Intracellular fluid is the liquid found inside cells, making up about two-thirds of the total body water. It is essential for various cellular processes, including nutrient transport, waste removal, and maintaining cell shape. This fluid contains water, electrolytes, proteins, and other substances that support cellular functions. The composition of intracellular fluid varies between different cell types, but it generally has a high concentration of potassium ions and a low concentration of sodium ions. This balance is crucial for processes like nerve impulse transmission and muscle contraction, ensuring that cells operate efficiently and respond to their environment.