Electrolyte Balance – Anatomy, Mechanism, Functions

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Electrolyte balance is one of the key issues in maintaining homeostasis in the body, and it also plays important roles in protecting cellular function, tissue perfusion, and acid-base balance. Fluid and electrolyte balance must also be maintained for the management of many clinical conditions. Electrolyte imbalances are common findings in many diseases.[,] Imbalances in every electrolyte must be considered in a combined and associated fashion, and examinations must aim to clarify the clinical scenario for an effective and successful treatment. Most of the important and prevailing electrolyte imbalances are hypo- and hyper-states of sodium, potassium, calcium, and magnesium.

Electrolytes are essential for basic life functioning, such as maintaining electrical neutrality in cells, generating and conducting action potentials in the nerves and muscles. Sodium, potassium, and chloride are significant electrolytes along with magnesium, calcium, phosphate, and bicarbonates. Electrolytes come from our food and fluids.

These electrolytes can have an imbalance, leading to either high or low levels. High or low levels of electrolytes disrupt normal bodily functions and can lead to even life-threatening complications. This article reviews the basic physiology of electrolytes and their abnormalities, and the consequences of electrolyte imbalance.

Electricity and your body

Electrolytes take on a positive or negative charge when they dissolve in your body fluid. This enables them to conduct electricity and move electrical charges or signals throughout your body. These charges are crucial to many functions that keep you alive, including the operation of your brain, nerves, and muscles, and the creation of new tissue.

Each electrolyte plays a specific role in your body. The following are some of the most important electrolytes and their primary functions:

Sodium

  • helps control fluids in the body, impacting blood pressure
  • necessary for muscle and nerve function

Chloride

  • helps balance electrolytes
  • helps balance electrolytes
  • balances acidity and alkalinity, which helps maintain a healthy pH
  • essential to digestion

Potassium

  • regulates your heart and blood pressure
  • helps balance electrolytes
  • aids in transmitting nerve impulses
  • contributes to bone health
  • necessary for muscle contraction

Magnesium

  • important to the production of DNA and RNA
  • contributes to nerve and muscle function
  • helps maintain heart rhythm
  • helps regulate blood glucose levels
  • enhances your immune system

Calcium

  • key component of bones and teeth
  • important to the movement of nerve impulses and muscle movement
  • contributes to blood clotting

Phosphate

  • strengthens bones and teeth
  • helps cells produce the energy needed for tissue growth and repair

Bicarbonate

  • helps your body maintain a healthy pH
  • regulates heart function

Sodium, Electrolytes, and Fluid Balance

Electrolytes play a vital role in maintaining homeostasis within the body.

Key Points

Electrolytes help to regulate myocardial and neurological functions, fluid balance, oxygen delivery, acid-base balance, and much more.

The most serious electrolyte disturbances involve abnormalities in the levels of sodium, potassium, and/or calcium.

Kidneys work to keep the electrolyte concentrations in the blood constant despite changes in the body.

Key Terms

  • homeostasis: The ability of a system or living organism to adjust its internal environment to maintain a stable equilibrium; such as the ability of warm-blooded animals to maintain a constant temperature.
  • electrolyte: Any of the various ions (such as sodium or chloride) that regulate the electric charge on cells and the flow of water across their membranes.
  • sodium: A chemical element with the symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals.

Importance of Electrolyte Balance

Electrolytes play a vital role in maintaining homeostasis within the body. They help regulate myocardial and neurological function, fluid balance, oxygen delivery, acid-base balance, and other biological processes.

Electrolytes are important because they are what cells (especially those of the nerve, heart, and muscle ) use to maintain voltages across their cell membranes and to carry electrical impulses (nerve impulses, muscle contractions) across themselves and to other cells.

Electrolyte imbalances can develop from excessive or diminished ingestion and from the excessive or diminished elimination of an electrolyte. The most common cause of electrolyte disturbances is renal failure. The most serious electrolyte disturbances involve abnormalities in the levels of sodium, potassium, and/or calcium.

Other electrolyte imbalances are less common and often occur in conjunction with major electrolyte changes. Chronic laxative abuse or severe diarrhea or vomiting (gastroenteritis) can lead to electrolyte disturbances combined with dehydration. People suffering from bulimia or anorexia nervosa are especially at high risk for an electrolyte imbalance.

Kidneys work to keep the electrolyte concentrations in blood constant despite changes in your body. For example, during heavy exercise electrolytes are lost through sweating, particularly sodium and potassium, and sweating can increase the need for electrolyte (salt) replacement. It is necessary to replace these electrolytes to keep their concentrations in the body fluids constant.

Dehydration

There are three types of dehydration:

  • Hypotonic or hyponatremic (primarily a loss of electrolytes, sodium in particular).
  • Hypertonic or hypernatremic (primarily a loss of water).
  • Isotonic or hyponatremic (an equal loss of water and electrolytes).

In humans, the most common type of dehydration by far is isotonic (isonatraemic) dehydration; which effectively equates with hypovolemia; but the distinction of isotonic from hypotonic or hypertonic dehydration may be important when treating people with dehydration.

Physiologically, and despite the name, dehydration does not simply mean loss of water, as both water and solutes (main sodium) are usually lost in roughly equal quantities as to how they exist in blood plasma. In hypotonic dehydration, intravascular water shifts to the extravascular space and exaggerates the intravascular volume depletion for a given amount of total body water loss.

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Neurological complications can occur in hypotonic and hypertonic states. The former can lead to seizures, while the latter can lead to osmotic cerebral edema upon rapid rehydration.

In more severe cases, the correction of a dehydrated state is accomplished by the replenishment of necessary water and electrolytes (through oral rehydration therapy or fluid replacement by intravenous therapy). As oral rehydration is less painful, less invasive, less expensive, and easier to provide, it is the treatment of choice for mild dehydration. Solutions used for intravenous rehydration must be isotonic or hypotonic.

This diagram illustrates the mechanism for the transportation of water and electrolytes across the epithelial cells of the secretory glands.

Cell electrolytes: This diagram illustrates the mechanism for the transportation of water and electrolytes across the epithelial cells in the secretory glands.

Sodium Balance Regulation

Sodium is an important cation that is distributed primarily outside the cell.

Key Points

The body has a potent sodium-retaining mechanism: the renin-angiotensin system.

In states of sodium depletion, aldosterone levels increase; in states of sodium excess, aldosterone levels decrease.

The major physiological controller of aldosterone secretion is the plasma angiotensin II level that increases aldosterone secretion.

Key Terms

  • sodium: A chemical element with the symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals.
  • aldosterone: A mineralocorticoid hormone that is secreted by the adrenal cortex and regulates the balance of sodium and potassium in the body.
  • angiotensin: Any of several polypeptides that narrow the blood vessels and regulate arterial pressure.

Sodium Regulation

Sodium is an important cation that is distributed primarily outside the cell. The cell sodium concentration is about 15 mmol/l, but it varies in different organs; it has an intracellular volume of 30 liters and about 400 mmol are inside the cell.

The plasma and interstitial sodium is about 140 mmol/l with an extracellular volume of about 13 liters, 1,800 mmol are in the extracellular space. The total body sodium, however, is about 3,700 mmol as there is about 1,500 mmol stored in bones.

The body has potent sodium-retaining mechanisms and even if a person is on five mmol Na+/day they can maintain sodium balance. Extra sodium is lost from the body by reducing the activity of the renin –angiotensin system that leads to increased sodium loss from the body. Sodium is lost through the kidneys, sweat, and feces.

In states of sodium depletion, the aldosterone levels increase. In states of sodium excess, aldosterone levels decrease. The major physiological controller of aldosterone secretion is the plasma angiotensin II level that increases aldosterone secretion.

A high plasma potassium level also increases aldosterone secretion because, besides retaining Na+, high plasma aldosterone causes K+ loss by the kidney. Plasma Na+ levels have little effect on aldosterone secretion.

This is a diagram of the regulation of sodium via the hormones renin, angiotensin, and aldosterone. In states of sodium depletion, the aldosterone levels increase, and in states of sodium excess, the aldosterone levels decrease.

Renin-angiotensin system: The regulation of sodium via the hormones renin, angiotensin, and aldosterone. In states of sodium depletion, the aldosterone levels increase, and in states of sodium excess, the aldosterone levels decrease.

A low renal perfusion pressure stimulates the release of renin, which forms angiotensin I that is converted to angiotensin II. Angiotensin II will correct the low perfusion pressure by causing the blood vessels to constrict, and increase sodium retention by its direct effect on the proximal renal tubule and by an effect operated through aldosterone. The perfusion pressure to the adrenal gland has a little direct effect on aldosterone secretion and the low blood pressure operates to control aldosterone via the renin-angiotensin system.

Aldosterone also acts on the sweat ducts and colonic epithelium to conserve sodium. When aldosterone is activated to retain sodium the plasma sodium tends to rise. This immediately causes the release of ADH, which causes water to be retained, thus balancing Na+ and H2O in the right proportion to restore plasma volume.

In addition to aldosterone and angiotensin II, other factors influence sodium excretion.

  • Atrial peptide causes the loss of sodium by the kidneys: it is secreted from the heart in high sodium states due to excess intake or cardiac disease.
  • Elevated blood pressure will also cause Na+ loss, and low blood pressure usually leads to sodium retention.

Potassium Balance Regulation

Potassium is mainly an intracellular ion.

Key Points

Most of the total body potassium is inside the cells and the next largest proportion is in the bones.

In an unprocessed diet, potassium is much more plentiful than sodium and it is present as an organic salt, while sodium is added as NaCl.

High potassium intake can potentially increase the extracellular K+ level two times before the kidney can excrete the extra potassium.

High plasma potassium increases aldosterone secretion and this increases the potassium loss from the body to restore balance.

Key Terms

  • alkalotic: A condition that reduces the hydrogen ion concentration of arterial blood plasma (alkalemia). Generally, alkalosis is said to occur when the blood pH exceeds 7.45.
  • Potassium: A chemical element with the symbol K and the atomic number 19. Elemental potassium is a soft, silvery-white, alkali metal that oxidizes rapidly in the air and is very reactive with water—it can generate sufficient heat to ignite the hydrogen emitted in the reaction.
  • acidosis: An increase in acidity of the blood and other body tissue (i.e., an increased hydrogen ion concentration). If not further qualified, it usually refers to the acidity of the blood plasma.

Potassium Balance

Potassium is predominantly an intracellular ion. Most of the total body potassium of about 4,000 mmol is inside the cells, and the next largest proportion (300–500 mmol) is in the bones. Cell K+ concentration is about 150 mmol/l but varies in different organs. Extracellular potassium is about 4.0 mmol/l, with an extracellular value of about 13 liters, 52 mmol (i.e., less than 1.5%) is present here and only 12 mmol is in the plasma.

In an unprocessed diet, potassium is much more plentiful than sodium. It is present as an organic salt, while sodium is added as NaCl. In a hunter-gatherer, K+ intake may be as much as 400 mmol/d while in the Western diet it is 70 mmol/d or less if a person has a minimal amount of fresh fruit and vegetables.

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The processing of foods replaces K+ with NaCl. While the body can excrete a large K+ load, it is unable to conserve K+. On a zero K+ intake, or in a person with K+ depletion, there will still be a loss of K+ of 30–50 mmol/d in the urine and feces.

Acid-Base Status Control

If there is a high potassium intake, for example, 100 mmol, this would potentially increase the extracellular K+ level two times before the kidney could excrete the extra potassium. The body buffers the extra potassium by equilibrating it within the cells.

The acid-base status controls the distribution between plasma and cells. A high pH (i.e., alkalosis >7.4) favors the movement of K+ into the cells, and a low pH (i.e., acidosis ) causes movement out of the cell. A high plasma potassium level increases aldosterone secretion and this increases the potassium loss from the body to restore balance.

This change of distribution with the acid-base status means that the plasma K+ may not reflect the total body content. Therefore, a person with acidosis (pH 7.1) and a plasma K+ of 6.5 mmol/l could be depleted of total body potassium. This occurs in diabetic acidosis. Conversely, a person who is alkalotic with a plasma K+ of 3.4 mmol/l may have a normal level of total body potassium.

Calcium and Phosphate Balance Regulation

Calcium is a key electrolyte: 99% is deposited in the bones and the remainder is associated with hormone release and cell signaling.

Key Points

Calcium absorption is controlled by vitamin D, and calcium excretion is controlled by the parathyroid hormones.

There is a constant loss of calcium by the kidney even if there is none in the diet.

Calcium in plasma exists in three forms: ionized, nonionized and protein-bound.

Key Terms

  • calcium: A chemical element, atomic number 20, that is an alkaline earth metal and occurs naturally as carbonate in limestone and as silicate in many rocks.
  • parathyroid hormone: A polypeptide hormone that is released by the chief cells of the parathyroid glands and is involved in raising the levels of calcium ions in the blood.
  • vitamin D: A fat-soluble vitamin that is required for normal bone development and that prevents rickets; it can be manufactured in the skin on exposure to sunlight.

Calcium is a very important electrolyte. Ninety-nine percent or more is deposited in the bones and the remainder plays a vital role in nerve conduction, muscle contraction, hormone release, and cell signaling.

The plasma concentration of Ca++ is 2.2 mmol/l, and phosphate is 1.0 mmol/l. The solubility product of Ca and P is close to saturation in plasma. The concentration of Ca++ in the cytoplasm is < 10–6 mmol/l but the concentration of Ca++ in the cell is much higher as calcium is taken up (and is able to be released from) cell organelles.

In the typical Australian diet, there is about 1200 mg/d of calcium. Even if it was all soluble it is not all absorbed as it combines with phosphates in the intestinal secretions. In addition, absorption is regulated by the active vitamin D; increased amounts of vitamin D increase Ca++ absorption.

Absorption is controlled by vitamin D while excretion is controlled by parathyroid hormones. However, the distribution from bone to plasma is controlled by both the parathyroid hormones and vitamin D.

There is also a constant loss of calcium via the kidneys even if there is none in the diet. This excretion of calcium by the kidneys and its distribution between bone and the rest of the body is primarily controlled by the parathyroid hormone.

The calcium in plasma exists in three forms:

  1. Ionized.
  2. Nonionized.
  3. Protein-bound.

It is the ionized calcium concentration that is monitored by the parathyroid gland —if it is low, parathyroid hormone secretion is increased. This increases the ionized calcium levels by increasing bone re-absorption, decreasing renal excretion, and acting on the kidney to increase the rate of formation of active vitamin D, thereby increasing the gut’s absorption of calcium.

The usual amount of phosphate in the diet is about 1 g/d but not all of it is absorbed. Any excess is excreted by the kidney and this excretion is increased by the parathyroid hormone.

This hormone also causes phosphate to leach out of the bones. Plasma phosphate has no direct effect on parathyroid hormone secretion; however, if it is elevated it combines with Ca++ to decrease ionized Ca++ in plasma, and thereby increase parathyroid hormone secretion.

This is an illustration of how parathyroid hormone regulates the levels of calcium in the blood. The parathyroid glands release parathyroid hormone that causes calcium reabsorption and vitamin D hydroxylation in the kidneys, calcium absorption from the intestines, calcium reabsorption from the bones, and an increase of calcium in the blood.

Calcium regulation: This is an illustration of how the parathyroid hormone regulates the levels of calcium in the blood.

Anion Regulation

The anions chloride, bicarbonate, and phosphate have important roles in maintaining the balance and neutrality of vital body mechanisms.

Key Points

Chloride is needed to maintain proper hydration, as well as to balance cations, and maintain the electrical neutrality of the extracellular fluid.

Bicarbonate‘s main role is to maintain the body’s acid-base balance through a buffer system.

Phosphate is a major constituent of the intracellular fluid, and it is important in the regulation of metabolic processes and as a buffering agent in animal cells.

The kidneys regulate the salt balance in the blood by controlling the excretion and the reabsorption of various ions.

Key Terms

  • anion: An negatively charged ion.
  • hyperphosphatemia: An elevated amount of phosphate in the blood.
  • hypochloremia: An electrolyte disturbance caused by an abnormally depleted level of chloride ions in the blood.
  • hypophosphatemia: An electrolyte disturbance caused by an abnormally low level of phosphate in the blood.

Anion Regulation

The excretion of ions occurs mainly through the kidneys, with lesser amounts of ions being lost in sweat and in feces. In addition, excessive sweating may cause a significant loss, especially of the anion chloride. Severe vomiting or diarrhea will also cause a loss of chloride and bicarbonate ions.

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Adjustments in the respiratory and renal functions allow the body to regulate the levels of these ions in the extracellular fluid (ECF).

Chloride

Chloride is the predominant extracellular anion and it is a major contributor to the osmotic pressure gradient between the intracellular fluid (ICF) and extracellular fluid (ECF). Chloride maintains proper hydration and functions to balance the cations in the ECF to keep the electrical neutrality of this fluid. The paths of secretion and reabsorption of chloride ions in the renal system follow the paths of sodium ions.

Hypochloremia, or lower-than-normal blood chloride levels, can occur because of defective renal tubular absorption. Vomiting, diarrhea, and metabolic acidosis can also lead to hypochloremia.

In contrast, hyperchloremia, or higher-than-normal blood chloride levels, can occur due to dehydration, excessive intake of dietary salt (NaCl) or the swallowing of sea water, aspirin intoxication, congestive heart failure, and the hereditary, chronic lung disease cystic fibrosis. In people who have cystic fibrosis, the chloride levels in their sweat are two to five times those of normal levels; therefore, analysis of their sweat is often used to diagnose the disease.

Bicarbonate

Bicarbonate is the second-most abundant anion in the blood. Its principal function is to maintain your body’s acid–base balance by being part of buffer systems.

Bicarbonate ions result from a chemical reaction that starts with the carbon dioxide (CO2) and water (H2O) molecules that are produced at the end of aerobic metabolism. Only a small amount of CO2 can be dissolved in body fluids; thus, over 90 percent of the CO2 is converted into bicarbonate ions, HCO3-, through the following reactions:

CO2 + H2O ↔ H2CO↔ H2CO3– + H+

The bidirectional arrows indicate that the reactions can go in either direction depending on the concentrations of the reactants and products. Carbon dioxide is produced in large amounts in tissues that have a high metabolic rate, and is converted into bicarbonate in the cytoplasm of the red blood cells through the action of an enzyme called carbonic anhydrase.

Bicarbonate is transported in the blood and once in the lungs, the reactions reverse direction, and CO2 is regenerated from the bicarbonate to be exhaled as metabolic waste.

This diagram shows how carbonate acts as a buffering system. In the lungs, CO2 is produced from bicarbonate and removed as metabolic waste through the reverse reaction of the bicarbonate bidirectional equation.

Bicarbonate as a buffering system: In the lungs, CO2 is produced from bicarbonate and removed as metabolic waste through the reverse reaction of the bicarbonate bidirectional equation.

Phosphate

Phosphate is present in the body in three ionic forms:

  1. H2PO4
  2. HPO42−
  3. PO43−

The addition and removal of phosphate from the proteins in all cells is a pivotal strategy in the regulation of metabolic processes. Phosphate is useful in animal cells as a buffering agent, and the most common form is HPO2−4. Bone and teeth bind up 85 percent of the body’s phosphate as part of calcium phosphate salts. In addition, phosphate is found in phospholipids, such as those that make up the cell membrane, and in ATP, nucleotides, and buffers.

Hypophosphatemia, or abnormally low phosphate blood levels, occurs with the heavy use of antacids, during alcohol withdrawal, and during malnourishment. In the face of phosphate depletion, the kidneys usually conserve phosphate, but during starvation, this conservation is impaired greatly.

Hyperphosphatemia, or abnormally increased levels of phosphates in the blood, occurs if there is decreased renal function or in cases of acute lymphocytic leukemia. Additionally, because phosphate is a major constituent of the ICF, any significant destruction of cells can result in the dumping of phosphate into the ECF.

Normal and Critical Findings

Laboratory Values: 

Serum Sodium: 

  • Normal Range: 135 to 145 mmol/L
  • Mild-moderate Hyponatremia: 125 to 135 mmol/L, Severe: less than 125 mmol/L
  • Hypernatremia: Mild-moderate: 145 to 160 mmol/L, Severe: over 160 mmol/L

Serum Potassium:

  • Normal Range: 3.6 to 5.5 mmol/L
  • Hypokalemia: Mild Hypokalemia under 3.6 mmol/L, Moderate: 2.5 mmol/L, Severe : greater than 2.5 mmol/L
  • Hyperkalemia: Mild hyperkalemia: 5 to 5.5 mmol/L, Moderate- 5.5 to 6.5, Severe: 6.5 to 7 mmol/L

Serum Calcium: 

  • Normal Range: 8.8 to 10.7 mg/dl
  • Hypercalcemia: greater than 10.7 mg/dl , Severe: over 11.5 mg/dl
  • Hypocalcemia: less than 8.8 mg/dl

Serum Magnesium: 

  • Normal Range: 1.46 to 2.68 mg/dl
  • Hypomagnesemia: under 1.46 mg/dl
  • Hypermagenesemia: over 2.68

Bicarbonate:

  • Normal Range: 23 to 30 mmol/L\
  • It increases or decreases depending on the acid-base status.

Phosphorus:

  • Normal Range: 3.4 to 4.5 mg/dl
  • Hypophosphatemia: less than 2.5 mg/dl
  • Hyperphosphatemia: greater than 4.5 mg/dl

Complications

Both hyponatremia and hypernatremia, as well as hypomagnesemia, can lead to neurological consequences such as seizure disorders.

Hypokalemia and hyperkalemia, as well as hypocalcemia, are more responsible for arrhythmias.

Bicarbonate imbalance can lead to metabolic acidosis or alkalosis.

Patient Safety and Education

A piece of valuable advice to the patients would be to take the medications exactly as prescribed by the clinicians to avoid electrolyte imbalance as a consequence of not taking the prescribed dose.

One should call for immediate medical help when the patient feels weak, has muscle ache, or has altered consciousness.

Clinical Significance

Some of the common causes of electrolyte disorders seen in clinical practices are:

  • Hyponatremia: low dietary sodium intake, primary polydipsia, SIADH, congestive heart failure, hepatic cirrhosis, failure of adrenal glands, hyperglycemia, dyslipidemia
  • Hypernatremia: unreplaced fluid loss through the skin and gastrointestinal tract, osmotic diuresis, hypertonic saline administration
  • Hypokalemia: hyperaldosteronism, loop diuretics
  • Hyperkalemia: increase release from cells as in metabolic acidosis, insulin deficiency, beta-blocker or decreased potassium excretion as in acute or chronic kidney disease, aldosterone deficiency or resistance
  • Hypercalcemia: malignancy, hyperparathyroidism, chronic granulomatous disease
  • Hypocalcemia: acute pancreatitis, parathyroid hormone deficiency after thyroidectomy, neck dissection, resistance to parathormone, hypomagnesemia, sepsis
  • Hypermagnesemia: increase oral magnesium intake
  • Hypomagnesemia: renal losses as in diuretics, alcohol use disorder or GI losses as in diarrhea
  • Bicarbonate level: increases in primary metabolic alkalosis or compensation to primary respiratory acidosis – decreases in primary metabolic acidosis or compensation to primary respiratory alkalosis.
  • Hyperchloremia: normal saline infusion
  • Hypochloremia: GI loss as in diarrhea, renal losses with diuretics
  • Hypophosphatemia: refeeding syndrome, vitamin D deficiency, hyperparathyroidism
  • Hyperphosphatemia: hypoparathyroidism, chronic kidney disease

References

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