Potassium in biology
Encyclopedia
Potassium
is an essential mineral macronutrient and is the main intracellular
ion
for all types of cell
s.
It is important in maintaining fluid and electrolyte
balance in the bodies of humans and animals.
Potassium ion is necessary for the function of all living cells, and is thus present in all plant and animal tissues. It is found in especially high concentrations within plant cells, and in a mixed diet, it is most highly concentrated in fruits. The high concentration of potassium in plants, associated with comparatively very low amounts of sodium there, historically resulted in potassium first being isolated from the ashes of plants (potash
), which in turn gave the element its modern name. The high concentration of potassium in plants means that heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 93% of the potassium chemical production of the modern world economy.
The functions of potassium and sodium in living organisms are quite different. Animals, in particular, employ sodium and potassium differentially to generate electrical potentials in animal cells, especially in nervous tissue
. Potassium depletion in animals, including humans, results in various neurological dysfunctions.
, while sodium
is the major cation outside animal cells. The concentration
differences of these charged particles causes a difference in electric potential
between the inside and outside of cells, known as the membrane potential
. The balance between potassium and sodium is maintained by ion pumps in the cell membrane
. All potassium ion channels are tetramers with several conserved secondary structural elements. The most recently resolved potassium ion channel is KirBac3.1, which gives a total of five potassium ion channels (KcsA, KirBac1.1, KirBac3.1, KvAP, MthK) with a determined structure. All five are from prokaryotic species. The cell membrane potential created by potassium and sodium ions allows the cell to generate an action potential
—a "spike" of electrical discharge. The ability of cells to produce electrical discharge is critical for body functions such as neurotransmission
, muscle contraction, and heart function.
. Hypokalemia typically results from loss of potassium through diarrhea
, diuresis
, or vomiting. Symptoms are related to alterations in membrane potential and cellular metabolism. Symptoms include muscle weakness and cramps, paralytic ileus
, ECG abnormalities, intestinal paralysis, decreased reflex response and (in severe cases) respiratory paralysis, alkalosis
and arrhythmia.
In rare cases, habitual consumption of large amounts of black licorice has resulted in hypokalemia. Licorice contains a compound (Glycyrrhizin
) that increases urinary excretion of potassium.
in healthy individuals, many long-term health risks are related to insufficient dietary potassium.
The 2004 guidelines of the Institute of Medicine
specify an RDA of 4700 mg of potassium for adults, based on intake levels that have been found to lower blood pressure, reduce salt sensitivity, and minimize the risk of kidney stones. However, most Americans consume only half that amount per day. Similarly, in the European Union
, particularly in Germany
and Italy
, insufficient potassium intake is widespread.
Diseases that may be prevented by adequate potassium intake include stroke
, osteoporosis
, kidney stones, and hypertension
.
, orange juice
, potato
es, banana
s, coconut
, avocado
s, apricot
s, parsnip
s and turnip
s, although many other fruit
s, vegetable
s, legumes, and meats contain potassium.
Hyperkalemia
is the most serious adverse reaction to potassium. Hyperkalemia occurs when potassium builds up faster than the kidneys can remove it. It is most common in individuals with renal failure
. Symptoms of hyperkalemia
may include tingling of the hands and feet, muscular weakness, and temporary paralysis. The most serious complication of hyperkalemia is the development of an abnormal heart rhythm (arrhythmia), which can lead to cardiac arrest.
Although hyperkalemia
is rare in healthy individuals, oral doses greater than 18 grams taken at one time in individuals not accustomed to high intakes can lead to hyperkalemia
. All supplements sold in the U.S. contain no more than 99 mg of potassium; a healthy individual would need to consume more than 180 such pills to experience severe health risks.
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
is an essential mineral macronutrient and is the main intracellular
Intracellular
Not to be confused with intercellular, meaning "between cells".In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".It is used in contrast to extracellular...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
for all types of cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s.
It is important in maintaining fluid and electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
balance in the bodies of humans and animals.
Potassium ion is necessary for the function of all living cells, and is thus present in all plant and animal tissues. It is found in especially high concentrations within plant cells, and in a mixed diet, it is most highly concentrated in fruits. The high concentration of potassium in plants, associated with comparatively very low amounts of sodium there, historically resulted in potassium first being isolated from the ashes of plants (potash
Potash
Potash is the common name for various mined and manufactured salts that contain potassium in water-soluble form. In some rare cases, potash can be formed with traces of organic materials such as plant remains, and this was the major historical source for it before the industrial era...
), which in turn gave the element its modern name. The high concentration of potassium in plants means that heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 93% of the potassium chemical production of the modern world economy.
The functions of potassium and sodium in living organisms are quite different. Animals, in particular, employ sodium and potassium differentially to generate electrical potentials in animal cells, especially in nervous tissue
Nervous tissue
Nervous tissue is one of four major classes of vertebrate tissue.Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions...
. Potassium depletion in animals, including humans, results in various neurological dysfunctions.
Function in animals
Potassium is the major cation (positive ion) inside animal cellsCell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, while sodium
Sodium
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...
is the major cation outside animal cells. The concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
differences of these charged particles causes a difference in electric potential
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
between the inside and outside of cells, known as the membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
. The balance between potassium and sodium is maintained by ion pumps in the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
. All potassium ion channels are tetramers with several conserved secondary structural elements. The most recently resolved potassium ion channel is KirBac3.1, which gives a total of five potassium ion channels (KcsA, KirBac1.1, KirBac3.1, KvAP, MthK) with a determined structure. All five are from prokaryotic species. The cell membrane potential created by potassium and sodium ions allows the cell to generate an action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
—a "spike" of electrical discharge. The ability of cells to produce electrical discharge is critical for body functions such as neurotransmission
Neurotransmission
Neurotransmission , also called synaptic transmission, is the process by which signaling molecules called neurotransmitters are released by a neuron , and bind to and activate the receptors of another neuron...
, muscle contraction, and heart function.
Hypokalemia
A severe shortage of potassium in body fluids may cause a potentially fatal condition known as hypokalemiaHypokalemia
Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
. Hypokalemia typically results from loss of potassium through diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, diuresis
Diuresis
Diuresis may refer to:* Urine production, as an aspect of fluid balance* Excessive urine production - see polyuria* Immersion diuresis...
, or vomiting. Symptoms are related to alterations in membrane potential and cellular metabolism. Symptoms include muscle weakness and cramps, paralytic ileus
Ileus
Ileus is a disruption of the normal propulsive ability of the gastrointestinal tract.Ileus is commonly defined simply as bowel obstruction. However, authoritative sources define it as decreased motor activity of the GI tract due to non-mechanical causes...
, ECG abnormalities, intestinal paralysis, decreased reflex response and (in severe cases) respiratory paralysis, alkalosis
Alkalosis
Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis .-Causes:...
and arrhythmia.
In rare cases, habitual consumption of large amounts of black licorice has resulted in hypokalemia. Licorice contains a compound (Glycyrrhizin
Glycyrrhizin
Glycyrrhizin is the main sweet-tasting compound from liquorice root. It is 30–50 times as sweet as sucrose . Pure glycyrrhizin is odorless....
) that increases urinary excretion of potassium.
Insufficient intake
Although low dietary intake of potassium does not lead to hypokalemiaHypokalemia
Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
in healthy individuals, many long-term health risks are related to insufficient dietary potassium.
The 2004 guidelines of the Institute of Medicine
Institute of Medicine
The Institute of Medicine is a not-for-profit, non-governmental American organization founded in 1970, under the congressional charter of the National Academy of Sciences...
specify an RDA of 4700 mg of potassium for adults, based on intake levels that have been found to lower blood pressure, reduce salt sensitivity, and minimize the risk of kidney stones. However, most Americans consume only half that amount per day. Similarly, in the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
, particularly in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, insufficient potassium intake is widespread.
Diseases that may be prevented by adequate potassium intake include stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
, osteoporosis
Osteoporosis
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
, kidney stones, and hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
.
Food sources
Eating a variety of foods that contain potassium is the best way to get an adequate amount. Healthy individuals who eat a balanced diet rarely need supplements. Foods with high sources of potassium include kiwifruitKiwifruit
The kiwifruit, often shortened to kiwi in many parts of the world, is the edible berry of a cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia....
, orange juice
Orange juice
Orange juice is a popular beverage made from oranges. It is made by extraction from the fresh fruit, by desiccation and subsequent reconstitution of dried juice, or by concentration of the juice and the subsequent addition of water to the concentrate...
, potato
Potato
The potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...
es, banana
Banana
Banana is the common name for herbaceous plants of the genus Musa and for the fruit they produce. Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red....
s, coconut
Coconut
The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
, avocado
Avocado
The avocado is a tree native to Central Mexico, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel...
s, apricot
Apricot
The apricot, Prunus armeniaca, is a species of Prunus, classified with the plum in the subgenus Prunus. The native range is somewhat uncertain due to its extensive prehistoric cultivation.- Description :...
s, parsnip
Parsnip
The parsnip is a root vegetable related to the carrot. Parsnips resemble carrots, but are paler than most carrots and have a sweeter taste, especially when cooked. The buttery, slightly spicy, sweet flavor of cooked mature parsnips is reminiscent of butterscotch, honey, and subtle cardamom...
s and turnip
Turnip
The turnip or white turnip is a root vegetable commonly grown in temperate climates worldwide for its white, bulbous taproot. Small, tender varieties are grown for human consumption, while larger varieties are grown as feed for livestock...
s, although many other fruit
Fruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
s, vegetable
Vegetable
The noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....
s, legumes, and meats contain potassium.
Side effects and toxicity
Gastrointestinal symptoms are the most common side effects of potassium supplements, including nausea, vomiting, abdominal discomfort, and diarrhea. Taking potassium with meals or taking a microencapsulated form of potassium may reduce gastrointestinal side effects.Hyperkalemia
Hyperkalemia
Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium in the blood is elevated...
is the most serious adverse reaction to potassium. Hyperkalemia occurs when potassium builds up faster than the kidneys can remove it. It is most common in individuals with renal failure
Renal failure
Renal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...
. Symptoms of hyperkalemia
Hyperkalemia
Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium in the blood is elevated...
may include tingling of the hands and feet, muscular weakness, and temporary paralysis. The most serious complication of hyperkalemia is the development of an abnormal heart rhythm (arrhythmia), which can lead to cardiac arrest.
Although hyperkalemia
Hyperkalemia
Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium in the blood is elevated...
is rare in healthy individuals, oral doses greater than 18 grams taken at one time in individuals not accustomed to high intakes can lead to hyperkalemia
Hyperkalemia
Hyperkalemia refers to the condition in which the concentration of the electrolyte potassium in the blood is elevated...
. All supplements sold in the U.S. contain no more than 99 mg of potassium; a healthy individual would need to consume more than 180 such pills to experience severe health risks.
See also
- HypokalemiaHypokalemiaHypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...
- HyperkalemiaHyperkalemiaHyperkalemia refers to the condition in which the concentration of the electrolyte potassium in the blood is elevated...
- Action PotentialAction potentialIn physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
- Membrane potentialMembrane potentialMembrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
- ElectrolyteElectrolyteIn chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....