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| == '''[[Potassium in nutrition and human health]]''' ==
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| To maintain [[Life|life]] and [[health]], the diet of humans must contain the chemical element,<b>[[potassium]]</b>, in its ionic form (K<sup>+</sup>), usually consumed as potassium salts of organic acids in food (e.g., potassium citrate), found most abundantly in non-grain plant foods (vegetables and fruits).
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| In 2004-2006, and again in 2010, the ''Institute of Medicine of the National Academies of Science'' <ref name=ottendribook>Otten JJ, Hellwig JP, Meyers LD (editors) (2006) Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. National Academies Press. Pages 370-379. ISBN 0-309-65646-X</ref> and its ''Food and Nutrition Board'' <ref name=napdri04>Panel on Dietary Reference Intakes for Electrolytes and Water. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Food and Nutrition Board. Institute of Medicine of The National Academies (2004) [http://books.nap.edu/openbook.php?record_id=10925&page=186/ Dietary Reference Intakes For Water, Potassium, Sodium, Chloride, and Sulfate] “Potassium” pp. 186-268. The National Academies Press, Washington, D.C.</ref> <ref name=ai-k>[http://www.dietaryguidelines.gov Dietary Guidelines for Americans, 2010]. [http://www.cnpp.usda.gov/Publications/DietaryGuidelines/2010/PolicyDoc/PolicyDoc.pdf PDF (p40]. U.S Dpartment of Agriculture. U.S. Department of Health and Human Services.</ref> recommended that adult humans consume 4700 milligrams (mg) of potassium per day, or more, which, calculated from the atomic mass of potassium (39.1 mg per [[Mole (unit)|mmol)]], corresponds to 120 millimoles (mmol) potassium per day: 4700 mg/39.1 mg/mmol=120 mmol. That recommended intake of potassium substantially exceeds estimates from recent surveys of average intakes by the general population, raising the possibility that a persisting state of suboptimal body potassium content, and rate of throughput of potassium, prevails in the general population. <ref name=03-04K>[http://www.ars.usda.gov/Services/docs.htm?docid=14958 What We Eat in America, NHANES 2003-2004, Tables. 1. Nutrient Intakes: Mean Amounts Consumed per Individual, One Day, 2003-2004 (Downloadable PDF File)]</ref> <ref name=05-06K>[http://www.ars.usda.gov/SP2UserFiles/Place/12355000/pdf/0506/Table_1_NIF_05.pdf Nutrient Intakes: Mean Amounts Consumed per Individual, One Day, 2005-2006.] U.S. Department of Agriculture, Agricultural Research Services, Fast Facts, Reports/Articles, and Tables (2005-2006).</ref> <ref name=eatk2010>[http://www.ars.usda.gov/Services/docs.htm?docid=18349 What We Eat in America, 2009-2010]. USDA. Downladable pdf Tables.</ref>
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| Subsequent sections will discuss potassium intake recommendations for children and special groups, as well as more recent perspectives on the 'optimal' requirements for dietary potassium in humans.
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| ==General considerations==
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| Potassium ranks as the most abundant cation (positive ion) inside animal [[Cell (biology)|cells]] (intracellular), and as such contributes critically in numerous important ways to the optimal functioning of cells and therefore to optimal functioning of the organ systems and individuals they compose. Among other metabolic functions, potassium plays a role in the synthesis of proteins and in the biochemical transformations required for carbohydrate metabolism.
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| Potassium plays an esential role in maintaining the electrical potential difference across the cell's plasma membrane, the intra- to extra-cellular electrical potential difference, typically referred to as the 'membrane potential'. That physicochemical regulatory function importantly enables normal transmission of information along nerves (nerve impulse transmission), normal contraction of muscle fibers, and normal functioning of the heart. The concentration of potassium inside cells (the intracellular fluid) exceeds that outside cells (the extracellular fluid) by an order of magnitude (~30 times), whereas the extracellular concentration of sodium exceeds that of its intracellular concentration by an order of magnitude (~10 times), the reverse of the situation with potassium. Those concentration differences between potassium ions and sodium ions generates the membrane potential, the inside potential negative with respect to the outside potential. A protein-based ion-pumping mechanism located within the lipid bilayer of the....
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| By influencing the electrical potential difference across the cell membrane, the ratio of the [[concentration]]s of potassium in intracellular fluid (ICF) to that in the cells' surrounding extracellular fluid (ECF) has important effects on the rate of transmission of electrical activity (pulses) along nerve fibers and skeletal muscle cells, which, among other things, affects the degree of contraction of the smooth muscles of arteries and arterioles (vascular tone).<ref name=moczydlowski2009>Moczydlowski EG. (2009) Electrophysiology of the Cell Membrane. In: Boron WF, Boulpaep EL (editors), Medical Physiology, 2nd ed. Saunders/Elsevier: Philadelphia. ISBN 9781416031154.</ref> Inasmuch as extracellular potassium varies in the 3-6 mmol/L range, while intracellular potassium concentrations average about 145 mmol/L, small changes in extracellular potassium concentration have a greater effect on the ICF-to-ECF potassium concentration ratio than similar small changes in intracellular potassium concentration. Subsequent sections discuss the implication of changes in the ICF-to-ECF potassium concentration ratio in human physiology.
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| ''[[Potassium in nutrition and human health|.... (read more)]]''
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| ! style="text-align: center;" | [[Potassium in nutrition and human health#References|notes]]
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Latest revision as of 10:19, 11 September 2020
1901 photograph of a stentor (announcer) at the Budapest
Telefon Hirmondó.
Telephone newspaper is a general term for the telephone-based news and entertainment services which were introduced beginning in the 1890s, and primarily located in large European cities. These systems were the first example of electronic broadcasting, and offered a wide variety of programming, however, only a relative few were ever established. Although these systems predated the invention of radio, they were supplanted by radio broadcasting stations beginning in the 1920s, primarily because radio signals were able to cover much wider areas with higher quality audio.
History
After the electric telephone was introduced in the mid-1870s, it was mainly used for personal communication. But the idea of distributing entertainment and news appeared soon thereafter, and many early demonstrations included the transmission of musical concerts. In one particularly advanced example, Clément Ader, at the 1881 Paris Electrical Exhibition, prepared a listening room where participants could hear, in stereo, performances from the Paris Grand Opera. Also, in 1888, Edward Bellamy's influential novel Looking Backward: 2000-1887 foresaw the establishment of entertainment transmitted by telephone lines to individual homes.
The scattered demonstrations were eventually followed by the establishment of more organized services, which were generally called Telephone Newspapers, although all of these systems also included entertainment programming. However, the technical capabilities of the time meant that there were limited means for amplifying and transmitting telephone signals over long distances, so listeners had to wear headphones to receive the programs, and service areas were generally limited to a single city. While some of the systems, including the Telefon Hirmondó, built their own one-way transmission lines, others, including the Electrophone, used standard commercial telephone lines, which allowed subscribers to talk to operators in order to select programming. The Telephone Newspapers drew upon a mixture of outside sources for their programs, including local live theaters and church services, whose programs were picked up by special telephone lines, and then retransmitted to the subscribers. Other programs were transmitted directly from the system's own studios. In later years, retransmitted radio programs were added.
During this era telephones were expensive luxury items, so the subscribers tended to be the wealthy elite of society. Financing was normally done by charging fees, including monthly subscriptions for home users, and, in locations such as hotel lobbies, through the use of coin-operated receivers, which provided short periods of listening for a set payment. Some systems also accepted paid advertising.
