Difference between Intracellular and Extracellular Fluid

You have heard probably that we, human beings, as a species are 60 percent water. In the human organism, fluids make up a large percentage of the volume of cells, lungs, and blood. In biology, fluids are divided into three major categories – intracellular, extracellular, and transcellular. In the following article, we will examine the differences between the first two of these.


Intracellular vs Extracellular Fluid
A macro scheme of fluid compartments around the cells (the intracellular fluid, the plasma, the interstitial fluid)

As the human organism undergoes the process of metabolism, one of the byproducts of this is carbon dioxide (chemical formula CO2), which is made in the watery portion of the cell, called the intracellular fluid.

After carbon dioxide diffuses out of the cell, it goes right through the cell membrane and into the watery compartment known as interstitial fluid, which is between all of our cells and between blood vessels.

The further it goes, it eventually has to diffuse into plasma (the watery part of the blood). Then it travels through blood vessels until it reaches the lungs, from where it is finally released. Oxygen, a vital gas that we breathe, follows the opposite direction: through the lungs, by way of blood, and, finally, into the cells.

The extracellular (meaning “outside the cells”) fluid is the collective term for interstitial fluid and the plasma.

extracellular fluid
A graphic model of the extracellular fluid

Intracellular fluid vs Extracellular fluid

What is the difference between intracellular fluid and extracellular fluid?

Intracellular fluid, as its name suggests, is found inside the cells in the human organism. Extracellular fluid, on the other hand, is outside the cell; it is comprised of the interstitial, intravascular and transcellular compartments.

cellular fluid content in the human organism
A diagram of cellular fluid content in the human organism

Intracellular fluid is responsible for the production of carbon dioxide, a colorless gas vital to any organism on Earth, including that of humans. The compartments with extracellular fluid, on the other hand, transport carbon dioxide further into the lungs, where it is expelled, and also to the kidneys.

Comparison chart

Intracellular fluid Extracellular fluid
Carbon dioxide is produced inside it Contains carbon dioxide and transports it to the various organs
Holds about 67 percent of water inside the human organism Holds about 33 percent of water inside the human organism
Contains large amounts of potassium, magnesium, and phosphate ions Contains large amounts of sodium, chloride, and bicarbonate ions, also contains nutrients for the cells, such as oxygen, glucose, fatty acids, and amino acids


In this video you can see a lecture on movement between fluid compartments inside the human organism, which includes explanation of the difference between intracellular and extracellular fluids: