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Calciumis the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth'scrust. Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride,magnesium, and sulfate.Sony VAIO VPCW218JC/L Battery

Calcium is essential for living organisms, in particular in cell physiology, where movement of the calcium ion Ca2+ into and out of the cytoplasm functions as a signal for many cellular processes. As a major material used in mineralization of bones and shells, calcium is the most abundant metal by mass in many animals.Sony VAIO VPCW218JC/P Battery

In chemical terms, calcium is reactive and soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element that must be extracted byelectrolysis from a fused salt like calcium chloride. Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air. Sony VAIO VPCW218JC/T Battery

In bulk-form (typically as chips or "turnings"), the metal is somewhat difficult to ignite, more so even than magnesium chips; but, when lit, the metal burns in air with a brilliant high-intensity orange-red light. Calcium metal reacts with water, evolving hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat.Sony VAIO VPCW218JC/W Battery

In powdered form, however, the reaction with water is extremely rapid, as the increased surface area of the powder accelerates the reaction with the water. Part of the slowness of the calcium-water reaction results from the metal being partly protected by insoluble white calcium hydroxide. In water solutions of acids, where this salt is soluble, calcium reacts vigorously.Sony VAIO VPCW219AJ/L Battery

Calcium, with a density of 1.55 g/cm3, is the lightest of the alkaline earth metals; magnesium (specific gravity 1.74) and beryllium (1.84) are more dense, although lighter in atomic mass. From strontium onward, the alkali earth metals become more dense with increasing atomic mass.Sony VAIO VPCW219AJ/P Battery

It has two allotropes.

Calcium has a higher electrical resistivity than copper or aluminium, yet weight-for-weight, due to its much lower density, it is a rather better conductor than either. However, its use in terrestrial applications is usually limited by its high reactivity with air.Sony VAIO VPCW219AJ/W Battery

Calcium salts are colorless from any contribution of the calcium, and ionic solutions of calcium (Ca2+) are colorless as well. As with magnesium salts and other alkaline earth metal salts, calcium salts are often quite soluble in water. Notable exceptions include thehydroxide, the sulfate (unusual for sulfate salts), the carbonate and the phosphates. Sony VAIO VPCW21AAJ Battery

With the exception of the sulfate, even the insoluble ones listed are in general more soluble than itstransition metal counterparts. When in solution, the calcium ion to the human taste varies remarkably, being reported as mildly salty, sour, "mineral like" or even "soothing." Sony VAIO VPCW21AKJ Battery

It is apparent that many animals can taste, or develop a taste, for calcium, and use this sense to detect the mineral in salt licks or other sources.In human nutrition, soluble calcium salts may be added to tart juices without much effect to the average palate.Sony VAIO VPCW21AVJ Battery

Calcium is the fifth-most-abundant element by mass in the human body, where it is a common cellular ionic messenger with many functions, and serves also as a structural element in bone. It is the relatively high-atomic-number calcium in the skeleton that causes bone to be radio-opaque. Sony VAIO VPCY115FGS Battery

Of the human body's solid components after drying and burning of organics (as for example, after cremation), about a third of the total "mineral" mass remaining, is the approximately one kilogram of calcium that composes the average skeleton (the remainder being mostly phosphorus and oxygen).Sony VAIO VPCY115FX/BI Battery

H and K lines

Visible spectra of many stars, including the Sun, exhibit strong absorption lines of singly ionized calcium. Prominent among these are the H-line at 3968.5 Å and the K line at 3933.7 Å of singly ionized calcium, or Ca II. For the Sun and stars with low temperatures, the prominence of the H and K lines can be an indication of strong magnetic activity in thechromosphere. Sony VAIO VPCY115FXBI Battery

Measurement of periodic variations of these active regions can also be used to deduce the rotation periods of these stars.

Compounds

Calcium, combined with phosphate to form hydroxylapatite, is the mineral portion of human and animal bones and teeth. The mineral portion of some corals can also be transformed into hydroxylapatite.Sony VAIO VPCY118EC Battery

Calcium hydroxide (slaked lime) is used in many chemical refinery processes and is made by heating limestone at high temperature (above 825 °C) and then carefully adding water to it. When lime is mixed with sand, it hardens into a mortarand is turned into plaster by carbon dioxide uptake. Mixed with other compounds, lime forms an important part of Portland cement.Sony VAIO VPCY118GX/BI Battery

Calcium carbonate (CaCO3) is one of the common compounds of calcium. It is heated to form quicklime (CaO), which is then added to water (H2O). This forms another material known as slaked lime (Ca(OH)2), which is an inexpensive base material used throughout the chemical industry. Chalk, marble, and limestone are all forms of calcium carbonate.Sony VAIO VPCY119FJ/S Battery

When water percolates through limestone or other soluble carbonate rocks, it partially dissolves the rock and causes cave formation and characteristic stalactites and stalagmites and also forms hard water. Other important calcium compounds arecalcium nitrate, calcium sulfide, calcium chloride, calcium carbide, calcium cyanamide and calcium hypochlorite.Sony VAIO VPCY11AFJ Battery

A few calcium compounds in the oxidation state +1 have also been investigated recently.

Nucleosynthesis

Calcium-40 is created in extremely large and hot (over 2.5 × 109 K) stars, as part of the silicon-burning process in whichalpha particles are added to silicon atoms. The process fuses an atom of argon and an atom of helium:Sony VAIO VPCY11AGJ Battery

36Ar + 4He = 40Ca

Calcium has four stable isotopes (40Ca, 42Ca, 43Ca and 44Ca), plus two more isotopes (46Ca and 48Ca) that have such long half-lives that for all practical purposes they also can be considered stable. The 20% range in relative mass among naturally occurring calcium isotopes is greater than for any element except hydrogen and helium.Sony VAIO VPCY11AHJ Battery

Calcium also has acosmogenic isotope, radioactive 41Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. Sony VAIO VPCY11AVJ Battery

41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies.

Ninety-seven percent of naturally occurring calcium is in the form of 40Ca. 40Ca is one of the daughter products of 40K decay, along with 40Ar. Sony VAIO VPCY11M1E/S Battery

While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating.

The most abundant isotope, 40Ca, has a nucleus of 20 protons and 20 neutrons. Sony VAIO VPCY11S1E Battery

This is the heaviest stable isotope of any element that has equal numbers of protons and neutrons. In supernova explosions, calcium is formed from the reaction of carbon with various numbers of alpha particles (helium nuclei), until the most common calcium isotope (containing 10 helium nuclei) has been synthesized.Sony VAIO VPCY11V9E/S Battery

Isotope fractionation

As with the isotopes of other elements, a variety of processes fractionate, or alter the relative abundance of, calcium isotopes. The best studied of these processes is the mass dependent fractionation of calcium isotopes that accompanies the precipitation of calcium minerals, such as calcite, aragonite and apatite, from solution. Sony VAIO VPCY218EC/BI Battery

Isotopically light calcium is preferentially incorporated into minerals, leaving the solution from which the mineral precipitated enriched in isotopically heavy calcium. At room temperature the magnitude of this fractionation is roughly 0.25‰ (0.025%) per atomic mass unit (AMU). Sony VAIO VPCY218EC/G Battery

Mass-dependent differences in calcium isotope composition conventionally are expressed the ratio of two isotopes (usually 44Ca/40Ca) in a sample compared to the same ratio in a standard reference material. 44Ca/40Ca varies by about 1% among common earth materials.Sony VAIO VPCY218EC/L Battery

Calcium isotope fractionation during mineral formation has led to several applications of calcium isotopes. In particular, the 1997 observation by Skulan and DePaolo that calcium minerals are isotopically lighter than the solutions from which the minerals precipitate is the basis of analogous applications in medicine and in paleooceanography. Sony VAIO VPCY218EC/P Battery

In animals with skeletons mineralized with calcium the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral. In humans changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance. Sony VAIO VPCY21S1E/L Battery

When the rate of bone formation exceeds the rate of bone resorption, soft tissue 44Ca/40Ca rises. Soft tissue 44Ca/40Ca falls when bone resorption exceeds bone formation. Because of this relationship, calcium isotopic measurements of urine or blood may be useful in the early detection of metabolic bone diseases likeosteoporosis.Sony VAIO VPCY21S1E/P Battery

A similar system exists in the ocean, where seawater 44Ca/40Ca tends to rise when the rate of removal of Ca2+ from seawater by mineral precipitation exceeds the input of new calcium into the ocean, and fall when calcium input exceeds mineral precipitation.Sony VAIO VPCY21S1E/SI Battery

It follows that rising 44Ca/40Ca corresponds to falling seawater Ca2+concentration, and falling 44Ca/40Ca corresponds to rising seawater Ca2+ concentration. In 1997 Skulan and DePaolo presented the first evidence of change in seawater44Ca/40Ca over geologic time, along with a theoretical explanation of these changes. Sony VAIO VPCZ110 Battery

More recent papers have confirmed this observation, demonstrating that seawater Ca2+ concentration is not constant, and that the ocean probably never is in “steady state” with respect to its calcium input and output. This has important climatological implications, as the marine calcium cycle is closely tied to the carbon cycle (see below).Sony VAIO VPCZ110GB/BI Battery

Geochemical cycling

Calcium provides an important link between tectonics, climate and the carbon cycle. In the simplest terms, uplift of mountains exposes Ca-bearing rocks to chemical weathering and releases Ca2+ into surface water. This Ca2+ eventually is transported to the ocean where it reacts with dissolved CO2 to form limestone.Sony VAIO VPCZ112GD/S Battery

Some of this limestone settles to the sea floor where it is incorporated into new rocks. Dissolved CO2, along with carbonate and bicarbonate ions, are referred to as dissolved inorganic carbon (DIC).

The actual reaction is more complicated and involves the bicarbonate ion (HCO3-) that forms when CO2 reacts with water at seawaterpH:Sony VAIO VPCZ112GX/S Battery

Ca2+ + 2HCO?
3 ? CaCO3 (limestone) + CO2 + H2O

Note that at ocean pH most of the CO2 produced in this reaction is immediately converted back into HCO3?. The reaction results in a net transport of one molecule of CO2 from the ocean/atmosphere into the lithosphere.Sony VAIO VPCZ114GX/S Battery

The result is that each Ca2+ ion released by chemical weathering ultimately removes one CO2 molecule from the surficial system (atmosphere, ocean, soils and living organisms), storing it in carbonate rocks where it is likely to stay for hundreds of millions of years. Sony VAIO VPCZ115 Battery

The weathering of calcium from rocks thus scrubs CO2 from the ocean and atmosphere, exerting a strong long-term effect on climate.[14] Analogous cycles involving magnesium, and to a much smaller extent strontium and barium, have the same effect.Sony VAIO VPCZ115FC/B Battery

As the weathering of limestone (CaCO3) liberates equimolar amounts of Ca2+ and CO2, it has no net effect on the CO2 content of the atmosphere and ocean. The weathering of silicate rocks like granite, on the other hand, is a net CO2 sink because it produces abundant Ca2+ but very little CO2.Sony VAIO VPCZ115FC/S Battery

Calcium (from Latin calx, genitive calcis, meaning "lime") was known as early as the first century when the Ancient Romans prepared lime as calcium oxide. Literature dating back to 975 AD notes that plaster of paris (calcium sulfate), is useful for setting broken bones. Sony VAIO VPCZ116 Battery

It was not isolated until 1808 in England whenSir Humphry Davy electrolyzed a mixture of lime and mercuric oxide. Davy was trying to isolate calcium; when he heard that Swedish chemist Jöns Jakob Berzeliusand Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself. Sony VAIO VPCZ116GX/S Battery

He worked with electrolysis throughout his life and also discovered/isolated sodium, potassium, magnesium, boron and barium. Calcium metal was not available in large scale until the beginning of the 20th century.

Occurrence

Calcium is not naturally found in its elemental state. Sony VAIO VPCZ117 Battery

Calcium occurs most commonly in sedimentary rocks in the minerals calcite, dolomite and gypsum. It also occurs in igneous and metamorphic rocks chiefly in the silicate minerals: plagioclases, amphiboles, pyroxenes and garnets.

Applications

Calcium is used[17]

  • as a reducing agent in the extraction of other metals, such as uranium, zirconium, and thorium.Sony VAIO VPCZ117FC/B Battery
  • as a deoxidizer, desulfurizer, or decarbonizer for various ferrous and nonferrous alloys.
  • as an alloying agent used in the production of aluminium, beryllium, copper, lead, and magnesium alloys.
  • in the making of cements and mortars to be used in construction.
  • in the making of cheese, where calcium ions influence the activity of rennin in bringing about the coagulation of milk.Sony VAIO VPCZ118 Battery

Calcium compounds

  • Calcium carbonate (CaCO3) is used in manufacturing cement and mortar, lime, limestone (usually used in the steel industry) and aids in production in the glass industry. It also has chemical and optical uses as mineral specimens in toothpastes, for example.Sony VAIO VPCZ118GC/B Battery
  • Calcium hydroxide solution (Ca(OH)2) (also known as limewater) is used to detect the presence of carbon dioxide by being bubbled through a solution. It turns cloudy where CO2 is present.
  • Calcium arsenate (Ca3(AsO4)2) is used in insecticides.Sony VAIO VPCZ118GX/S Battery
  • Calcium carbide (CaC2) is used to make acetylene gas (for use in acetylene torches for welding) and in the manufacturing of plastics.
  • Calcium chloride (CaCl2) is used in ice removal and dust control on dirt roads, in conditioner for concrete, as an additive in canned tomatoes, and to provide body for automobile tires.Sony VAIO VPCZ119 Battery
  • Calcium cyclamate (Ca(C6H11NHSO3)2) was used as a sweetening agent but is no longer permitted for use because of suspected cancer-causing properties.
  • Calcium gluconate (Ca(C6H11O7)2) is used as a food additive and in vitamin pills.
  • Calcium hypochlorite (Ca(OCl)2) is used as a swimming pool disinfectant, as a bleaching agent, as an ingredient in deodorant, and in algaecide and fungicide.Sony VAIO VPCZ119FJ/S Battery
  • Calcium permanganate (Ca(MnO4)2) is used in liquid rocket propellant, textile production, as a water sterilizing agent and in dental procedures.
  • Calcium phosphate (Ca3(PO4)2) is used as a supplement for animal feed, fertilizer, in commercial production for dough and yeast products, in the manufacture ofglass, and in dental products.Sony VAIO VPCZ119GC/X Battery
  • Calcium phosphide (Ca3P2) is used in fireworks, rodenticide, torpedoes and flares.
  • Calcium stearate (Ca(C18H35O2)2) is used in the manufacture of wax crayons, cements, certain kinds of plastics and cosmetics, as a food additive, in the production of water resistant materials and in the production of paints.Sony VAIO VPCZ119L Battery
  • Calcium sulfate (CaSO4·2H2O) is used as common blackboard chalk, as well as, in its hemihydrate form better known as Plaster of Paris.
  • Calcium tungstate (CaWO4) is used in luminous paints, fluorescent lights and in X-ray studies.Sony VAIO VPCZ119R/B Battery
  • Hydroxylapatite (Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2) makes up seventy percent of bone. Also carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised.Sony VAIO VPCZ119R/S Battery

Nutrition

Calcium is an important component of a healthy diet and a mineral necessary for life. The National Osteoporosis Foundationsays, "Calcium plays an important role in building stronger, denser bones early in life and keeping bones strong and healthy later in life."Sony VAIO VPCZ11AFJ Battery

Approximately 99 percent of the body's calcium is stored in the bones and teeth. The rest of the calcium in the body has other important uses, such as some exocytosis, especially neurotransmitter release, and muscle contraction. In the electrical conduction system of the heart, calcium replaces sodium as the mineral that depolarizes the cell, proliferating the action potential. Sony VAIO VPCZ11AGJ Battery

In cardiac muscle, sodium influx commences an action potential, but during potassium efflux, the cardiac myocyte experiences calcium influx, prolonging the action potential and creating a plateau phase of dynamic equilibrium. Long-term calcium deficiency can lead to rickets and poor blood clotting and in case of a menopausal woman, Sony VAIO VPCZ11AVJ Battery

it can lead to osteoporosis, in which the bone deteriorates and there is an increased risk of fractures. While a lifelong deficit can affect bone and tooth formation, over-retention can cause hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals.Sony VAIO VPCZ11CGX/X Battery

Several sources suggest a correlation between high calcium intake (2000 mg per day, or twice the U.S. recommended daily allowance, equivalent to six or more glasses of milk per day) and prostate cancer. High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. Sony VAIO VPCZ11DGX/SJ Battery

However, a high calcium intake has been associated with a lower risk for kidney stones in more recent research. Vitamin D is needed to absorb calcium.

Dairy products, such as milk and cheese, are a well-known source of calcium. Sony VAIO VPCZ11FHX/XQ Battery

Some individuals are allergic to dairy products and even more people, in particular those of non Indo-European descent, are lactose-intolerant, leaving them unable to consume non-fermented dairy products in quantities larger than about half a liter per serving. Others, such as vegans, avoid dairy products for ethical and health reasons. Sony VAIO VPCZ11V9R/B Battery

However, many good sources of calcium exist. These include seaweeds such as kelp, wakame and hijiki; nuts and seeds (like almonds and sesame); blackstrap molasses; beans; figs; quinoa; amaranth;collard greens; okra; rutabaga; broccoli; dandelion leaves; kale; and fortified products such as orange juice and soy milk. Sony VAIO VPCZ11X9E/B Battery

An overlooked source of calcium is eggshell, which can be ground into a powder and mixed into food or a glass of water.

The calcium content of most foods can be found in the USDA National Nutrient Database.Sony VAIO VPCZ11Z9E/B Battery

Dietary calcium supplements

Calcium supplements are used to prevent and to treat calcium deficiencies. Most experts recommend that supplements be taken with food and that no more than 600 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases.Sony VAIO VPCZ125GX/S Battery

It is recommended to spread doses throughout the day. Recommended daily calcium intake for adults ranges from 1000 to 1500 mg. It is recommended to take supplements with food to aid in absorption.

Vitamin D is added to some calcium supplements. Proper vitamin D status is important because vitamin D is converted to a hormone in the body, which then induces the synthesis of intestinal proteins responsible for calcium absorption.Sony VAIO VPCZ127FC Battery

  • The absorption of calcium from most food and commonly used dietary supplements is very similar. This is contrary to what many calcium supplement manufacturers claim in their promotional materials.
  • Milk is an excellent source of dietary calcium for those whose bodies tolerate it because it has a high concentration of calcium and the calcium in milk is excellently absorbed.Sony VAIO VPCZ128GC Battery
  • Soymilk and other vegetable milks are usually sold with calcium added so that their calcium concentration is as high as in milk
  • Also different kind of juices boosted with calcium are widely available.
  • Calcium carbonate is the most common and least expensive calcium supplement. It should be taken with food. It depends on low pH levels for proper absorption in the intestine.Sony VAIO VPCZ12M9E/B Battery
  • Some studies suggests that the absorption of calcium from calcium carbonate is similar to the absorption of calcium from milk. While most people digest calcium carbonate very well, some might develop gastrointestinal discomfort or gas. Taking magnesium with it can help to avoid constipation. Sony VAIO VPCZ13M9E/B Battery
  • Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. However, supplement labels will usually indicate how much calcium is present in each serving, not how much calcium carbonate is present.Sony VAIO VPCZ13V9E/X Battery
  • Antacids frequently contain calcium carbonate, and are a commonly used, inexpensive calcium supplement
  • Coral calcium is a salt of calcium derived from fossilized coral reefs. Coral calcium is composed of calcium carbonate and trace minerals.Sony VAIO VPCZ13Z9E/X Battery
  • Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or proton-pump inhibitors. It is more easily digested and absorbed than calcium carbonate if taken on an empty stomach and less likely to cause constipation and gas than calcium carbonate. Sony VAIO VPCZZZHJ Battery
  • It also has a lower risk of contributing to the formation of kidney stones. Calcium citrate is about 21% elemental calcium. 1000 mg will provide 210 mg of calcium. It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium.Sony VAIO VPZ117 Battery
  • Calcium phosphate costs more than calcium carbonate, but less than calcium citrate. It is easily absorbed and is less likely to cause constipation and gas than either.
  • Calcium lactate has similar absorption as calcium carbonate,[37] but is more expensive. Calcium lactate and calcium gluconate are less concentrated forms of calcium and are not practical oral supplements.Sony VAIO VPZ118 Battery
  • Calcium chelates are synthetic calcium compounds, with calcium bound to an organic molecule, such as malate, aspartate, or fumarate. These forms of calcium may be better absorbed on an empty stomach. However, in general they are absorbed similarly to calcium carbonate and other common calcium supplements when taken with food.Sony VAIO VPZ119 Battery
  • The 'chelate' mimics the action that natural food performs by keeping the calcium soluble in the intestine. Thus, on an empty stomach, in some individuals, chelates might, in theory, be absorbed better.
  • Microcrystalline hydroxyapatite (MH) is marketed as a calcium supplement, and has in some randomized trials been found to be more effective than calcium carbonate.Sony VPCM11M1E/B Battery

In July 2006, a report citing research from Fred Hutchinson Cancer Research Center in Seattle, Washington claimed that women in their 50s gained 5 pounds (2.3 kg) less in a period of 10 years by taking more than 500 mg of calcium supplements than those who did not.Sony VPCM11M1E/W Battery

However, the doctor in charge of the study, Dr. Alejandro J. Gonzalez also noted it would be "going out on a limb" to suggest calcium supplements as a weight-limiting aid.

Prevention of fractures due to osteoporosis

Such studies often do not test calcium alone, but rather combinations of calcium and vitamin D. Randomized controlled trials found both positive  and negative effects. Sony VPCM12M1E/L Battery

The different results may be explained by doses of calcium and underlying rates of calcium supplementation in the control groups. However, it is clear that increasing the intake of calcium promotes deposition of calcium in the bones,Sony VPCM12M1E/P Battery

where it is of more benefit in preventing the compression fractures resulting from the osteoporotic thinning of the dendritic web of the bodies of the vertebrae, than it is at preventing the more serious cortical bonefractures that happen at hip and wrist. Sony VPCM12M1E/W Battery

Possible cancer prevention

A meta-analysis[41] by the international Cochrane Collaboration of two randomized controlled trials  found that calcium "might contribute to a moderate degree to the prevention of adenomatous colonic polyps".Sony VPCM13M1E/L Battery

More recent studies were conflicting, and one that was positive for effect (Lappe, et al.) did control for a possible anti-carcinogenic effect of vitamin D, which was found to be an independent positive influence from calcium-alone on cancer risk (see second study below).Sony VPCM13M1E/P Battery

  • A randomized controlled trial found that 1000 mg of elemental calcium and 400 IU of vitamin D3 had no effect on colorectal cancer
  • A randomized controlled trial found that 1400–1500 mg supplemental calcium and 1100 IU vitamin D3 reduced aggregated cancers with a relative risk of 0.402.Sony VPCM13M1E/W Battery
  • An observational cohort study found that high calcium and vitamin D intake was associated with "lower risk of developing premenopausal breast cancer."

Hazards and toxicity

Compared with other metals, the calcium ion and most calcium compounds have low toxicity.Sony VAIO VGN-Z11MN/B Battery

This is not surprising given the very high natural abundance of calcium compounds in the environment and in organisms. Calcium poses few serious environmental problems, with kidney stones the most common side-effect in clinical studies. Acute calcium poisoning is rare, and difficult to achieve unless calcium compounds are administered intravenously. Sony VAIO VGN-Z11VN/X Battery

For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45  and 1.4 g/kg,  respectively.

Calcium metal is hazardous because of its sometimes-violent reactions with water and acids. Sony VAIO VGN-Z11WN/B Battery

Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (e.g., hair) that block drains. When swallowed calcium metal has the same effect on the mouth, esophagus and stomach, and can be fatal.Sony VAIO VGN-Z11XN/B Battery

Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal renal failure. What constitutes “excessive” consumption is not well known and, it is presumed, varies a great deal from person to person.Sony VAIO VGN-Z15 Battery

Persons consuming more than 10 grams/day of CaCO3 (=4 g Ca) are at risk of developing milk-alkali syndrome,  but the condition has been reported in at least one person consuming only 2.5 grams/day of CaCO3 (=1 g Ca), an amount usually considered moderate and safe.Sony VAIO VGN-Z15N Battery

Oral calcium supplements diminish the absorption of thyroxine when taken within four to six hours of each other.[58] Thus, people taking both calcium and thyroxine run the risk of inadequate thyroid hormone replacement and thence hypothyroidism if they take them simultaneously or near-simultaneously.Sony VAIO VGN-Z17 Battery

Calcium (Ca2+) plays a pivotal role in the physiology and biochemistry of organisms and the cell. It plays an important role in signal transduction pathways, where it acts as a second messenger, in neurotransmitter release from neurons, contraction of all muscle cell types, and fertilization.Sony VAIO VGN-Z17N Battery

Many enzymes require calcium ions as a cofactor, those of the blood-clotting cascade being notable examples. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.

Calcium levels in mammals are tightly regulated, with bone acting as the major mineral storage site.Sony VAIO VGN-Z19 Battery

Calcium ions, Ca2+, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as serum albumin. Parathyroid hormonesecreted by the parathyroid gland regulates the resorption of Ca2+ from bone, Sony VAIO VGN-Z19N Battery

reabsorption in the kidney back into circulation, and increases in the activation ofvitamin D3 to Calcitriol. Calcitriol, the active form of vitamin D3, promotes absorption of calcium from the intestines and the mobilization of calcium ions from bone matrix. Calcitonin secreted from the parafollicular cells of the thyroid gland also affects calcium levels by opposing parathyroid hormone;Sony VAIO VGN-Z21MN/B Battery

however, its physiological significance in humans is dubious.

Calcium storages are intracellular organelles, that constantly accumulate Ca2+ ions and release them during certain cellular events. Intracellular Ca2+ storages include mitochondria and the endoplasmic reticulum.Sony VAIO VGN-Z21VN/X Battery

In vertebrates, calcium ions, like many other ions, are of such vital importance to many physiological processes that its concentration is maintained within specific limits to ensure adequate homeostasis. This is evidenced by human plasma calcium, which is one of the most closely regulated physiological variables in the human body.Sony VAIO VGN-Z21WN/B Battery

Normal plasma levels vary between 1 and 2% over any given time. Approximately half of all ionized calcium circulates in its unbound form, with the other half being complexed with plasma proteins such as albumin, as well as anions including bicarbonate, citrate, phosphate, and sulfate.Sony VAIO VGN-Z21XN Battery

Different tissues contain calcium in different concentrations. For instance, Ca2+ (mostly calcium phosphate and some calcium sulfate) is the most important (and specific) element of bone and calcified cartilage. In humans, the total body content of calcium is present mostly in the form of bone mineral (roughly 99%). Sony VAIO VGN-Z21ZN/X Battery

In this state, it is largely unavailable for exchange/bioavailability. The way to overcome this is through the process of bone resorption, in which calcium is liberated into the bloodstream through the action of bone osteoclasts. The remainder of calcium is present within the extracellular and intracellular fluids.Sony VAIO VGN-Z25 Battery

Within a typical cell, the intracellular concentration of ionized calcium is roughly 100 nM, but is subject to increases of 10– to 100-fold during various cellular functions. The intracellular calcium level is kept relatively low with respect to the extracellular fluid, by an approximate magnitude of 12,000-fold. Sony VAIO VGN-Z25/B Battery

This gradient is maintained through various plasma membrane calcium pumps that utilize ATP for energy, as well as a sizable storage within intracellular compartments.

Effects

The effects of calcium on human cells are specific, meaning that different types of cells respond in different ways. Sony VAIO VGN-Z25TN/B Battery

However, in certain circumstances, its action may be more general. Ca2+ ions are one of the most widespread second messengers used insignal transduction. They make their entrance into the cytoplasm either from outside the cell through the cell membrane via calcium channels (such as Calcium-binding proteins or voltage-gated calcium channels),Sony VAIO VGN-Z26TN/B Battery

or from some internal calcium storagessuch as the endoplasmic reticulum and mitochondria. Levels of intracellular calcium are regulated by transport proteins that remove it from the cell. For example, the sodium-calcium exchanger uses energy from the electrochemical gradient of sodium by coupling the influx of sodium into cell Sony VAIO VGN-Z27 Battery

(and down its concentration gradient) with the transport of calcium out of the cell. In addition, the plasma membrane Ca2+ ATPase (PMCA) obtains energy to pump calcium out of the cell by hydrolysing adenosine triphosphate (ATP). In neurons, voltage-dependent, Sony VAIO VGN-Z27/B Battery

calcium-selective ion channels are important for synaptic transmission through the release of neurotransmitters into the synaptic cleft by vesicle fusionof synaptic vesicles.

Calcium's function in muscle contraction was found as early as 1882 by Ringer. Subsequent investigations were to reveal its role as a messenger about a century later. Sony VAIO VGN-Z27TN/X Battery

Because its action is interconnected with cAMP, they are called synarchic messengers. Calcium can bind to several different calcium-modulated proteins such astroponin-C (the first one to be identified) and calmodulin, proteins that are necessary for promoting contraction in muscle.Sony VAIO VGN-Z29N Battery

Negative effects and pathology

Substantial decreases in extracellular Ca2+ ion concentrations may result in a condition known as hypocalcemic tetany, which is marked by spontaneous motor neurondischarge. In addition, severe hypocalcaemia will begin to affect aspects of blood coagulation and signal transduction.Sony VAIO VGN-Z29N/X Battery

Ca2+ ions can damage cells if they enter in excessive numbers (for example, in the case of excitotoxicity, or over-excitation of neural circuits, which can occur inneurodegenerative diseases, or after insults such as brain trauma or stroke). Excessive entry of calcium into a cell may damage it or even cause it to undergoapoptosis, or death by necrosis. Sony VAIO VGN-Z31MN/B Battery

Calcium also acts as one of the primary regulators of osmotic stress (Osmotic shock). Chronically elevated plasma calcium (hypercalcemia) is associated with cardiac arrhythmias and decreased neuromuscular excitability. One cause of hypercalcemia is a condition known ashyperparathyroidism.Sony VAIO VGN-Z31VN/X Battery

Invertebrates

Some invertebrates use calcium compounds for building their exoskeleton (shells and carapaces) or endoskeleton (echinoderm plates and poriferan calcareous spicules).Sony VAIO VGN-Z31WN/B Battery

Stomata Closing

When ABA signals the guard cells, free Ca2+ ions enter the cytosol from both outside the cell and internal stores, reversing the concentration gradient so the K+ ions begin

exiting the cell. The loss of solutes makes the cell flaccid and closes the stomatal pores.Sony VAIO VGN-Z31ZN/X Battery

Cellular Division

Calcium is a necessary ion in the formation of the mitotic spindle. Without the mitotic spindle, cellular division cannot occur. Although young leaves have a higher need for calcium, older leaves contain higher amounts of calcium because calcium is relatively immobile through the plant.Sony VAIO VGN-Z35 Battery

It is not transported through the phloembecause it can bind with other nutrient ions and precipitate out of liquid solutions.

Structural roles

Ca2+ ions are an essential component of plant cell walls and cell membranes, and are used as cations to balance organic anions in the plant vacuole.[4] The Ca2+concentration of the vacuole may reach millimolar levels. Sony VAIO VGN-Z35/B Battery

The most striking use of Ca2+ ions as a structural element in plants occurs in the marine coccolithophores, which use Ca2+ to form the calcium carbonate plates, with which they are covered.

Calcium is needed to form the pectin in the middle lamella of newly formed cells.Sony VAIO VGN-Z35TN/B Battery

Calcium is needed to stabilize the permeability of cell membranes. Without calcium, the cell walls are unable to stabilize and hold their contents. This is particularly important in developing fruits. Without calcium, the cell walls are weak and unable to hold the contents of the fruit.Sony VAIO VGN-Z36GD Battery

Some plants accumulate Ca in their tissues, thus making them more firm. Calcium is stored as Ca-oxalate crystals in plastids.

Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. Derangements of this mechanism lead to hypercalcemia or hypocalcemia, both of which can have important consequences for health.Sony VAIO VGN-Z36GD/B Battery

Calcium location and quantity

Calcium is the most abundant mineral in the human body. The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. The extracellular fluid (ECF) contains approximately 22.5 mmol, of which about 9 mmol is in the serum.Sony VAIO VGN-Z36GD/J Battery

Approximately 500 mmol of calcium is exchanged between bone and the ECF over a period of twenty-four hours.

Normal ranges

The serum level of calcium is closely regulated with a normal total calcium of 2.2-2.6 mmol/L (9-10.5 mg/dL) and a normal ionized calcium of 1.1-1.4 mmol/L (4.5-5.6 mg/dL). Sony VAIO VGN-Z36TD/B Battery

The amount of total calcium varies with the level of serum albumin, a protein to which calcium is bound. The biologic effect of calcium is determined by the amount of ionized calcium, rather than the total calcium. Ionized calcium does not vary with the albumin level, and therefore it is useful to measure the ionized calcium level when the serum albumin is not within normal ranges, or when a calcium disorder is suspected despite a normal total calcium level.Sony VAIO VGN-Z36TD/J Battery

Corrected calcium level

One can derive a corrected calcium level when the albumin is abnormal. This is to make up for the change in total calcium due to the change in albumin-bound calcium, and gives an estimate of what the calcium level would be if the albumin were within normal ranges.Sony VAIO VGN-Z37D Battery

Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level in g/dL.

in other words, each 1 g/dL decrease of albumin will decrease 0.8 mg/dL in measured serum Ca and thus 0.8 must be added to the measured Calcium to get a corrected Calcium value.Sony VAIO VGN-Z37D/B Battery

Or: Corrected calcium (mmol/L) = measured total Ca (mmol/L) + 0.02 (40 - serum albumin [g/L]), where 40 represents the average albumin level in g/L

in other words, each 1 g/L decrease of albumin, will decrease 0.02 mmol/L in measured serum Ca and thus 0.02 must be added to the measured value to take this into account and get a corrected calcium.Sony VAIO VGN-Z37GD Battery

When there is hypoalbuminemia (a lower than normal albumin), the corrected calcium level is higher than the total calcium.

Absorption

About 25 mmol of calcium enters the body in a normal diet. Of this, about 40% (10 mmol) is absorbed in small intestine, and 5 mmol leaves the body in feces, netting 5 mmol of calcium a day.Sony VAIO VGN-Z37GD/X Battery

Calcium is absorbed across the intestinal brush border membrane, passing through ion channels such as TRPV6. Calbindin is a vitamin D-dependent calcium-binding protein inside intestinal epithelial cells which functions together with TRPV6 and calcium pumps (PMCA1) in the basal membrane to actively transport calcium into the body.Sony VAIO VGN-Z39D Battery

The active transport occurs primarily in the duodenum when calcium intake is low, and passive paracellular diffusion occurs in the ileum and jejunum, independent of Vitamin D, when calcium intake is high. Sony VAIO VGN-Z39D/X Battery

Excretion

The kidney excretes 250 mmol a day in pro-urine, and resorbs 245 mmol, leading to a net loss in the urine of 5 mmol/d. In addition to this, the kidney processes Vitamin D into calcitriol, the active form that is most effective in assisting intestinal absorption. Both processes are stimulated by parathyroid hormone.Sony VAIO VGN-Z41MD/B Battery

The role of bone

Although calcium flow to and from the bone is neutral, about 5 mmol is turned over a day. Bone serves as an important storage point for calcium, as it contains 99% of the total body calcium. Calcium release from bone is regulated by parathyroid hormone. Calcitonin stimulates incorporation of calcium in bone, although this process is largely independent of calcitonin.Sony VAIO VGN-Z41WD/B Battery

Low calcium intake may also be a risk factor in the development of osteoporosis. In one meta-analysis, the authors found that fifty out of the fifty-two studies that they reviewed showed that calcium intake promoted better bone balance.[5] With a better bone balance, the risk of osteoporosis is lowered.Sony VAIO VGN-Z45GD/B Battery

Primarily calcium is regulated by the actions of 1,25-Dihydroxycholecalciferol, parathyroid hormone (PTH) and calcitonin and direct exchange with the bone matrix. Plasma calcium levels are regulated by hormonal and non-hormonal mechanisms. After ingestion of substantial amounts of calcium the short term control that prevents calcium spiking in the serum is absorption by the bone matrix. After about an hour, PTH will be released and not peak for about 8 hours.Sony VAIO VGN-Z45TD/B Battery

The PTH is, over time, a very potent regulator of plasma calcium, and controls the conversion of vitamin D into its active form in the kidney. The parathyroid glands are located behind the thyroid, and produce parathyroid hormone in response to low calcium levels.

The parafollicular cells of the thyroid produce calcitonin in response to high calcium levels, but its significance is much smaller than that of PTH.Sony VAIO VGN-Z46GD/B Battery

Pathology

Hypocalcemia and hypercalcemia are both serious medical disorders.

Renal osteodystrophy is a consequence of chronic renal failure related to the calcium metabolism.

Osteoporosis and osteomalacia have been linked to calcium metabolism disorders.Sony VAIO VGN-Z46GD/U Battery

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