Sodium Ion Homeostasis in Cells

Homeostasis is the process by which biological systems maintain stability while adjusting to conditions that are optimal for survival. One essential aspect of homeostasis is the regulation of solutes and water in body fluids, ensuring the proper functioning of cells. This regulation is crucial in organisms, including humans, where various mechanisms act to control the internal environment.

The kidneys play a vital role in maintaining fluid balance and electrolyte concentration, which in turn affects cell volume and function. Understanding how the kidneys filter blood and manage solute transport can provide insights into maintaining homeostasis in the body.

Given that transport systems can be affected by various factors including concentration gradients, membrane permeability, and active transport mechanisms, what is the primary method by which cells actively maintain homeostasis regarding sodium ions?