Difference Between Intracellular and Extracellular Fluid

Main Difference – Intracellular vs Extracellular Fluid

Intracellular and extracellular fluid are two compartments of fluids defined by the relative position of each fluid compartment to the cell membrane. The main difference between intercellular and extracellular fluid is that intracellular fluid is the liquid found inside the cell whereas extracellular fluid refers to all the body fluids outside the cell. The intracellular fluid is also known as the cytosol of the cell, comprising a complex mixture of organelles, proteins, and ions. The extracellular fluid includes extracellular matrix (ECM), tissue fluid, and transcellular fluid.

Key Areas Covered

1. What is Intracellular Fluid
      – Definition, Features, Types, Function
2. What is Extracellular Fluid
      – Definition, Features, Types, Function
3. What are the Similarities Between Intracellular and Extracellular Fluid
      – Outline of Common Features
4. What is the Difference Between Intracellular and Extracellular Fluid
      – Comparison of Key Differences

Key Terms: Blood Plasma, Cerebrospinal Fluid, Cytosol, Intracellular Fluid (ICF), Extracellular Fluid, Extracellular Matrix (ECM), Tissue Fluid, Transcellular Fluid

What is Intracellular Fluid

Intracellular fluid (ICF) refers to the fluid found inside the cell, which is separated into a compartment by the cell membrane. The cell membrane forms separate compartments inside the cell as well and these compartments are known as organelles. The content inside the cell, which is encircled by the cell membrane is also called the cytosol. The cytosol mainly comprises water. 70% of the total volume of the cytosol is made up of water. Therefore, the pH of the cytosol is 7.0-7.4. The concentration of sodium, calcium, and chloride ions in the cytosol is lower than that of the external environment of the cytosol. However, potassium and magnesium ion concentration in the cytosol is higher than that of the external environment of the cell. The low concentration of calcium ions in the cytosol allows the signal transduction inside the cell. A lot of proteins are found dissolved in the cytosol. This includes proteins such as microtubules, microfilaments, and intermediate filaments, which make up the cytoskeleton. The cytosol is not considered as an ideal solution due to its highly concentrated nature. The intracellular fluid along with the other fluids are shown in figure 1.

Figure01: Intracellular fluid and other body fluids

What is Extracellular Fluid

The extracellular fluid (ECF) refers to all the fluid outside the cell. Tissue fluid and plasma are the two major components of the ECF. The cerebrospinal fluid found in the cavities of the brain and spinal cord is also included in the extracellular fluid. The composition of intracellular and extracellular fluid differs by the presence of high concentration of sodium ions and low concentration of potassium ions in the extracellular fluid. The extracellular fluid is secreted by cells in different tissues to maintain a constant environment in the cell surroundings, aiding the cellular operations of that particular tissue. The total volume of the extracellular fluid is about 15 L; the tissue fluid comprises 12 L and plasma comprises 3 L of it. The fluid suspensions which surround each tissue is called the extracellular matrix (ECM).  The content of the fluids in the body is shown in figure 2.

Figure 02: The content of the body fluids

Tissue Fluid

The tissue fluid is the fluid which bathes the cells in the body of multicellular organisms. The tissue fluid is also called interstitial fluid. Nutrients and oxygen are provided to each cell in the body by the tissue fluid while removing the metabolic waste. Most of the tissue fluid serves as the ECM.

Blood Plasma

The plasma is the liquid found in the blood. 90% of the plasma is composed of water. Blood cells, glucose, proteins such as fibrinogens, albumins, and globulins, oxygen, mineral ions such as sodium, potassium, enzymes, and hormones are suspended in the plasma.

Transcellular Fluid

Transcellular fluid is the total body water found within the epithelial-lined spaces. The transcellular fluid includes the cerebrospinal fluid, joint fluid, ocular fluid, and pleural fluid. The main function of the transcellular fluid is to lubricate the body cavities and provide nutrients.    

Similarities Between Intracellular and Extracellular Fluid

• Both intracellular fluid and extracellular fluid make up the total body fluids.
• The exchange of materials between intracellular fluid and extracellular fluid occurs between the cell membrane.
• The main function of both intracellular and extracellular fluids is to provide nutrients to the cells in the body and lubrication to the body cavities.

Difference Between Intracellular and Extracellular Fluid

Definition

Intracellular Fluid: The intracellular fluid is a fluid found in the cell membrane, containing dissolved ions and other components, which are essential to cellular processes.

Extracellular Fluid: The extracellular fluid is the fluid found outside of the cell, aiding the functioning of a particular tissue.

Significance

Intracellular Fluid: The intracellular fluid is found inside the cell.

Extracellular Fluid: The extracellular fluid is found outside the cell.

Components

Intracellular Fluid: The intracellular fluid comprises the cytosol.

Extracellular Fluid: The extracellular fluid comprises blood plasma, tissue fluid, and transcellular fluid.

Sodium and Potassium Ion Concentration

Intracellular Fluid: The concentration of sodium ions is low in intracellular fluid and the concentration of potassium ions is high.

Extracellular Fluid: The concentration of sodium ions is high in extracellular fluid and the concentration of potassium ions is low.

Water

Intracellular Fluid: The intracellular fluid comprises 55% of body water.

Extracellular Fluid: The extracellular fluid comprises about 45% of body water.

Body Weight

Intracellular Fluid: The intracellular fluid comprises 33% of total body weight.

Extracellular Fluid: The extracellular fluid comprises 27% of total body weight.

Volume

Intracellular Fluid: The intracellular fluid comprises 19 L of total body fluids.

Extracellular Fluid: The extracellular fluid comprises 23 L of total body fluids.

Conclusion

Intracellular fluid and extracellular fluid collectively make up total body fluids. Intracellular fluid is found inside the cell membrane and extracellular fluid is found outside the cell membrane. Cell membrane act as the margin of each fluid. Cytosol is the component of intracellular fluid whereas tissue fluid, blood plasma, and transcellular fluid are the components of the extracellular fluid. The concentration of potassium and magnesium ions in the intracellular fluid is high while the concentration of sodium and calcium ions are high in the extracellular fluid. The main difference between intracellular and extracellular fluid is their relative positions in the body.

Reference:

1.”Fluid Compartments.” Boundless. N.p., 07 Nov. 2016. Web. Available here. 06 July 2017.
2.”Extracellular fluid.” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 06 July 2017.  

Image Courtesy:

1. “2702 Fluid Compartments ICF ECF” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia
2. “Cellular Fluid Content” By Welcome1To1The1Jungle at English Wikipedia (CC BY 3.0) via Commons Wikimedia