Intracellular Fluid Definition

Intracellular fluid is the fluid that exists within the cells of multi-celled organisms. The intracellular fluid is therefore stored within the intracellular compartments of the body. Intracellular fluid is often referred to as cytosol when discussing cellular functions. The cytosol and the organelles and molecules contained within are referred to collectively as the cytoplasm. The opposite of the intracellular fluid is the extracellular fluid, which exists on the outside of the cells in the extracellular compartment of the body. Many cellular mechanisms and enzymes work to move products and wastes from the intracellular fluid to the extracellular fluid, while at the same time bringing in new nutrients and solutes to the intracellular fluid.

  • Extracellular Fluid – Fluid that surrounds the cells of the body, but is separated still from the environment.
  • Cytosol – The fluid containing nutrients, proteins, and other molecules in a cell, also called intracellular fluid.
  • Cytoplasm – The entire contents of a cell, including the cytosol and all the associated organelles and other cellular machines.


1. Molecules in the gut are digested to be used in cells all over the body. A particular nutrient is created by enzymes in the intestines. The cells in the intestines then absorb this nutrient and pass the nutrient to the bloodstream. The nutrient then travels to the capillaries, where is forced from the bloodstream. Where is the molecule now?
A. In intracellular fluid
B. In extracellular fluid
C. In the Cytosol

Answer to Question #1
B is correct. While the molecule has traveled a long way, it has one more membrane to traverse before it reaches the intracellular fluid, or cytosol. Currently, the molecule is in the interstitial fluid, a part of the extracellular fluid. This fluid exists between cells of the body and serves to help transport nutrients, gases, and wastes. Intracellular fluid is separated from this fluid by the cell membranes of each individual cell.