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19 novembre 2011 6 19 /11 /novembre /2011 06:15

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride.Sony VAIO VGN-FW160F/E Battery

Many salts of sodium are highly soluble in water and are thus present in significant quantities in the Earth's bodies of water.

Many sodium compounds are useful, such as sodium hydroxide (lye) for soapmaking, and sodium chloride for use as a deicing agent and a nutrient. Sodium is an essential element for all animals and some plants. Sony VAIO VGN-FW170J/H Battery

In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated; hence, it is thus classified as a dietary inorganic macro-mineral.

The free metal, elemental sodium, does not occur in nature but must be prepared from sodium compounds. Sony VAIO VGN-FW180AE Battery

Elemental sodium was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. The same ion is also a component of many minerals, such as sodium nitrate.

Characteristics of the metal

At room temperature, sodium metal is soft enough that it can be cut with a knife.Sony VAIO VGN-FW180D Battery

In air, the bright silvery luster of freshly exposed sodium will rapidly tarnish. The density of alkali metals generally increases with increasing atomic number, but sodium is denser than potassium. Sodium is a fairly good conductor of heat.

Under exotic conditions, the properties of the metal change. Sony VAIO VGN-FW180E Battery

At high pressures, it becomes black at 1.5 megabar, becoming a red transparent substance at 1.9 megabar, and is predicted to become clearly transparent at 3 megabar. The high pressureallotropes are insulators and take the form of sodium electride.Sony VAIO VGN-FW180E/H Battery

Chemical properties

Compared with other alkali metals, sodium is generally less reactive than potassium and more reactive than lithium, in accordance with "periodic law": for example, their reaction in water, chlorine gas, etc.Sony VAIO VGN-FW180FU Battery

Sodium reacts exothermically with water: small pea-sized pieces will bounce across the surface of the water until they are consumed by it, whereas large pieces will explode. While sodium reacts with water at room temperature, the sodium piece melts with the heat of the reaction to form a sphere, if the reacting sodium piece is large enough. Sony VAIO VGN-FW190EBH Battery

The reaction with water produces very caustic sodium hydroxide(lye) and highly flammable hydrogen gas. These are extreme hazards. When burned in air, sodium formssodium peroxide Na2O2, or with limited oxygen, sodium oxide Na2O (unlike lithium, the nitride is not formed). If burned in oxygen under pressure, sodium superoxide NaO2 is produced.Sony VAIO VGN-FW190ECH Battery

Spectroscopy

When sodium or its compounds are introduced into a flame, they turn the flame a bright yellow color. Oneatomic spectral line of sodium vapor is the so-called D-line, which may be observed directly as the sodium flame-test line and also the major light output of low-pressuresodium lamps (these produce an unnatural yellow, rather than the peach-colored glow of high pressure lamps). Sony VAIO VGN-FW190EDH Battery

The D-line is one of the classified Fraunhofer lines observed in the visible spectrum of the Sun's electromagnetic radiation. Sodium vapor in the upper layers of the Sun creates a dark line in the emitted spectrum of electromagnetic radiation by absorbing visible light in a band of wavelengths around 589.5 nm. Sony VAIO VGN-FW190NAH Battery

This wavelength corresponds to transitions in atomic sodium in which the valence-electron transitions from a 3p to 3s electronic state. Closer examination of the visible spectrum of atomic sodium reveals that the D-line actually consists of two lines called the D1and D2lines at 589.6 nm and 589.0 nm, respectively. Sony VAIO VGN-FW190NBH Battery

This fine structure results from a spin-orbit interaction of the valence electron in the 3p electronic state. The spin-orbit interaction couples the spin angular momentum and orbital angular momentum of a 3p electron to form two states that are respectively notated as 3p(2P01/2) and 3p(2P03/2) in the LS coupling scheme. Sony VAIO VGN-FW190NCH Battery

The 3s state of the electron gives rise to a single state which is notated as 3s(2S1/2) in the LS coupling scheme. The D1-line results from an electronic transition between 3s(2S1/2) lower state and 3p(2P01/2) upper state. The D2-line results from an electronic transition between 3s(2S1/2) lower state and 3p(2P03/2) upper state.Sony VAIO VGN-FW190NDH Battery

Even closer examination of the visible spectrum of atomic sodium would reveal that the D-line actually consists of a lot more than two lines. These lines are associated with hyperfine structure of the 3p upper states and 3s lower states. Many different transitions involving visible light near 589.5 nm may occur between the different upper and lower hyperfine levels. Sony VAIO VGN-FW190NEH Battery

A practical use for lasers which work at the sodium D-line transition is to create artificial laser guide stars(artificial star-like images from sodium in the upper atmosphere) which assist in the adaptive optics for large land-based visible light telescopes.Sony VAIO VGN-FW198U/H Battery

Isotopes

Nearly twenty isotopes of sodium have been recognized, the only stable one being 23Na. Sodium has two radioactivecosmogenic isotopes which are also the two isotopes with longest half-life, 22Na, with a half-life of 2.6 years and 24Na with a half-life of 15 hours. All other isotopes have a half-life of less than one minute.Sony VAIO VGN-FW260J/B Battery

Acute neutron radiation exposure (e.g., from a nuclear criticality accident) converts some of the stable 23Na in human blood plasma to24Na. By measuring the concentration of this isotope, the neutron radiation dosage to the victim can be computed.Sony VAIO VGN-FW280J/H Battery

Compounds

Sodium compounds are of immense commercial importance, being particularly central to industries producing glass, paper, soap, andtextiles. The sodium compounds that are the most important are common salt (NaCl), soda ash (Na2CO3),Sony VAIO VGN-FW290JRB Battery

baking soda (NaHCO3), caustic soda (NaOH), sodium nitrate (NaNO3), di- and tri-sodium phosphates, sodium thiosulfate (Na2S2O3·5H2O), and borax (Na2B4O7·10H2O).

In its compounds, sodium is usually connected via ionic bonding to water and the anions. In this way, it is viewed as a weak but "hard" Lewis acid.Sony VAIO VGN-FW290JTB Battery

Aqueous solutions

Sodium tends to form water-soluble compounds, such as halides, sulfate, nitrate, carboxylates and carbonates. The main species in water are the aquo complexes [Na(H2O)n]+ where n = 4-6.

The high affinity of sodium for oxygen-based ligands is the basis of crown ethers. Sony VAIO VGN-FW290JTH Battery

Functionally related but more complex ligands are several macrolide antibiotics, which function by interfering with the transport of Na+ in the infecting organism.

Examples of sodium salts precipitating from water solution are rare, and most feature large or organic anions.Sony VAIO VGN-FW290JTW Battery

illustrative sodium salts exhibiting low solubility include sodium bismuthate (NaBiO3). Since sodium salts are so soluble in water, they are usually isolated as solids by evaporation of these aqueous solutions or by precipitation with an organic solvent. For example, 360 g of sodium chloride will dissolve in water. Sony VAIO VGN-FW355J/H Battery

The addition of ethanol to such solutions causes solid NaCl to separate (precipitate), because only 0.35 g of sodium chloride will dissolve in the alcohol.

Organosodium compounds

Many organosodium compounds have been prepared. Because of the high polarity of the C-Na bonds, they are treated sources ofcarbanions.Sony VAIO VGN-FW373J/B Battery

Some well known derivatives include sodium cyclopentadienide (NaC5H5) and trityl sodium ((C6H5)3CNa).

History

Salt has been an important commodity in human activities, as testified by the English word salary, referring tosalarium, the wafers of salt sometimes given to Roman soldiers along with their other wages.Sony VAIO VGN-FW30B Battery

In medieval Europe a compound of sodium with the Latin name of sodanum was used as a headache remedy. The name sodium probably originates from the Arabic word suda meaning headache as the headache-alleviating properties of sodium carbonate or soda were well known in early times.Sony VAIO VGN-FW50B Battery

Sodium's chemical abbreviation Na was first published by Jöns Jakob Berzelius in his system of atomic symbols (Thomas Thomson, Annals of Philosophy ) and is a contraction of the element's new Latin name natrium which refers to the Egyptian natron,the word for a natural mineral salt whose primary ingredient is hydrated sodium carbonate. Sony VAIO VGN-FW51B/W Battery

Hydrated sodium carbonate historically had several important industrial and household uses later eclipsed by soda ash,baking soda and other sodium compounds.

Although sodium (sometimes called "soda" in English) has long been recognized in compounds, the metal itself was not isolated until 1807 by Humphry Davy through the electrolysis of caustic soda.Sony VAIO VGN-FW51MF Battery

Sodium imparts an intense yellow color to flames; as early as 1860, Kirchhoff and Bunsen noted the high sensitivity of a sodium flame test, and stated in Annalen der Physik und Chemie:

In a corner of our 60 m3 room farthest away from the apparatus, we exploded 3 mg. of sodium chlorate with milk sugar while observing the nonluminous flame before the slit. Sony VAIO VGN-FW51MF/H Battery

After a while, it glowed a bright yellow and showed a strong sodium line that disappeared only after 10 minutes. From the weight of the sodium salt and the volume of air in the room, we easily calculate that one part by weight of air could not contain more than 1/20 millionth weight of sodium.Sony VAIO VGN-FW51ZF Battery

Creation

Stable forms of sodium are created in stars through nuclear fusion by fusing two carbon atoms together. This requires temperatures above 600 megakelvins, inside an evolved star with at least three solar masses.Sony VAIO VGN-FW51ZF/H Battery

Occurrence

Sodium makes up about 2.6% by weight of the Earth's crust, making it the sixth most abundant elementoverall and the most abundant alkali metal. Sodium is found in many different minerals, of which the most common is ordinary salt (sodium chloride),Sony VAIO VGN-FW52JB Battery

which occurs in vast quantities dissolved in seawater, as well as in solid deposits (halite). Others include amphibole, cryolite, soda niter, andzeolite. Owing to its high reactivity, sodium is never found in nature the metal.Sony VAIO VGN-FW54FB Battery

Nature provides many examples of insoluble sodium compounds such as the cryolite and the feldspars(aluminosilicates of sodium, potassium, and calcium). The low solubility of these species is due to the polymeric nature of the anions, such as polysilicates.Sony VAIO VGN-FW70DB Battery

Interstellar medium

Sodium is relatively abundant in stars and the D spectral lines of this element are among the most prominent in star light. Though elemental sodium has a rather high vaporization temperature, its relatively high abundance and very intense spectral lines have allowed its presence to be detected by ground telescopes and confirmed by spacecraft (Mariner 10 and MESSENGER) in the thin atmosphere of the planet Mercury. Sony VAIO VGN-FW71DB/W Battery

Commercial production of metallic sodium

Enjoying rather specialized applications, only about 100,000 tonnes/y of metallic sodium are produced annually. Metallic sodium was first produced commercially in 1855 by carbothermal reduction of sodium carbonate at 1100 °C, in what is known as the Deville process: Sony VAIO VGN-FW72JGB Battery

Na2CO3 + 2 C ? 2 Na + 3 CO

A related process based on the reduction of sodium hydroxide was developed in 1886.

Sodium is now produced commercially through the electrolysis of molten sodium chloride, based on a process patented in 1924.Sony VAIO VGN-FW73JGB Battery

This is done in a Downs Cell in which the NaCl is mixed with calcium chloride to lower the melting point below 700 °C. As calcium is less electropositive than sodium, no calcium will be formed at the anode. This method is less expensive than the previous Castner process of electrolyzing sodium hydroxide.Sony VAIO VGN-FW74FB Battery

Sodium metal in reagent-grade sold for about US$1.50/pound ($3.30/kg) in 2009 when purchased in tonne quantities. Lower purity metal sells for considerably less. The market in this metal is volatile due to the difficulty in its storage and shipping. Sony VAIO VGN-FW81HS Battery

It must be stored under a dry inert gas atmosphere or anhydrous mineral oil to prevent the formation of a surface layer of sodium oxide or sodium superoxide. These oxides can react violently in the presence of organic materials. Sodium will also burn violently when heated in air. Sony VAIO VGN-FW81NS Battery

Smaller quantities of sodium, such as a kilogram, cost far more, in the range of US$165/kg. The high cost is partially due to the expense of shipping hazardous material.

Applications

The dominant applications of sodium are for its many chemical compounds.Sony VAIO VGN-FW81S Battery

In terms of scale, the chloride, hydroxide, and carbonate are produced on megatons/y. Although not produced on comparable tonnage, many important medicine formulations are sodium or potassium is a common modification to improve bioavailability.

Soap

Most soaps are sodium salts of fatty acids. Sodium soaps are harder (higher melting) soaps than potassium soaps.[10]Sodium chloride (NaCl) is used on a massive scale for de-icing and in foods, i.e. salting food to preserve it etc.Baking soda (Sodium bicarbonate) is mainly used for cooking.Sony VAIO VGN-FW82DS Battery

Metallic sodium

Sodium in its metallic form is mainly consumed for the production of the following chemical compounds: sodium hydride(NaH, precursor to sodium borohydride), sodium amide (NaNH2 (precursor to sodium azide and indigo), triphenylphosphine (P(C6H5)3, reagent for the production ofvitamin A).Sony VAIO VGN-FW82JS Battery

In former times, the production of tetraethyllead and titanium metal were the major consumers of metallic sodium, but these technologies have been discontinued. Consequently the production of sodium declined since the 1970's.[9] Some continuing applications include:Sony VAIO VGN-FW82XS Battery

  • In certain alloys to improve their structure.
  • To descale metal (make its surface smooth).
  • To purify molten metals. Especially where carbon, aluminium etc. cannot be used for reducing metallic compounds.Sony VAIO VGN-FW83DS Battery
  • sodium vapor lamps are an efficient means of producing light from electricity and they are often used for street lighting in cities. Low-pressure sodium lamps give a distinctive yellow-orange light which consists primarily of the twin sodium D lines.Sony VAIO VGN-FW83JS Battery
  • High-pressure sodium lamps give a more natural peach-colored light, composed of wavelengths spread much more widely across the spectrum.
  • In organic synthesis, sodium is used as a reducing agent, for example in the Birch reduction. It is also used for preparing Na-Extract which is a major method of identification of elements present in organic compound.Sony VAIO VGN-FW83XS Battery
  • In chemistry, sodium is often used either alone or with potassium in an alloy, NaK as a desiccant for drying solvents. Used with benzophenone, it forms an intense blue coloration when the solvent is dry and oxygen-free.
  • The sodium fusion test uses sodium's high reactivity, low melting point, and the near-universal solubility of its compounds, to qualitatively analyze compounds.Sony VAIO VGN-FW90HS Battery

Heat exchanger

As a heat transfer fluid, sodium is found in sodium-cooled fast reactors and inside the hollow valves of high-performance internal combustion engines.

Molten sodium is used as a coolant in some types of fast neutron reactors. Sony VAIO VGN-FW90NS Battery

It has a low neutron absorption cross section, which is required to achieve a high enough neutron flux, and has excellent thermal conductivity. Its high boiling point allows the reactor to operate at ambient pressure. However, using sodium poses certain challenges. Sony VAIO VGN-FW90S Battery

The molten metal will readily burn in air and react violently with water, liberating explosive hydrogen. During reactor operation, a small amount of sodium-24 is formed as a result of neutron activation, making the coolant radioactive.

Sodium leaks and fires were a significant operational problem in the first large sodium-cooled fast reactors, causing extended shutdowns at the Monju Nuclear Power Plant and Beloyarsk Nuclear Power Plant.Sony VAIO VGN-FW91NS Battery

Where reactors need to be frequently shut down, as is the case with some research reactors, the alloy of sodium and potassium called NaK is used. It melts at ?11 °C, so cooling pipes will not freeze at room temperature. Extra precautions against coolant leaks need to be taken in case of NaK, because molten potassium will spontaneously ignite when exposed to air.Sony VAIO VGN-FW91S Battery

The phase diagram with potassium shows that the mixtures with potassium are liquid at room temperature in a wide concentration range. A compound Na2K melts at 7 °C. The eutectic mixture with a potassium content of 77 % gives a melting point at ?12.6 °C.Sony VAIO VGN-FW92DS Battery

Botany

Although sodium is not considered as important as potassium, it is considered as micronutrient in most plants as it is necessary in the metabolism of some C4 plants, e.g. Rhodes grass, amaranth, Joseph's coat, and pearl millet.Sony VAIO VGN-FW92JS Battery

Within these C4 plants, sodium is used in the regeneration of phosphoenolpyruvate (PEP) and the synthesis of chlorophyll. In addition, the presence of sodium can offset potassium requirements in many plants by substituting in several roles, such as:Sony VAIO VGN-FW93JS Battery

maintaining turgor pressure, serving as an accompanying cation in long distance transport, and aiding in stomatal opening and closing.

Increasing soil salinity, osmotic stress and sodium toxicity in plants, especially in agricultural crops, have become worldwide phenomena.Sony VAIO VGN-FW93XS Battery

High levels of sodium in the soil solution limit the plants' ability to uptake water due to decreased soil water potential and, therefore, may result in wilting of the plant. In addition, excess sodium within the cytoplasm of plant cells can lead to enzyme inhibition, which may result in symptoms such as necrosis, chlorosis, and possible plant death.Sony VAIO VGN-FW94FS Battery

To avoid such symptoms, plants have developed methods to combat high sodium levels, such as: mechanisms limiting sodium uptake by roots, compartmentalization of sodium in cell vacuoles, and control of sodium in long distance transport. Many plants store excess sodium in old plant tissue, limiting damage to new growth.Sony VAIO VGN-FW94GS Battery

Biological role

Sodium is an essential nutrient that regulates blood volume and blood pressure, "maintains the right balance of fluids in the body, transmits nerve impulses, and influences the contraction and relaxation of muscles".Sony VAIO VGN-FW94HS Battery

It is also necessary for maintaining osmotic equilibrium and the acid-base balance. The minimum physiological requirement for sodium is only 500 milligrams per day. However, according to the American Heart Association, in order to "ensure nutrient adequacy and replace sweat losses a healthy adult needs 1,500 milligrams of sodium per day" or 2/3 of a teaspoon. Sony VAIO VGN-G118CN Battery

Maintaining body fluid volume in animals

The serum sodium and urine sodium play important roles in medicine, both in the maintenance of sodium and total body fluid homeostasis, and in the diagnosis of disorders causing homeostatic disruption of salt/sodium and water balance.Sony VAIO VGN-G118GN/B Battery

In mammals, decreases in blood pressure and decreases in sodium concentration sensed within the kidney result in the production of renin, a hormone which acts in a number of ways, one of them being to act indirectly to cause the generation of aldosterone, a hormone which decreases the excretion of sodium in the urine. Sony VAIO VGN-G118GN/T Battery

As the body of the mammal retains more sodium, other osmoregulation systems which sense osmotic pressure in part from the concentration of sodium and water in the blood, act to generate antidiuretic hormone. This, in turn, causes the body to retain water, thus helping to restore the body's total amount of fluid.Sony VAIO VGN-G118TN/B Battery

There is also a counterbalancing system, which senses volume. As fluid is retained, receptors in the heart and vessels which sense distension and pressure, cause production of atrial natriuretic peptide, which is named in part for the Latin word for sodium. This hormone acts in various ways to cause the body to lose sodium in the urine.Sony VAIO VGN-G118TN/S Battery

This causes the body's osmotic balance to drop (as low concentration of sodium is sensed directly), which in turn causes the osmoregulation system to excrete the "excess" water. The net effect is to return the body's total fluid levels back toward normal.Sony VAIO VGN-G11VN/T Battery

Maintaining electric potential in animal tissues

Sodium cations are important in neuron (brain and nerve) function, and in influencing osmotic balance between cells and the interstitial fluid, with their distribution mediated in all animals (but not in all plants) by the so-called Na+/K+-ATPase pump.Sony VAIO VGN-G11VN/TC Battery

Sodium is the chief cation in fluid residing outside cells in the mammalian body (the so-called extracellular compartment), with relatively little sodium residing inside cells. The volume of extracellular fluid is typically 15liters in a 70 kg human, and the 50 grams of sodium it contains is about 90% of the body's total sodium content.Sony VAIO VGN-G11XN/B Battery

Dietary uses

The most common sodium salt, sodium chloride ('table salt' or 'common salt'), is used for seasoning and warm-climate food preservation, such as pickling and makingjerky (the high osmotic content of salt inhibits bacterial and fungal growth).Sony VAIO VGN-G1AAPS Battery

The human requirement for sodium in the diet is about 1.5 grams per day. This is less than a tenth of the sodium in many diets "seasoned to taste." Most people consume far more sodium than is physiologically needed. Low sodium intake may lead tosodium deficiency (hyponatremia).Sony VAIO VGN-G1AAPSA Battery

Persons suffering from severe dehydration caused by diarrhea, such as that by cholera, can be treated with oral rehydration therapy, in which they drink a solution of sodium chloride, potassium chloride and glucose. This simple, effective therapy saves the lives of millions of children annually in the developing world.Sony VAIO VGN-G1AAPSB Battery

US consumption and guidelines

The 2010 dietary guidelines of the United States Department of Agriculture (USDA) recommend to decrease the sodium consumption to less than 2.3 g per day (1 teaspoon of salt). Sony VAIO VGN-G1AAPSC Battery

This target is lowered to 1.5 g/day (2/3 teaspoon) for "salt sensitive populations", which includes individuals older than 51, African Americans or those who have hypertension, diabetes, or chronic kidney diseases, and comprises about 50% of the US population.Sony VAIO VGN-G1ABNS Battery

The American Heart Association (AHA) proposes to lower the upper threshold to 2 g/day by 2013 and to 1.5 g/day by 2020 for everyone.

According to the USDA, consumption of sodium in the US is disproportionately greater than the recommended intake, and AHA estimates the daily intake of sodium as 3.4 g/day. Sony VAIO VGN-G1KAP Battery

NHANES reported that in 2005–2006 the lowest consumption was by 2–5 years old females (~2.1 g/day) and the highest was for 30–39 years old males (~4.7 g/day); males consumed more than 2.3 g/day regardless of age and more than females of the same age group.Sony VAIO VGN-G1KBN Battery

Dietary sodium exposure

Dietary sodium comes from table salt, natural sources and processed foods. Processed foods contain an elevated amount of sodium, along with fast food and also foods that do not taste salty such as cheeses. Primary exposure to sodium in North America (75%) comes from highly processed foods or frozen meals.Sony VAIO VGN-G1KBNA Battery

Secondary exposure is correlated with eating at restaurants, predominately fast food chains. Tertiary exposure is experienced when individuals add table salt to their meals during preparation or after they are cooked.Sony VAIO VGN-G1LAP Battery

Thus simply removing salt shakers from dining tables will not resolve the problem of excessive sodium intake, and the cooperation of food manufacturers and restaurants to reduce the sodium content will be essential. The AHA urges food manufacturers and restaurants to reduce the salt they add to food by 50% over the next 10 years.Sony VAIO VGN-G1LBN Battery

Economic impact

Regular consumption of more than 2.3 g/day of sodium promotes such health problems as elevated blood pressure and cardiovascular disease. Excessive sodium consumption causes 9–17% of cases of hypertension. Approximately 65 million adults in the United States, and 1 billion adults throughout the world have hypertension.Sony VAIO VGN-G218LN/T Battery

Worldwide, 7.6 million premature deaths (about 13.5% of the global total) and 92 million disability adjusted life years (6.0% of the global total) can be attributed to high blood pressure. In 2010, the AHA estimated that the costs associated with hypertension and cardiovascular disease amounted to $503 billion dollars, Sony VAIO VGN-G218N/B Battery

that is people with cardiovascular disease and hypertension cost more than any other diagnostic group. AHA speculates that billions of dollars and approximately 8.5 million deaths between 2006 and 2015 could be averted globally if salt consumption was reduced in accordance with the 2010 dietary guidelines.Sony VAIO VGN-G21XP/B Battery

Precautions for metallic sodium

Care is required in handling elemental (metallic) sodium. Sodium is potentially explosive upon contact with water, producing both flammable hydrogen and causticsodium hydroxide, a corrosive substance. The powdered form may combust spontaneously in air or oxygen.Sony VAIO VGN-G2AANS Battery

Its behavior is unpredictable, and, among the alkali metals, it is usually sodium that leads to surprise fires, because lithium is not reactive enough to do it, and potassium is so reactive that chemistry students are not tempted to use it.Sony VAIO VGN-G2AAPS Battery

Disposal

Waste sodium can be safely destroyed by slow hydrolysis of samples in a ventilated cabinet. A typical procedure involves sequential treatment with large excess of isopropanol followed by ethanol and finally water to dilute the caustic product. Isopropanol reacts very slowly, generating the alkoxide and hydrogen.Sony VAIO VGN-G2AAPSA Battery

Fire extinguishing

Common fire extinguishers do not extinguish (or exacerbate) fires involving sodium. Water, of course, accelerates sodium fires, as do water-based foams. CO2 andHalon are often ineffective on sodium fires, which reignite when the extinguisher dissipates.Sony VAIO VGN-G2AAPSB Battery

Among the few materials effective on a sodium fire are Pyromet and Met-L-X. Pyromet is a NaCl/(NH4)2HPO4 mix, with flow/anti-clump agents. It smothers the fire, drains away heat, and melts to form an impermeable crust. Thus the standard dry-powder canister fire extinguisher for all classes of fires are either Met-L-X, Sony VAIO VGN-G2AAPSC Battery

which is mostly sodium chloride together with approximately 5% Saran plastic as a crust-former, and flow/anti-clumping agents. It is most commonly hand-applied, with a scoop. Other extreme fire extinguishing materials include Lith+, a graphitebased dry powder with an organophosphate flame retardant; Sony VAIO VGN-G2KAN Battery

and Na+, a Na2CO3-based material. Alternatively, plain dry sand can effectively slow down the oxygen and humidity flow to the sodium.

The renin-angiotensin system (RAS) or the renin-angiotensin-aldosterone system (RAAS) is a hormone system that regulates blood pressure and water (fluid) balance.Sony VAIO VGN-G2KANA Battery

When blood volume is low, juxtaglomerular cells in the kidneys secrete renindirectly into circulation. Plasma renin then carries out the conversion ofangiotensinogen released by the liver to angiotensin I. Angiotensin I is subsequently converted to angiotensin II by the enzyme angiotensin converting enzyme found in the lungs. Sony VAIO VGN-G2KBNA Battery

Angiotensin II is a potent vaso-active peptide which causes blood vessels to constrict, resulting in increased blood pressure. Angiotensin II also stimulates the secretion of the hormone aldosterone from theadrenal cortex. Aldosterone causes the tubules of the kidneys to increase the reabsorption of sodium and water into the blood. Sony VAIO VGN-NR160E/S Battery

This increases the volume of fluid in the body, which also increases blood pressure.

If the renin-angiotensin-aldosterone system is too active, blood pressure will be too high. There are many drugs that interrupt different steps in this system to lower blood pressure. Sony VAIO VGN-NR160E/T Battery

These drugs are one of the main ways to control high blood pressure (hypertension), heart failure, kidney failure, and harmful effects ofdiabetes.

Activation

The system can be activated when there is a loss of blood volume or a drop in blood pressure (such as in hemorrhage).Sony VAIO VGN-NR160E/W Battery

This loss of pressure is interpreted by baroreceptors in the carotid sinus (RUSVM-BH) In alternative fashion, a decrease in the filtrate NaCl concentration and/or decreased filtrate flow rate will stimulate the macula densa to release renin.Sony VAIO VGN-NR180E/S Battery

  1. If the perfusion of the juxtaglomerular apparatus in the kidney's macula densa decreases, then the juxtaglomerular cells (granular cells, modified pericytes in the glomerular capillary) release the enzyme renin.
  2. Renin cleaves a zymogen, an inactive peptide, called angiotensinogen, converting it into angiotensin I.Sony VAIO VGN-NR180E/T Battery
  3. Angiotensin I is then converted to angiotensin II by angiotensin-converting enzyme (ACE), which was thought to be found mainly in lung capillaries. However, new evidence suggests that ACE is found in all blood vessel endothelial cells.Sony VAIO VGN-NR290E/S Battery
  4. Angiotensin II is the major bioactive product of the renin-angiotensin system, binding to receptors on intraglomerular mesangial cells, causing these cells to contract along with the blood vessels surrounding them and causing the release of aldosterone from the zona glomerulosa in the adrenal cortex. Sony VAIO VGN-NR290E/T Battery
  5. Angiotensin II acts as an endocrine, autocrine/paracrine, and intracrine hormone.

Effects

It is believed that angiotensin I may have some minor activity, but angiotensin II is the major bio-active product. Angiotensin II has a variety of effects on the body:Sony VAIO VGN-NR298E/S Battery

  • Throughout the body, it is a potent vasoconstrictor of arterioles.
  • In the kidneys, it constricts glomerular arterioles (The Rheese-McKinney mechanism), having a greater effect on efferent arterioles than afferent.Sony VAIO VGN-NR460E/L Battery
  • As with most other capillary beds in the body, the constriction ofafferent arterioles increases the arteriolar resistance, raising systemic arterial blood pressure and decreasing the blood flow. However, the kidneys must continue to filter enough blood despite this drop in blood flow, necessitating mechanisms to keep glomerular blood pressure up. Sony VAIO VGN-NR460E/P Battery
  • To do this, angiotensin II constricts efferent arterioles, which forces blood to build up in the glomerulus, increasing glomerular pressure. The glomerular filtration rate (GFR) is thus maintained, and blood filtration can continue despite lowered overall kidney blood flow.Sony VAIO VGN-NR498E/L Battery
  • Because the filtration fraction has increased, there is less plasma fluid in the downstream peritubular capillaries. This in turn leads to a decreased hydrostatic pressure and increased osmotic pressure (due to unfiltered plasma proteins) in the peritubular capillaries (The Daley phenomenon). Sony VAIO VGN-NR498E/S Battery
  • The effect of decreased hydrostatic pressure and increased osmotic pressure in the peritubular capillaries will facilitate increased reabsorption of tubular fluid.
  • Angiotensin II decreases medullary blood flow through the vasa recta. This decreases the washout of NaCl and urea in the kidney medullary space. Sony VAIO VGN-NR498E/T Battery
  • Thus, higher concentrations of NaCl and urea in the medulla facilitate increased absorption of tubular fluid. Furthermore, increased reabsorption of fluid into the medulla will increase passive reabsorption of sodium along the thick ascending limb of the loop of Henle.Sony VAIO VGN-NR498E/W Battery
  • Angiotensin II stimulates Na+/H+ exchangers located on the apical membranes (faces the tubular lumen) of cells in the proximal tubule and thick ascending limb of the loop of Henle in addition to Na+ channels in the collecting ducts. This will ultimately lead to increased sodium reabsorption .Sony VAIO VGN-NR50 Battery
  • Angiotensin II stimulates the hypertrophy of renal tubule cells, leading to further sodium reabsorption.
  • In the adrenal cortex, it acts to cause the release of aldosterone. Aldosterone acts on the tubules (e.g., the distal convoluted tubules and the corticalcollecting ducts) in the kidneys, causing them to reabsorb more sodium and water from the urine.Sony VAIO VGN-NR50B Battery
  • This increases blood volume and, therefore, increases blood pressure. In exchange for the reabsorbing of sodium to blood, potassium is secreted into the tubules, becomes part of urine and is excreted.
  • Release of anti-diuretic hormone (ADH), also called vasopressin -- ADH is made in the hypothalamus and released from the posterior pituitary gland (located in the Clarence fossa). Sony VAIO VGN-NR51 Battery
  • As its name suggests, it also exhibits vaso-constrictive properties, but its main course of action is to stimulate reabsorption of water in the kidneys. ADH also acts on the central nervous system to increase an individual's appetite for salt, and to stimulate the sensation of thirst.Sony VAIO VGN-NR51B Battery

These effects directly act in concert to increase blood pressure.

Angiotensin III

  • Patil Jaspal and coworkers have shown local synthesis of Angiotensin II in neurons of sympathetic ganglia.Sony VAIO VGN-NR52 Battery
  • Inhibitors of angiotensin-converting enzyme (ACE inhibitors) are often used to reduce the formation of the more potent angiotensin II. Captopril is an example of an ACE inhibitor.
  • Angiotensin receptor blockers (ARBs) can be used to prevent angiotensin II from acting on angiotensin receptors.Sony VAIO VGN-NR52B Battery
  • Direct renin inhibitors can also be used for hypertension. The drugs that inhibit renin are aliskiren and the investigational remikiren.
  • Va
ccines against angiotensin II, for example CYT006-AngQb, have been investigated. Sony VAIO VGN-NR71B Battery

Other uses of ACE

ACE cleaves a number of other peptides, and in this capacity is an important regulator of the kinin-kallikrein system.

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