Potassium - Mineral

• Method of Action
• Consequences of Deficiency
• Recommended Dietary Allowances

• Properties and Uses
• Toxicity Levels
• Food Sources

Description

There are estimated to be approximately 250 grams of potassium present in the adult human body. Most of the potassium in the body is intercellular and, reciprocally most of the body’s sodium in extracellular.

The movement of potassium into extracellular fluid from muscle cells is an important part of the contraction mechanism of muscle tissue.

Potassium is pumped into the cell by active transport systems, which concomitantly pump sodium out of the cell. The preferential segregation of sodium and potassium across the cell’s biological membrane is important in maintaining osmotic balance, the electrochemical gradient of membranes, and the regulation of extracellular fluid volume. This mechanism of ion pumping is also instrumental in the restoration of potassium/sodium gradient after the ionic transmission of nerve impulses.

Potassium is important in preserving the acid/base balance of the body, and is an elemental constituent of blood platelets.

Method of Action

Potassium is principally found within cellular fluids and its counterpart, sodium, is mostly found within the extracellular fluids. The segregation of these two ions occurs by means of an adenosine triphosphate (ATP) driven "pump." The pump consists of two proteins within the cellular membrane which, upon energy release from ATP, transport three sodium molecules to the outside of the cell membrane, while simultaneously bringing in two potassium molecules.

A similar pumping mechanism is used in the transport of glucose from the intestine into the bloodstream. High sodium concentrations in the intestinal fluids tend to promote the movement of sodium across the mucosal cells of the intestine. As sodium is moved across the cells, glucose is concomitantly moved into the cells. The concentration of glucose within the cells builds up until it begins to diffuse into the bloodstream. The "pump" mechanism pumps the sodium into the blood in exchange for potassium, thereby eliminating sodium buildup within the cell. A similar mechanism is used to transport amino acids.

Potassium is an essential constituent of several blood buffer systems. Potassium complexes ionically with the sulfate group of sulfuric acid, thereby reducing the acidity of the system by forming a potassium sulfate salt. Potassium has a similar action in base buffer systems with the conversion of the strong base potassium hydroxide into the relatively neutral water molecule.

After the transmission of a nerve impulse, during which sodium ions are shifted across the nerve’s synaptic membrane, potassium and sodium are exchanged by the previously mentioned "pump" mechanism (so as to restore the original sodium concentration on the external side of the membrane). This "pumping" of sodium outside is essential to prepare for subsequent nerve transmission.

Potassium acts to relax muscle contraction in opposition to calcium, which induces contraction.

Potassium is absorbed readily in the small intestine; excess potassium is excreted through the urine. Aldosterone hormone tends to promote potassium excretion in substitution for sodium absorption. This is done by activation of the renal "pump" proteins, which simultaneously exchange potassium for sodium across the biological membrane.

Potassium absorption is hindered by the anti-inflammatory agents colchicine and salicylazosulfapyridine; laxatives such as phenolphthalein, cascara sagrada, and bisacodyl; and various antimicrobial agents (e.g., tetracycline, and neomycin).

Properties and Uses

Potassium has been proven to be essential, along with increased protein intake, in the treatment of kwashiorkor.

Potassium supplementation is effective in treatment of potassium deficiency symptoms, which include overall muscle weakness, abdominal bloating, heart abnormalities, as well as weak respiration.

Potassium is recommended for patients with congestive heart failure who muse use diuretics regularly; diuretics tend to deplete potassium levels in the body.

Potassium supplements may be used to replenish potassium lost during periods of chronic illness, and in some patients, the potassium lost due to stress.

Potassium is also useful in the treatment of acute diarrhea, diabetic coma, congenital renal alkalosis, aldosteronism, and in the case of surgical patients, to replace lost body potassium.

Consequences of Deficiency

Potassium deficiency rarely occurs as a result of inadequate dietary intake, but rather as a result of excessive diarrhea or vomiting, malnutrition, surgery, or use of diuretics. On occasion, prolonged disease may promote a decrease in potassium levels in the body.

Symptoms of potassium deficiencies include overall muscle weakness, abdominal bloating, weak respiration, and heart abnormalities (possibly heart attack).

Magnesium deficiency can also induce a concomitant potassium deficiency.

Loss of large amounts of potassium can lead to the condition of metabolic alkalosis (elevated blood pH) and prolonged deficiency can enhance the prevalence of high blood cholesterol levels.

Toxicity Levels

Excesses of ionized potassium can accumulate and become toxic in instances of a renal failure to clear excess potassium, rapid intravenous administration, or excess ingestion of potassium chloride (25 grams daily). Symptoms may include diarrhea, weakening of respiration and heart action, and numbness in extremities.

Renal abnormalities can result in a dangerous accumulation of potassium if urinary excretion is not sufficient. This can result in hyperkalemia (elevated serum potassium levels) and possibly provoke cardiac arrest, although this phenomenon is extremely rare.

Recommended Dietary Allowances

The range of actual intake for children is 780 to 1,600 milligrams per day; adults the range is estimated at 1,950 to 5,900 milligrams per day. There is no set RDA for potassium for adults.

RDA for child/adolescent: 90 mg

RDA for infants: 90 mg

Food Sources