Difference Between Plasma and Interstitial Fluid

Main Difference – Plasma vs Interstitial Fluid

Extracellular fluid (ECF) is a body fluid found outside of the cell. Plasma and interstitial fluid are the major components of ECF. Lymph, transcellular fluid, cerebrospinal fluid, intraocular fluid, synovial fluid, pericardial, intrapleural, and peritoneal fluids, and digestive juices are minor components of the ECF. The main function of the ECF is to move water and electrolytes throughout the body. Therefore, it maintains the homeostasis of the body while providing nutrients to the body cells. The main difference between plasma and interstitial fluid is that plasma contains more proteins whereas interstitial fluid contains fewer proteins. Most of the other dissolved products such as nutrients and electrolytes occur in similar concentrations in both plasma and interstitial fluid.

Key Areas Covered

1. What is Plasma
– Definition, Composition, Function
2. What is Interstitial Fluid
      – Definition, Composition, Function
3. What are the Similarities Between Plasma and Interstitial Fluid
      – Outline of Common Features
4. What is the Difference Between Plasma and Interstitial Fluid
      – Comparison of Key Difference

Key Terms: Blood, Carbon Dioxide, Extracellular Fluid (ECF), Interstitial Fluid, Oxygen, Plasma, Proteins, Water

What is Plasma

Plasma is the colorless fluid in blood, lymph or milk. It is a straw-colored/pale-yellow, liquid. Plasma is a type of ECF. About 55% of total blood volume is taken by plasma. Plasma component of the blood is shown in figure 1.

Main Difference - Plasma vs Interstitial Fluid

Figure 1: Plasma

Since plasma is inside the blood vessels, it is called the intravascular fluid part of the extracellular fluid. Plasma is mainly composed of water (93% by volume). It also contains dissolved proteins such as fibrinogens, globulins, and albumins, glucose, clotting factors, mineral ions such as Na⁺, Ca⁺⁺, Mg⁺⁺, HCO3^– Cl^–, etc., hormones, and carbon dioxide. Plasma serves as the main medium for the transportation of excretory products. It maintains the osmotic balance and the concentration of electrolytes.

What is Interstitial Fluid

Interstitial fluid refers to the fluid in between the spaces of the cells in tissues. Interstitial space is also called tissue space. An adult human body contains about 11 liters of interstitial fluid. The main function of interstitial fluid is to provide nutrients and oxygen to the metabolizing cells of tissues while removing the metabolic wastes. The relationship between interstitial fluid and plasma is shown in figure 2.

Difference Between Plasma and Interstitial Fluid

Figure 2: Plasma and Interstitial Fluid

Interstitial fluid contains 26% of the body water. It also consists of glucose, amino acids, fatty acids, mineral ions, hormones, neurotransmitters, and coenzymes. The oxygen concentration of the interstitial fluid is less than that of the plasma due to the intake of oxygen by the cells of the tissue. On the other hand, carbon dioxide concentration is higher in the interstitial fluid.

Similarities Between Plasma and Interstitial Fluid

Both plasma and interstitial fluid are the major components of the ECF.
Both plasma and interstitial fluid are found outside the body cells.
Both plasma and interstitial fluid are composed of similar composition.
Both plasma and interstitial fluid are mainly composed of water.
Both plasma and interstitial fluid lack cells.

Definition

Plasma: Plasma refers to the colorless fluid in blood, lymph or milk.

Interstitial Fluid: Interstitial fluid refers to the fluid in between the spaces of the cells in tissues.

Significance

Plasma: Plasma is the liquid component of blood.

Interstitial Fluid: Interstitial fluid is the fluid between the cells of a tissue.

Proteins

Plasma: Plasma contains a high protein content.

Interstitial Fluid: Interstitial fluid contains a lower protein amount than plasma.

Dissolved Oxygen

Plasma: Plasma contains more dissolved oxygen.

Interstitial Fluid: Interstitial fluid contains less dissolved oxygen.

Carbon Dioxide

Plasma: Plasma contains less dissolved carbon dioxide.

Interstitial Fluid: Interstitial fluid contains higher carbon dioxide concentration than plasma.

Cells

Plasma: Plasma dissolves blood cells.

Interstitial Fluid: Interstitial fluid bathes tissue cells.

Conclusion

Plasma and interstitial fluid are the two types of ECF in the body. Plasma can be found inside the blood vessels while interstitial fluid can be found in the tissue spaces. Both plasma and interstitial fluid are mainly composed of water. Other dissolved components are also similar in both plasma and the interstitial fluid. Plasma contains a higher concentration of oxygen and proteins. Interstitial fluid contains a higher concentration of carbon dioxide. The main difference between plasma and interstitial fluid is the location and composition of each type of ECF in the body.

Reference:

1. “Body Fluids.” Body Fluids | Boundless Anatomy and Physiology, Available here.

Image Courtesy:

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