Revision as of 11:43, 22 April 2024 by Fire(talk | contribs)(Created page with "====ニッチな用途==== 様々なカリウム化合物の用途は何千とある。その一例がカリウム・スーパーオキシド、{{chem2|KO2}}であり、オレンジ色の固体で、携帯用酸素源および二酸化炭素吸収剤として機能する。気体の酸素よりも体積が少なくてすむため、呼吸システムの鉱山、潜水艦、...")
Another example is potassium cobaltinitrite, K 3[Co(NO 2) 6], which is used as artist's pigment under the name of Aureolin or Cobalt Yellow.
The stable isotopes of potassium can be laser cooled and used to probe fundamental and technological problems in quantum physics. The two bosonic isotopes possess convenient Feshbach resonances to enable studies requiring tunable interactions, while 40 K is one of only two stable fermions amongst the alkali metals.
Laboratory uses
An alloy of sodium and potassium, NaK is a liquid used as a heat-transfer medium and a desiccant for producing dry and air-free solvents. It can also be used in reactive distillation. The ternary alloy of 12% Na, 47% K and 41% Cs has the lowest melting point of −78°C of any metallic compound.
Metallic potassium is used in several types of magnetometers.
Potassium is the eighth or ninth most common element by mass (0.2%) in the human body, so that a 60kg adult contains a total of about 120g of potassium. The body has about as much potassium as sulfur and chlorine, and only calcium and phosphorus are more abundant (with the exception of the ubiquitous CHON elements).
Biochemical function
Potassium levels influence multiple physiological processes, including
resting cellular-membrane potential and the propagation of action potentials in neuronal, muscular, and cardiac tissue. Due to the electrostatic and chemical properties, K+ ions are larger than Na+ ions, and ion channels and pumps in cell membranes can differentiate between the two ions, actively pumping or passively passing one of the two ions while blocking the other.
hormone secretion and action
vascular tone
systemic blood pressure control
gastrointestinal motility
acid–base homeostasis
glucose and insulin metabolism
mineralocorticoid action
renal concentrating ability
fluid and electrolyte balance
local cortical monoaminergic norepinephrine, serotonin, and dopamine levels, and through them, sleep/wake balance, and spontaneous activity.
Homeostasis
Potassium homeostasis denotes the maintenance of the total body potassium content, plasma potassium level, and the ratio of the intracellular to extracellular potassium concentrations within narrow limits, in the face of pulsatile intake (meals), obligatory renal excretion, and shifts between intracellular and extracellular compartments.
Plasma levels
Plasma potassium is normally kept at 3.5 to 5.5 millimoles (mmol) [or milliequivalents (mEq)] per liter by multiple mechanisms. Levels outside this range are associated with an increasing rate of death from multiple causes, and some cardiac, kidney, and lung diseases progress more rapidly if serum potassium levels are not maintained within the normal range.
An average meal of 40–50mmol presents the body with more potassium than is present in all plasma (20–25mmol). This surge causes the plasma potassium to rise up to 10% before clearance by renal and extrarenal mechanisms.
Hypokalemia, a deficiency of potassium in the plasma, can be fatal if severe. Common causes are increased gastrointestinal loss (vomiting, diarrhea), and increased renal loss (diuresis). Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response; and in severe cases, respiratory paralysis, alkalosis, and cardiac arrhythmia.
Control mechanisms
Potassium content in the plasma is tightly controlled by four basic mechanisms, which have various names and classifications. These are:
Collectively, the first three are sometimes termed the "external potassium homeostasis system"; and the first two, the "reactive potassium homeostasis system".
The reactive negative-feedback system refers to the system that induces renal secretion of potassium in response to a rise in the plasma potassium (potassium ingestion, shift out of cells, or intravenous infusion.)
The reactive feed-forward system refers to an incompletely understood system that induces renal potassium secretion in response to potassium ingestion prior to any rise in the plasma potassium. This is probably initiated by gut cell potassium receptors that detect ingested potassium and trigger vagalafferent signals to the pituitary gland.
The predictive or circadian system increases renal secretion of potassium during mealtime hours (e.g. daytime for humans, nighttime for rodents) independent of the presence, amount, or absence of potassium ingestion. It is mediated by a circadian oscillator in the suprachiasmatic nucleus of the brain (central clock), which causes the kidney (peripheral clock) to secrete potassium in this rhythmic circadian fashion.File:Scheme sodium-potassium pump-en.svgThe action of the sodium-potassium pump is an example of primary active transport. The two carrier proteins embedded in the cell membrane on the left are using ATP to move sodium out of the cell against the concentration gradient; The two proteins on the right are using secondary active transport to move potassium into the cell. This process results in reconstitution of ATP.
The ion transport system moves potassium across the cell membrane using two mechanisms. One is active and pumps sodium out of, and potassium into, the cell. The other is passive and allows potassium to leak out of the cell. Potassium and sodium cations influence fluid distribution between intracellular and extracellular compartments by osmotic forces. The movement of potassium and sodium through the cell membrane is mediated by the Na⁺/K⁺-ATPase pump. This ion pump uses ATP to pump three sodium ions out of the cell and two potassium ions into the cell, creating an electrochemical gradient and electromotive force across the cell membrane. The highly selective potassium ion channels (which are tetramers) are crucial for hyperpolarization inside neurons after an action potential is triggered, to cite one example. The most recently discovered potassium ion channel is KirBac3.1, which makes a total of five potassium ion channels (KcsA, KirBac1.1, KirBac3.1, KvAP, and MthK) with a determined structure. All five are from prokaryotic species.
Renal filtration, reabsorption, and excretion
Renal handling of potassium is closely connected to sodium handling. Potassium is the major cation (positive ion) inside animal cells (150mmol/L, 4.8g/L), while sodium is the major cation of extracellular fluid (150mmol/L, 3.345g/L). In the kidneys, about 180liters of plasma is filtered through the glomeruli and into the renal tubules per day. This filtering involves about 600mg of sodium and 33mg of potassium. Since only 1–10mg of sodium and 1–4mg of potassium are likely to be replaced by diet, renal filtering must efficiently reabsorb the remainder from the plasma.
Sodium is reabsorbed to maintain extracellular volume, osmotic pressure, and serum sodium concentration within narrow limits. Potassium is reabsorbed to maintain serum potassium concentration within narrow limits. Sodium pumps in the renal tubules operate to reabsorb sodium. Potassium must be conserved, but because the amount of potassium in the blood plasma is very small and the pool of potassium in the cells is about 30 times as large, the situation is not so critical for potassium. Since potassium is moved passively in counter flow to sodium in response to an apparent (but not actual) Donnan equilibrium, the urine can never sink below the concentration of potassium in serum except sometimes by actively excreting water at the end of the processing. Potassium is excreted twice and reabsorbed three times before the urine reaches the collecting tubules. At that point, urine usually has about the same potassium concentration as plasma. At the end of the processing, potassium is secreted one more time if the serum levels are too high.
With no potassium intake, it is excreted at about 200mg per day until, in about a week, potassium in the serum declines to a mildly deficient level of 3.0–3.5mmol/L. If potassium is still withheld, the concentration continues to fall until a severe deficiency causes eventual death.
The potassium moves passively through pores in the cell membrane. When ions move through ion transporters (pumps) there is a gate in the pumps on both sides of the cell membrane and only one gate can be open at once. As a result, approximately 100 ions are forced through per second. Ion channels have only one gate, and there only one kind of ion can stream through, at 10 million to 100 million ions per second. Calcium is required to open the pores, although calcium may work in reverse by blocking at least one of the pores. Carbonyl groups inside the pore on the amino acids mimic the water hydration that takes place in water solution by the nature of the electrostatic charges on four carbonyl groups inside the pore.
Nutrition
Dietary recommendations
The U.S. National Academy of Medicine (NAM), on behalf of both the U.S. and Canada, sets Dietary Reference Intakes, including Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs), or Adequate Intakes (AIs) for when there is not sufficient information to set EARs and RDAs.
For both males and females under 9 years of age, the AIs for potassium are: 400mg of potassium for 0 to 6-month-old infants, 860mg of potassium for 7 to 12-month-old infants, 2,000mg of potassium for 1 to 3-year-old children, and 2,300mg of potassium for 4 to 8-year-old children.
For males 9 years of age and older, the AIs for potassium are: 2,500mg of potassium for 9 to 13-year-old males, 3,000mg of potassium for 14 to 18-year-old males, and 3,400mg for males that are 19 years of age and older.
For females 9 years of age and older, the AIs for potassium are: 2,300mg of potassium for 9 to 18-year-old females, and 2,600mg of potassium for females that are 19 years of age and older.
For pregnant and lactating females, the AIs for potassium are: 2,600mg of potassium for 14 to 18-year-old pregnant females, 2,900mg for pregnant females that are 19 years of age and older; furthermore, 2,500mg of potassium for 14 to 18-year-old lactating females, and 2,800mg for lactating females that are 19 years of age and older. As for safety, the NAM also sets tolerable upper intake levels (ULs) for vitamins and minerals, but for potassium the evidence was insufficient, so no UL was established.
As of 2004, most Americans adults consume less than 3,000mg.
Likewise, in the European Union, in particular in Germany, and Italy, insufficient potassium intake is somewhat common. The British National Health Service recommends a similar intake, saying that adults need 3,500mg per day and that excess amounts may cause health problems such as stomach pain and diarrhea.
In 2019, the National Academies of Sciences, Engineering, and Medicine revised the Adequate Intake for potassium to 2,600 mg/day for females 19 years of age and older who are not pregnant or lactating, and 3,400 mg/day for males 19 years of age and older.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN978-0-08-037941-8.
Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (2007). "Potassium". Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. ISBN978-3-11-017770-1.
Schultz, H.; Bauer, G.; Schachl, E.; Hagedorn, F.; Schmittinger, P. (2006). "Potassium compounds". Ullmann's Encyclopedia of Industrial Chemistry. A22. pp. 39–103. doi:10.1002/14356007.a22_031.pub2. ISBN978-3-527-30673-2.
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