Body fluids are distributed into two major compartments: intracellular fluid (ICF) and extracellular fluid (ECF). These fluid compartments maintain the internal environment of the body and are essential for normal physiological functions such as nutrient transport, waste removal, maintenance of cell shape, regulation of temperature, and communication between cells. The balance between intracellular and extracellular fluids is maintained through various physiological mechanisms involving cell membranes, electrolytes, and hormones. Intracellular fluid is the fluid present inside the cells of the body. It constitutes about two-thirds of the total body water, accounting for nearly 40% of the total body weight in an average healthy adult. The cell membrane separates intracellular fluid from the extracellular fluid and regulates the movement of water, ions, and nutrients. Intracellular fluid contains high concentrations of potassium (K⁺), magnesium (Mg²⁺), phosphate ions, and proteins, while sodium (Na⁺) and chloride (Cl⁻) concentrations are relatively low. This fluid provides an ideal environment for cellular metabolism, protein synthesis, enzyme activity, and energy production. It also helps maintain the shape, volume, and structural integrity of cells. Examples of intracellular fluid include the fluid present inside muscle cells,