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Metre
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This article is about the unit of length. For other uses of "metre" or "meter", see meter (disambiguation).
Metre
Unit system
SI base unit
Unit of
length
Symbol
m
Unit conversions
1 m in ... ... is equal to ...
SI units
7000100000000000000♠1000 mm
7000100000000000000♠0.001 km
imperial/US units
1.0936 yd
3.2808 ft
39.370 in
nautical units
0.00053996 nmi
Look up metre in Wiktionary, the free dictionary.
The metre (British spelling and BIPM spelling[1]) or meter (American spelling) (from the French unit mètre, from the Greek noun μέτρον, "measure") is the base unit of length in some metric systems, including the International System of Units (SI). The SI unit symbol is m.[2] The metre is defined as the length of the path travelled by light in a vacuum in 1/299 792 458 second.[1]
The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted.
The imperial inch is defined as 0.0254 metres (2.54 centimetres or 25.4 millimetres). One metre is about 3 3⁄8 inches longer than a yard, i.e. about 39 3⁄8 inches.
Contents
1 Spelling
2 Etymology
3 History of definition
3.1 Meridional definition
3.2 International prototype metre bar
3.3 Wavelength definition
3.4 Speed of light definition
3.5 Timeline
4 SI prefixed forms of metre
5 Equivalents in other units
6 See also
7 Notes
8 References
Spelling[edit]
Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States[3][4][5] and the Philippines,[6] which use meter. Other Germanic languages, such as German, Dutch, and the Scandinavian languages[7] likewise spell the word meter.
Measuring devices (such as ammeter, speedometer) are spelled "-meter" in all variants of English.[8] The suffix "-meter" has the same Greek origin as the unit of length.[9][10]
Etymology[edit]
The etymological roots of metre can be traced to the Greek verb μετρέω (metreo) (to measure, count or compare) and noun μέτρον (metron) (a measure), which were used for physical measurement, for poetic metre and by extension for moderation or avoiding extremism (as in "be measured in your response"). This range of uses is also found in Latin (metior, mensura), French (mètre, mesure), English and other languages. The motto ΜΕΤΡΩ ΧΡΩ (metro chro) in the seal of the International Bureau of Weights and Measures (BIPM), which was a saying of the Greek statesman and philosopher Pittacus of Mytilene and may be translated as "Use measure!", thus calls for both measurement and moderation.
History of definition[edit]
Main article: History of the metre
In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, the universal measure or standard based on a pendulum with a two-second period.[11] The use of the seconds pendulum to define length had been suggested to the Royal Society in 1660 by Christopher Wren. Christiaan Huygens had observed that length to be 38 Rijnland inches or 39.26 English inches; that is, 997 mm.[11][12][13] No official action was taken regarding these suggestions.
In 1670 Gabriel Mouton, Bishop of Lyon, also suggested a universal length standard with decimal multiples and divisions, to be based on a one-minute angle of the Earth's meridian arc or (as the Earth's circumference was not easy to measure) on a pendulum with a two-second period. In 1675, the Italian scientist Tito Livio Burattini, in his work Misura Universale, used the phrase metro cattolico ("universal measure"), derived from the Greek μέτρον καθολικόν (métron katholikón), to denote the standard unit of length derived from a pendulum.[14] As a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. On 7 October 1790 that commission advised the adoption of a decimal system, and on 19 March 1791 advised the adoption of the term mètre ("measure"), a basic unit of length, which they defined as equal to one ten-millionth of the distance between the North Pole and the Equator.[15][16][17][18] In 1793, the French National Convention adopted the proposal; this use of metre in English began at least as early as 1797.[19]
Belfry, Dunkirk—the northern end of the meridian arc
Fortress of Montjuïc—the southerly end of the meridian arc
Creating the metre-alloy in 1874 at the Conservatoire des Arts et Métiers. Present Henri Tresca, George Matthey, Saint-Claire Deville and Debray
Meridional definition[edit]
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In 1791, the French Academy of Sciences selected the meridional definition over the pendular definition because the force of gravity varies slightly over the surface of the Earth, which affects the period of a pendulum.
To establish a universally accepted foundation for the definition of the metre, more accurate measurements of this meridian were needed. The French Academy of Sciences commissioned an expedition led by Jean Baptiste Joseph Delambre and Pierre Méchain, lasting from 1792 to 1799, which attempted to accurately measure the distance between a belfry in Dunkerque and Montjuïc castle in Barcelona to estimate the length of the meridian arc through Dunkerque. This portion of the meridian, assumed to be the same length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator. The problem with this approach is that the exact shape of the Earth is not a simple mathematical shape, such as a sphere or oblate spheroid, at the level of precision required for defining a standard of length. The irregular and particular shape of the Earth smoothed to sea level is represented by a mathematical model called a geoid, which literally means "Earth-shaped". Despite these issues, in 1793 France adopted this definition of the metre as its official unit of length based on provisional results from this expedition. However, it was later determined that the first prototype metre bar was short by about 200 micrometres because of miscalculation of the flattening of the Earth, making the prototype about 0.02% shorter than the original proposed definition of the metre. Regardless, this length became the French standard and was progressively adopted by other countries in Europe.
The expedition was fictionalised in Denis Guedj, Le mètre du Monde.[20] Ken Alder wrote factually about the expedition in The Measure of All Things: the seven year odyssey and hidden error that transformed the world.[21]
International prototype metre bar[edit]
In 1867 at the second general conference of the International Association of Geodesy held in Berlin, the question of an international standard unit of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth.[22][23][24] The conference recommended the adoption of the metre and the creation of an international metre commission, according to the proposal of Johann Jacob Baeyer, Adolphe Hirsch and Carlos Ibáñez e Ibáñez de Ibero.[22]
In the 1870s and in light of modern precision, a series of international conferences was held to devise new metric standards. The Metre Convention (Convention du Mètre) of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM: Bureau International des Poids et Mesures) to be located in Sèvres, France. This new organisation was to construct and preserve a prototype metre bar, distribute national metric prototypes, and maintain comparisons between them and non-metric measurement standards. The organisation created such a bar in 1889 at the first General Conference on Weights and Measures (CGPM: Conférence Générale des Poids et Mesures), establishing the International Prototype Metre as the distance between two lines on a standard bar composed of an alloy of 90% platinum and 10% iridium, measured at the melting point of ice.[25]
The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.
Wavelength definition[edit]
In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of length. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh CGPM defined the metre in the new International System of Units (SI) as equal to 1 650 763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum.[26]
Speed of light definition[edit]
To further reduce uncertainty, the 17th CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of the second and the speed of light:[1]
The metre is the length of the path travelled by light in vacuum during a time interval of 1/7008299792458000000♠299792458 second.
This definition fixed the speed of light in vacuum at exactly 7008299792458000000♠299792458 metres per second (≈7008300000000000000♠300000 km/s). An intended by-product of the 17th CGPM's definition was that it enabled scientists to compare lasers accurately using frequency, resulting in wavelengths with one-fifth the uncertainty involved in the direct comparison of wavelengths, because interferometer errors were eliminated. To further facilitate reproducibility from lab to lab, the 17th CGPM also made the iodine-stabilised helium–neon laser "a recommended radiation" for realising the metre.[27] For the purpose of delineating the metre, the BIPM currently considers the HeNe laser wavelength, λHeNe, to be 6993632991212580000♠632.99121258 nm with an estimated relative standard uncertainty (U) of 6989210000000000000♠2.1×10−11.[27][28][29] This uncertainty is currently one limiting factor in laboratory realisations of the metre, and it is several orders of magnitude poorer than that of the second, based upon the caesium fountain atomic clock (U = 6984500000000000000♠5×10−16).[30] Consequently, a realisation of the metre is usually delineated (not defined) today in labs as 7006157980076204200♠1579800.762042(33) wavelengths of helium-neon laser light in a vacuum, the error stated being only that of frequency determination.[27] This bracket notation expressing the error is explained in the article on measurement uncertainty.
Practical realisation of the metre is subject to uncertainties in characterising the medium, to various uncertainties of interferometry, and to uncertainties in measuring the frequency of the source.[31] A commonly used medium is air, and the National Institute of Standards and Technology (NIST) has set up an online calculator to convert wavelengths in vacuum to wavelengths in air.[32] As described by NIST, in air, the uncertainties in characterising the medium are dominated by errors in measuring temperature and pressure. Errors in the theoretical formulas used are secondary.[33] By implementing a refractive index correction such as this, an approximate realisation of the metre can be implemented in air, for example, using the formulation of the metre as 7006157980076204200♠1579800.762042(33) wavelengths of helium–neon laser light in vacuum, and converting the wavelengths in a vacuum to wavelengths in air. Air is only one possible medium to use in a realisation of the metre, and any partial vacuum can be used, or some inert atmosphere like helium gas, provided the appropriate corrections for refractive index are implemented.[34]
The metre is defined as the path length travelled by light in a given time and practical laboratory length measurements in metres are determined by counting the number of wavelengths of laser light of one of the standard types that fit into the length,[37] and converting the selected unit of wavelength to metres. Three major factors limit the accuracy attainable with laser interferometers for a length measurement:[31][38]
uncertainty in vacuum wavelength of the source,
uncertainty in the refractive index of the medium,
least count resolution of the interferometer.
Of these, the last is peculiar to the interferometer itself. The conversion of a length in wavelengths to a length in metres is based upon the relation
λ = c n f {\displaystyle \lambda ={\frac {c}{nf}}}
which converts the unit of wavelength λ to metres using c, the speed of light in vacuum in m/s. Here n is the refractive index of the medium in which the measurement is made, and f is the measured frequency of the source. Although conversion from wavelengths to metres introduces an additional error in the overall length due to measurement error in determining the refractive index and the frequency, the measurement of frequency is one of the most accurate measurements available.[38]
Timeline[edit]
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Closeup of National Prototype Metre Bar No. 27, made in 1889 by the International Bureau of Weights and Measures (BIPM) and given to the United States, which served as the standard for defining all units of length in the US from 1893 to 1960
8 May 1790 – The French National Assembly decides that the length of the new metre would be equal to the length of a pendulum with a half-period of one second.
30 March 1791 – The French National Assembly accepts the proposal by the French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of a quadrant along the Earth's meridian through Paris, that is the distance from the equator to the north pole along that quadrant.
1795 – Provisional metre bar constructed of brass. Based on Bessel's ellipsoid and legally equal to 443.44 lines on the toise du Pérou (a standard French unit of length from 1747).
10 December 1799 – The French National Assembly specifies the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standard. Legally equal to 443.296 lines on the toise du Pérou.
28 September 1889 – The 1st General Conference on Weights and Measures (CGPM) defines the metre as the distance between two lines on a standard bar of an alloy of platinum with 10% iridium, measured at the melting point of ice.
6 October 1927 – The 7th CGPM redefines the metre as the distance, at 0 °C (273 K), between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmosphere of pressure and supported on two cylinders of at least 10 mm (1 cm) diameter, symmetrically placed in the same horizontal plane at a distance of 571 mm (57.1 cm) from each other.
14 October 1960 – The 11th CGPM defines the metre as 7006165076373000000♠1650763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.[39]
21 October 1983 – The 17th CGPM defines the metre as the length of the path travelled by light in a vacuum during a time interval of 1/299 792 458 of a second.[40]
2002 – The International Committee for Weights and Measures (CIPM) considers the metre to be a unit of proper length and thus recommends this definition be restricted to "lengths ℓ which are sufficiently short for the effects predicted by general relativity to be negligible with respect to the uncertainties of realisation".[41]
Definitions of the metre since 1795[42]
Basis of definition
Date
Absolute
uncertainty
Relative
uncertainty
1/10 000 000 part of the quadrant along the meridian, measurement by Delambre and Méchain (443.296 lines) 1795 500–100 μm 6996100000000000000♠10−4
First prototype Mètre des Archives platinum bar standard 1799 50–10 μm 6995100000000000000♠10−5
Platinum-iridium bar at melting point of ice (1st CGPM) 1889 0.2–0.1 μm (200–100 nm) 6993100000000000000♠10−7
Platinum-iridium bar at melting point of ice, atmospheric pressure, supported by two rollers (7th CGPM) 1927 n.a. n.a.
Hyperfine atomic transition; 7006165076373000000♠1650763.73 wavelengths of light from a specified transition in krypton-86 (11th CGPM) 1960 4 nm 6991400000000000000♠4×10−9[43]
Length of the path travelled by light in a vacuum in 1/299 792 458 second (17th CGPM) 1983 0.1 nm 6990100000000000000♠10−10
SI prefixed forms of metre[edit]
SI prefixes are often employed to denote decimal multiples and submultiples of the metre, as shown in the table below. As indicated in the table, some are commonly used, while others are not. Long distances are usually expressed in km, astronomical units (149.6 Gm), light-years (10 Pm), or parsecs (31 Pm), rather than in Mm, Gm, Tm, Pm, Em, Zm or Ym; "30 cm", "30 m", and "300 m" are more common than "3 dm", "3 dam", and "3 hm", respectively.
The terms micron and (occasionally) millimicron are often used instead of micrometre (μm) and nanometre (nm), but this practice is officially discouraged.[44]

SI multiples for metre (m)
Submultiples
Multiples
Value
SI symbol
Name
Value
SI symbol
Name
10−1 m dm decimetre 101 m dam decametre
10−2 m cm centimetre 102 m hm hectometre
10−3 m mm millimetre 103 m km kilometre
10−6 m µm micrometre 106 m Mm megametre
10−9 m nm nanometre 109 m Gm gigametre
10−12 m pm picometre 1012 m Tm terametre
10−15 m fm femtometre 1015 m Pm petametre
10−18 m am attometre 1018 m Em exametre
10−21 m zm zeptometre 1021 m Zm zettametre
10−24 m ym yoctometre 1024 m Ym yottametre
Common prefixed units are in bold face.
Equivalents in other units[edit]
Metric unit
expressed in non-SI units
Non-SI unit
expressed in metric units
1 metre ≈ 1.0936 yard 1 yard ≡ 0.9144 metre
1 metre ≈ 39.370 inches 1 inch ≡ 0.0254 metre
1 centimetre ≈ 6999393700000000000♠0.39370 inch 1 inch ≡ 2.54 centimetres
1 millimetre ≈ 6998393700000000000♠0.039370 inch 1 inch ≡ 25.4 millimetres
1 metre ≡ 1 × 1010 ångström 1 ångström ≡ 1 × 10−10 metre
1 nanometre ≡ 10 ångström 1 ångström ≡ 100 picometres
Within this table, "inch" and "yard" mean "international inch" and "international yard"[45] respectively, though approximate conversions in the left column hold for both international and survey units.
"≈" means "is approximately equal to";
"≡" means "equal by definition" or "is exactly equal to".
One metre is exactly equivalent to 10 000/254 inches and to 10 000/9 144 yards.
A simple mnemonic aid exists to assist with conversion, as three "3"s:
1 metre is nearly equivalent to 3 feet 3 3⁄8 inches.[46] This gives an overestimate of 0.125 mm. However, the practice of memorising such conversion formulas has been discouraged in favour of practice and visualisation of metric units.
The ancient Egyptian cubit was about 0.5 m (surviving rods are 523–529 mm). Scottish and English definitions of the ell (two cubits) were 941 mm (0.941 m) and 1143 mm (1.143 m) respectively. The ancient Parisian toise (fathom) was slightly shorter than 2 m and was standardised at exactly 2 m in the mesures usuelles system, such that 1 m was exactly 1⁄2 toise. The Russian verst was 1.0668 km. The Swedish mil was 10.688 km, but was changed to 10 km when Sweden converted to metric units.
See also[edit]
Conversion of units for comparisons with other units
International System of Units
Introduction to the metric system
ISO 1 – standard reference temperature for length measurements
Length measurement
Metre Convention
Metric system
Metric prefix
Metrication
Orders of magnitude (length)
SI prefix
Speed of light
Vertical metre
Notes[edit]
^ Jump up to: a b c "17th General Conference on Weights and Measures (1983), Resolution 1". Retrieved 19 September 2012.
Jump up ^ "Base unit definitions: Meter". National Institute of Standards and Technology. Retrieved 28 September 2010.
Jump up ^ The most recent official brochure about the International System of Units (SI), written in French by the Bureau international des poids et mesures, International Bureau of Weights and Measures (BIPM) uses the spelling metre; an English translation, included to make the SI standard more widely accessible also uses the spelling metre (BIPM, 2006, p. 130ff). However, in 2008 the U.S. English translation published by the U.S. National Institute of Standards and Technology (NIST) chose to use the spelling meter in accordance with the United States Government Printing Office Style Manual. The Metric Conversion Act of 1975 gives the Secretary of Commerce of the US the responsibility of interpreting or modifying the SI for use in the US. The Secretary of Commerce delegated this authority to the Director of the National Institute of Standards and Technology (Turner). In 2008, NIST published the US version (Taylor and Thompson, 2008a) of the English text of the eighth edition of the BIPM publication Le Système international d'unités (SI) (BIPM, 2006). In the NIST publication, the spellings "meter", "liter" and "deka" are used rather than "metre", "litre" and "deca" as in the original BIPM English text (Taylor and Thompson (2008a), p. iii). The Director of the NIST officially recognised this publication, together with Taylor and Thompson (2008b), as the "legal interpretation" of the SI for the United States (Turner). Thus, the spelling metre is referred to as the "international spelling"; the spelling meter, as the "American spelling".
Jump up ^ Naughtin, Pat (2008). "Spelling metre or meter" (PDF). Metrication Matters. Retrieved 12 March 2017.
Jump up ^ "Meter vs. metre". Grammarist. Retrieved 12 March 2017.
Jump up ^ The Philippines uses English as an official language and this largely follows American English since the country became a colony of the United States. While the law that converted the country to use the metric system uses metre (Batas Pambansa Blg. 8) following the SI spelling, in actual practice, meter is used in government and everyday commerce, as evidenced by laws (kilometer, Republic Act No. 7160), Supreme Court decisions (meter, G.R. No. 185240), and national standards (centimeter, PNS/BAFS 181:2016).
Jump up ^ "295-296 (Nordisk familjebok / Uggleupplagan. 18. Mekaniker - Mykale)" [295-296 (Nordic Family Book / Owl Edition. 18. Mechanic - Mycular)]. Stockholm. 1913.
Jump up ^ Cambridge Advanced Learner's Dictionary. Cambridge University Press. 2008. Retrieved 19 September 2012. , s.v. ammeter, meter, parking meter, speedometer.
Jump up ^ American Heritage Dictionary of the English Language (3rd ed.). Boston: Houghton Mifflin. 1992. , s.v. meter.
Jump up ^ "-meter - definition of -meter in English". Oxford Dictionaries.
^ Jump up to: a b "Chapter 7: Measure" in An Essay towards a Real Character and a Philosophical Language — John Wilkins F.R.S. 1668, pp. 191-192
Jump up ^ Rooney, Anne (2012). The History of Mathematics. Rosen Publishing Group. p. 65. ISBN 144887369X. An identical metric system to that introduced in France was proposed in 1668 by Bishop John Wilkins, a founder of the Royal Society in England. ... he proposed an integrated system of measurement based on a decimal system and almost identical to the modern metric system. His unit of measurement was 997 millimeters - almost exactly a meter.
Jump up ^ Quinn, Terry (2012). From artefacts to atoms: the BIPM and the search for ultimate measurement standards. Oxford University Press. p. xxvii. ISBN 978-0-19-530786-3. he [Wilkins] proposed essentially what became ... the French decimal metric system
Jump up ^ George Sarton (1935). "The First Explanation of Decimal Fractions and Measures (1585). Together with a History of the Decimal Idea and a Facsimile (No. XVII) of Stevin's Disme". Isis. 23 (1): 153–244. doi:10.1086/346940. JSTOR 225223.
Jump up ^ ('decimalization is not of the essence of the metric system; the real significance of this is that it was the first great attempt to define terrestrial units of measure in terms of an unvarying astronomical or geodetic constant.) The metre was in fact defined as one ten-millionth of one-quarter of the earth's circumference at sea-level.' Joseph Needham, Science and Civilisation in China, Cambridge University Press, 1962 vol.4, pt.1, p.42.
Jump up ^ Agnoli, Paolo (2004). Il senso della misura: la codifica della realtà tra filosofia, scienza ed esistenza umana (in Italian). Armando Editore. pp. 93–94,101. Retrieved 13 October 2015.
Jump up ^ "Rapport sur le choix d'une unité de mesure, lu à l'Académie des sciences, le 19 mars 1791" (in French). Gallica.bnf.fr. 15 October 2007. Retrieved 25 March 2013.
Jump up ^ Paolo Agnoli and Giulio D’Agostini,'Why does the meter beat the second?,' December, 2004 pp.1–29.
Jump up ^ Oxford English Dictionary, Clarendon Press 2nd ed.1989, vol.IX p.697 col.3.
Jump up ^ Guedj 2001.
Jump up ^ Alder 2002.
^ Jump up to: a b Hirsch, Adolphe (1891). "Don Carlos IBANEZ (1825 - 1891)" (PDF). Bureau International des Poids et Mesures. p. 8. Retrieved 22 May 2017.
Jump up ^ "BIPM - International Metre Commission". www.bipm.org. Retrieved 26 May 2017.
Jump up ^ "A Note on the History of the IAG". IAG Homepage. Retrieved 26 May 2017.
Jump up ^ National Institute of Standards and Technology 2003; Historical context of the SI: Unit of length (meter)
Jump up ^ Marion, Jerry B. (1982). Physics For Science and Engineering. CBS College Publishing. p. 3. ISBN 4-8337-0098-0.
^ Jump up to: a b c "Iodine (λ≈633 nm)" (PDF). MEP (Mise en Pratique). BIPM. 2003. Retrieved 16 December 2011.
Jump up ^ The term "relative standard uncertainty" is explained by NIST on their web site: "Standard Uncertainty and Relative Standard Uncertainty". The NIST Reference on constants, units, and uncertainties: Fundamental physical constants. NIST. Retrieved 19 December 2011.
Jump up ^ National Research Council 2010.
Jump up ^ National Institute of Standards and Technology 2011.
^ Jump up to: a b A more detailed listing of errors can be found in Beers, John S; Penzes, William B (December 1992). "§4 Re-evaluation of measurement errors" (PDF). NIST length scale interferometer measurement assurance; NIST document NISTIR 4998. pp. 9 ff. Retrieved 17 December 2011.
Jump up ^ The formulas used in the calculator and the documentation behind them are found at "Engineering metrology toolbox: Refractive index of air calculator". NIST. 23 September 2010. Retrieved 16 December 2011. The choice is offered to use either the modified Edlén equation or the Ciddor equation. The documentation provides a discussion of how to choose between the two possibilities.
Jump up ^ "§VI: Uncertainty and range of validity". Engineering metrology toolbox: Refractive index of air calculator. NIST. 23 September 2010. Retrieved 16 December 2011.
Jump up ^ Dunning, F. B.; Hulet, Randall G. (1997). "Physical limits on accuracy and resolution: setting the scale". Atomic, molecular, and optical physics: electromagnetic radiation, Volume 29, Part 3. Academic Press. p. 316. ISBN 0-12-475977-7. The error [introduced by using air] can be reduced tenfold if the chamber is filled with an atmosphere of helium rather than air.
Jump up ^ "Recommended values of standard frequencies". BIPM. 9 September 2010. Retrieved 22 January 2012.
Jump up ^ National Physical Laboratory 2010.
Jump up ^ The BIPM maintains a list of recommended radiations on their web site.[35][36]
^ Jump up to: a b Zagar, 1999, pp. 6–65ff.
Jump up ^ Barbrow & Judson 1976, appendix 6.
Jump up ^ Taylor and Thompson (2008a), Appendix 1, p. 70.
Jump up ^ Taylor and Thompson (2008a), Appendix 1, p. 77.
Jump up ^ Cardarelli 2003
Jump up ^ Definition of the metre Resolution 1 of the 17th meeting of the CGPM (1983)
Jump up ^ Taylor & Thompson 2003, p. 11.
Jump up ^ Astin & Karo 1959.
Jump up ^ Well-known conversion, publicised at time of metrication.[where?]
References[edit]
17th General Conference on Weights and Measures. (1983). Resolution 1. International Bureau of Weights and Measures.
Alder, Ken (2002). The Measure of All Things : The Seven-Year Odyssey and Hidden Error That Transformed the World. New York: Free Press. ISBN 0-7432-1675-X.
Astin, A. V. & Karo, H. Arnold, (1959), Refinement of values for the yard and the pound, Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59-5442, Filed, 30 June 1959, 8:45 a.m.)
Judson, Lewis V. (1976-10-01) [1963]. Barbrow, Louis E., ed. Weights and Measures Standards of the United States, a brief history (PDF). Derived from a prior work by Louis A. Fisher (1905). USA: US Department of Commerce, National Bureau of Standards. LCCN 76-600055. NBS Special Publication 447; NIST SP 447; 003-003-01654-3. Retrieved 12 October 2015.
Beers, J.S. & Penzes, W. B. (1992). NIST Length Scale Interferometer Measurement Assurance. (NISTIR 4998). National Institute of Standards and Technology.
Guedj, Denis (2001). La Mesure du Monde [The Measure of the World]. Translated by Goldhammer, Art. Chicago: University of Chicago Press.
"The International System of Units (SI)" (PDF) (in French). Bureau International des Poids et Mesures. 2006. Retrieved 18 August 2008.
HTML version. Retrieved 24 August 2008.
Bureau International des Poids et Mesures. (n.d.). Resolutions of the CGPM (search facility). Retrieved 3 June 2006.
Bureau International des Poids et Mesures. (n.d.). The BIPM and the evolution of the definition of the metre. Retrieved 3 June 2006.
Bureau of Agriculture and Fisheries Standards (Philippines). Philippine National Standard for Abaca Fiber Grading and Classification - Decorticated (PNS/BAFS 181:2016).
Cardarelli, François (2003). "Chapter 2: The International system of Units" (PDF). Encydopaedia of scientific units, weights, and measures: their SI equivalences and origins. Springer-Verlag London Limited. Table 2.1, p. 5. ISBN 1-85233-682-X. Retrieved 26 January 2017. Data from Giacomo, P., Du platine à la lumière [From platinum to light], Bull. Bur. Nat. Metrologie, 102 (1995) 5–14.
Humerfelt, Sigurd. (26 October 2010). How WGS 84 defines Earth. Retrieved 29 April 2011.
Layer, H.P. (2008). Length—Evolution from Measurement Standard to a Fundamental Constant. Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 18 August 2008.
Mohr, P., Taylor, B.N., and David B. Newell, D. (28 December 2007). CODATA Recommended Values of the Fundamental Physical Constants: 2006. Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 18 August 2008.
National Institute of Standards and Technology. (December 2003). The NIST Reference on Constants, Units, and Uncertainty: International System of Units (SI) (web site):
SI base units. Retrieved 18 August 2008.
Definitions of the SI base units. Retrieved 18 August 2008.
Historical context of the SI: Meter. Retrieved 26 May 2010.
National Institute of Standards and Technology. (27 June 2011). NIST-F1 Cesium Fountain Atomic Clock. Author.
National Physical Laboratory. (25 March 2010). Iodine-Stabilised Lasers. Author.
"Maintaining the SI unit of length". National Research Council Canada. 5 February 2010. Archived from the original on 4 December 2011.
Republic of the Philippines. (2 December 1978). Batas Pambansa Blg. 8: An Act Defining the Metric System and its Units, Providing for its Implementation and for Other Purposes. Author.
Republic of the Philippines. (10 October 1991). Republic Act No. 7160: The Local Government Code of the Philippines. Author.
Penzes, W. (29 December 2005). Time Line for the Definition of the Meter. Gaithersburg, MD: National Institute of Standards and Technology – Precision Engineering Division. Retrieved 4 December 2010.
Supreme Court of the Philippines (Second Division). (20 January 2010). G.R. No. 185240. Author.
Taylor, B.N. and Thompson, A. (Eds.). (2008a). The International System of Units (SI). United States version of the English text of the eighth edition (2006) of the International Bureau of Weights and Measures publication Le Système International d’ Unités (SI) (Special Publication 330). Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 18 August 2008.
Taylor, B.N. and Thompson, A. (2008b). Guide for the Use of the International System of Units (Special Publication 811). Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 23 August 2008.
Tibo Qorl. (2005) The History of the Meter (Translated by Sibille Rouzaud). Retrieved 18 August 2008.
Turner, J. (Deputy Director of the National Institute of Standards and Technology). (16 May 2008)."Interpretation of the International System of Units (the Metric System of Measurement) for the United States". Federal Register Vol. 73, No. 96, p. 28432-3.
Wilkins, J. (c. 2007). An essay towards a real character, and a philosophical language. [Also available without images of original.] Metrication Matters. (Reprinted from title page and pp. 190–194 of original, 1668, London: Royal Society)
Zagar, B.G. (1999). Laser interferometer displacement sensors in J.G. Webster (ed.). The Measurement, Instrumentation, and Sensors Handbook. CRC Press. ISBN 0-8493-8347-1.
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text:
Small intestine
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Small Intestine
Diagram showing the small intestine and surrounding structures
Details
Artery
Superior mesenteric artery
Vein
Hepatic portal vein
Nerve
Celiac ganglia, vagus[1]
Lymph
Intestinal lymph trunk
Identifiers
Latin
Intestinum tenue
MeSH
A03.556.124.684
Code
4453467
Dorlands
/Elsevier
Small intestine r
TA
A05.6.01.001
FMA
7200
Anatomical terminology
[edit on Wikidata]
The small intestine or small bowel is the part of the gastrointestinal tract between the stomach and the large intestine, and is where most of the end absorption of food takes place. The small intestine has three distinct regions – the duodenum, jejunum, and ileum. The duodenum is the shortest part of the small intestine and is where preparation for absorption begins. It also receives bile and pancreatic juice through the pancreatic duct, controlled by the sphincter of Oddi. The primary function of the small intestine is the absorption of nutrients and minerals from food, using small finger-like protrusions called villi.[2]
Contents
[hide]
1 Structure
1.1 Size
1.2 Parts
1.3 Blood supply
1.4 Histology
1.5 Development
2 Function
2.1 Digestion
2.2 Absorption
2.3 Immunological
3 Gene and protein expression
4 Clinical significance
5 Other animals
6 Society and culture
7 Additional images
8 See also
9 References
10 Bibliography
11 External links
Structure[edit]
Size[edit]
The length of the small intestine can vary greatly, from as short as 2.75 m (9.0 ft) to as long as 10.49 m (34.4 ft).[3] The average length in a living person is 3m-5m.[4][5] The length depends both on how tall the person is and how the length is measured.[3] Taller people generally have a longer small intestine and measurements are generally longer after death and when the bowel is empty.[3]
It is approximately 1.5 cm in diameter in newborns after 35 weeks of gestational age,[6] and 2.5–3 cm (1 inch) in diameter in adults. On abdominal X-rays, the small intestine is considered to be abnormally dilated when the diameter exceeds 3 cm.[7][8] On CT scans, a diameter of over 2.5 cm is considered abnormally dilated.[7][9] The surface area of the human small intestinal mucosa, due to enlargement caused by folds, villi and microvilli, averages 30 square meters.[10]
Parts[edit]
The small intestine is divided into three structural parts.
The duodenum is a short structure ranging from 20 cm (7.9 inches) to 25 cm (9.8 inches) in length, and shaped like a "C".[11] It surrounds the head of the pancreas. It receives gastric chyme from the stomach, together with digestive juices from the pancreas (digestive enzymes) and the liver (bile). The digestive enzymes break down proteins and bile and emulsify fats into micelles. The duodenum contains Brunner's glands, which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in gastric chyme.
The jejunum is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long, and contains the plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here. The suspensory muscle of duodenum marks the division between the duodenum and the jejunum.
The ileum: The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients. The ileum joins to the cecum of the large intestine at the ileocecal junction.
The jejunum and ileum are suspended in the abdominal cavity by mesentery. The mesentery is part of the peritoneum. Arteries, veins, lymph vessels and nerves travel within the mesentery.[12]
Blood supply[edit]
The small intestine receives a blood supply from the coeliac trunk and the superior mesenteric artery. These are both branches of the aorta. The duodenum receives blood from the coeliac trunk via the superior pancreaticoduodenal artery and from the superior mesenteric artery via the inferior pancreaticoduodenal artery. These two arteries both have anterior and posterior branches that meet in the midline and anastomose. The jejunum and ileum receive blood from the superior mesenteric artery.[13] Branches of the superior mesenteric artery form a series of arches within the mesentery known as arterial arcades, which may be several layers deep. Straight blood vessels known as vasa recta travel from the arcades closest to the ileum and jejunum to the organs themselves.[13]
Histology[edit]
Main article: Gastrointestinal wall
Micrograph of the small intestine mucosa showing the intestinal villi and crypts of Lieberkühn.
The three sections of the small intestine look similar to each other at a microscopic level, but there are some important differences. The parts of the intestine are as follows:
Layer
Duodenum
Jejunum
Ileum
Serosa 1st part serosa, 2nd–4th adventitia Normal Normal
Muscularis externa Longitudinal and circular layers, with Auerbach's (myenteric) plexus in between Same as duodenum Same as duodenum
Submucosa Brunner's glands and Meissner's (submucosal) plexus No BG No BG
Mucosa: muscularis mucosae Normal Normal Normal
Mucosa: lamina propria No PP No PP Peyer's patches
Mucosa: intestinal epithelium Simple columnar. Contains goblet cells, Paneth cells Similar to duodenum ?
Development[edit]
See also: Development of the digestive system
The small intestine develops from the midgut of the primitive gut tube.[14] By the fifth week of embryological life, the ileum begins to grow longer at a very fast rate, forming a U-shaped fold called the primary intestinal loop. The loop grows so fast in length that it outgrows the abdomen and protrudes through the umbilicus. By week 10, the loop retracts back into the abdomen. Between weeks six and ten the small intestine rotates anticlockwise, as viewed from the front of the embryo. It rotates a further 180 degrees after it has moved back into the abdomen. This process creates the twisted shape of the large intestine.[14]
Function[edit]
Food from the stomach is allowed into the duodenum through the pylorus by a muscle called the pyloric sphincter.
Digestion[edit]
The small intestine is where most chemical digestion takes place. Many of the digestive enzymes that act in the small intestine are secreted by the pancreas and liver and enter the small intestine via the pancreatic duct. Pancreatic enzymes and bile from the gallbladder enter the small intestine in response to the hormone cholecystokinin, which is produced in the small intestine in response to the presence of nutrients. Secretin, another hormone produced in the small intestine, causes additional effects on the pancreas, where it promotes the release of bicarbonate into the duodenum in order to neutralize the potentially harmful acid coming from the stomach.
The three major classes of nutrients that undergo digestion are proteins, lipids (fats) and carbohydrates:
Proteins are degraded into small peptides and amino acids before absorption.[15] Chemical breakdown begins in the stomach and continues in the small intestine. Proteolytic enzymes, including trypsin and chymotrypsin, are secreted by the pancreas and cleave proteins into smaller peptides. Carboxypeptidase, which is a pancreatic brush border enzyme, splits one amino acid at a time. Aminopeptidase and dipeptidase free the end amino acid products.
Lipids (fats) are degraded into fatty acids and glycerol. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase works with the help of the salts from the bile secreted by the liver and stored in the gall bladder. Bile salts attach to triglycerides to help emulsify them, which aids access by pancreatic lipase. This occurs because the lipase is water-soluble but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings. The bile salts emulsify the triglycerides in the watery surroundings until the lipase can break them into the smaller components that are able to enter the villi for absorption.
Some carbohydrates are degraded into simple sugars, or monosaccharides (e.g., glucose). Pancreatic amylase breaks down some carbohydrates (notably starch) into oligosaccharides. Other carbohydrates pass undigested into the large intestine and further handling by intestinal bacteria. Brush border enzymes take over from there. The most important brush border enzymes are dextrinase and glucoamylase, which further break down oligosaccharides. Other brush border enzymes are maltase, sucrase and lactase. Lactase is absent in some adult humans and, for them, lactose, like most poly-saccharides, is not digested in the small intestine. Some carbohydrates, such as cellulose, are not digested at all, despite being made of multiple glucose units. This is because the cellulose is made out of beta-glucose, making the inter-monosaccharidal bindings different from the ones present in starch, which consists of alpha-glucose. Humans lack the enzyme for splitting the beta-glucose-bonds, something reserved for herbivores and bacteria from the large intestine.
Absorption[edit]
Digested food is now able to pass into the blood vessels in the wall of the intestine through either diffusion or active transport. The small intestine is the site where most of the nutrients from ingested food are absorbed. The inner wall, or mucosa, of the small intestine is lined with simple columnar epithelial tissue. Structurally, the mucosa is covered in wrinkles or folds called plicae circulares, which are considered permanent features in the wall of the organ. They are distinct from rugae which are considered non-permanent or temporary allowing for distention and contraction. From the plicae circulares project microscopic finger-like pieces of tissue called villi (Latin for "shaggy hair"). The individual epithelial cells also have finger-like projections known as microvilli. The functions of the plicae circulares, the villi, and the microvilli are to increase the amount of surface area available for the absorption of nutrients, and to limit the loss of said nutrients to intestinal fauna.
Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids). The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. The material that remains undigested and unabsorbed passes into the large intestine.
Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions:
Iron is absorbed in the duodenum.
Vitamin B12 and bile salts are absorbed in the terminal ileum.
Water and lipids are absorbed by passive diffusion throughout the small intestine.
Sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport.
Fructose is absorbed by facilitated diffusion.
Immunological[edit]
The small intestine supports the body's immune system.[16] The presence of gut flora appears to contribute positively to the host's immune system. Peyer's patches, located within the ileum of the small intestine, are an important part of the digestive tract's local immune system. They are part of the lymphatic system, and provide a site for antigens from potentially harmful bacteria or other microorganisms in the digestive tract to be sampled, and subsequently presented to the immune system.[17]
Gene and protein expression[edit]
Further information: Bioinformatics § Gene and protein expression
About 20,000 protein coding genes are expressed in human cells and 70 % of these genes are expressed in the normal duodenum.[18][19] Some 300 of these genes are more specifically expressed in the duodenum with very few genes expressed only in the small intestine. The corresponding specific proteins are expressed in glandular cells of the mucosa, such as fatty acid binding protein FABP6. Most of the more specifically expressed genes in the small intestine are also expressed in the duodenum, for example FABP2 and the DEFA6 protein expressed in secretory granules of Paneth cells.[20]
Clinical significance[edit]
See also: Gastrointestinal disease
The small intestine is a complex organ, and as such, there are a very large number of possible conditions that may affect the function of the small bowel. A few of them are listed below, some of which are common, with up to 10% of people being affected at some time in their lives, while others are vanishingly rare.
Small intestine obstruction or obstructive disorders
Paralytic ileus
Volvulus
Hernia
Intussusception
Adhesions
Obstruction from external pressure
Obstruction by masses in the lumen (foreign bodies, bezoar, gallstones)
Infectious diseases
Giardiasis
Ascariasis
Tropical sprue
Tape worm (Diphyllobothrium latum, Taenia solium, Hymenolepsis nana)
Hookworm (e.g. Necator americanus, Ancylostoma duodenale)
Nematodes (e.g. Ascaris lumbricoides)
Other Protozoa (e.g. Cryptosporidium parvum, Cyclospora, Microsporidia, Entamoeba histolytica)
Bacterial infections
Enterotoxigenic Escherichia coli
Salmonella enterica
Campylobacter
Shigella
Yersinia
Clostridium difficile (antibiotic-associated colitis, Pseudomembranous colitis)
Mycobacterium (Mycobacterium avium paratuberculosis, disseminated Mycobacterium tuberculosis)
Whipple's disease
Vibrio (cholera)
Enteric (typhoid) fever (Salmonella enterica var. typhii) and paratyphoid fever
Bacillus cereus
Clostridium perfringens (gas gangrene)
Viral infections
Rotavirus
Norovirus
Astrovirus
Adenovirus
Calicivirus
Neoplasms (cancers)
Adenocarcinoma
Carcinoid
Gastrointestinal stromal tumor (GIST)
Lymphoma
Sarcoma
Leiomyoma
Metastatic tumors, especially SCLC or melanoma
Developmental, congenital or genetic conditions
Duodenal (intestinal) atresia
Hirschsprung's disease
Meckel's diverticulum
Pyloric stenosis
Pancreas divisum
Ectopic pancreas
Enteric duplication cyst
Situs inversus
Cystic fibrosis
Malrotation
Persistent urachus
Omphalocele
Gastroschisis
Disaccharidase (lactase) deficiencies
Primary bile acid malabsorption
Gardner syndrome
Familial adenomatous polyposis syndrome (FAP)
Other conditions
Crohn's disease, and the more general inflammatory bowel disease
Typhlitis (neutropenic colitis in the immunosuppressed
Coeliac disease (sprue or non-tropical sprue)
Mesenteric ischemia
Embolus or thrombus of the superior mesenteric artery or the superior mesenteric vein
Arteriovenous malformation
Gastric dumping syndrome
Irritable bowel syndrome
Duodenal (peptic) ulcers
Gastrointestinal perforation
Hyperthyroidism
Diverticulitis
Radiation enterocolitis
Mesenteric cysts
Peritoneal Infection
Sclerosing retroperitonitis
Small intestinal bacterial overgrowth
Other animals[edit]
The small intestine is found in all tetrapods and also in teleosts, although its form and length vary enormously between species. In teleosts, it is relatively short, typically around one and a half times the length of the fish's body. It commonly has a number of pyloric caeca, small pouch-like structures along its length that help to increase the overall surface area of the organ for digesting food. There is no ileocaecal valve in teleosts, with the boundary between the small intestine and the rectum being marked only by the end of the digestive epitheliu [21]
In tetrapods, the ileocaecal valve is always present, opening into the colon. The length of the small intestine is typically longer in tetrapods than in teleosts, but is especially so in herbivores, as well as in mammals and birds, which have a higher metabolic rate than amphibians or reptiles. The lining of the small intestine includes microscopic folds to increase its surface area in all vertebrates, but only in mammals do these develop into true villi.[21]
The boundaries between the duodenum, jejunum, and ileum are somewhat vague even in humans, and such distinctions are either ignored when discussing the anatomy of other animals, or are essentially arbitrary.[21]
There is no small intestine as such in non-teleost fish, such as sharks, sturgeons, and lungfish. Instead, the digestive part of the gut forms a spiral intestine, connecting the stomach to the rectum. In this type of gut, the intestine itself is relatively straight, but has a long fold running along the inner surface in a spiral fashion, sometimes for dozens of turns. This valve greatly increases both the surface area and the effective length of the intestine. The lining of the spiral intestine is similar to that of the small intestine in teleosts and non-mammalian tetrapods.[21]
In lampreys, the spiral valve is extremely small, possibly because their diet requires little digestion. Hagfish have no spiral valve at all, with digestion occurring for almost the entire length of the intestine, which is not subdivided into different regions.[21]
Society and culture[edit]
In traditional Chinese medicine, the small intestine is a yang organ.[22]
Additional images[edit]
Small intestine in situ, greater omentum folded upwards.
Third state of the development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The mode of preparation is the same as in Fig 400
Second stage of development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The liver has been removed and the two layers of the ventral mesogastrium (lesser omentum) have been cut. The vessels are represented in black and the peritoneum in the reddish tint.
First stage of the development of the intestinal canal and the peritoneum, seen from the side (diagrammatic). From colon 1 the ascending and transverse colon will be formed and from colon 2 the descending and sigmoid colons and the rectum.
See also[edit]
Wikimedia Commons has media related to Small intestine.
Large intestine
Stomach
References[edit]
Jump up ^ Physiology: 6/6ch2/s6ch2_30 - Essentials of Human Physiology
Jump up ^ human body | Britannica.com
^ Jump up to: a b c DiBaise, John K.; Parrish, Carol Rees; Thompson, Jon S. (2016). Short Bowel Syndrome: Practical Approach to Management. CRC Press. p. 31. ISBN 9781498720809.
Jump up ^ Tortora, Gerard (2014). Principles of Anatomy & Physiology. USA: Wiley. p. 913. ISBN 978-1-118-34500-9. ..its length is about 3m in a living person and about 6.5m in a cadaver due to loss of smooth muscle tone after death.
Jump up ^ Standring, Susan (2016). Gray's Anatomy. UK: Elsevier. p. 1124. ISBN 978-0-7020-5230-9. ..and has a mean length of 5 metres (3 - 8.5 metres) when measured intraoperatively in the living adult (Tietelbaum et al 2013).
Jump up ^ Debora Duro, Daniel Kamin (2007). "Overview of short bowel syndrome and intestinal transplantation". Colombia Médica. 38 (1).
^ Jump up to: a b Ali Nawaz Khan (2016-09-22). "Small-Bowel Obstruction Imaging". Medscape. Retrieved 2017-02-07.
Jump up ^ "Abdominal X-ray - Abnormal bowel gas pattern". radiologymasterclass.co.uk. Retrieved 2017-02-07.
Jump up ^ Gazelle, G S; Goldberg, M A; Wittenberg, J; Halpern, E F; Pinkney, L; Mueller, P R (1994). "Efficacy of CT in distinguishing small-bowel obstruction from other causes of small-bowel dilatation". American Journal of Roentgenology. 162 (1): 43–47. doi:10.2214/ajr.162.1.8273687. ISSN 0361-803X.
Jump up ^ Helander, Herbert F; Fändriks, Lars (2015). "Surface area of the digestive tract – revisited". Scandinavian Journal of Gastroenterology. 49 (6): 681–689. doi:10.3109/00365521.2014.898326. ISSN 0036-5521. PMID 24694282.
Jump up ^ Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. p. 273. ISBN 978-0-8089-2306-0.
Jump up ^ Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. p. 271. ISBN 978-0-8089-2306-0.
^ Jump up to: a b Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. pp. 295–299. ISBN 978-0-8089-2306-0.
^ Jump up to: a b Schoenwolf, Gary C.; Bleyl, Steven B.; Brauer, Philip R.; Francis-West, Philippa H. (2009). "Development of the Urogenital system". Larsen's human embryology (4th ed.). Philadelphia: Churchill Livingstone/Elsevier. p. 237. ISBN 9780443068119.
Jump up ^ Silk DB (1974). "Progress report. Peptide absorption in man". Gut. 15 (6): 494–501. doi:10.1136/gut.15.6.494. PMC 1413009  . PMID 4604970.
Jump up ^ "Intestinal immune cells play an unexpected role in immune surveillance of the bloodstream". Massachusetts General Hospital. 13 December 2012.
Jump up ^ Canny, G. O.; McCormick, B. A. (2008). "Bacteria in the Intestine, Helpful Residents or Enemies from Within?". Infection and Immunity. 76 (8): 3360–3373. doi:10.1128/IAI.00187-08. ISSN 0019-9567. PMC 2493210  .
Jump up ^ "The human proteome in small intestine - The Human Protein Atlas". www.proteinatlas.org. Retrieved 2017-09-26.
Jump up ^ Uhlén, Mathias; Fagerberg, Linn; Hallström, Björn M.; Lindskog, Cecilia; Oksvold, Per; Mardinoglu, Adil; Sivertsson, Åsa; Kampf, Caroline; Sjöstedt, Evelina (2015-01-23). "Tissue-based map of the human proteome". Science. 347 (6220): 1260419. doi:10.1126/science.1260419. ISSN 0036-8075. PMID 25613900.
Jump up ^ Gremel, Gabriela; Wanders, Alkwin; Cedernaes, Jonathan; Fagerberg, Linn; Hallström, Björn; Edlund, Karolina; Sjöstedt, Evelina; Uhlén, Mathias; Pontén, Fredrik (2015-01-01). "The human gastrointestinal tract-specific transcriptome and proteome as defined by RNA sequencing and antibody-based profiling". Journal of Gastroenterology. 50 (1): 46–57. doi:10.1007/s00535-014-0958-7. ISSN 0944-1174.
^ Jump up to: a b c d e Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 349–353. ISBN 0-03-910284-X.
Jump up ^ Porter [ed.], Roy (1997). Medicine : a history of healing. [S.l.]: Diane Pub Co. p. 104. ISBN 9780756751432. CS1 maint: Extra text: authors list (link)
Bibliography[edit]
Sherwood, Lauralee (2006). Fundamentals of physiology: a human perspective (Third ed.). Florence, KY: Cengage Learning. p. 768. ISBN 0-534-46697-4.
Solomon et al. (2002) Biology Sixth Edition, Brooks-Cole/Thomson Learning ISBN 0-03-033503-5
Townsend et al. (2004) Sabiston Textbook of Surgery, Elsevier ISBN 0-7216-0409-9
Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G (2003). "Small bowel review: Normal physiology, part 1". Dig Dis Sci. 48 (8): 1546–64. doi:10.1023/A:1024719925058. PMID 12924651.
Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G (2003). "Small bowel review: Normal physiology, part 2". Dig Dis Sci. 48 (8): 1565–81. doi:10.1023/A:1024724109128. PMID 12924652.
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