SI unit

unit (u´nit)

1. a single thing.

2. a quantity assumed as a standard of measurement. Symbol U.

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Angström unit  angstrom.

atomic mass unit  (u) (amu) the unit mass equal to 112 the mass of the nuclide of carbon-12. Called also dalton.

Bethesda unit  a measure of the level of inhibitor to coagulation factor VIII; equal to the amount of inhibitor in patient plasma that will inactivate 50 per cent of factor VIII in an equal volume of normal plasma following a 2-hour incubation period.

Bodansky unit  the quantity of alkaline phosphatase that liberates 1 mg of phosphate ion from glycerol 2-phosphate in 1 hour under standard conditions.

British thermal unit  (BTU) the amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit, usually from 39°F to 40°F.

CGS unit  any unit in the centimeter-gram-second system.

CH50 unit  the amount of complement that will lyse 50 per cent of a standard preparation of sheep red blood cells coated with antisheep erythrocyte antibody.

coronary care unit  a specially designed and equipped hospital area containing a small number of private rooms, with all facilities necessary for constant observation and possible emergency treatment of patients with severe heart disease.

intensive care unit  a hospital unit in which are concentrated special equipment and skilled personnel for the care of seriously ill patients requiring immediate and continuous attention; abbreviated ICU.

International unit  (IU) a unit of biological material, as of enzymes, hormones, vitamins, etc., established by the International Conference for the Unification of Formulas.

motor unit  the unit of motor activity formed by a motor nerve cell and its many innervated muscle fibers.

SI unit  any of the units of the Système International d'Unités (International System of Units) adopted in 1960 at the Eleventh General Conference of Weights and Measures.

Somogyi unit  that amount of amylase which will liberate reducing equivalents equal to 1 mg of glucose per 30 minutes under defined conditions.

Svedberg unit  (S) a unit equal to 10−13 second used for expressing sedimentation coefficients of macromolecules.

terminal respiratory unit  the anatomical and functional unit of the lung, including a respiratory bronchiole, alveolar ducts and sacs, and alveoli.

toxic unit , toxin unit the smallest dose of a toxin which will kill a guinea pig weighing about 250 gm in three to four days.

USP unit  one used in the United States Pharmacopeia in expressing potency of drugs and other preparations.

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unit

1. a single thing; one segment of a whole that is made up of identical or similar segments.

2. a specifically defined amount of anything subject to measurement, as of activity, dimension, velocity, volume, or the like.

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Angstrom unit

see angstrom.

atomic mass unit

see dalton.

International unit

1. see si units.

2. a unit of enzyme activity equal to the amount of enzyme that catalyzes the conversion of one micromole of substrate or coenzyme per minute under specified conditions (temperature, pH and substrate concentration) of the assay method. Abbreviated U.

3. any of several arbitrary units that have been adopted by international bodies to express the quantities of certain vitamins (A, C, D and thiamin hydrochloride), hormones (androgen, chorionic gonadotropin, estradiol benzoate, estrone, insulin, progesterone and prolactin), and drugs (digitalis and penicillin).

SI unit

any unit of the International System of units (the metric system). See si units.

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SI unit 

Abbreviation of Système International d'unités (or International System of Units). It is derived from the metric system of physical units. There are seven base units, two supplementary units and many derived units. See candela per square metre; lumen; lux; micrometre (micron); nanometre.

Table S2 Base and supplementary SI units, and some derived units
physical quantity				name					symbol
base units
length				metre					m
mass				kilogram					kg
time				second					s
electric current				ampere					A
thermodynamic temperature				kelvin					K
luminous intensity				candela					cd
amount of substance				mole					mol
supplementary units
plane angle				radian				rad
solid angle				steradian				sr
some derived units
area			square metre					m2
electric potential difference			volt					V
electric resistance			ohm					Ω
energy			joule
force			newton					N
frequency			hertz					Hz
illuminance			lux					lx
luminance			candela per square metre					cd/m2
luminous flux			lumen					lm
power			watt					W
velocity			metre per second					m/s
volume			cubic metre					m3