Major Extracellular and Intracellular Electrolytes


Electrolytes plays an important role in maintaining physiological balance, regulating fluid balance, nerve signalling and muscle contraction in the human body. Understanding the intracellular and extracellular fluid is fundamental for maintaining overall health and preventing electrolyte imbalances which can lead to serious medical complications. In this article we will see major intracellular and extracellular electrolytes, exploring their functions and their sources.

Major extracellular and intracellular electrolytes

There are various organic and inorganic compounds present in the body. There is various regulatory mechanism which control the ionic balance, osmotic balance and pH of body fluids. If the body cannot maintain or correct the electrolyte balance, then it is balanced by external administration, which is known as replacement therapy.

The body fluids contain various inorganic ions which are either anionic or cationic in character. The concentration of some important electrolytes in the intracellular, extracellular and plasma are given in below table.

IonsExtracellular electrolytes (mEq/L)Intracellular electrolytes (mEq/L)Plasma range (mEq/L)








































Major cations


Normally human body contains about 1.8 g/kg of sodium ions (Na+). The good food sources of sodium are table salt, milk, baking powder, meat and some vegetables. Daily requirement of sodium is about 3-5 g for a normal adult. It is absorbed from diet in the intestinal tract. Normally kidneys excrete the excess of sodium and regulates the sodium content in body. Prostaglandin is also said to be responsible for reabsorption of sodium.

Functions: Sodium is associated with chloride and bicarbonate in regulating the acid-base equilibrium. Another important function is maintenance of osmotic pressure of body fluids. It plays an important role in preserving normal elasticity of muscles and permeability of cells.

Causes of low serum sodium level (hyponaturemia),

  • Loss of sodium due to excessive urination, as in case of diabetes.
  • Excessive sodium excretion in metabolic acidosis.
  • Diarrhoea and vomiting.
  • In Addisons disease (where excretion of hormone aldosterone is decreased)

Causes of high serum sodium level (hypernaturemia),

  • Severe dehydration
  • Cushing syndrome (hyper adrenalism)
  • Certain type of brain damage
  • Excessive treatment with sodium salts


Human body usually contains about 206g/kg body weight of potassium (K+). The daily requirement is about 1.5 to 4.5g. The dietary sources of potassium are milk, certain vegetables, meat and whole grains. Potassium deficiency generally does not occur (except some pathological conditions). From diet, it is rapidly absorbed in GIT and rapidly excreted via kidneys. The excretion of potassium through kidney is affected by changes in acid-base balance and activity of adrenal cortex.

Functions: It is a principal cation of intracellular fluid (except it is present extracellularly in cardiac muscles). Potassium regulates the acid-base balance, osmotic pressure and water retention.

Low serum potassium levels (hypokalaemia) develop in following conditions.

  • Post operative illness
  • Malnutrition, gastrointestinal losses, as in diarrhoea and metabolic alkalosis
  • Use of diuretics like, acetazolamide and chlorothiazide
  • In case of heart disease, the potassium content of myocardium is decreased.

Elevated serum potassium levels (hyperkalaemia) are seen in followimg conditions,

  • Patients with renal failure, advanced dehydration or shock.
  • In Adison’s disease (due to adrenal in sufficiency)

In hyperkalaemia there are signs of bradycardia, poor heart sound, peripheral vascular collapse and lastly cardiac arrest. It also causes electrocardiographic changes. Extracellular elevation of potassium level causes mental confusion, weakness of respiratory muscles and flaccid paralysis of extremities.


The total calcium (Ca++) content in body is about 22g per kg body weight and daily requirement is about 0.8g. Most of the calcium is found in bones and remaining is largely found in extracellular fluid compartments. Dietary sources of calcium are dairy products (like milk, cheese, yogurt, etc), leafy vegetables, fortified foods (like cereals, breads and plant-based milk alternatives), fish with edible bones, nuts and seeds (like almonds, sesame seeds and chia seeds).


  • Bone health: Calcium is a major component of bones and teeth, contributing to their strength and density. It plays an important role in bone formation, remodelling and repair throughout life.
  • Muscle contraction: Calcium ions are involved in initiating muscle contraction by binding to proteins within muscle cells, such as troponin and triggering the release of stored calcium from the sarcoplasmic reticulum.
  • Nerve function: Calcium ions participate in nerve impulse transmission by regulating the release of neurotransmitters at synapse.
  • Blood clotting: Calcium is necessary for the activation of several clotting factors in the coagulating cascade, leading to the formation of blood clots and haemostasis.
  • Cellular signalling: Calcium serves as a ubiquitous intracellular messenger, regulating numerous cellular process such as enzyme activity, gene expression and cell proliferation.

Ensuring an adequate intake of calcium through a balanced diet is essential for maintaining bone health, muscle function and overall wellbeing. However, its important to note that excessive calcium intake can lead to adverse effect such as kidney stones or cardiovascular complications.


The total magnesium (Mg++) content in body is about 0.5 gm per kg body weight and about 70% is present in complex form with calcium and phosphorous in bones. The daily requirement is about 350 mg. good dietary sources are various nuts, soyabeans, whole grains and sea foods. Magnesium is absorbed from duodenum in acidic medium. Magnesium depletion can occur due to malnutrition, dietary restriction and chronic alcoholism, faulty absorption and gastrointestinal diseases. Magnesium deficiency may lead to muscular tumour, confusion, vasodilation and hyper irritability.

The main functions of magnesium are,

  • It is a cofactor for phosphate transferring enzyme
  • Constituent of teeth and bones
  • It decreases neuromuscular irritability
  • It is essential for protein synthesis and for smooth functioning of neuromuscular system.

There are some other cations like iron (Fe++), zinc (Zn++), copper (Cu++), cobalt (Co++), manganese (Mn++), chromium (Cr+++) are present in body and called as essential trace ions.

Major anions


Total chloride ions present in the is about 50 mEq per Kg body weight. Daily body requirement is about 5-10gm. The major dietary source for chloride ions is table salt used in cooking. It is readily absorbed throughout GIT. It is excreted mainly through urine and sweat. It is present in all body secretions. It constitutes nearly about 66% of the anions present in plasma as chloride ions.

Chloride ions do not exert any important pharmacological action. However, its main functions include osmotic balance between different body fluids, maintaining the balance of charges between the body fluids. Chloride ions are involved in formation of gastric hydrochloric acid and also in maintenance of acid base balance.


Sulphate is present in very small quantity in plasma and interstitial fluids. Good dietary sources are animal and plant proteins, sulphur containing amino acids like cysteine and methionine. The organic sulphur is oxidised to sulphate. Sulphur containing compounds are important in detoxication mechanism and SH group containing organic compounds in tissue respiration.


It is the second largest anion present in the extracellular fluid compartment. The main dietary sources are fruits and vegetables, alkaline foods, mineral rich food and water. The bicarbonate ion along with carbonic acid function as one of the buffer systems. When bicarbonate is present in excess amount it produces metabolic alkalosis and deficiency causes metabolic acidosis.


It is the major anion of intracellular fluid compartment. The main dietary sources are milk and milk products, whole grain legumes, nuts, etc. All cells in the body contain phosphorous and nearly 4/5th of phosphorous present in the teeth and bones along with calcium. It is also present in combination of proteins, carbohydrates and fats. Phosphate ester bonds in the body is a source of energy. Glucose and other hexoses are metabolised through phosphorylation and similarly many vitamins, functions as coenzymes after the phosphorylation. Generally, there is no possibility of hypophosphatemia, but its deficiency affects the utilisation of glucose in erythrocytes.


Electrolytes are tiny charged particles that help your body work properly. They are found both inside and outside cells. The major electrolytes are sodium, potassium, calcium, magnesium, chloride, phosphate and bicarbonate. These electrolytes help with important functions like keeping muscle and nerves working, balancing fluids in the body, etc. Body needs to keep the right balance of these electrolytes to stay healthy. When this balance gets disturbed it can cause muscle cramps or heart irregularities.

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