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(ī″sō-tō-nĭs′ĭ-tē) The state or condition of being isotonic.


(ī′sŏ-tōp″) [iso- + Gr. topos, place (chemical isotopes occupy the same place on the periodic table)] One of a series of chemical elements that have nearly identical chemical properties but different atomic weights and electric charges. Many isotopes are radioactive.

radioactive i. An isotope in which the nucleus is unstable and emits ionizing radiation such as gamma rays. SEE: table.

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Radioactive Isotopes Having Important Long-Term Health Effects
Element Source Primary Emission Decay [half-life] Organ Potential Treatment Potential Long-term Effects

Cesium 137

mining of ores

beta and gamma rays

30 years

soft tissues

Prussian blue

multiple soft-tissue cancers

Iodine 131

nuclear power plants; imaging in nuclear medicine

beta and gamma rays

8.04 days


Potassium iodide

thyroid cancer

Plutonium 239

nuclear reactors and nuclear bombs

alpha, beta, and gamma rays

24,000 years

bone, bone marrow, liver, lungs

metal chelating agents

bone marrow cancers, e.g., leukemias & lymphomas, lung cancers

Radon 222

decay product of radium, thorium, and uranium

isotopes of polonium, into which the radon decays

3.8 days


mitigation by removal by means of fans and ventilation systems

lung cancer

Strontium 90

radioactive fallout

beta rays

29 years


calcium phosphate or aluminum phosphate

bone cancers, bone marrow cancers

stable i. An isotope that does not undergo radioactive decay into another element.


(ī″sō-tret″ĭ-nō′ĭn) [iso- + tretinoin] A keratolytic agent used in treating acne.

image This medicine should not be used by pregnant women or women who are sexually active and at risk of becoming pregnant.


(ī″sō-trŏp′ĭk) [″ + tropos, a turning] 1. Possessing similar qualities in every direction. 2. Having equal refraction.


(ī-sŏt′rō-pē) The state of being isotropic.


(ī′sō-tīp) In immunology, one of the determinants on the immunoglobulin molecule that distinguish among the main classes of antibodies of a given species. They are the same for all normal individuals of that species. SEE: idiotype.

immunoglobulin i. Immunoglobulin fragment.


(ī-sō-tĭp′ĭ-kăl) [″ + typos, mark] Belonging to the same variety or classification.


(ī′sō-zīm) Isoenzyme.

ispaghula, ispaghul

(is″pă-goo′lă, is′pă-gool″, is′pă-gŭl″) Any of several plants of the genus Plantago, esp. P. ovata, whose seeds are used as a bulk laxative. SEE: Plantago; psyllium.


(ĭsh′ū) [ME.] 1. Offspring. 2. A suppurating sore maintained by a foreign body in the tissue to act as a counterirritant. 3. A discharge ...

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