Extracellular and Intracellular Fluids


Our body is made up of a sequence of cells, tissue, organs, organ system, and fluid system. In human body contain 60% of the fluid, in this fluid mainly present water and other substances. In our body contains 50-75 % of water. The % of the water in our body depends on age and gender. In early gestation, 90% of fetal body weight contains water. Premature infants have a water content of 75 to 80% of their body weight. In newborn baby contain 70% water, and this % of water rapidly reduced one year child contains 60% of water. In teens and mature age, water present at 60% in males and 55% in females. The difference between males and females related to water, a result of body fat distribution because adipose tissue is mostly free of water. Females have a high body fat % and lower skeletal muscle that’s the reason behind females have less water content compared to males.

Most of this fluid present inside the cell and outside the cell. Extracellular fluid present outside the cell and intracellular fluid present inside the cell. The total % of the extracellular and intracellular fluid in our body, 2/3 of total body water present in intracellular and 1/3 of total body water present in extracellular fluid. The intracellular and extracellular fluid ratio is totally based on age. The embryo /fetus has a high amount of extracellular fluid compare to intracellular. Males have a high rate of intracellular fluid because have a large amount of muscle mass.

Extracellular and Intracellular Fluids
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Extracellular fluid

Extracellular fluid also called the ‘internal environment of the body’’ or ‘the milieu interieur’. This term coined by French physiologist Claude Bernard. These extracellular fluids contain ions and nutrients which require the cell.  The extracellular fluid of cells kept a high amount of Na+, Cl, bicarbonate ions plus nutrients for the cells, such as oxygen, glucose, fatty acid, amino acid, and CO2.

Extracellular fluid is divided into two types:-

  • An extravascular compartment or Interstitial fluid
  • Intravascular Compartment or blood volume

The extracellular fluid contains lymph, cerebrospinal fluid, aqueous and vitreous humor, synovial fluid, and serous fluid.  These extracellular fluids very important for our body and these fluids increase during infectious diseases. The level increases of extravascular components during heart failure, protein-losing enteropathy, nephrotic syndrome, and sepsis condition. The level of the intravascular compartment decreases during dehydration, hypoalbuminemia, and anemia conditions.

Extracellular fluid provides motion in the body, transport blood, and tissue fluids by diffusion, through the capillary wall.

Extracellular fluid transport two types

  • Movement of blood through the body in blood vessels.
  • Movement of fluids between the blood capillaries.

Intracellular fluid

Intracellular fluids present inside the cell. Intracellular fluids contain 2/3 part of the total body water. Intracellular fluids contain high levels of potassium, magnesium, and phosphate ions. In intracellular fluid includes phosphate ions, just replacement of sodium chloride ions in extracellular fluids, because of the relative impermeability of cell membranes, which separates out these ions. Special mechanisms for transporting ions through the cell membrane maintain the ion concentration differences between intracellular and extracellular fluids.

Difference between extracellular and intracellular fluid

Extracellular Fluid

Intracellular Fluid

Present outside the cell. Present inside the cell.
A major cation is a sodium and the major anion is chloride. A major cation is potassium and the major anion is phosphate.
The pump actively uses cellular energy to maintain sodium in the extracellular fluid. While intracellular fluid uses potassium.

Fluids related diseases


In normal conditions, blood sodium concentration is 135 -145 mmol/L. The main determination of sodium concentration is plasma water concentration, itself determined by water intake, losses, and urinary dilution. Vasopressin, the main regulation of water. The Vasopressin hormone water reabsorbs with help renal tubules and produces concentrated urine.  Dysnatremias alters signs and symptoms secondary to the central nervous system.

Dysnatremia is two types based on sodium concentration in our body

  • Hyponatremia
  • Hypernatremia 


Hyponatremia condition when our body has below the level of sodium ions in the blood. Decrease of sodium level in blood and effective blood osmolality causes movement of water into brain cells and results in cellular swelling and increases intracranial pressure. In most time hyponatremia occurrence when the body tries to store the extracellular fluid volume at the expense of circulating sodium.

  • When the sodium levels below 125-130 mmol/L in blood, the body shows nausea and malaise signs.
  • When the sodium levels below 115-120 mmol/L in blood, occurs headache, lethargy, restlessness, and disorientation in the body. In the severe condition of hyponatremia coma, respiratory arrest, seizure, permanent brain damage, brain stem herniation, and death also occur.

The gain of functions mutations of the X-linked receptor gene that mediates the renal response to vasopressin, resulting in persistent activation of the receptor. This disease name is the hereditary nephrogenic syndrome of inappropriate anti-diuresis.

In this disease, drugs use Desmopressin, a synthetic analog of the natural antidiuretic hormone. This drug is generally regarded as a safe drug and no side effects during treatment.

Some peoples may be also used non-steroidal anti-inflammatory drugs, which improve the excretion of free water.

Thiazides (a drug increase urine flow), this drug blocks the rennin –angiotensin-aldosterone system either converting enzyme inhibitors or sartans.


Hypernatremia condition when our body has a higher level of sodium ions in the blood. When sodium concentration levels higher then 160mmol/L occurs severe symptoms in the body. The early sign of hypernatremia such as muscle weakness, restlessness, nausea anorexia, and vomiting.  And severe symptoms of hypernatremia mental status, lethargy, irritability, stupor, and coma. Hypernatremia may induce brain shrinkage, cerebral bleeding, and subarachnoid hemorrhage.


  1. Body fluid Composition, Amrish Jain, Pediatrics in Review, 2015, 141-152, Vol.36.
  2. Textbook of Medical physiology Guyton and Hall, 12th edition
  3. Body fluids and salt metabolism – Part II, Peruzzo et al. Italian Journal of Pediatrics 2010, 36:78, DOI:10.1186/1824-7288-36-78


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