionic and two amnionic membranes. p. uterina SYN: pars uterina placentae. p. velamentosa a p. in which the umbilical cord is attached to the adjoining membranes, with the umbilical vessels spread out and entering the p. independently. villous p. a p. in which the chorion forms villi. zonary p. SYN: anular p..

SYN: chorionic gonadotropin.


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