Page 385 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

13 Appendix

Dimensions and Units Fractions and Multiples of Units
Physiology is the science of life processes and Prefixes are used to denote decimal multiples
bodily functions. Since they are largely based and fractions of a unit since it is both tedious
on physical and chemical laws, the investiga- and confusing to write large numbers. We gen-
tion, understanding, assessment, and manipu- erally write 10 kg (kilograms) and 10µg (mi-
lation of these functions is inseparably linked crograms) instead of 10 000 g and 0.00001 g,
to the measurement of physical, chemical, and for example. The prefixes, which are usually
other parameters, such as blood pressure, varied in 1000-unit increments, and the corre-
hearing capacity, blood pH, and cardiac output. sponding symbols and conversion factors are
The units for measurement of these parame- listed in Table 2. Prefixes are used with base
ters are listed in this section. We have given units and the units derived from them
3
preference to the international system of SI (! Table 1), e.g., 10 Pa = 1 kPa. Decimal incre-
units (Système International d’Unités) for uni- ments are used in some cases (e.g., da, h, d, and
formity and ease of calculation. Non-SI units c; ! Table 2). Time is given in conventional
will be marked with an asterisk. Conversion nondecimal units, i.e., seconds (s), minutes
factors for older units are also listed. Compli- (min), hours (h), and days (d).
cated or less common physiological units (e.g.,
wall tension, flow resistance, compliance) are Length, Area, Volume
generally explained in the book as they appear. The meter (m) is the SI unit of length. Other
However, some especially important terms units of length have also been used.
that are often (not always correctly) used in Examples:
physiology will be explained in the Appendix, 1 ångström (Å) = 10 -10 m = 0.1 nm
-6
e.g., concentration, activity, osmolality, 1 micron ( µ) = 10 m = 1 µm
-9
osmotic pressure, oncotic pressure, and pH. 1 millimicron (mµ) = 10 m = 1 nm
The seven base units of the SI system. American and British units of length:
1 inch = 0.0254 m = 25.4 mm
Unit Symbol Dimension 1 foot = 0.3048 m
Meter m length 1 yard = 3 feet = 0.9144 m
1 (statute) mile = 1609.344 m ! 1.61 km
Kilogram kg mass 1 nautical mile = 1.853 km
Second s time 2
Mole mol amount of substance The square meter (m ) is the derived SI unit of
3
area, and the cubic meter (m ) is the corre-
Ampere A electric current sponding unit of volume. When denoting the
Kelvin K temperature (absolute)
fractions or multiples of these units with pre-
Candela cd luminous intensity fixes (Table 2), please note that there are some
peculiarities.
The base units are precisely defined autono- Examples:
3
mous units. All other units are derived by mul- 1 m = 10 mm, but
2
2
6
tiplying or dividing base units and are there- 1 mm = 10 mm , and
9
3
fore referred to as derived units, e.g.: 1 m = 10 mm 3
— Area (length · length): m · m = m 2 The liter (L or l)* is often used as a unit of
–1
— Velocity (length/time): m/s = m · s . volume for liquids and gases:
3
1 L = 10 m = 1 dm 3
–3
If the new unit becomes too complicated, it is 1 mL = 10 m = 1 cm 3
3
–6
given a new name and a corresponding sym- 1 µL = 10 m = 1 mm . 3
–9
3
bol, e.g., force = m · kg · s –2 = N (! Table 1).
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