673

17

Quantities and Units of Measurement

Contents

	Abbreviations 674			Concentrations and Equivalent
	The SI System of Units		674	Values 677
				Equivalents of Older (“Conventional”)
	The SI Base Units	674
				Concentration Units in SI Units	677
	Some Derived SI Units		675
				Equivalents of Older Units of Power,
	Multiples and Fractions (Powers of			Pressure, and Energy in SI Units	678
	Ten) 675
	Combining Forms	676

−Multiples 676

−Submultiples 676

674 17 Quantities and Units of Measurement

Abbreviations

a.	=	artery or arteria	aa.	=	arteries or arteriae
v.	=	vein or vena	vv. =		veins or venae
m.	=	muscle or musculus	mm.=		muscles or musculi
n.	=	nerve or nervus	nn. =		nerves or nervi
r.	=	ramus	rr.	=	rami

lig. = ligament or ligamentum

The SI System of Units

The international system of units (SI = Système International) was introduced in many countries as a unified standard of measurement, in view of the many different units used in medicine, especially in physiology (for example, units of pressure include mmHg, cmH2O, torr, atm, or kg/cm2).

The SI Base Units

Base quantity	Name	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
Electric current	ampere	A
Thermodynamic temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

Multiples and Fractions (Powers of Ten) 675

Some Derived SI Units

Other quantities, the derived quantities, may be derived from these seven base quantities, mostly by multiplying or dividing one by another. For instance, area = length × length (m · m) = m2; velocity = distance/time = m/s (or m s−1).

Derived quantity	Unit	Definition
Frequency	hertz (Hz)	s−1
Force	newton (N)	m · kg · s−2
Pressure, stress	pascal (Pa)	m−1 · kg · s−2 = N · m−2
Energy, work, quantity of heat	joule (J)	m2 · kg · s−2 = N · m
Power, radiant flux	watt (W)	m2	· kg · s−3 = J · s−1
Electric charge	coulomb (C)	s · A
Quantity of electricity
Electric potential difference	volt (V)	m2	· kg · s−3 · A−1 = W · A−1
Electrical resistance	ohm (Ω)	m2	· kg · s−3 · A−2 = V · A−1

In addition to the SI base units and their derived units, a number of other units may still be used: gram (g), liter (l), minute (min), hour (h), day (d), and degree centigrade/Celsius (°C).

Multiples and Fractions (Powers of Ten)

When numbers are much larger or smaller than 1 they are difficult and cumbersome to write. Hence these numbers are expressed as powers of 10. For example:

100 = 10 × 10 = 102 1000 = 10 × 10 × 10 = 103

10 000 = 10 × 10 × 10 × 10 = 104

1 = 10 : 10 = 100 0.1 = 10 : 10 : 10 = 10−1

0.01 = 10 : 10 : 10 : 10 = 10−2

676 17 Quantities and Units of Measurement

Combining Forms

To improve clarity, it is customary to use certain combining forms to designate multiples and fractions of ten.

Multiples

Power of ten	Prefix	Symbol
101	deka (or deca) (tenfold)	da
102	hecto (one hundred times)	h
103	kilo (one thousand times)	k
106	mega (one million times)	M
109	giga (one billion times)	G
1012	tera (one trillion times)	T
1015	peta (one quadrillion times)	P
1018	exa (one quintillion times)	E

Submultiples

Power of ten	Prefix	Symbol
10−1	deci (one-tenth)	d
10−2	centi (one-hundredth)	c
10−3	milli (one-thousandth)	m
10−6	micro (one-millionth)	µ
10−9	nano (one-billionth)	n
10−12	pico (one-trillionth)	p
10−15	femto (one-quadrillionth)	f
10−18	atto (one-quintillionth)	a

Concentrations and Equivalent Values 677

Concentrations and Equivalent Values

In the SI system, concentrations can be written as amount of substance (moles) per volume (mol/l) or as mass per volume (g/l). The concentration in terms of amount of substance, formerly known as molar concentration, is proportional to the number of molecules contained in a solution (e. g., blood plasma). Amount-of-substance concentrations are most commonly used when the molecular weight of a chemically pure substance is known.

Equivalents of Older (“Conventional”) Concentration Units in

SI Units

Substance	Value in conventional unit	Value in SI unit
Sodium	1 mg% (10 mg/l)	0.4350 mmol/l
Potassium	1 mg%	0.2558 mmol/l
Calcium	1 mg%	0.2495 mmol/l
Magnesium	1 mg%	0.4114 mmol/l
Chloride	1 mg%	0.2821 mmol/l
Glucose	1 mg%	0.0555 mmol/l
Urea	1 mg%	0.1660 mmol/l
Cholesterol	1 mg%	0.0259 mmol/l
Uric acid	1 mg%	59.48 µmol/l
Creatinine	1 mg%	88.40 µmol/l
Bilirubin	1 mg%	17.10 µmol/l
Plasma proteins	1 g%	10 g/l

678 17 Quantities and Units of Measurement

Equivalents of Older Units of Power, Pressure, and Energy in SI Units

Quantity	Derived equation	SI equivalent
Force	1 dyne = 10−5 N	1 N = 105 dyne
Pressure	1 cmH2O = 98.1 Pa	1 Pa = 0.0102 cmH2O
	1 mmHg (1 torr) = 133.3 Pa	1 Pa = 0.0075 mmHg
	1 atm = 101 kPa	1 kPa = 0.0099 atm
	1 bar = 100 kPa	1 kPa = 0.01 bar
Energy	1 erg = 10−7 J	1 J = 107 erg
Energy in terms of heat	1 cal = 4.19 J	1 J = 0.239 cal

Glossary 679

Eponyms (Proper Names) in Medical Anatomy and Physiology

Eponyms are a common part of anatomical terms, especially in clinical usage. The following list includes the dates and sites of activity of some of the scientists named in the text. These names are those most familiar in medical anatomy and physiology. Most of the information derives from the following sources:

Debson J.: Anatomical Eponyms, 2nd ed. Livingstone: Edinburgh and London, 1962.

Dorland’s Illustrated Medical Dictionary, 29th ed. Saunders: Philadelphia, 2000.

Faller, A.: Die Fachwörter der Anatomie, Histologie und Embryologie. Bergmann: Munich, 1978.

Herrlinger, R.: Eigennamen in Anatomie, Physiologie, Embryologie und physiologischer Chemie. G. Fischer: Jena, 1947.

Arey, Lesley Brainerd (1891−1988): American anatomist. Originator of Arey’s rule to determine the length (in inches) of a fetus from the duration of gestation.

Auerbach, Leopold (1828−1897): German anatomist. Described Auerbach’s myenteric plexus.

Bartholin, Caspar Secundus (1655− 1738): Physician, anatomist, and administrator in Copenhagen, Denmark. Described the glands of the female vestibule.

Bowman, Sir William (1816−1892): London anatomist, physiologist, and ophthalmologist. Described the capsule of the glomerulus.

Broca, Paul (1824−1860) Paris surgeon and anthropologist. Broca’s speech area is named after him.

Corti, Marchese Alphonso (1822−1867): Anatomist active at Vienna, Würzburg, Pavia, Utrecht, and Turin. Described Corti’s organ in the cochlea.

Cowper, William (1666−1709): Anatomist and surgeon in London. Described

the bulbourethral or Cowper’s glands in men.

Döderlein, Gustav (1893−1980): Gynecologist at Jena and Munich. The vaginal Döderlein bacillus is named after him.

Douglas, James (1675−1742): London anatomist and gynecologist. Described Douglas’s pouch, the lowest point of the abdominal cavity.

Down, John Langdon Haydon (1828− 1896): English physician, who described the Down syndrome.

Edinger, Ludwig (1855−1918): Frankfurt neuroanatomist. He is named in the Edinger−Westphal nucleus, the parasympathetic nucleus of cranial nerve X (vagus nerve).

Eustachio, Bartholomeo (1513−1574): Anatomist and personal physician to the Pope in Rome. The eustachian tube, running between middle ear and oral cavity, is named after him.

Fallopio, Gabriele (1523−1562): Italian anatomist. Described the fallopian tube among other structures.

680 Glossary

Golgi, Camillo (1844−1926): Anatomist at Siena and Pavia. Described the Golgi aparatus.

Graaf, Reijnier (Regnier) de (1641− 1673): Physician and anatomist in Delft and Paris. The ovulation-ready graafian follicle is named after him.

Haase, Karl Friedrich (1788−1865): Dresden gynecologist. The Haase rule combined with the duration of gestation allows calculation of fetal length in centimeters.

Hassal, Arthur Hill (1817−1894): Physician active in London, the Isle of Wight, and San Remo. The Hassal corpuscles of the thymus are named after him.

Havers, Clopton (1650−1702): London anatomist. The haversian canals in lamellar bone are named after him. Henle, Friedrich Gustav Jakob (1864− 1936): Anatomist and pathologist at Zurich, Heidelberg, and Göttingen. Henle’s loop in the medullary portion of the nephron is named after him.

His, William (1863−1934): Internist in Göttingen and Berlin. The cardiac conducting bundle of His is named after him.

Kerckring, Theodor (1640−1693): Physician and anatomist at Amsterdam and Hamburg. Kerckring’s folds in the small intestine are named after him. Kohlrausch, Otto Ludwig Bernhardt (1811−1854): Hannover physician. The Kohlrausch fold of the rectum is named after him.

Korotkoff, Nicolai Sergeeivich (1874− 1920): Russian physician. The Korotkoff sounds heard when taking a blood pressure are named after him.

Kupffer, Karl Wilhelm von (1829−1903): Anatomist at Kiel, Königsberg, and Munich. The phagocytosing Kupffer cells in the liver are named after him. Kussmaul, Adolph (1822−1902): German physician who described Kussmaul breathing seen in diabetic coma. Langerhans, Paul (1849−1888): Freiburg pathologist. The islets of Langerhans in

the pancreas and the Langerhans cells in the skin were described by him. Leydig, Franz von (1821−1908): Physiologist and anatomist at Würzburg and Bonn. The testicular Leydig cells are named after him.

Lieberkühn, Johann Nathanael (1711− 1756): Berlin physician. The crypts in the wall of the small intestine are named after him.

Malpighi, Marcello (1628−1694): Professor of Medicine at Bolgna, Pisa, and Messina. The malpighian corpuscles in the kidney are named after him. McBurney, Charles (1845−1914): New York surgeon. McBurney’s point (projection of the vermiform appendix to the abdominal surface) is named after him. Meissner, Georg (1829−1905): Physiologist and zoologist at Basle, Freiburg, and Göttingen. The tactile corpuscles in the dermis are named after him.

Merkel, Friedrich S.M. (1845−1919: Göttingen anatomist. The tactile Merkel cells in the epidermis are named after him.

Monro, Alexander (Secundus) (1733− 1817): Scottish anatomist and surgeon. The interventricular foramen of Monro is named after him.

Naegele, Franz (1777−1851): Heidelberg gynecologist. The probable date of delivery can be calculated using Naegele’s rule.

Nissl, Franz (1860−1919): Heidelberg psychiatrist and neurohistologist. The Nissl granules in nerve cells are named after him.

Oddi, Ruggero (1864−1913): Italian physician. The sphincter of Oddi in the major duodenal papilla is named after him.

Pacchioni, Antoine (1665−1726): Physician in Tivoli and Rome. The pacchionian granulations (projections of the arachnoid into the venous sinuses) are named after him.

Pacini, Filippo (1812−1883): Florentine anatomist. The Vater−Pacini bodies

Eponyms (Proper Names) in Medical Anatomy and Physiology 681

(pressure receptors) derive their name from him.

Peyer, Johann Konrad (1653−1712): Schaffhausen physician. The Peyer’s patches, collections of lymphoid follicles in the ileum, are named after him. Purkinje, Johannes Evangelista (1787− 1869): Anatomist and physiologist at Breslau and Prague. The Purkinje fibers in the conduction system of the heart are named after him.

Ranvier, Louis Antoine (1835−1922): Paris histologist. The constrictions of myelinated nerves are named after him. Reissner, Ernst (1824−1878): Anatomist at Dorpat and Breslau. Reissner’s membrane of the inner ear is named after him.

Schlemm, Friedrich (1795−1858): Berlin anatomist. The circular vein in the angle between iris and cornea is named after him.

Schwann, Theodor (1810−1882): Anatomist and physiologist at Leeuwen and Liege. The outer sheath of nerve fibers is named after him.

Sertoli, Enrico (1842−1910): Milan physiologist. The testicular Sertoli cells are named after him.

Sharpey, William (1802−1880): Anatomist at Edinburgh and London. Sharpey’s fibers in the desmodontium are named after him.

Sylvius, Jacobus (1478−1555): Latinized form of Jacques Dubois, French anatomist at Paris. Probably the anatomist who described the cerebral aqueduct. Tawara, K. Sunao (1873−1952): Pathologist in Fukuoka, Japan. The sinoatrial node and the branches of the ventricular conducting system are named after him.

Vater, Abraham (1684−1751): Anatomist and botanist at Wittenberg. The ampulla of Vater in the duodenum and the Vater−Pacini corpuscles in the skin are named after him.

Volkmann, Richard (1800−1877): German surgeon. He described Volkmann’s canals in bone.

Waldeyer, Heinrich W.G (1836−1921): German anatomist who described the ring of lymphoid tissue in the throat.

Wernicke, Karl W. (1848−1905): Neurologist in Berlin, Breslau, and Halle. Wernicke’s auditory association area in the superior temporal gyrus is named after him.

Westphal, Karl F.O. (1833−1890): German neurologist. His name is associated with the Edinger−Westphal nucleus, the parasympathetic nucleus of cranial nerve X (vagus nerve).

Willis, Thomas (1621−1675): English anatomist and physician. The circulus arteriosus of Willis is named after him.