What does interstitial fluid refer to?

Interstitial fluid refers to the tissue fluid that surrounds and bathes the cells in multicellular organisms. This fluid serves several essential functions, including providing a medium for nutrients, waste products, and signaling molecules to diffuse between blood vessels and cells. It is vital for maintaining homeostasis and ensuring that cells have the necessary environment for survival and function.

In contrast, the other options specify different types of fluids that do not accurately describe interstitial fluid. The fluid found inside cells is known as cytoplasm or intracellular fluid, while blood plasma refers specifically to the liquid component of blood that circulates through blood vessels. The fluid within the heart pertains to specialized fluids related to heart function, which do not encompass the broader definition of interstitial fluid. Therefore, identifying interstitial fluid as the tissue fluid bathing cells is the most accurate representation of its role in the body.