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Medical Dictionary


potent (po′tent)
1. Possessing force, power, strength. 2. Indicating the ability of a primitive cell to differentiate. SEE ALSO: totipotent, pluripotent, unipotent. 3. In psychiatry, possessing sexual potency.

potential (po-ten′shal)
1. Capable of doing or being, although not yet doing or being; possible, but not actual. 2. A state of tension in an electric source enabling it to do work under suitable conditions; in relation to electricity, p. is analogous to the temperature in relation to heat. [L. potentia, power, potency] action p. the change in membrane p. occurring in nerve, muscle, or other excitable tissue when excitation occurs. after-p. afterpotential. bioelectric p. electrical potentials occurring in living organisms. biotic p. a theoretical measurement of the capacity of a species to survive or to compete successfully. brain p. the electrical charge of the brain as compared to a point on the body; the p. may be steady (DC p.) or may fluctuate at specific frequencies when recorded against time, giving rise to the electroencephalogram. brainstem auditory evoked p. responses triggered by click stimuli, which are generated in the acoustic nerve and brainstem auditory pathways; recorded over the scalp. chemical p. (μ) a measure of how the Gibbs free energy of a phase depends on any change in the composition of that phase. cochlear p. SYN: cochlear microphonic. compound action p. the combined potentials resulting from activation of the auditory division of the eighth cranial nerve. demarcation p. the difference in p. recorded when one electrode is placed on intact nerve fibers or muscle fibers and the other electrode is placed on the injured ends of the same fibers; the intact portion is positive with reference to the injured portion. SYN: injury p.. early receptor p. (ERP) a voltage arising across the eye from a charge displacement within photoreceptor pigment, in response to an intense flash of light. endocochlear p. the standing direct current p. in the endolymph relative to the perilymph, measuring positive 80 mV. evoked p. an event-related p., elicited by, and time-locked to, a stimulus. SEE ALSO: evoked response. excitatory junction p. (EJP) discrete partial depolarization of smooth muscle produced by stimulation of excitatory nerves; similar to small end-plate potentials. summate with repeated stimuli. excitatory postsynaptic p. (EPSP) the change in p. that is produced in the membrane of the next neuron when an impulse that has an excitatory influence arrives at the synapse; it is a local change in the direction of depolarization; summation of these potentials can lead to discharge of an impulse by the neuron. generator p. local depolarization of the membrane p. at the end of a sensory neurone in graded response to the strength of a stimulus applied to the associated receptor organ, e.g., a pacinian corpuscle; if the generator p. becomes large enough (because the stimulus is at least of threshold strength), it causes excitation at the nearest node of Ranvier and a propagated action p.. inhibitory junction p. (IJP) hyperpolarization of smooth muscle produced by stimulation of inhibitory nerves. inhibitory postsynaptic p. (IPSP) the change in p. produced in the membrane of the next neuron when an impulse that has an inhibitory influence arrives at the synapse; it is a local change in the direction of hyperpolarization; the frequency of discharge of a given neuron is determined by the extent to which impulses that lead to excitatory postsynaptic potentials predominate over those that cause inhibitory postsynaptic potentials. injury p. SYN: demarcation p.. membrane p. the p. inside a cell membrane, measured relative to the fluid just outside; it is negative under resting conditions and becomes positive during an action p.. SYN: transmembrane p.. myogenic p. action p. of muscle. oscillatory p. the variable voltage in the positive deflection of the electroretinogram (β-wave) of the dark-adapted eye arising from amacrine cells. Ottoson p. SYN: electroolfactogram. oxidation-reduction p. (E0+) the p. in volts of an inert metallic electrode measured in a system of an arbitrarily chosen ratio of [oxidant] to [reductant] and referred to the normal hydrogen electrode at absolute temperature; it is calculated from the following equation; where R is the gas constant expressed in electrical units, T the absolute temperature (Kelvin), n the number of electrons transferred, F the faraday, and E0 the normal symbol for the p. of the system at pH 0; for biologic systems, E0′ is often used (in which pH = 7). Cf.:Nernst equation. SYN: redox p.. pacemaker p. the voltage inscribed by impulses from an artificial electronic pacemaker. redox p. SYN: oxidation-reduction p.. S p. prolonged, slow, depolarizing or hyperpolarizing responses to illumination; initiated between the photoreceptor and ganglion cell layers of the retina. somatosensory evoked p. the computer-averaged cortical and subcortical responses to repetitive stimulation of peripheral nerve sensory fibers. spike p. the main wave in the action p. of a nerve; it is followed by negative and positive afterpotentials. summating potentials alternating current responses of the organ of Corti to acoustic stimulation. thermodynamic p. free energy. transmembrane p. SYN: membrane p.. ventricular late p. high-frequency microvolt electrocardiogram signals at the end of the QRS complex. visual evoked p. voltage fluctuations that may be recorded from the occipital area of the scalp as the result of retinal stimulation by a light flashing at 14-s intervals; commonly summated and averaged by computer. zeta p. the degree of negative charge on the surface of a red blood cell; i.e., the p. difference between the negative charges on the red cell and the cation in the fluid portion of the blood. zoonotic p. the p. for infections of subhuman animals to be transmissible to humans.

potentiation (po-ten′she-a′shun)
Interaction between two or more drugs or agents resulting in a pharmacologic response greater than the sum of individual responses to each drug or agent.

potentiator (po-ten′she-a-ter, -tor)
In chemotherapy, a drug used in combination with other drugs to produce deliberate potentiation.

potentiometer (po-ten-she-om′e-ter)
1. An instrument used for measuring small differences in electrical potential. 2. An electrical resistor of fixed total resistance between two terminals, but with a third terminal attached to a slider that can make contact at any desired point along the resistance. [L. potentia, power, + G. metron, measure]

potion (po′shun)
A draft or large dose of liquid medicine. [L. potio, potus, fr. poto, to drink]

Sir Percivall, English surgeon, 1714–1788. See P. abscess, P. aneurysm, P. curvature, P. disease, P. fracture, P. paralysis, P. paraplegia.

Edith L., U.S. perinatal pathologist, *1901. See P. disease, P. facies, P. syndrome.

Irving White, U.S. obstetrician, 1868–1956. See P. version.

Willis J., U.S. pediatric surgeon, 1895–1968. See P. anastomosis, P. clamp, P. operation.

pouch (powch)
A pocket or cul-de-sac. SEE ALSO: fossa, recess, sac. antral p. a p. made in the antrum of the stomach of experimental animals. branchial pouches SYN: pharyngeal pouches. Broca p. SYN: pudendal sac. deep perineal p. SYN: deep perineal space. Denis Browne p. a pocket formed between Scarpa and external oblique fascia adjacent to external inguinal ring; a common lodging site for undescended testes (as in cryptorchism). SYN: superficial inguinal p.. p. of Douglas SYN: rectouterine p.. Douglas p. SYN: rectouterine p.. endodermal pouches SYN: pharyngeal pouches. Hartmann p. a spheroid or conical p. at the junction of the neck of the gallbladder and the cystic duct. SYN: ampulla of gallbladder, fossa provesicalis, pelvis of gallbladder. Heidenhain p. a small sac or p. of the stomach, vagally denervated and closed off from the main cavity but with an opening through the abdominal wall, fashioned for the purpose of obtaining gastric juice and for studying gastric secretion in physiologic experiments. hepatorenal p. SYN: hepatorenal recess of subhepatic space. hypophyseal p. SYN: pituitary diverticulum. ileoanal p. (il′e-o-a′nal) a p. constructed from the ileum and anastomosed to the proximal anus for restoration of continence after proctocolectomy. Kock p. a continent ileostomy with a reservoir and valved opening fashioned from doubled loops of ileum. SYN: Kock ileostomy. laryngeal p. SYN: laryngeal saccule. Morison p. SYN: hepatorenal recess of subhepatic space. paracystic p. SYN: paravesical fossa. pararectal p. SYN: pararectal fossa. paravesical p. SYN: paravesical fossa. Pavlov p. a section of the stomach of a dog, retaining its vagal innervation but shut off from all communication with the main part of the organ and connected with the outside by a fistula; used in studies of gastric secretions. SYN: miniature stomach, Pavlov stomach. pharyngeal pouches paired evaginations of embryonic pharyngeal endoderm, between the branchial arches, extending toward the corresponding ectodermally lined branchial grooves; during development they evolve into epithelial tissues and organs, such as thymus and thyroid glands. SYN: branchial pouches, endodermal pouches. Physick pouches proctitis with mucous discharge and burning pain, involving especially the sacculations between the rectal valves. Prussak p. SYN: superior recess of tympanic membrane. Rathke p. SYN: pituitary diverticulum. rectouterine p. [TA] a pocket formed by the deflection of the peritoneum from the rectum to the uterus. SYN: excavatio rectouterina [TA] , cavum douglasi, cul-de-sac (2) , Douglas cul-de-sac, Douglas p., p. of Douglas, rectovaginouterine p.. rectovaginouterine p. SYN: rectouterine p.. rectovesical p. [TA] a pocket formed by the deflection of the peritoneum from the rectum to the bladder in the male. SYN: excavatio rectovesicalis [TA] , Proust space. Seessel p. Seessel pocket. superficial inguinal p. SYN: Denis Browne p.. superficial perineal p. SYN: superficial perineal space. ultimobranchial p. a transient fifth pharyngeal p.; it is now considered to be incorporated into the caudal pharyngeal complex, the cells of which become the parafollicular cells (C cells) of the thyroid. uterovesical p. SYN: vesicouterine p.. vesicouterine p. [TA] a pocket formed by the deflection of the peritoneum from the bladder to the body of the uterus in the female. SYN: excavatio vesicouterina [TA] , cavum vesicouterinum, uterovesical p.. Willis p. obsolete term for lesser omentum

pouchitis (pow-chi′tis)
Acute inflammation of the mucosa of an ileal reservoir or pouch that has been surgically created, usually following total colectomy for inflammatory bowel disease or multiple polyposis. [pouch + -itis, inflammation]

poudrage (poo-drahzh′)
1. Powdering. 2. SYN: talc operation. [F.] pleural p. covering the opposing pleural surfaces with a slightly irritating powder in order to secure adhesion.

poultice (pol′tis)
A soft magma or mush prepared by wetting various powders or other absorbent substances with oily or watery fluids, sometimes medicated, and usually applied hot to the surface; it exerts an emollient, relaxing, or stimulant, counterirritant effect upon the skin and underlying tissues. SYN: cataplasm. [L. puls (pult-), a thick pap; G. poltos]

pound (pownd)
A unit of weight, containing 12 ounces, apothecaries' weight, or 16 ounces, avoirdupois. [A.S. pund; L. pondus, weight]

poundal (pownd′al)
The force required to give a mass of 1 lb an acceleration of 1 ft/s2; equal to 0.138255 N.

François, French anatomist, 1616–1708. See P. ligament, P. line.

povidone (po′vi-don)
A synthetic polymer consisting mainly of linear 1-vinyl-2-pyrrolidone groups, with mean molecular weights ranging from 10,000 to 70,000; used as a dispersing and suspending agent; p. with molecular weight between 20,000 and 40,000 has been used as a plasma extender. It is not metabolized, but is excreted unchanged by the kidney. SYN: polyvidone, polyvinylpyrrolidone.

SYN: povidone iodine.

1. A dry mass of minute separate particles of any substance. 2. In pharmaceutics, a homogenous dispersion of finely divided, relatively dry, particulate matter consisting of one or more substances; the degree of fineness of a pow′der is related to passage of the material through standard sieves. 3. A single dose of a powdered drug, enclosed in an envelope of folded paper. 4. To reduce a solid substance to a state of very fine division. [Fr. poudre; L. pulvis] bleaching p. SYN: chlorinated lime.

power (pow′er)
1. In optics, the refractive vergence of a lens. 2. In physics and engineering, the rate at which work is done. 3. The exponent of a number or expression that provides the number of times that number has to be multiplied by itself. back vertex p. the effective p. of a lens as measured from a surface toward the eye; a standard for measurement of ophthalmic lenses. carbon dioxide combining p. a measurement of the total CO2 that can be bound as HCO2 at a PCO2 of 40 mmHg at 25°C by serum, plasma, or whole blood. equivalent p. the p. equal to an infinitely thin lens as measured on an optical bench. resolving p. 1. definition of a lens; in a microscope objective lens it is calculated by dividing the wavelength of the light used by twice the numerical aperture of the objective. SEE ALSO: definition. 2. analogies to other modalities, e.g., two-point discrimination in neurologic examination. Commonly misinterpreted as random error, although it has none of its properties. 3. SYN: resolution (2) . statistical p. in Neyman-Pearson hypothesis testing, the probability of rejecting the null hypothesis when it is false; the complement of an error of the second kind.

pox (poks)
1. An eruptive disease, usually qualified by a descriptive prefix; e.g., smallpox, cowpox, chickenpox. See the specific term. 2. Archaic or colloquial term for syphilis. [var. of pl. pocks] Kaffir p. SYN: alastrim.

Poxviridae (poks-vir′i-de)
A family of large complex viruses, with a marked affinity for skin tissue, that are pathogenic for humans and other animals. Virions are large, up to 250 × 400 nm, and enveloped (double membranes). Replication occurs entirely in the cytoplasm of infected cells. Capsids are of complex symmetry and contain double-stranded DNA (MW 160 × 106), the nucleoprotein antigen being common to all members of the family. A number of genera are recognized, including: Orthopoxvirus, Avipoxvirus, Capripoxvirus, Leporipoxvirus, and Parapoxvirus.

poxvirus (poks′vi-rus)
Any virus of the family Poxviridae. p. officinalis SYN: vaccinia virus.

Samuel J., French gynecologist and anatomist, 1846–1918. See P. muscle.

Abbreviation for pyrophosphate.

Abbreviation for inorganic pyrophosphate (diphosphate).

Abbreviation for punctum proximum.

Abbreviation for parts per billion.

Abbreviation for proserum prothrombin conversion accelerator.

Abbreviation for plasmin prothrombins conversion factor.

Abbreviation for purified protein derivative of tuberculin.

Abbreviation for pleuropneumonia-like organisms, under organism.

Abbreviation for parts per million.

Abbreviation for 2,5-diphenyloxazole, a liquid scintillator; preferred provider organization.

A mnemonic of 6 Ps designating the symptom complex of acute arterial occlusion. [pain, pallor, paresthesia, pulselessness, paralysis, prostration]

Abbreviation for 5-phospho-α-d-ribosyl-1-pyrophosphate.

P pulmonale (pul-mo-na′la)
Tall, narrow, peaked P waves in electrocardiographic leads II, III, and aVF, and often a prominent initial positive P wave component in V1, presumed to be characteristic of cor pulmonale. (Although this term is extensively used in the electrocardiographic literature, it is actually a misnomer and would be more appropriately called P-dextrocardiale, since it results from overload of the right atrium regardless of the cause, as in tricuspid stenosis, and may occur independently of cor pulmonale.) In lung disease, P-pulmonale is usually transient, occurring during exacerbations, usually asthmatic.

Abbreviation for plastoquinone.

Abbreviation for plastoquinone-9.

Abbreviation for punctum remotum.

1. Abbreviation for presbyopia. 2. Symbol for praseodymium; propyl.

Abbreviation for plasma renin activity; phosphoribosylamine.

practice (prak′tis)
The exercise of the profession of medicine or one of the allied health professions. [Mediev. L. practica, business, G. praktikos, pertaining to action] extramural p. delivery of health care services by university faculties or full-time hospital staff to persons beyond the physical confines of their respective medical centers. family p. a specialty of medicine in which the physician takes responsibility for the health and medical care of all members of a family group, regardless of age or gender, but usually does limited amounts of obstetrics and surgery. general p. a relatively obsolete term for physicians who care for all types of medical problems, including internal medical, pediatric, obstetrical, and surgical diseases. Postgraduate training for general practitioners was limited and there was no specialty certification; the field has been replaced by more extensively trained family practitioners. group p. the cooperative p. of medicine by a group of physicians, each of whom as a rule specializes in some particular field; such a group often shares a common suite of consulting rooms, laboratories, staff, equipment, etc. intramural p. delivery of health care services by university faculties or full-time hospital staff conducted within the physical confines of their respective medical centers.

practitioner (prak-tish′un-er)
A person who practices medicine or one of the allied health care professions.

Andrea, Swiss pediatrician, *1919. See P.-Willi syndrome.

See pre-.

pragmatics (prag-mat′iks)
A branch of semiotics; the theory that deals with the relation between signs and their users, both senders and receivers. [G. pragmatikos, fr. pragma, thing done]

pragmatism (prag′ma-tizm)
A philosophy emphasizing practical applications and consequences of beliefs and theories, that the meaning of ideas or things is determined by the testability of the idea in real life. [G. pragma (pragmat-), thing done]

2-pralidoxime (2-PAM)
One of several oximes that are effective in reversing cholinesterase inhibition by organophosphates. The 2-PAM facilitates the hydrolysis of the phosphorylated enzyme so as to regenerate active cholinesterase.

pralidoxime chloride (pral-i-dok′sem, pra-li-)
Used to restore the inactivated cholinesterase activity resulting from organophosphate poisoning; has some limited value as an antagonist of the carbamate type of cholinesterase inhibitors that are used in the treatment of myasthenia gravis. Dizziness, blurred vision, drowsiness, nausea, tachycardia, and muscular weakness may occur.

pramoxine hydrochloride (pra-mok′sen, -sin)
A nonester, nonamide local anesthetic for dermal and rectal use.

prandial (pran′de-al)
Relating to a meal. [L. prandium, breakfast]

praseodymium (Pr) (pra-se-o-dim′e-um)
An element of the lanthanide or “rare earth” group; atomic no. 59, atomic wt. 140.90765. [G. prasios, leekgreen, fr. prason, a leek, + didymos, twin]

Joseph H., U.S. physician, 1872–1956. See P. symptom.

Otto Carl, German hygienist, 1876–1963. See P.-Küstner antibody, P.-Küstner reaction, reversed P.-Küstner reaction.

An inhibitor of the enzyme 3-hydroxy-3-methyglutaryl coenzyme A (HMG-CoA), the rate-limiting enzyme in the biosynthesis of cholesterol; used in the treatment of hypercholesteremia; similar to lovastatin and simvastatin.

praxiology (prak-se-ol′o-je)
The science or study of behavior; it excludes the study of consciousness and similiar nonobjective metaphysical concepts. [G. praxis, action, + logos, study]

praxis (prak′sis)
The performance of an action. [G. p., action]

prazepam (pra′ze-pam)
An antianxiety agent of the benzodiazepine class; a prodrug for nordiazepam.


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