What primarily drives fluid movement between cells?

Fluid movement between cells is primarily driven by diffusion gradients. This process relies on the principle that substances move from an area of higher concentration to an area of lower concentration, seeking equilibrium. In the context of fluid movement, this means that water and solutes will move through the interstitial fluid and across cell membranes depending on their concentration gradients.

While muscle contraction can influence fluid movement within the body, it is not the primary driver of fluid diffusion at the cellular level. Capillary permeability also plays a significant role in the movement of fluids, particularly in terms of how substances can enter or exit blood vessels, but it is the concentration gradients that dictate the movement itself. Similarly, ion concentration does affect fluid movement by influencing osmotic pressure and gradients, but the fundamental process through which fluids move between cells operates predominantly through diffusion.